Answers Prepared by mehellipso pls refer book for full understandinghellip

Answer ALL QuestionsPART A mdash (10 2 = 20 Marks)

1 Differentiate Serial Engineering from Concurrent EngineeringSlNo

Serial Engineering Concurrent Engineering

1 Traditional Engineering approach also known as Serial Engineering towards development had been largely sequential in nature

CE approach encourages teamwork and it harnesses the expertise from all the disciplines that are involved to work closely together in parallel right from the early stage of the product design and development stage

2 control of two parameter Attempt to control all three parameter (Good Quick Cheap)

3SERIAL ENGINEERING APPROACH

CONCURRENT ENGINEERING APPROACH

2 Classify the three categories of Design standardso Performanceo Test methodso Codes of practice

3 Define House of Qualitybull QFD is a planning and problem-solving tool that is finding growing acceptance for

translating customer requirements into the engineering characteristics of a productbull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

4 What are the essential elements of IPR

o Patentso Copyrightso Trademarkso Trade secrets

5 Classify conceptual decompositiono Decomposition in the physical Domain

o Functional Decomposition6 State the principle of prototyping7 State the importance of Value Engineering Lowering O amp M costs Improving quality management Improving resource efficiecy Simplifying procedures Minimizing paperwork Lowering staff costs Increasing procedural efficiency Optimizing construction expenditures Developing value attitudes in staff Competing more sucessfully in marketplace

8 Define Material Performance IndexA Material Performance Index is a group of material properties which governs some

aspect of the performance of a component If the performance index is maximized it gives the best solution to the design requirement

9 Differentiate between MTBF and MTTF

Slno MTBF MTTF1 MTBF (mean time between

failures) is the expected time between two successive failures of a system

MTTF (mean time to failure) is the expected time to failure of asystem

2 MTBF is akey reliability metric for systems that can be repaired or restored

Non-repairable systems can fail only once Therefore for a non-repairable system MTTF is equivalent to the mean ofits failure time distribution Repairable systems can fail several times

3 MTBF can be calculated as the inverse of the failure rate for constant failure rate systems

For constant failure rate systems MTTF is the inverse of the failure rate If failure rate is in failuresmillion hours MTTF = 1000000 Failure Rate for components with exponential distributions

10 What is meant by Fractional Factorial Designbull fractional factorial designs are experimental designs consisting of a carefully chosen

subset (fraction) of the experimental runs of a full factorial design bull The subset is chosen so as to exploit the sparsity-of-effects principle using a fraction

of the effort of a full factorial design in terms of experimental runs and resourcesbull Fractional designs are expressed using the notation lk minus p bull where l is the number of levels of each factor investigated bull k is the number of factors investigated and

bull p describes the size of the fraction of the full factorial used bull A design with p such generators is a 1(lp) fraction of the full factorial design

A way to reduce a huge full factorial to somethingmanageablendash Considerations

1048707 Required time resources1048707 Complexity of set-up for experiments

ndash Major use is in screening experiments where the knowledge ofbasic effects is not well known

ndash If 2k is very large may need to run reduced experiment

PART B mdash (5 times 16 = 80 Marks)11 (a) (i) Explain the Morris Asimovrsquos morphology of design with a blockdiagram (12)

Morphology of designndash Detailed description of the complete design process

The design Process

Phase I Conceptual Design

o It requires the creativityo Single best concept feasibility studyo Coordination among many functions in the business organizations

bull Identification of customer needsbull Problem definition

Problem Statement Benchmarking Quality Function Deployment (QFD) Product Design Specification (PDS)

bull Gathering information Internet Patents Trade Literature

bull Conceptualization Brainstorming Functional Decomposition Morphological Chart

bull Concept selection Pugh Concept Selection Decision Matrix

bull Refinement of the PDSbull Design review

Phase II Embodiment design or preliminary design

- Strength material selection size shape and spatial compatibilitybull Product architecture

Dividing overall design system into sub system or modules Arrangement of Physical Elements to carry out Function

bull Configuration design of parts and components Preliminary Selection of Parts and Materials Modeling and Sizing of Parts

Evaluate

OutcomeDesignProcess

GeneralInformation

SpecificInformation

NO YES

Parts are made up of features like holes ribs splines and curves To determine what features will be present amphow those

features are arranged in spacebull Parametric design To establish the exact dimensions and tolerances

Robust Design Tolerances Final Dimensions Design for Manufacturability (DFM)

Phase III Detail Designndash Complete engineering description of a tested and producible productndash Form dimensions tolerances properties materials and manufacturing process

of each partndash Engineering drawings ampcomputer generated drawings-determine assembly

drgndash Before the information passed on to manufacturing

Phase IV Planning For Manufacturendash Process sheet establishedndash List of manufacturing operations that must be performed on the component

bull It specifies the form and condition of material and tooling ampproduction mcrsquosbull Estimation of production cost of the component

ndash Designing specialized tools and fixturesndash Specify production plant to be usedndash Planning the work schedules amp inventory controlndash Planning the quality assurance systemndash Establishing the standard time and labor cost for each operation ndash Establish the system of information flow

Phase V Planning For Distributionndash Effective distribution to the consumer of the systemndash Marketing advertising and news media techniquesndash Shipping Packagendash Documentationndash Shelf Life

Define Problem

Problem StatementBenchmarking

QFD PDS

Gathering information

InternetPatentsTrade

Literature

Concept Generation

BrainstormingFunctional

DecompositionMorphological

Chart

Evaluation of concepts

Pugh Concept Selection

Decision Matrix

Product architecture

Arrangement of physical elements to carry out function

Configuration design

Preliminary Selection matls amp

mfgModelingsizing

Parametric design

Robust designTolerances

Final dimenDFM

Detail Design

Detailed drawings and specifications

ndash WarehousesPhase VI Planning For Use

ndash User oriented design processndash Ease of maintenance reliability safety aesthetic appeal economy of

operation duration of servicePhase VII Planning For Retirement Of The Product

ndash Disposal of the product end of its useful life

ndash Green design-recycling of materials remanufacture Useful Life

o Deteriorationo Technical Obsolescenceo Fashion or Tasteo Environmental Issues

Industrial Ecology Green Designo RFIo Power Consumption

(ii) State the characteristics of an environmentally responsible design(4)

o Easy to disassembleo Able to be recycledo Contains recycled materialso Uses identifiable and recyclable plasticso Reduces use of energy and natural materials in its manufactureo Manufactured without producing hazardous wasteo Avoids use of hazardous materialso Reduces product chemical emissionso Reduces product energy consumption

Or(b) Explain material cycle product cycle and manufacturing process cyclewith neat sketches (16)

12 (a) (i) Explain the process of identifying customer requirements withsuitable example (8)

bull Define the Scopendash Mission Statement

bull Gather Raw Datandash Interviewsndash Focus Groupsndash Observation

bull Interpret Raw Datandash Need Statements

bull Organize the Needsndash Hierarchy

bull Establish Importance

ndash Surveysndash Quantified Needs

bull Reflect on the Processndash Continuous Improvement

Example Screwdriver ProjectProduct Description

bull A hand-held power-assisted device for installing threaded fastenersKey Business Goals

bull Product introduced in 4th Q of 2000bull 50 gross marginbull 10 share of cordless screwdriver market by 2004

Primary Marketbull Do-it-yourself consumer

Secondary Marketsbull Casual consumerbull Light-duty professional

Assumptionsbull Hand-heldbull Power assistedbull Nickel-metal-hydride rechargeable battery technology

Stakeholdersbull Userbull Retailerbull Sales forcebull Service centerbull Productionbull Legal department

The process1 Gather raw data from customers2 Interpret raw data in terms of customer needs3 Organize needs into a hierarchy (primary secondary etc)4 Establish relative importance of each need5 Reflect on the results and the process

2 Gather raw data from customers1 Interviews2 Focus groups3 Observing product in use

3 Interpret raw data in terms of customer needs1 Express need as ldquowhatrdquo not ldquohowrdquo2 Express the need as specifically as the raw data3 Use positive not negative phrasing4 Express the need as an attribute to the product5 Avoid the words must and should

3 Organize needs into a hierarchy(one method)

bull Print each need on separate cardpost-itbull Eliminate redundant statementsbull Group cards according to similar needs metbull Choose a label for each group

bull Create supergroups (2 to 5 groups) where possiblebull Review edit the organized need statements

4 Establish relative importance of each needbull Develop a weighting system for customer needs

ndash Rely on consensus of the team based on their experience with customers

Orndash Use further customer surveys

5 Reflect on the results and the processbull Are results consistent with results of teamrsquos interaction with the customersbull Have all important types of customers in target market been interacted withbull What do we know that we didnrsquot know when we started Any surprisesbull How can we improve the process

(ii) Explain the procedure to solve ethical conflicts (8)

1 DETERMINE whether there is an ethical issue orand dilemma Is there a conflict of values or rights or professional responsibilities (For example there may be an issue of self-determination of an adolescent versus the well-being of the family)

2 IDENTIFY the key values and principles involved What meanings and limitations are typically attached to these competing values (For example rarely is confidential information held in absolute secrecy however typically decisions about access by third parties to sensitive content should be contracted with clients)

3 RANK the values or ethical principles which - in your professional judgement - are most relevant to the issue or dilemmaWhat reasons can you provide for prioritizing one competing valueprinciple over another (For example your clients right to choose a beneficial course of action could bring hardship or harm to others who would be affected)

4 DEVELOP an action plan that is consistent with the ethical priorities that have been determined as central to the dilemmaHave you conferred with clients and colleagues as appropriate about the potential risks and consequences of alternative courses of action Can you support or justify your action plan with the valuesprinciples on which the plan is based (For example have you conferred with all the necessary persons regarding the ethical dimensions of planning for a battered wifes quest to secure secret shelter and the implications for her teen-aged children)

5 IMPLEMENT your plan utilizing the most appropriate practice skills and competencies How will you make use of core social work skills such as sensitive communication skillful negotiation and cultural competence (For example skillful colleague or supervisory communication and negotiation may enable an impaired colleague to see herhis impact on clients and to take appropriate action)

6 REFLECT on the outcome of this ethical decision making process How would you evaluate the consequences of this process for those involved Client(s) professional(s) and agency (ies) (Increasingly professionals have begun to seek support further professional training and consultation through the development of Ethics review Committees or Ethics Consultation processes)

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

o Functional Decomposition6 State the principle of prototyping7 State the importance of Value Engineering Lowering O amp M costs Improving quality management Improving resource efficiecy Simplifying procedures Minimizing paperwork Lowering staff costs Increasing procedural efficiency Optimizing construction expenditures Developing value attitudes in staff Competing more sucessfully in marketplace

8 Define Material Performance IndexA Material Performance Index is a group of material properties which governs some

aspect of the performance of a component If the performance index is maximized it gives the best solution to the design requirement

9 Differentiate between MTBF and MTTF

Slno MTBF MTTF1 MTBF (mean time between

failures) is the expected time between two successive failures of a system

MTTF (mean time to failure) is the expected time to failure of asystem

2 MTBF is akey reliability metric for systems that can be repaired or restored

Non-repairable systems can fail only once Therefore for a non-repairable system MTTF is equivalent to the mean ofits failure time distribution Repairable systems can fail several times

3 MTBF can be calculated as the inverse of the failure rate for constant failure rate systems

For constant failure rate systems MTTF is the inverse of the failure rate If failure rate is in failuresmillion hours MTTF = 1000000 Failure Rate for components with exponential distributions

10 What is meant by Fractional Factorial Designbull fractional factorial designs are experimental designs consisting of a carefully chosen

subset (fraction) of the experimental runs of a full factorial design bull The subset is chosen so as to exploit the sparsity-of-effects principle using a fraction

of the effort of a full factorial design in terms of experimental runs and resourcesbull Fractional designs are expressed using the notation lk minus p bull where l is the number of levels of each factor investigated bull k is the number of factors investigated and

bull p describes the size of the fraction of the full factorial used bull A design with p such generators is a 1(lp) fraction of the full factorial design

A way to reduce a huge full factorial to somethingmanageablendash Considerations

1048707 Required time resources1048707 Complexity of set-up for experiments

ndash Major use is in screening experiments where the knowledge ofbasic effects is not well known

ndash If 2k is very large may need to run reduced experiment

PART B mdash (5 times 16 = 80 Marks)11 (a) (i) Explain the Morris Asimovrsquos morphology of design with a blockdiagram (12)

Morphology of designndash Detailed description of the complete design process

The design Process

Phase I Conceptual Design

o It requires the creativityo Single best concept feasibility studyo Coordination among many functions in the business organizations

bull Identification of customer needsbull Problem definition

Problem Statement Benchmarking Quality Function Deployment (QFD) Product Design Specification (PDS)

bull Gathering information Internet Patents Trade Literature

bull Conceptualization Brainstorming Functional Decomposition Morphological Chart

bull Concept selection Pugh Concept Selection Decision Matrix

bull Refinement of the PDSbull Design review

Phase II Embodiment design or preliminary design

- Strength material selection size shape and spatial compatibilitybull Product architecture

Dividing overall design system into sub system or modules Arrangement of Physical Elements to carry out Function

bull Configuration design of parts and components Preliminary Selection of Parts and Materials Modeling and Sizing of Parts

Evaluate

OutcomeDesignProcess

GeneralInformation

SpecificInformation

NO YES

Parts are made up of features like holes ribs splines and curves To determine what features will be present amphow those

features are arranged in spacebull Parametric design To establish the exact dimensions and tolerances

Robust Design Tolerances Final Dimensions Design for Manufacturability (DFM)

Phase III Detail Designndash Complete engineering description of a tested and producible productndash Form dimensions tolerances properties materials and manufacturing process

of each partndash Engineering drawings ampcomputer generated drawings-determine assembly

drgndash Before the information passed on to manufacturing

Phase IV Planning For Manufacturendash Process sheet establishedndash List of manufacturing operations that must be performed on the component

bull It specifies the form and condition of material and tooling ampproduction mcrsquosbull Estimation of production cost of the component

ndash Designing specialized tools and fixturesndash Specify production plant to be usedndash Planning the work schedules amp inventory controlndash Planning the quality assurance systemndash Establishing the standard time and labor cost for each operation ndash Establish the system of information flow

Phase V Planning For Distributionndash Effective distribution to the consumer of the systemndash Marketing advertising and news media techniquesndash Shipping Packagendash Documentationndash Shelf Life

Define Problem

Problem StatementBenchmarking

QFD PDS

Gathering information

InternetPatentsTrade

Literature

Concept Generation

BrainstormingFunctional

DecompositionMorphological

Chart

Evaluation of concepts

Pugh Concept Selection

Decision Matrix

Product architecture

Arrangement of physical elements to carry out function

Configuration design

Preliminary Selection matls amp

mfgModelingsizing

Parametric design

Robust designTolerances

Final dimenDFM

Detail Design

Detailed drawings and specifications

ndash WarehousesPhase VI Planning For Use

ndash User oriented design processndash Ease of maintenance reliability safety aesthetic appeal economy of

operation duration of servicePhase VII Planning For Retirement Of The Product

ndash Disposal of the product end of its useful life

ndash Green design-recycling of materials remanufacture Useful Life

o Deteriorationo Technical Obsolescenceo Fashion or Tasteo Environmental Issues

Industrial Ecology Green Designo RFIo Power Consumption

(ii) State the characteristics of an environmentally responsible design(4)

o Easy to disassembleo Able to be recycledo Contains recycled materialso Uses identifiable and recyclable plasticso Reduces use of energy and natural materials in its manufactureo Manufactured without producing hazardous wasteo Avoids use of hazardous materialso Reduces product chemical emissionso Reduces product energy consumption

Or(b) Explain material cycle product cycle and manufacturing process cyclewith neat sketches (16)

12 (a) (i) Explain the process of identifying customer requirements withsuitable example (8)

bull Define the Scopendash Mission Statement

bull Gather Raw Datandash Interviewsndash Focus Groupsndash Observation

bull Interpret Raw Datandash Need Statements

bull Organize the Needsndash Hierarchy

bull Establish Importance

ndash Surveysndash Quantified Needs

bull Reflect on the Processndash Continuous Improvement

Example Screwdriver ProjectProduct Description

bull A hand-held power-assisted device for installing threaded fastenersKey Business Goals

bull Product introduced in 4th Q of 2000bull 50 gross marginbull 10 share of cordless screwdriver market by 2004

Primary Marketbull Do-it-yourself consumer

Secondary Marketsbull Casual consumerbull Light-duty professional

Assumptionsbull Hand-heldbull Power assistedbull Nickel-metal-hydride rechargeable battery technology

Stakeholdersbull Userbull Retailerbull Sales forcebull Service centerbull Productionbull Legal department

The process1 Gather raw data from customers2 Interpret raw data in terms of customer needs3 Organize needs into a hierarchy (primary secondary etc)4 Establish relative importance of each need5 Reflect on the results and the process

2 Gather raw data from customers1 Interviews2 Focus groups3 Observing product in use

3 Interpret raw data in terms of customer needs1 Express need as ldquowhatrdquo not ldquohowrdquo2 Express the need as specifically as the raw data3 Use positive not negative phrasing4 Express the need as an attribute to the product5 Avoid the words must and should

3 Organize needs into a hierarchy(one method)

bull Print each need on separate cardpost-itbull Eliminate redundant statementsbull Group cards according to similar needs metbull Choose a label for each group

bull Create supergroups (2 to 5 groups) where possiblebull Review edit the organized need statements

4 Establish relative importance of each needbull Develop a weighting system for customer needs

ndash Rely on consensus of the team based on their experience with customers

Orndash Use further customer surveys

5 Reflect on the results and the processbull Are results consistent with results of teamrsquos interaction with the customersbull Have all important types of customers in target market been interacted withbull What do we know that we didnrsquot know when we started Any surprisesbull How can we improve the process

(ii) Explain the procedure to solve ethical conflicts (8)

1 DETERMINE whether there is an ethical issue orand dilemma Is there a conflict of values or rights or professional responsibilities (For example there may be an issue of self-determination of an adolescent versus the well-being of the family)

2 IDENTIFY the key values and principles involved What meanings and limitations are typically attached to these competing values (For example rarely is confidential information held in absolute secrecy however typically decisions about access by third parties to sensitive content should be contracted with clients)

3 RANK the values or ethical principles which - in your professional judgement - are most relevant to the issue or dilemmaWhat reasons can you provide for prioritizing one competing valueprinciple over another (For example your clients right to choose a beneficial course of action could bring hardship or harm to others who would be affected)

4 DEVELOP an action plan that is consistent with the ethical priorities that have been determined as central to the dilemmaHave you conferred with clients and colleagues as appropriate about the potential risks and consequences of alternative courses of action Can you support or justify your action plan with the valuesprinciples on which the plan is based (For example have you conferred with all the necessary persons regarding the ethical dimensions of planning for a battered wifes quest to secure secret shelter and the implications for her teen-aged children)

5 IMPLEMENT your plan utilizing the most appropriate practice skills and competencies How will you make use of core social work skills such as sensitive communication skillful negotiation and cultural competence (For example skillful colleague or supervisory communication and negotiation may enable an impaired colleague to see herhis impact on clients and to take appropriate action)

6 REFLECT on the outcome of this ethical decision making process How would you evaluate the consequences of this process for those involved Client(s) professional(s) and agency (ies) (Increasingly professionals have begun to seek support further professional training and consultation through the development of Ethics review Committees or Ethics Consultation processes)

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

bull p describes the size of the fraction of the full factorial used bull A design with p such generators is a 1(lp) fraction of the full factorial design

A way to reduce a huge full factorial to somethingmanageablendash Considerations

1048707 Required time resources1048707 Complexity of set-up for experiments

ndash Major use is in screening experiments where the knowledge ofbasic effects is not well known

ndash If 2k is very large may need to run reduced experiment

PART B mdash (5 times 16 = 80 Marks)11 (a) (i) Explain the Morris Asimovrsquos morphology of design with a blockdiagram (12)

Morphology of designndash Detailed description of the complete design process

The design Process

Phase I Conceptual Design

o It requires the creativityo Single best concept feasibility studyo Coordination among many functions in the business organizations

bull Identification of customer needsbull Problem definition

Problem Statement Benchmarking Quality Function Deployment (QFD) Product Design Specification (PDS)

bull Gathering information Internet Patents Trade Literature

bull Conceptualization Brainstorming Functional Decomposition Morphological Chart

bull Concept selection Pugh Concept Selection Decision Matrix

bull Refinement of the PDSbull Design review

Phase II Embodiment design or preliminary design

- Strength material selection size shape and spatial compatibilitybull Product architecture

Dividing overall design system into sub system or modules Arrangement of Physical Elements to carry out Function

bull Configuration design of parts and components Preliminary Selection of Parts and Materials Modeling and Sizing of Parts

Evaluate

OutcomeDesignProcess

GeneralInformation

SpecificInformation

NO YES

Parts are made up of features like holes ribs splines and curves To determine what features will be present amphow those

features are arranged in spacebull Parametric design To establish the exact dimensions and tolerances

Robust Design Tolerances Final Dimensions Design for Manufacturability (DFM)

Phase III Detail Designndash Complete engineering description of a tested and producible productndash Form dimensions tolerances properties materials and manufacturing process

of each partndash Engineering drawings ampcomputer generated drawings-determine assembly

drgndash Before the information passed on to manufacturing

Phase IV Planning For Manufacturendash Process sheet establishedndash List of manufacturing operations that must be performed on the component

bull It specifies the form and condition of material and tooling ampproduction mcrsquosbull Estimation of production cost of the component

ndash Designing specialized tools and fixturesndash Specify production plant to be usedndash Planning the work schedules amp inventory controlndash Planning the quality assurance systemndash Establishing the standard time and labor cost for each operation ndash Establish the system of information flow

Phase V Planning For Distributionndash Effective distribution to the consumer of the systemndash Marketing advertising and news media techniquesndash Shipping Packagendash Documentationndash Shelf Life

Define Problem

Problem StatementBenchmarking

QFD PDS

Gathering information

InternetPatentsTrade

Literature

Concept Generation

BrainstormingFunctional

DecompositionMorphological

Chart

Evaluation of concepts

Pugh Concept Selection

Decision Matrix

Product architecture

Arrangement of physical elements to carry out function

Configuration design

Preliminary Selection matls amp

mfgModelingsizing

Parametric design

Robust designTolerances

Final dimenDFM

Detail Design

Detailed drawings and specifications

ndash WarehousesPhase VI Planning For Use

ndash User oriented design processndash Ease of maintenance reliability safety aesthetic appeal economy of

operation duration of servicePhase VII Planning For Retirement Of The Product

ndash Disposal of the product end of its useful life

ndash Green design-recycling of materials remanufacture Useful Life

o Deteriorationo Technical Obsolescenceo Fashion or Tasteo Environmental Issues

Industrial Ecology Green Designo RFIo Power Consumption

(ii) State the characteristics of an environmentally responsible design(4)

o Easy to disassembleo Able to be recycledo Contains recycled materialso Uses identifiable and recyclable plasticso Reduces use of energy and natural materials in its manufactureo Manufactured without producing hazardous wasteo Avoids use of hazardous materialso Reduces product chemical emissionso Reduces product energy consumption

Or(b) Explain material cycle product cycle and manufacturing process cyclewith neat sketches (16)

12 (a) (i) Explain the process of identifying customer requirements withsuitable example (8)

bull Define the Scopendash Mission Statement

bull Gather Raw Datandash Interviewsndash Focus Groupsndash Observation

bull Interpret Raw Datandash Need Statements

bull Organize the Needsndash Hierarchy

bull Establish Importance

ndash Surveysndash Quantified Needs

bull Reflect on the Processndash Continuous Improvement

Example Screwdriver ProjectProduct Description

bull A hand-held power-assisted device for installing threaded fastenersKey Business Goals

bull Product introduced in 4th Q of 2000bull 50 gross marginbull 10 share of cordless screwdriver market by 2004

Primary Marketbull Do-it-yourself consumer

Secondary Marketsbull Casual consumerbull Light-duty professional

Assumptionsbull Hand-heldbull Power assistedbull Nickel-metal-hydride rechargeable battery technology

Stakeholdersbull Userbull Retailerbull Sales forcebull Service centerbull Productionbull Legal department

The process1 Gather raw data from customers2 Interpret raw data in terms of customer needs3 Organize needs into a hierarchy (primary secondary etc)4 Establish relative importance of each need5 Reflect on the results and the process

2 Gather raw data from customers1 Interviews2 Focus groups3 Observing product in use

3 Interpret raw data in terms of customer needs1 Express need as ldquowhatrdquo not ldquohowrdquo2 Express the need as specifically as the raw data3 Use positive not negative phrasing4 Express the need as an attribute to the product5 Avoid the words must and should

3 Organize needs into a hierarchy(one method)

bull Print each need on separate cardpost-itbull Eliminate redundant statementsbull Group cards according to similar needs metbull Choose a label for each group

bull Create supergroups (2 to 5 groups) where possiblebull Review edit the organized need statements

4 Establish relative importance of each needbull Develop a weighting system for customer needs

ndash Rely on consensus of the team based on their experience with customers

Orndash Use further customer surveys

5 Reflect on the results and the processbull Are results consistent with results of teamrsquos interaction with the customersbull Have all important types of customers in target market been interacted withbull What do we know that we didnrsquot know when we started Any surprisesbull How can we improve the process

(ii) Explain the procedure to solve ethical conflicts (8)

1 DETERMINE whether there is an ethical issue orand dilemma Is there a conflict of values or rights or professional responsibilities (For example there may be an issue of self-determination of an adolescent versus the well-being of the family)

2 IDENTIFY the key values and principles involved What meanings and limitations are typically attached to these competing values (For example rarely is confidential information held in absolute secrecy however typically decisions about access by third parties to sensitive content should be contracted with clients)

3 RANK the values or ethical principles which - in your professional judgement - are most relevant to the issue or dilemmaWhat reasons can you provide for prioritizing one competing valueprinciple over another (For example your clients right to choose a beneficial course of action could bring hardship or harm to others who would be affected)

4 DEVELOP an action plan that is consistent with the ethical priorities that have been determined as central to the dilemmaHave you conferred with clients and colleagues as appropriate about the potential risks and consequences of alternative courses of action Can you support or justify your action plan with the valuesprinciples on which the plan is based (For example have you conferred with all the necessary persons regarding the ethical dimensions of planning for a battered wifes quest to secure secret shelter and the implications for her teen-aged children)

5 IMPLEMENT your plan utilizing the most appropriate practice skills and competencies How will you make use of core social work skills such as sensitive communication skillful negotiation and cultural competence (For example skillful colleague or supervisory communication and negotiation may enable an impaired colleague to see herhis impact on clients and to take appropriate action)

6 REFLECT on the outcome of this ethical decision making process How would you evaluate the consequences of this process for those involved Client(s) professional(s) and agency (ies) (Increasingly professionals have begun to seek support further professional training and consultation through the development of Ethics review Committees or Ethics Consultation processes)

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Phase I Conceptual Design

o It requires the creativityo Single best concept feasibility studyo Coordination among many functions in the business organizations

bull Identification of customer needsbull Problem definition

Problem Statement Benchmarking Quality Function Deployment (QFD) Product Design Specification (PDS)

bull Gathering information Internet Patents Trade Literature

bull Conceptualization Brainstorming Functional Decomposition Morphological Chart

bull Concept selection Pugh Concept Selection Decision Matrix

bull Refinement of the PDSbull Design review

Phase II Embodiment design or preliminary design

- Strength material selection size shape and spatial compatibilitybull Product architecture

Dividing overall design system into sub system or modules Arrangement of Physical Elements to carry out Function

bull Configuration design of parts and components Preliminary Selection of Parts and Materials Modeling and Sizing of Parts

Evaluate

OutcomeDesignProcess

GeneralInformation

SpecificInformation

NO YES

Parts are made up of features like holes ribs splines and curves To determine what features will be present amphow those

features are arranged in spacebull Parametric design To establish the exact dimensions and tolerances

Robust Design Tolerances Final Dimensions Design for Manufacturability (DFM)

Phase III Detail Designndash Complete engineering description of a tested and producible productndash Form dimensions tolerances properties materials and manufacturing process

of each partndash Engineering drawings ampcomputer generated drawings-determine assembly

drgndash Before the information passed on to manufacturing

Phase IV Planning For Manufacturendash Process sheet establishedndash List of manufacturing operations that must be performed on the component

bull It specifies the form and condition of material and tooling ampproduction mcrsquosbull Estimation of production cost of the component

ndash Designing specialized tools and fixturesndash Specify production plant to be usedndash Planning the work schedules amp inventory controlndash Planning the quality assurance systemndash Establishing the standard time and labor cost for each operation ndash Establish the system of information flow

Phase V Planning For Distributionndash Effective distribution to the consumer of the systemndash Marketing advertising and news media techniquesndash Shipping Packagendash Documentationndash Shelf Life

Define Problem

Problem StatementBenchmarking

QFD PDS

Gathering information

InternetPatentsTrade

Literature

Concept Generation

BrainstormingFunctional

DecompositionMorphological

Chart

Evaluation of concepts

Pugh Concept Selection

Decision Matrix

Product architecture

Arrangement of physical elements to carry out function

Configuration design

Preliminary Selection matls amp

mfgModelingsizing

Parametric design

Robust designTolerances

Final dimenDFM

Detail Design

Detailed drawings and specifications

ndash WarehousesPhase VI Planning For Use

ndash User oriented design processndash Ease of maintenance reliability safety aesthetic appeal economy of

operation duration of servicePhase VII Planning For Retirement Of The Product

ndash Disposal of the product end of its useful life

ndash Green design-recycling of materials remanufacture Useful Life

o Deteriorationo Technical Obsolescenceo Fashion or Tasteo Environmental Issues

Industrial Ecology Green Designo RFIo Power Consumption

(ii) State the characteristics of an environmentally responsible design(4)

o Easy to disassembleo Able to be recycledo Contains recycled materialso Uses identifiable and recyclable plasticso Reduces use of energy and natural materials in its manufactureo Manufactured without producing hazardous wasteo Avoids use of hazardous materialso Reduces product chemical emissionso Reduces product energy consumption

Or(b) Explain material cycle product cycle and manufacturing process cyclewith neat sketches (16)

12 (a) (i) Explain the process of identifying customer requirements withsuitable example (8)

bull Define the Scopendash Mission Statement

bull Gather Raw Datandash Interviewsndash Focus Groupsndash Observation

bull Interpret Raw Datandash Need Statements

bull Organize the Needsndash Hierarchy

bull Establish Importance

ndash Surveysndash Quantified Needs

bull Reflect on the Processndash Continuous Improvement

Example Screwdriver ProjectProduct Description

bull A hand-held power-assisted device for installing threaded fastenersKey Business Goals

bull Product introduced in 4th Q of 2000bull 50 gross marginbull 10 share of cordless screwdriver market by 2004

Primary Marketbull Do-it-yourself consumer

Secondary Marketsbull Casual consumerbull Light-duty professional

Assumptionsbull Hand-heldbull Power assistedbull Nickel-metal-hydride rechargeable battery technology

Stakeholdersbull Userbull Retailerbull Sales forcebull Service centerbull Productionbull Legal department

The process1 Gather raw data from customers2 Interpret raw data in terms of customer needs3 Organize needs into a hierarchy (primary secondary etc)4 Establish relative importance of each need5 Reflect on the results and the process

2 Gather raw data from customers1 Interviews2 Focus groups3 Observing product in use

3 Interpret raw data in terms of customer needs1 Express need as ldquowhatrdquo not ldquohowrdquo2 Express the need as specifically as the raw data3 Use positive not negative phrasing4 Express the need as an attribute to the product5 Avoid the words must and should

3 Organize needs into a hierarchy(one method)

bull Print each need on separate cardpost-itbull Eliminate redundant statementsbull Group cards according to similar needs metbull Choose a label for each group

bull Create supergroups (2 to 5 groups) where possiblebull Review edit the organized need statements

4 Establish relative importance of each needbull Develop a weighting system for customer needs

ndash Rely on consensus of the team based on their experience with customers

Orndash Use further customer surveys

5 Reflect on the results and the processbull Are results consistent with results of teamrsquos interaction with the customersbull Have all important types of customers in target market been interacted withbull What do we know that we didnrsquot know when we started Any surprisesbull How can we improve the process

(ii) Explain the procedure to solve ethical conflicts (8)

1 DETERMINE whether there is an ethical issue orand dilemma Is there a conflict of values or rights or professional responsibilities (For example there may be an issue of self-determination of an adolescent versus the well-being of the family)

2 IDENTIFY the key values and principles involved What meanings and limitations are typically attached to these competing values (For example rarely is confidential information held in absolute secrecy however typically decisions about access by third parties to sensitive content should be contracted with clients)

3 RANK the values or ethical principles which - in your professional judgement - are most relevant to the issue or dilemmaWhat reasons can you provide for prioritizing one competing valueprinciple over another (For example your clients right to choose a beneficial course of action could bring hardship or harm to others who would be affected)

4 DEVELOP an action plan that is consistent with the ethical priorities that have been determined as central to the dilemmaHave you conferred with clients and colleagues as appropriate about the potential risks and consequences of alternative courses of action Can you support or justify your action plan with the valuesprinciples on which the plan is based (For example have you conferred with all the necessary persons regarding the ethical dimensions of planning for a battered wifes quest to secure secret shelter and the implications for her teen-aged children)

5 IMPLEMENT your plan utilizing the most appropriate practice skills and competencies How will you make use of core social work skills such as sensitive communication skillful negotiation and cultural competence (For example skillful colleague or supervisory communication and negotiation may enable an impaired colleague to see herhis impact on clients and to take appropriate action)

6 REFLECT on the outcome of this ethical decision making process How would you evaluate the consequences of this process for those involved Client(s) professional(s) and agency (ies) (Increasingly professionals have begun to seek support further professional training and consultation through the development of Ethics review Committees or Ethics Consultation processes)

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Parts are made up of features like holes ribs splines and curves To determine what features will be present amphow those

features are arranged in spacebull Parametric design To establish the exact dimensions and tolerances

Robust Design Tolerances Final Dimensions Design for Manufacturability (DFM)

Phase III Detail Designndash Complete engineering description of a tested and producible productndash Form dimensions tolerances properties materials and manufacturing process

of each partndash Engineering drawings ampcomputer generated drawings-determine assembly

drgndash Before the information passed on to manufacturing

Phase IV Planning For Manufacturendash Process sheet establishedndash List of manufacturing operations that must be performed on the component

bull It specifies the form and condition of material and tooling ampproduction mcrsquosbull Estimation of production cost of the component

ndash Designing specialized tools and fixturesndash Specify production plant to be usedndash Planning the work schedules amp inventory controlndash Planning the quality assurance systemndash Establishing the standard time and labor cost for each operation ndash Establish the system of information flow

Phase V Planning For Distributionndash Effective distribution to the consumer of the systemndash Marketing advertising and news media techniquesndash Shipping Packagendash Documentationndash Shelf Life

Define Problem

Problem StatementBenchmarking

QFD PDS

Gathering information

InternetPatentsTrade

Literature

Concept Generation

BrainstormingFunctional

DecompositionMorphological

Chart

Evaluation of concepts

Pugh Concept Selection

Decision Matrix

Product architecture

Arrangement of physical elements to carry out function

Configuration design

Preliminary Selection matls amp

mfgModelingsizing

Parametric design

Robust designTolerances

Final dimenDFM

Detail Design

Detailed drawings and specifications

ndash WarehousesPhase VI Planning For Use

ndash User oriented design processndash Ease of maintenance reliability safety aesthetic appeal economy of

operation duration of servicePhase VII Planning For Retirement Of The Product

ndash Disposal of the product end of its useful life

ndash Green design-recycling of materials remanufacture Useful Life

o Deteriorationo Technical Obsolescenceo Fashion or Tasteo Environmental Issues

Industrial Ecology Green Designo RFIo Power Consumption

(ii) State the characteristics of an environmentally responsible design(4)

o Easy to disassembleo Able to be recycledo Contains recycled materialso Uses identifiable and recyclable plasticso Reduces use of energy and natural materials in its manufactureo Manufactured without producing hazardous wasteo Avoids use of hazardous materialso Reduces product chemical emissionso Reduces product energy consumption

Or(b) Explain material cycle product cycle and manufacturing process cyclewith neat sketches (16)

12 (a) (i) Explain the process of identifying customer requirements withsuitable example (8)

bull Define the Scopendash Mission Statement

bull Gather Raw Datandash Interviewsndash Focus Groupsndash Observation

bull Interpret Raw Datandash Need Statements

bull Organize the Needsndash Hierarchy

bull Establish Importance

ndash Surveysndash Quantified Needs

bull Reflect on the Processndash Continuous Improvement

Example Screwdriver ProjectProduct Description

bull A hand-held power-assisted device for installing threaded fastenersKey Business Goals

bull Product introduced in 4th Q of 2000bull 50 gross marginbull 10 share of cordless screwdriver market by 2004

Primary Marketbull Do-it-yourself consumer

Secondary Marketsbull Casual consumerbull Light-duty professional

Assumptionsbull Hand-heldbull Power assistedbull Nickel-metal-hydride rechargeable battery technology

Stakeholdersbull Userbull Retailerbull Sales forcebull Service centerbull Productionbull Legal department

The process1 Gather raw data from customers2 Interpret raw data in terms of customer needs3 Organize needs into a hierarchy (primary secondary etc)4 Establish relative importance of each need5 Reflect on the results and the process

2 Gather raw data from customers1 Interviews2 Focus groups3 Observing product in use

3 Interpret raw data in terms of customer needs1 Express need as ldquowhatrdquo not ldquohowrdquo2 Express the need as specifically as the raw data3 Use positive not negative phrasing4 Express the need as an attribute to the product5 Avoid the words must and should

3 Organize needs into a hierarchy(one method)

bull Print each need on separate cardpost-itbull Eliminate redundant statementsbull Group cards according to similar needs metbull Choose a label for each group

bull Create supergroups (2 to 5 groups) where possiblebull Review edit the organized need statements

4 Establish relative importance of each needbull Develop a weighting system for customer needs

ndash Rely on consensus of the team based on their experience with customers

Orndash Use further customer surveys

5 Reflect on the results and the processbull Are results consistent with results of teamrsquos interaction with the customersbull Have all important types of customers in target market been interacted withbull What do we know that we didnrsquot know when we started Any surprisesbull How can we improve the process

(ii) Explain the procedure to solve ethical conflicts (8)

1 DETERMINE whether there is an ethical issue orand dilemma Is there a conflict of values or rights or professional responsibilities (For example there may be an issue of self-determination of an adolescent versus the well-being of the family)

2 IDENTIFY the key values and principles involved What meanings and limitations are typically attached to these competing values (For example rarely is confidential information held in absolute secrecy however typically decisions about access by third parties to sensitive content should be contracted with clients)

3 RANK the values or ethical principles which - in your professional judgement - are most relevant to the issue or dilemmaWhat reasons can you provide for prioritizing one competing valueprinciple over another (For example your clients right to choose a beneficial course of action could bring hardship or harm to others who would be affected)

4 DEVELOP an action plan that is consistent with the ethical priorities that have been determined as central to the dilemmaHave you conferred with clients and colleagues as appropriate about the potential risks and consequences of alternative courses of action Can you support or justify your action plan with the valuesprinciples on which the plan is based (For example have you conferred with all the necessary persons regarding the ethical dimensions of planning for a battered wifes quest to secure secret shelter and the implications for her teen-aged children)

5 IMPLEMENT your plan utilizing the most appropriate practice skills and competencies How will you make use of core social work skills such as sensitive communication skillful negotiation and cultural competence (For example skillful colleague or supervisory communication and negotiation may enable an impaired colleague to see herhis impact on clients and to take appropriate action)

6 REFLECT on the outcome of this ethical decision making process How would you evaluate the consequences of this process for those involved Client(s) professional(s) and agency (ies) (Increasingly professionals have begun to seek support further professional training and consultation through the development of Ethics review Committees or Ethics Consultation processes)

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

ndash WarehousesPhase VI Planning For Use

ndash User oriented design processndash Ease of maintenance reliability safety aesthetic appeal economy of

operation duration of servicePhase VII Planning For Retirement Of The Product

ndash Disposal of the product end of its useful life

ndash Green design-recycling of materials remanufacture Useful Life

o Deteriorationo Technical Obsolescenceo Fashion or Tasteo Environmental Issues

Industrial Ecology Green Designo RFIo Power Consumption

(ii) State the characteristics of an environmentally responsible design(4)

o Easy to disassembleo Able to be recycledo Contains recycled materialso Uses identifiable and recyclable plasticso Reduces use of energy and natural materials in its manufactureo Manufactured without producing hazardous wasteo Avoids use of hazardous materialso Reduces product chemical emissionso Reduces product energy consumption

Or(b) Explain material cycle product cycle and manufacturing process cyclewith neat sketches (16)

12 (a) (i) Explain the process of identifying customer requirements withsuitable example (8)

bull Define the Scopendash Mission Statement

bull Gather Raw Datandash Interviewsndash Focus Groupsndash Observation

bull Interpret Raw Datandash Need Statements

bull Organize the Needsndash Hierarchy

bull Establish Importance

ndash Surveysndash Quantified Needs

bull Reflect on the Processndash Continuous Improvement

Example Screwdriver ProjectProduct Description

bull A hand-held power-assisted device for installing threaded fastenersKey Business Goals

bull Product introduced in 4th Q of 2000bull 50 gross marginbull 10 share of cordless screwdriver market by 2004

Primary Marketbull Do-it-yourself consumer

Secondary Marketsbull Casual consumerbull Light-duty professional

Assumptionsbull Hand-heldbull Power assistedbull Nickel-metal-hydride rechargeable battery technology

Stakeholdersbull Userbull Retailerbull Sales forcebull Service centerbull Productionbull Legal department

The process1 Gather raw data from customers2 Interpret raw data in terms of customer needs3 Organize needs into a hierarchy (primary secondary etc)4 Establish relative importance of each need5 Reflect on the results and the process

2 Gather raw data from customers1 Interviews2 Focus groups3 Observing product in use

3 Interpret raw data in terms of customer needs1 Express need as ldquowhatrdquo not ldquohowrdquo2 Express the need as specifically as the raw data3 Use positive not negative phrasing4 Express the need as an attribute to the product5 Avoid the words must and should

3 Organize needs into a hierarchy(one method)

bull Print each need on separate cardpost-itbull Eliminate redundant statementsbull Group cards according to similar needs metbull Choose a label for each group

bull Create supergroups (2 to 5 groups) where possiblebull Review edit the organized need statements

4 Establish relative importance of each needbull Develop a weighting system for customer needs

ndash Rely on consensus of the team based on their experience with customers

Orndash Use further customer surveys

5 Reflect on the results and the processbull Are results consistent with results of teamrsquos interaction with the customersbull Have all important types of customers in target market been interacted withbull What do we know that we didnrsquot know when we started Any surprisesbull How can we improve the process

(ii) Explain the procedure to solve ethical conflicts (8)

1 DETERMINE whether there is an ethical issue orand dilemma Is there a conflict of values or rights or professional responsibilities (For example there may be an issue of self-determination of an adolescent versus the well-being of the family)

2 IDENTIFY the key values and principles involved What meanings and limitations are typically attached to these competing values (For example rarely is confidential information held in absolute secrecy however typically decisions about access by third parties to sensitive content should be contracted with clients)

3 RANK the values or ethical principles which - in your professional judgement - are most relevant to the issue or dilemmaWhat reasons can you provide for prioritizing one competing valueprinciple over another (For example your clients right to choose a beneficial course of action could bring hardship or harm to others who would be affected)

4 DEVELOP an action plan that is consistent with the ethical priorities that have been determined as central to the dilemmaHave you conferred with clients and colleagues as appropriate about the potential risks and consequences of alternative courses of action Can you support or justify your action plan with the valuesprinciples on which the plan is based (For example have you conferred with all the necessary persons regarding the ethical dimensions of planning for a battered wifes quest to secure secret shelter and the implications for her teen-aged children)

5 IMPLEMENT your plan utilizing the most appropriate practice skills and competencies How will you make use of core social work skills such as sensitive communication skillful negotiation and cultural competence (For example skillful colleague or supervisory communication and negotiation may enable an impaired colleague to see herhis impact on clients and to take appropriate action)

6 REFLECT on the outcome of this ethical decision making process How would you evaluate the consequences of this process for those involved Client(s) professional(s) and agency (ies) (Increasingly professionals have begun to seek support further professional training and consultation through the development of Ethics review Committees or Ethics Consultation processes)

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

ndash Surveysndash Quantified Needs

bull Reflect on the Processndash Continuous Improvement

Example Screwdriver ProjectProduct Description

bull A hand-held power-assisted device for installing threaded fastenersKey Business Goals

bull Product introduced in 4th Q of 2000bull 50 gross marginbull 10 share of cordless screwdriver market by 2004

Primary Marketbull Do-it-yourself consumer

Secondary Marketsbull Casual consumerbull Light-duty professional

Assumptionsbull Hand-heldbull Power assistedbull Nickel-metal-hydride rechargeable battery technology

Stakeholdersbull Userbull Retailerbull Sales forcebull Service centerbull Productionbull Legal department

The process1 Gather raw data from customers2 Interpret raw data in terms of customer needs3 Organize needs into a hierarchy (primary secondary etc)4 Establish relative importance of each need5 Reflect on the results and the process

2 Gather raw data from customers1 Interviews2 Focus groups3 Observing product in use

3 Interpret raw data in terms of customer needs1 Express need as ldquowhatrdquo not ldquohowrdquo2 Express the need as specifically as the raw data3 Use positive not negative phrasing4 Express the need as an attribute to the product5 Avoid the words must and should

3 Organize needs into a hierarchy(one method)

bull Print each need on separate cardpost-itbull Eliminate redundant statementsbull Group cards according to similar needs metbull Choose a label for each group

bull Create supergroups (2 to 5 groups) where possiblebull Review edit the organized need statements

4 Establish relative importance of each needbull Develop a weighting system for customer needs

ndash Rely on consensus of the team based on their experience with customers

Orndash Use further customer surveys

5 Reflect on the results and the processbull Are results consistent with results of teamrsquos interaction with the customersbull Have all important types of customers in target market been interacted withbull What do we know that we didnrsquot know when we started Any surprisesbull How can we improve the process

(ii) Explain the procedure to solve ethical conflicts (8)

1 DETERMINE whether there is an ethical issue orand dilemma Is there a conflict of values or rights or professional responsibilities (For example there may be an issue of self-determination of an adolescent versus the well-being of the family)

2 IDENTIFY the key values and principles involved What meanings and limitations are typically attached to these competing values (For example rarely is confidential information held in absolute secrecy however typically decisions about access by third parties to sensitive content should be contracted with clients)

3 RANK the values or ethical principles which - in your professional judgement - are most relevant to the issue or dilemmaWhat reasons can you provide for prioritizing one competing valueprinciple over another (For example your clients right to choose a beneficial course of action could bring hardship or harm to others who would be affected)

4 DEVELOP an action plan that is consistent with the ethical priorities that have been determined as central to the dilemmaHave you conferred with clients and colleagues as appropriate about the potential risks and consequences of alternative courses of action Can you support or justify your action plan with the valuesprinciples on which the plan is based (For example have you conferred with all the necessary persons regarding the ethical dimensions of planning for a battered wifes quest to secure secret shelter and the implications for her teen-aged children)

5 IMPLEMENT your plan utilizing the most appropriate practice skills and competencies How will you make use of core social work skills such as sensitive communication skillful negotiation and cultural competence (For example skillful colleague or supervisory communication and negotiation may enable an impaired colleague to see herhis impact on clients and to take appropriate action)

6 REFLECT on the outcome of this ethical decision making process How would you evaluate the consequences of this process for those involved Client(s) professional(s) and agency (ies) (Increasingly professionals have begun to seek support further professional training and consultation through the development of Ethics review Committees or Ethics Consultation processes)

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

bull Create supergroups (2 to 5 groups) where possiblebull Review edit the organized need statements

4 Establish relative importance of each needbull Develop a weighting system for customer needs

ndash Rely on consensus of the team based on their experience with customers

Orndash Use further customer surveys

5 Reflect on the results and the processbull Are results consistent with results of teamrsquos interaction with the customersbull Have all important types of customers in target market been interacted withbull What do we know that we didnrsquot know when we started Any surprisesbull How can we improve the process

(ii) Explain the procedure to solve ethical conflicts (8)

1 DETERMINE whether there is an ethical issue orand dilemma Is there a conflict of values or rights or professional responsibilities (For example there may be an issue of self-determination of an adolescent versus the well-being of the family)

2 IDENTIFY the key values and principles involved What meanings and limitations are typically attached to these competing values (For example rarely is confidential information held in absolute secrecy however typically decisions about access by third parties to sensitive content should be contracted with clients)

3 RANK the values or ethical principles which - in your professional judgement - are most relevant to the issue or dilemmaWhat reasons can you provide for prioritizing one competing valueprinciple over another (For example your clients right to choose a beneficial course of action could bring hardship or harm to others who would be affected)

4 DEVELOP an action plan that is consistent with the ethical priorities that have been determined as central to the dilemmaHave you conferred with clients and colleagues as appropriate about the potential risks and consequences of alternative courses of action Can you support or justify your action plan with the valuesprinciples on which the plan is based (For example have you conferred with all the necessary persons regarding the ethical dimensions of planning for a battered wifes quest to secure secret shelter and the implications for her teen-aged children)

5 IMPLEMENT your plan utilizing the most appropriate practice skills and competencies How will you make use of core social work skills such as sensitive communication skillful negotiation and cultural competence (For example skillful colleague or supervisory communication and negotiation may enable an impaired colleague to see herhis impact on clients and to take appropriate action)

6 REFLECT on the outcome of this ethical decision making process How would you evaluate the consequences of this process for those involved Client(s) professional(s) and agency (ies) (Increasingly professionals have begun to seek support further professional training and consultation through the development of Ethics review Committees or Ethics Consultation processes)

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Or(b) (i) Explain the relationship between QFD and PDS and classify

ergonomics and aesthetic needs (8)

Quality Function Deployment

bull QFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product

bull Group decision-making activitybull Graphical representation using a diagram called ldquoHouse of Qualityrdquo

1Customer Requirements

Affinity diagramUsed organize the ideas facts opinions

2Competitive assessmentCompetitive product rank wrto two or three products scale 1-5

3Important ratings

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Product of customer importance improvement ratio and sales point

Relative weight Each value of importance weight divided by sum of all values of importance weight

Sum of relative weight is equal to unity4 Engineering characteristics Satisfying the customer requirements are listed in column Characteristics that can be measure and given target value weight force velocity and etc

+ indicates higher value is better - Lower value is better5The correlation matrix The degree of interdependence among the engineering characteristics in the ldquoroof of house

9 or a strong relationship 3 or O medium relationship

6Relationship matrixndash the correlation between the engineering characteristics and customer

requirementsndash Non linear scale 9310 weight disproposonality those ECs strongly effect

customer requirements

7Absolute importancendash multiply the numerical value in each of the cells of the relationship matrix[6]

by the importance rating [3] then sum of the numbers in the cells each column8Relative importance

normalized scale 1 to 100 each value absolute importance divide by total and multiply by 100

9Technical competitive assessment bench mark scale1 to 5 10Technical Difficulty Ease with which each of the ease ECs can be achived1- low probability success 5- high probability of success11Target value satisfy the requirements

ndash By knowing important ECs technical competition feel for the technical difficulty team to said target value for each ECs

From customer requirement to production planning

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Product Design Specification (PDS)

The basic control and reference documents for the design and manufacture of the product

The PDS is a documents which contains all of the facts related to the outcome of the product development Elements

performancespeedcapacitypoweraccuracy

bull In-use purpose amp marketndash Product titlendash Function the product is to performndash Special features of the productndash What is the intended marketndash Relationship of the product to the other company productsndash Target company selling price and estimated retail price

bull Functional requirementsndash Functional performance flow of energy information materials operational

steps accuracy efficiencybull Physical requirements

ndash Size weightshapesurface finishndash Service requirementndash Factory floor transportation humidity dirt

bull Life ndashcycle issues human factorsndash Useful life aestheticsndash Reliability man-mc interfacendash Robustness user trainingndash Maintainabilityndash Testabilityndash Repairabilityndash Installabilityndash Retirement from service and recyclabilityndash Cost of operation

bull Corporative constraintsndash Time to marketndash Manufacturing requirementndash Suppliersndash Financial performancendash Corporate ethics

bull Social political legal requirementsndash Safety and environmental regulationsndash Standardsndash Product liabilityndash Patents and intellectual property

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

ndash Complete possible outset of designndash Quantitative

ERGONOMIC NEEDS

Planning the workflow to eliminate unnecessary lifting lowering and carrying of materials

Organizing work so that physical demands and work pace increase gradually Minimizing distances materials are lifted lowered and carried Reduce the frequency of lifting lowering and carrying and the amount of time spent

in these tasks by rotating workers through tasks Clear spaces to improve access to materials being handled which allows workers to

get closer and reduces reaching bending and twisting

(ii) Explain the various Sample Codes of Conduct (8)

A code of conduct is a set of rules outlining the responsibilities of or proper practices for an individual party or organization Related concepts include ethical codes and honor codes

13 (a) (i) Discuss the various types of creativity methods (8)(ii) Generate Morphological chart for the design of a CD case (4)

Steps to follow1 Arrange the functions and subfunctions in logical order2 List for each subfunction ldquohowrdquo3 Combine concepts

SubfunctionConcept

1 2 3 4 5

10 Open case

11 Hold and grip case

Flat box Groove boxCurved box Case with handle

Rubber grip strips

12 Disengage lock

Friction lock Inclined plane lock

Magnetic lock

Clamp lock Clicking hinge lock

13 Expose CD Conventional hinge

One-piece flex plastic hinge

Slide-out like match box

Tilt like shampoo bottle top

20 Extract CD

21 Disengage from securing system

Conventional Rosetta

Liftlock device

Padded cradle

1Open case

2Extract

CD

3Extractleaflet

4Replace

CD

5Replace

leaflet

6Closecase

7Store case

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

22 Grasp CD and remove

Hand

30 Extract leaflet

31 Disengage from securing system

Tabs Holding slot Velcro straps

Tab that swivels

No securing system

32 Remove leaflet

40 Replace CD

41 Place CD in securing system

Hand

42 Engage securing system

2-finger push

Whole hand

50 Replace leaflet

51 Place leaflet in securing system

Slide into position Lay in position

52 Engage securing system

Slide under tabs or in slot

Swivel tabs Attach Velcro

60 Close case

61 Engage lock

Friction surfaces Put magnet together Slide platen into position

70 Store case

71 Place case in desired location

Put on table Put on another CD Put in special CD holder

Assume that 5 concepts are drawn from the previous chartConcept 1 Conventional square box (1) with the incline plane lock (2) and a slide-out matchbox (3) for a hinge The CD is secured with a conventional ldquorosettardquo (1) while the leaflet is secured with tab (1)

Concept 2 A streamline curved box to fit the hand (3) with a friction lock (2) and a conventional hinge (3) The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2)

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Concept 3 The box is grooved to the shape of the finger (2) with a magnetic lock (3) and conventional hinges (1) A new liftlock secures the CD (2) The leaflet fits in a slot in the top of the case (2)Concept 4 A standard square box (1) with magnetic lock (3) and conventional hinges (1) The CD is secured with a padded cradle (3) while the leaflet is secured with Velcro straps (3)

Concept 5 A curved box (3) with inclined plane lock (2) with a slide-out matchbox (3) The CD is held by a rosetta (1) and the leaflet fits into a slot (2) The cases are designed to stack (2)

(iii) State the various levels in Pughrsquos concept selection method (4)1 Choose the criteria by which the concepts will be evaluated2 Formulate the decision matrix3 Clarify the design concept4 Choose the datum concept5 Run the matrix6 Evaluate the rating7 Establish a new datum and rerun the matrix8 Plan further work9 Second working session

Or(b) (i) Discuss in detail the levels and principle of Theory of InventiveProblem Solving (TRIZ) (8)

TRIZ ndash 40 Principles

1 Segmentation 2 Taking out 3 Local quality 4 Asymmetry 5 Merging 6 Universality 7 Russian dolls 8 Anti-weight 9 Preliminary anti-action 10 Preliminary action 11 Beforehand cushioning12 Equipotentiality 13 The other way round 14 Spheroidality - Curvature 15 Dynamics 16 Partial or excessive actions 17 Another dimension 18 Mechanical vibration 19 Periodic action 20 Continuity of useful action 21 Skipping22 Blessing in disguise

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

23 Feedback24 Intermediary25 Self-service26 Copying27 Cheap short-lived objects28 Mechanics substitution29 Pneumatics and hydraulics30 Flexible shells and thin films31 Porous materials32 Colour changes33 Homogeneity34 Discarding and recovering35 Parameter changes36 Phase transitions37 Thermal expansion38 Strong oxidants39 Inert atmosphere40 Composite materials

(ii) Explain the axiomatic design and parametric design (8)

o Developed by Professor Nam Suh and his colleagues at MITo Focus around 2 design axioms

Axiom 1 The independent axiomMaintain the independence of functional requirements (FRs)

Axiom 2 The information axiomMinimize the information content

Corollary 1Decoupling of a coupled designDecouple or separate parts or aspects of a solution if FRs are coupled or become interdependent in the proposed designCorollary 2

Minimize FRsMinimize the number of FRs and constraints

Corollary Integration of physical parts

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

3 Integrate design features in a single physical part if FRs can be independently satisfied in the proposed solution

Corollary 4

Use of standardizationUse standardized or interchangeable parts if the use of these parts is consistent with the FRs and constraints

Corollary 5

Use of symmetryUse symmetric shapes andor arrangement if they are consistent with the FRs and constraints Symmetrical parts require less information to manufacture and to orient in assembly

Corollary 6

Largest toleranceSpecify the largest allowable tolerance in stating FRs

Corollary 7

Uncoupled design with less informationSeek an uncoupled design that requires less information than coupled designs in satisfying a set of FRs

14 (a) State the general design guidelines for Machining Forging WeldingCasting Metal forming and Assembly (16)

Or(b) (i) Explain in detail the weighted Property Index and Economics ofdesign (8)(ii) Explain the design criteria for fatigue fracture and failure (8)

Criteria for fatigue design have evolved from infinite life to damage tolerance Each of the successively developed criteria still has its place depending on the application The criteria for fatigue design include usage of the four fatigue life models (S-N -N dadN-K two-stage method) These criteria are Infinite-Life Design Safe-Life Design Fail-Safe Design Damage-Tolerant Design

Infinite-Life Design Unlimited safety is the oldest criterion It requires local stresses or strains to be essentially elastic and safely below the fatigue limit For parts subjected to many millions of cycles like engine valve springs this is still a good design criterion This criterion may not be economical (ie global

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

competitiveness) or practical (ie excessive weight of aircraft) in many design situationsSafe-Life Design The practice of designing for a finite life is known as safe-life design It is used in many industries for instance automotive industry in pressure vessel design and in jet engine design The calculations may be based on stress-life strain-life or crack growth relations Ball bearings and roller bearings are examples of safe-life design The safe life must include a margin for the scatter of fatigue results and for other unknown factors The margin for safety in safe-life design may be taken in terms of life in terms of load or by specifying that both margins must be satisfied as in the ASME Boiler and Pressure Vessel Code

Fail-Safe Design Fail-safe design requires that if one part fails the system does not fail Fail-safe design recognizes that fatigue cracks may occur and structures are arranged so that cracks will not lead to failure of the structure before they are detected and repaired Multiple load paths load transfer between members crack stoppers built at intervals into the structure and inspection are some of the means used to achieve failsafe designDamage-Tolerant Design This philosophy is a refinement of the fail-safe philosophy It assumes that cracks will exist caused either by processing or by fatigue and uses fracture mechanics analyses and tests to check whether such cracks will grow large enough to produce failures before they are detected by periodic inspection Three key items are needed for successful damagetolerant design residual strength fatigue crack growth behavior and crack detection involving nondestructive inspectionResidual strength is the strength at any instant in the presence of a crack With no cracks this could be the ultimate tensile strength or yield strength depending upon failure criteria chosen As a crack forms and grows under cyclic loading the residual strength decreases Crack detection methods using different nondestructive inspection techniques have been developed Inspection periods must be laid out such that as the crack grows the applied stresses remain below the residual strength This philosophy looks for materials with slow crack growth and high fracture toughness Damage-tolerant design has been required by

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

the US Air Force In pressure vessel design ldquoleak before burstrdquo is an expression of damage-tolerant philosophy Retirement for cause (extended service life) is a special situation requiring damage-tolerant usage

15 (a) (i) Explain the different methods to improve reliability and discussabout the cost of reliability (8)

Reliabilitybull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time

ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

periodbull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

(ii) Explain the process of FMEA and state the importance of robustdesign (8)

Failure mode and effect analysis is a tool that examines potential product or process failures evaluates risk priorities and helps determine remedial actions to avoid identified problems

An FMEA is a tool to Identify the relative risks designed into a product or process Initiate action to reduce those risks with the highest potential impact Track the results of the action plan in terms of risk reduction

FMEA Procedure

bull Assign a label to each system component

bull Describe the functions of each part

bull Identify potential failures for each function

bull Determine the likelihood of detecting the failure

bull Determine which risks take priority

bull Address the highest risksndash Assign a Risk Priority Number

bull Update the FMEA as action

bull Determine the effects of the failures

bull Estimate the severity of the failure

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

bull Estimate the probability of occurrence

bull RPN= Severity Occurrence Detection

Failure Categoriesbull Complete Failure

bull Partial Failure

bull Intermittent Failure

bull Failure over Timebull Over- Performance of Function

Failure Modes are grouped into one of those five categoriesAsymmetrical pentagons

Control Groupings

bull Type 1 ndash prevent the causebull Type 2 ndash detect the causebull Type 3 ndash detect the failure modebull Any cause may be a failure mode Any effect in and of itself may be a failure mode

FMEA Worksheet

FMEA cycle

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Step 1 OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past A failure cause is looked upon as a design weakness All the potential causes for a failure mode should be identified and documented Again this should be in technical terms Examples of causes are erroneous algorithms excessive voltage or improper operating conditions A failure mode is given an occurrence ranking (O) again 1ndash10 Actions need to be determined if the occurrence is high (meaning gt 4 for non-safety failure modes and gt 1 when the severity-number from step 1 is 1 or 0) This step is called the detailed development section of the FMEA process Occurrence also can be defined as If a non-safety issue happened less than 1 we can give 1 to it It is based on your product and customer specification

Rating Meaning

1 No known occurrences on similar products or processes

23 Low (relatively few failures)

456 Moderate (occasional failures)

78 High (repeated failures)

910 Very high (failure is almost inevitable)

Step 2 SeverityDetermine all failure modes based on the functional requirements and their effects Examples of failure modes are Electrical short-circuiting corrosion or deformation A failure mode in one

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

component can lead to a failure mode in another component therefore each failure mode should be listed in technical terms and for function Hereafter the ultimate effect of each failure mode needs to be considered A failure effect is defined as the result of a failure mode on the function of the system as perceived by the user In this way it is convenient to write these effects down in terms of what the user might see or experience Examples of failure effects are degraded performance noise or even injury to a user Each effect is given a severity number (S) from 1 (no danger) to 10 (critical) These numbers help an engineer to prioritize the failure modes and their effects If the sensitivity of an effect has a number 9 or 10 actions are considered to change the design by eliminating the failure mode if possible or protecting the user from the effect A severity rating of 9 or 10 is generally reserved for those effects which would cause injury to a user or otherwise result in litigation

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system noticed by average customer)

456 Moderate (most customers are annoyed)

78 High (causes a loss of primary function customers are dissatisfied)

910Very high and hazardous (product becomes inoperative customers angered the failure may result unsafe operation and possible injury)

Step 3 DetectionWhen appropriate actions are determined it is necessary to test their efficiency In addition design verification is needed The proper inspection methods need to be chosen First an engineer should look at the current controls of the system that prevent failure modes from occurring or which detect the failure before it reaches the customer Hereafter one should identify testing analysis monitoring and other techniques that can be or have been used on similar systems to detect failures From these controls an engineer can learn how likely it is for a failure to be identified or detected Each combination from the previous 2 steps receives a detection number (D) This ranks the ability of planned tests and inspections to remove defects or detect failure modes in time The assigned detection number measures the risk that the failure will escape detection A high detection number indicates that the chances are high that the failure will escape detection or in other words that the chances of detection are low

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Rating Meaning

1 Certain - fault will be caught on test

2 Almost Certain

3 High

456 Moderate

78 Low

910 Fault will be passed to customer undetected

After these three basic steps risk priority numbers (RPN) are calculated

Risk priority number (RPN)RPN play an important part in the choice of an action against failure modes They are threshold values in the evaluation of these actions

After ranking the severity occurrence and detectability the RPN can be easily calculated by multiplying these three numbers RPN = S times O times D

This has to be done for the entire process andor design Once this is done it is easy to determine the areas of greatest concern The failure modes that have the highest RPN should be given the highest priority for corrective action This means it is not always the failure modes with the highest severity numbers that should be treated first There could be less severe failures but which occur more often and are less detectable

After these values are allocated recommended actions with targets responsibility and dates of implementation are noted These actions can include specific inspection testing or quality procedures redesign (such as selection of new components) adding more redundancy and limiting environmental stresses or operating range Once the actions have been implemented in the designprocess the new RPN should be checked to confirm the improvements These tests are often put in graphs for easy visualization Whenever a design or a process changes an FMEA should be updated

A few logical but important thoughts come in mind

Try to eliminate the failure mode (some failures are more preventable than others) Minimize the severity of the failure (severity of a failure cannot be changed) Reduce the occurrence of the failure mode Improve the detection

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Timing of FMEAThe FMEA should be updated whenever

A new cycle begins (new productprocess) Changes are made to the operating conditions A change is made in the design New regulations are instituted Customer feedback indicates a problem

Uses of FMEA

Development of system requirements that minimize the likelihood of failures Development of methods to design and test systems to ensure that the failures have been

eliminated Evaluation of the requirements of the customer to ensure that those do not give rise to

potential failures Identification of certain design characteristics that contribute to failures and minimize or

eliminate those effects Tracking and managing potential risks in the design This helps avoid the same failures in

future projects Ensuring that any failure that could occur will not injure the customer or seriously impact a

system To produce world class quality products

Advantages

Improve the quality reliability and safety of a productprocess Improve company image and competitiveness Increase user satisfaction Reduce system development timing and cost Collect information to reduce future failures capture engineering knowledge Reduce the potential for warranty concerns Early identification and elimination of potential failure modes Emphasize problem prevention Minimize late changes and associated cost Catalyst for teamwork and idea exchange between functions Reduce the possibility of same kind of failure in future Reduce impact of profit margin company Reduce possible scrap in production

SoftwareMost FMEAs are created as a spreadsheet Specialized FMEA software packages exist that offer some advantages over spreadsheets

Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

Process analysis of manufacturing and assembly processes Design analysis of products prior to production Concept analysis of systems or subsystems in the early design concept stages Equipment analysis of machinery and equipment design before purchase Service analysis of service industry processes before they are released to impact the

customer System analysis of the global system functions Software analysis of the software functions

Or(b) (i) Derive the expression for reliability and explain about the systemreliability (8)Reliability

bull Reliability provides a numerical measure of ldquodegree of excellencerdquo through time ndash Failure the inability of an equipment to perform its required functionndash Reliability the probability of no failure throughout a prescribed operating

period

bull Failure rates bull Reliability bull Constant failure rate and exponential distributionbull System Reliability

ndash Components in seriesndash Components in parallelndash Combination system

System Reliability

bull Most products are made up of a number of components

Failure rate the probability of a failure during a stated period is calculated as follows

The average life is calculated as follows

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

bull The reliability of each component and the configuration of the system consisting of these components determines the system reliability (ie the reliability of the product)

bull The components may be in ndash series system operates if all components operatendash parallel system operates is any component operatesndash combination of series and parallel

Components in Series

bull If the components are in series the system operates if all the components operatebull If there are n components in series where the reliability if the i-th component is

denoted by ri the system reliability is

A B C

Components in Parallelbull If the components are in parallel the system operates if any component operatesbull If there are n components in parallel where the reliability of the i-th component is

denoted by ri the system reliability is

B

C

A

Redundant Systems and Backup Components

bull If a system contains a backup or spare components it can be treated as the one with components in parallelThe following formula is equivalent to

is equivalent to

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA

PowerSource

Battery

(ii) Explain the various steps of hypothesis testing (8)

• Step 1 Occurrence
• Step 2 Severity
• Step 3 Detection
• Risk priority number (RPN)
• Timing of FMEA
• Uses of FMEA
• Advantages
• Types of FMEA