machinedesign intro ssroy

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4 February 2009 Machine Design 1

Under Graduate Course on

Machine Design-I

Design of Machine Elements

Shibendu Shekhar RoyRobotics & A.I Lab. (RAIL)

Department of Mechanical Engineering


Reference Books1. V.B. Bhandari, “Design of Machine Elements ”, <second edition>, Tata McGraw Hill.2. J.E. Shigley, C.R. Mischke, “Mechanical Engineering Design”, Tata McGraw Hill.3. M.F. Spotts & T.E. Shoup, “Design of Machine Elements”, Pearson Education.

Machine Design Handbook

1. “Design Data”, Compiled by Faculty of Mechanical Engineering, PSG College, Coimbatore2. “CMTI Hand Book”, Compiled by Scientists of Central Manufacturing technology Institute, Bangalore

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- Mechanical properties of Engineering materials- B.I.S system of designation of commonly used Engineering Materials

- Selection of Materials

Engineering Materials

- Design of Threaded Joints- Design of Welded Joints

Plate Joints

- Design of Cotter Joint- Design of Knuckle Joint

Rod Joints

- Review of Stress, Strain and Complex stresses in machine members

- Basic procedure of machine design & machine element design

- Manufacturing & other consideration in machine design- Modern Computational Tools for Machine Design- Role of CAD/CAE in Machine Design

Introduction TopicsChapter

Topics to be Covered


Topics to be Covered

TopicsChapter- Elastic failure theories, Factor of safety, Service factor

- General principles & procedures of design of machine elements

Design against Static Load

- Stress Concentration factor, Fatigue failure, Endurance limit etc.

- Reversed stresses- design for finite & infinite life, Impact stresses etc.

Design against Dynamic Load

- Design of Shaft under Torsion, Bending, Axial & Combined loads

- Design of keys like square & flat, saddle, sunk, woodruff keys etc.

Design of Shafts, Keys, Splines

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Design of Machine Element

Cam

C-frame

Spring

Brake

Connecting rod

GearDrive

Shaft & Axle

Welded Joint

Belt, Rope, chainDrive

Bearing

Key

IC engine parts

Pressure vessel

Cotter & KnuckleJoint Bolted JointRiveted

Joint

Clutch

Coupling

Power Screw


Machine Design

Introduction

Objective of a Designer is to design & develop a product (devices, machinery, mechanical system) or process that is functional, safe, reliable, usable, manufacturable, competitive & marketable by using different engineering tools [ like Mathematics, CAD-CAE etc.]

Design is the process of problem solving

Design is a decision making process

Design is an iterative process

Design is an innovative or creative process

In Mechanical Engineering

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Mechanical Engineering Systems

Mechanical Design

Structures & Motion Stem

Energy Stem

Energy Stem in Mechanical Engineering Design of heat exchangersDesign of IC enginesDesign of boilersDesign of air compressors, gas turbine etc…

They rely on the use of technical materials from thermodynamics, heat transfer, combustion etc.

Structures & Motion Stem in mechanical EngineeringDesign of gear boxDesign of belt drive, chain drive systemDesign of suspension systemsDesign of machine structure etc…

They draw on technical materials from solid mechanics, kinematics, dynamics etc.

Mechanical design applies to design in mechanical engineering systems where both stems can be involvedMachine Design is a sub-set of mechanical design where the focus is on Structures & Motion stem only


the use of scientific principles, technical information, skill & imagination in the description of configuration of a mechanical system/ machine to perform specific functions with maximum economy & efficiency

Mechanical Engineering Design/ Machine Design

uses principles of basic engineering sciencesDesigner

has technical information of basic elements of machine like fasteners, gear, belt drive, bearing etc.

- Relative advantages & disadvantages of basic elements & their suitability in different applications.

uses skill & imagination to produce a configuration, which is a combination of basic elements.

- Intellectual part of constructing a proper configuration is creative in nature

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Machine Design

Mechanism

Kinematic Link

MachineMachine Tool

Kinematic Pair

One link fixed

All Machines are Mechanism but all Mechanisms are not Machine

All Machine Tools are Machine but all Machines are not Machine Tool

Mechanismtransfers

transforms

Motion

transfers

transforms

Energy

Kinematic ChainMachine

Machine tool is a contrivance having a combination of mechanisms/machines whereby a cutting tool is enabled to operate in a pre-conceived manner in order to produce a surface of desired shape, size or a degree of finish by removing metal from workpiece in the form of chips.

Primary Objectives


Basics of Mechanism

Mechanism

Kinematic Link

Kinematic Pair

One link fixed

Mechanismtransfers

transforms

Motion

Kinematic Chain

Kinematic Link - Each part of a mechanism which has motion relative to some other part

Kinematic Pair - is a joint of two links having relative motion between them

Machine

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Basics of Mechanism

Types of Kinematic Pairs

According to Nature of Contact

According to Nature of

Relative Motion

Turning/ Revolute Pair

Screw Pair

Cylindrical Pair

Lower Pair

Sliding/ Prismatic Pair

Higher Pair

Spherical Pair


Kinematic Chain

Basics of Mechanism

- A combination of kinematic pairs joined in such a way the relative motion of any point on a link w.r.t the any other point on other link follows a definite law.

Mechanism

Kinematic Link

Kinematic Pair

One link fixed

Kinematic Chain

Machine

Mechanism - A kinematic chain in which one link fixed & used for transmitting & transforming motion.

transfers

transforms

EnergyMachine

Closed Chain

Open Chain

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Machine - Combination of resistant bodies having definite motions & capable of performing useful work.

Mechanism - assemblage of resistant bodies, connected by joints, to form a kinematic chain with one link fixed & having the purpose of transmitting & transforming motion.

- provides the definite motion of the parts of a machine.


Design

Design SynthesisDesign Analysis

Mechanismis given

Inputs Outputs

Machine Design

Given Configuration, material & assume mode of failure

determines the dimension

decision –making process

process of creating new configuration/ mechanism

Selecting optimum/best configuration from no. of existing mechanism

Selecting materials from no. of alternative materials

Determination of optimum shape & dimensions of the component on the basis of design analysis

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Identification of Need

Engineering Analysis

Problem definition, Design specification

Collecting relevant design information & feasibility study

Design Conceptualization/ Preliminary design i.e. Mechanism synthesis

General Procedure in Machine Design

Detail Design of Components

Design Optimization

Modeling & Simulation

Design Evaluation

CustomerManufacturer

CAD/CAE

Design Synthesis

Design Analysis

Design Communication & Documentation


Basic Procedure of Design of Machine Element

Specify functions of element

Determine forces acting on element

Check design at critical cross-sections

Determine failure mode (s) of element

Select suitable material for element

Check & modify dimensions for assembly & manufacture

Determine geometric dimensions of element based on above failure mode

Prepare detail engineering drawing of element

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Strength

Manufacturability

Minimum Dimensions & Weight

Rigidity

Wear Resistance

Basic Requirements of Machine ElementsBroad objective of designing a machine element is to ensure that it preserves its operating capacity during the stipulated service life with minimum manufacturing & operating costs.

In order to achieve these objectives, the machine element should satisfy following basic requirements.

- should have sufficient strength to avoid failure (fracture/ general yielding) due to force.

- should not deflect or bend beyond permissible limit due to forces/moments.

- Machine components like gear, cam should have sufficient wear resistance. Wear leads to the loss of accuracy, puts the part out of order.

- Machine part should be sufficiently strong, rigid & wear resistant & at the same time, with minimum possible dimensions & weight.

- ease of fabrication & assembly.- shape & material of the m/c part should be selected in such a way that it can be produced with minimum manufacturing cost


Conformance to Standards

Minimum Life Cycle cost

Reliability

Safety

Maintainability

Basic Requirements of Machine Elements

- shapes & dimensions of the machine parts should ensure safety to the user/operator.

- is probability that a machine part will perform its intended functions under desired operating conditions over a specified period of time.

- machine part should be reliable i.e. it should perform its function satisfactorily over its lifetime.

- ease with which a machine part can be serviced or repaired.- machine part should be maintainable

- machine part should confirm to the National or International standard.

- Total cost to be paid by the purchaser for purchasing the part and operating & maintaining it over its life span.

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“Standards” in Machine DesignStandardization Standardization is defined as obligatory norms, to which various characteristics of a

product should conform.

The characteristics include materials, dimensions and shape of the component, method of testing and method of marking, packing and storing of the product.

StandardStandard is defined as a set of specifications for parts, materials or processes

Code is defined as a set of specifications for the analysis, design, manufacture, testing and erection of the product

Purpose of Code to achieve a specified level of safety

Purpose of Standard to reduce the variety & limit the no. of items to a reasonable level

Code


“Standards” in Machine DesignAdvantages of Standardization

The reduction in types & dimensions of identical components, to a rational number, makes it possible to manufacture the standard component on mass scale in a centralized process.

Standard parts are easy to replace when worn out due to interchangeability.

The application of standard machine elements & especially the standard units reduce the time & effort needed to design a new machine.

Standardization results in substantial saving in Designer’s effort The standards of specifications & testing procedures of machine elements improve their quality & reliability.

In designing, the aim is to use as many standard components as possible for a given machine

International Standards

National Standards

Company Standards

Types of StandardsGermanD.I.N

USAA.I.S.I / S.A.EUKB.S

IndiaI.S / B.I.S

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“Standards” in Machine Design

Designation & Dimension of screw threads, bolts & nutsI.S. 4218 : 1996Geometrical tolerancing on technical drawingsI.S. 8000Guide for selection of fitsI.S. 2709Recommendations for Limits & Fits for EngineeringI.S. 919Mechanical Properties of wrought Al. & Al alloy Plates for general purposesI.S. 736 : 1986Mechanical Properties of wrought Al. & Al alloy Bars, Rods for general purposesI.S. 733 : 1983Chemical composition of various grades of alloy steelI.S. 1570 Seven grades of grey cast ironI.S. 210Bureau of Indian Standards on “Engineering Drawing Practice for Schools & CollegesSP 46

Indian Standards in Mechanical Engineering Design


Preferred NumbersWhen a machine is to be made in several sizes with different powers or capacities, it is necessary to decide what capacities will cover a certain range efficiently with minimum number of sizes.

For example, a company want to manufacture six different models of electric motors ranging from 1.0 HP to 105 HP to cater to the need of different customers.

Preferred numbers are used to specify the ‘sizes’ of the product in these cases.

French Engineer Charles Renard first introduced Preferred Numbers in the 19th century.

The system is based on the use of geometric progression to develop a set of numbers.

1.0,1.03, 1.06,1.09, 1.12,1.16, 1.18, 1.21,1.25,1.29,1.32,1.36,1.4,…..1.6, ………, 10.03%1.03101/80R 80 series

1.0,1.06,1.12,1.18,1.25,1.32,1.4,1.5,1.6, ……………………………………, 10.06%1.06101/40R 40 series

1.0,1.12,1.25,1.4,1.6,1.8,2.0,2.24,2.5,2.8,3.15,3.55,4.0,4.5,5.0,5.6,6.3,7.1,8.0,9.0,10.012%1.12101/20R 20 series

1.0, 1.25, 1.6, 2.0, 2.5, 3.15, 4.0, 5.0, 6.3, 8.0,10.026%1.26101/10R 10 series

1.0, 1.6, 2.5, 4.0, 6.3, 10.058%1.58101/5R 5 series

Preferred Numbers [in between 1 to 10]% increase in steps

Common Ratio

Basic series

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Aesthetic Considerations in Machine DesignWhen there are a number of products in the market, having the same qualities of efficiency, durability and cost, the customer will naturally attracted towards the most appealing product.

The external appearance is an important feature, which not only gives grace and luster to the product but also dominates the sale in market.

Automobiles Audio Visual EquipmentsHousehold Appliances

Industrial Design The job of an Industrial Designer is to create new forms & shapes, which are aesthetically pleasing.

The external appearance of the products is a cumulative effects of number of factors :

ColourForm Surface finish & Tolerances Materials Manufacturing Methods

In many cases, functional requirements result in shapes, which are aesthetically pleasing. The evolution of the streamlined shape of the boeing is the result of studies in aerodynamics for effortless speed.Chromium plating on the household appliances is for corrosion resistance rather than for pleasing appearance

Relationship between Functional requirement & Appearance of the Product

Stream

Sculpture

Step

TaperShear


Ergonomic Considerations in Machine Design

Ergonomics is defined as the relationship between Man & Machine and the application of anatomical, physiological and psychological principles to solve the problems arising from Man-Machine relationship.

Anatomical factors in design of driver’s seat.

Layout of instrument dials & display panels for accurate perception by the operators

Design of hand levers & hand wheels.

Topics of Ergonomic studies in Machine Design

Ergonomists have carried out experiments to determine the best dimensions of driver’s seat, the most convenient hand or foot pressure or dimensions of levers and hand wheels.

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Manufacturing Considerations

in Machine Element Design


General Principles :

Design Considerations of Castings

Round all external corners

All sections in a casting should be designed of uniform thickness, as far as possible. If variation is unavoidable, it should be done gradually

Avoid very thin section : Minimum thickness for CI component in sand casting is about 6 mm.

The cast components should be designed in such a way that it will require a simpler pattern & its moulding is easier.

In designing a casting, the various allowances must be provided in making a pattern.

The casting should be designed as simple as possible, but with a good appearance.

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General Principles :

Design Considerations of Machined Components

Machining is basically secondary & finishing manufacturing process.

Geometric / Form Accuracy

Dimensional Accuracy

Surface finish

Avoid sharp corners

Avoid too many shoulders & undercuts

Avoid hard materials.

Dimensional Tolerance

Geometric Tolerance

Surface roughness


Sequential Engineering Approach Vs. Concurrent Engineering Approach

Marketing Department

Design Office

Production Department

Sales & Service Department

Sequential Design Process

Customer

Prototype Development Stage

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Concurrent Engineering Concurrent Engineering is defined as the design process/approach that brings together a wide spectrum of expert/specialist from several functional areas (like R & D, Engineering, Manufacturing, Quality control, Marketing, sales & service etc.) during the early phases of the design process in new product development.

Sequential Engineering Approach Vs. Concurrent Engineering Approach

The team reviews the design from different aspects

design for Manufacturing & Assembly (DFx)

quality assurance & standardization

aesthetics & ergonomics

maintenance

reliability & safety

process, facility, capacity planning

tool design

functional / performance testing

cost


Cost,Sales &

servicing

Customer’s requirement

Ergonomics &

Appearance

Reliability, Maintainability

& safety

Manufacturability Assembly & Testability

Concurrent Engineering

Design Engineering: Concurrent Engineering

Approach

Sequential Engineering Approach Vs. Concurrent Engineering Approach Any possible bottleneck/mistake is thoroughly studied & rectified. This results in small nos. of modification in the design at a later stage & reduce time interval from conceptual stage to marketing stage.

Parallel Engineering

Cross Functional Team Approach

Simultaneous Engineering

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Requirements Most Productive

Most Economic

Improved Quality

Motivation

Successful entry of a product into the market can best occur if it can complete the above cycle in the shortest possible time & at the lowest cost while maintaining very high product quality & reliability

Computer Aided ManufacturingCAMVirtual Prototyping & Virtual RealityVP & VR

Computer Aided EngineeringCAEComputer Aided DesignCAD

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is the use of wide range of computer based tools that assist Engineers & other Design Professionals in their design activities.

is to design, develop and optimize the product.

is the use of Information technology/ computer based tools for supporting Engineers in tasks such as Design, Analysis, Simulation, Optimization, Manufacturing, Planning etc.

is to design, develop and optimize the product or process.

CAE areas:

Stress analysis, Vibration analysis using FEM

Thermal & fluid flow analysis using CFD

Kinematic & Dynamic Analysis & Simulation

Analysis tools for manufacturing process simulation

Optimization of the product or process

is the use of wide range of computer based tools that assist Production Engineers & Tool and Die maker, CNC machinists, in the manufacture or prototyping of products.


Geometric ModelingConcept

Design & Analysis Theories/ Tools

(FEA, CFD)

Computer GraphicsAlgorithmCAD/CAE

Scope of CAD/CAE

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Scope of CAD/CAM

Geometric Modeling & Computer Graphics

Manufacturing Process

(RP&T, CNC)

Automation(Robot, FMS,

CAPP)CAM/CAM


Scope of CAD-CAM-CAE

Geometric Modeling

Design & Analysis Theories

(FEM, CFD)

Computer Graphics

Manufacturing Process

(RP&T, CNC)

Automation(Robot, FMS, CAPP)

CAD-CAM-CAE

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Requirements Most Productive

Most Economic

Improved Quality

MotivationSuccessful entry of a product into the market can best occur if it can complete the above cycle in the shortest possible time & at the lowest cost while maintaining very high product quality & reliability

VP : Virtual PrototypingVP is about Presentation, Testing, & Analysis of 3-D CAD models prior to creating any physical prototype

Visualization Models : greater communication, productivity & efficiency through realistic graphical modelling based on full colour, natural texture & appearance, dynamic viewing of models from any user-specified angle & orientation.

Fit & Interference checking of mechanical assemblies

Testing & Verification of functions & performance : Structural & Physical phenomena analysis [FEM, CFD], Motion analysis.

Manufacturing Evaluation

Assembly analysis

Human factor analysis


VP : Virtual PrototypingVP is about Presentation, Testing, & Analysis of 3-D CAD models prior to creating any physical prototype

Visualization Models : greater communication, productivity & efficiency through realistic graphical modelling based on full colour, natural texture & appearance, dynamic viewing of models from any user-specified angle & orientation.

Fit & Interference checking of mechanical assemblies

Testing & Verification of functions & performance : Structural & Physical phenomena analysis [FEM, CFD], Motion analysis.

Manufacturing Evaluation

Assembly analysis

Human factor analysis

Digital Prototyping

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CAD-CAM-CAE Software

INVENTOR

SmartCAM

SolidCAM 3-D modeling & Manufacturing SimulationMasterCAM

Mechanical DESKTOP

SOLID EDGE

SOLID WORKS

PRO-ENGINEER

NX ( Siemens PLM ) 3-D modeling, Analysis & Simulation etc.CATIA ( CATIA PLM Express )

PurposeCAD/CAM/CAE software

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CAD-CAE Software

Multi-body dynamic analysis & simulationWorking Model

Multi-body dynamic analysis & simulationSimDESIGNER Motion with CATIA

Multi-body dynamic analysis & simulationADAMS

Computational Fluid DynamicsFLUENTMeshing for Finite Element AnalysisAltair Hyper Mesh

Finite Element Analysis, Crash simulationPAMCRASH

Finite Element Analysis, Crash simulationDEFORM

Finite Element Analysis, Crash simulationLS-DYNA

Finite Element AnalysisABAQUS

Finite Element Analysis NASTRAN

Finite Element AnalysisANSYS

PurposeCAE software


Computational Tools

MathCAD Design calculationMathematica

Design calculation, dynamic analysis & simulation, design optimization, control

MATLAB

Excel

TK Solver

Maple

PurposeSoftware

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CATIA -Drafting, AutoCAD, MATLAB, MS-EXCEL

Geometric modeling, Drafting moduleDesign communication & documentation

CATIA – DMU Navigator, Fitting, Space analysis, Tolerancing review

Geometric modeling, Customized programs & Package

Design Evaluation

CATIA – DMU Optimizer, MATLAB –Optimization tool box

Geometric modeling, Optimization module

Design Optimization

CATIA – SimDesigner Structural, NASTRAN, ANSYS

Geometric modeling, Analysis module, visualization

Design Analysis

CATIA – DMU Kinematics, SimDesigner Motion, ADAMS

Geometric modeling, Graphics aids, visualization, Simulation module

Modeling & Simulation

CATIA – Part design, Assembly, Generative Shape, Surface Design,

Geometric modeling, Graphics aids, visualization

Design conceptualization

Related Software (s)(available at ME, NITD)

Required Modules of CAD-CAE Tools

Design Phase

CAD-CAE Tools


3-D CAD model Pre-Processor Solver Post-Processor

CAD-CAE Tools

CAD

CAE

Define the model & environment factors to be

applied

Performed computation on

high end computer

Display results in graphical form using visualization tools

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CAE areas:

Stress analysis, Vibration analysis using FEM

Thermal & fluid flow analysis using CFD

Kinematics & Dynamic Analysis & Functional Simulation

Manufacturing process simulation

Optimization of the product or process

Engineering Analysis : CAD-CAE Tools

Analysis

Analytical methods: Simulation

Experimental methodsBoth are performed to assess product

performance


Thank You

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Assignment # 11. Explain with example, the different steps involved in machine design process & in design of machine

elements? What are the basic requirements of machine elements?

2. Distinguish between design synthesis and design analysis.

3. What is Standardization & what are the advantages of standardization? Give examples of Indian standards for commonly used engineering materials.

4. What are preferred numbers? How many basic series are used? What is R10 series? Develop R 10 series from 2 to 20.

5. What is an industrial design? What is the relationship between functional requirement and external appearance of the product.

6. Define ergonomics. What is the scope of ergonomics in machine design?

7. Distinguish between sequential design and concurrent engineering.

8. Explain the functional area of a basic CAD-CAE system & their applications & benefits in machine design process with examples.

Last date of submission : 02nd February, 2009

machinedesign intro ssroy

Documents

design of machine elements

design of shafts

design data

machine design role

machine design handbook1

iterative process design

threaded joints design

reversed stresses design