mpd 575 design for reliability jonathan weaver. 2 dreliability development history originally...

MPD 575MPD 575

Design for ReliabilityDesign for Reliability

Jonathan Weaver

2

DReliability Development History

• Originally developed by MPD Cohort 3 team of Julie Earle, Dave Herczeg, and Jim Van Gilder in Fall 2002.

Design for Reliability

Design for Reliability

4

Why Design for Reliability?

• Reliability can make or break the long-term success of a product: – Too high reliability will cause the product to

be too expensive– Too low reliability will cause warranty and

repair costs to be high and therefore market share will be lost

5

What is Reliability?

• Reliability is:• Elimination/avoidance of failure modes/mistakes • The probability that a product will perform its intended

function: • Under customer operating conditions • For a specified life • In a manner that meets or exceeds customer expectations

• A reliable product is robust and mistake-free

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• Probability is:• a measure that describes the chance or

likelihood that an event will occur. • The probability that event (A) occurs is

represented by a number between 0 (zero) and 1. • When P(A) = 0, the event cannot occur.

• When P(A) = 1, the event is certain to occur.

• When P(A) = 0.5, the event is as likely to occur as it is not.

What is Probability?

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Reliability Failure Modes

Two types of failure mode:a) hard = something breaksb) soft = performance degrades

Two root causes:1. lack of robustness (sensitivity to noise factors)2. mistakes

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What are Noise Factors?

• Noise Factors are sources of disturbing influences that can disrupt the ideal function, causing error states which lead

to quality problems.

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• A population is:• The entire group to be studied (e.g. all Ford Contours)

• A sample is:• A subset of a population selected randomly for analysis (e.g., every hundredth Ford Contour off the assembly line)

What is Population and Sample Size?

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Common Measures of Unreliability

• % Failure - % of failures in a total population

• MTTF (Mean Time To Failure) - the average time of operation to first failure.

• MTBF (Mean Time Between Failure) - the average time between product failures.

• Repairs Per Thousand (R/1000)

• Bq Life – Life at which q% of the population will fail

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Introduction to DFR

• DFR has many aliases:– Design for Durability– Design for Robustness– Design for Useful Life

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When to Use DFR

• DFR should be considered throughout the PD cycle:

• Early - to develop "product concepts" which are well suited for production (i.e., conceptual product design)

• Continually - to ensure that the chosen product concept is implemented through optimal component design

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Automotive Reliability Facts

• The shortest route to higher satisfaction is not only through the dealership service department –

it is mainly through keeping customers out of the service department in the first place.

• Customers who report zero problems with their new cars have an owner loyalty rate of 73 percent and dealer loyalty of 42 percent.• At 4 TGW, loyalty to the company drops by 1/3 to 44%,

while loyalty to the dealer drops to zero.

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Automotive Reliability Facts

• The average age of a purchased vehicle at

the time of replacement is 5.7 years in the

U.S. and 4-5 years in Europe.

• The average lifetime of a vehicle before scrap

is 12.7 years in the U.S. and 10 years in

Europe.

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Steps in Designing for Reliability

1. Develop a Reliability Plan• Determine Which Reliability Tools are

Needed

2. Analyze Noise Factors

3. Tests for Reliability

4. Track Failures and Determine Corrective Actions

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1. Develop a Reliability Plan

• Planning for reliability is just as important as planning for design and manufacturing. Why? To determine: • useful life of product• what accelerated life testing to be used • where to begin

• Reliability must be as close to perfect as possible for the product’s useful life.

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• A Reliability Plan helps ensure that product reliability is optimized within the cost and performance constraints of a program and customer requirements.

1. Develop a Reliability Product Plan

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1. Develop a Reliability Plan

• How much reliability do you need? Should you accelerate life testing? Where do you even begin?

• Planning for product reliability is just as important as planning for product design and manufacturing.

• The amount of product reliability must be in proportion to a product's usage and warranty goals. Too much reliability and the product will be too expensive. Too little reliability and warranty and repair costs will be high.

• You MUST know where your product's major points of failure are!

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Some Reliability Tools

• Block Diagram• P-Diagram• QFD• DFMEA & PFMEA• Design Verification Plan

– Key Life Testing– Weibull Testing

• Reliability Demonstration Matrix

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Reliability Block DiagramThree categories:

•Series •Parallel (Redundant)•Complex (combo of the two – shown below)

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P-Diagram

System

NoisesOutputs

error states/failure modes

Input

Control Factors

Signal(energy related)(energy related)

IDEAL Response

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Technical System Expectations

Relationship MatrixCustomer Wants Customer TargetsCustomer

Competitive Evaluations

Technical Importance

Technical Targets

Technical Competitive

Benchmarking

Safety & RegulatoryReqmts Matrix

WCR/SDS MatrixWCR/SDS

Safety & RegulatoryReqmts S

tds

Std

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Strategic CDICustomer Desirability Index

Technical Axis

Customer Axis

Quality Function Deployment

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FMEAs

• Potential Failure Mode

• Potential Effects of Failure

• Severity

• Classification

• Potential Cause/Mechanism of Failure

• Occurrence

• Design Controls (Prevention/Detection)

• Detection• Risk Priority Number• Recommended Actions• Responsibility/Target Completion

Date• Actions

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DVP&Rs

• Test Specification

• Acceptance Criteria

• Test Results

• Design Level

• Quantity Required

• Quantity Tested• Scheduled Start/

Complete• Actual Start/ Complete• Remarks

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Reliability Demonstration Matrix CD132 ELECTRICAL SUNROOF SYSTEM Updated: July 09, 1999

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VII Sunroof produce not acceptable windnoise (closed: windnoise, open: buffeting) VII NOISE FACTOR MANAGEMENTVI Sunroof rattles, sqeaks VIV Water management is insufficient V Cat Strategy M

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IV Sunroof seal comes away IV A Change TechnologyIII Anti Pinch device doesn't work proper III BI Apply Parameter DesignII Sunroof binds on rear edge II BII Upgrade Design Spec.I Sunroof doesn't operate proper (jamming, judder, no smooth movement) I C Reduce / Remove Noise

D Add Compensation DeviceE Disguise / Divert

Strategy10 NOISE 1: TOTAL DESIGN / MANUFACTURING VARIABILITY I II III IV V VI VII used Specifics applied (describe)11 Piece-to-piece variation or a) gear assy single parts variation x x x x C;A SPC on crit dim, encaps. glass I;VI I I VII I I I III I I VII I

drawing tolerance, b) gear assy assembly variation (PTA, Webasto) x x x x x C SPC on crit dim. I;II;V V I I III I VII Iwhichever is greater, and c) BIW component variation (single parts) x x x x A encap. glass I;II V VII VIItotal scope applicable d) BIW assembly variation (Body Construction) x x x x x A encap. glass I;II V VII III VII

e) BIW paint variation x x x x A Modified seal I;II IIIf) vehicle interior trim component variation x A new edge trim designg) vehicle interior trim assembly variation x A new edge trim designh) sunroof assembly variation (PTA, Genk) x x x x x x A new locator strategy I VII III VII

20 NOISE 2: COMPONENT CHANGES OVER TIME / MILEAGE -- over Useful Life Period21 Change in dimension or a) gear assy component wear x x x C,A SPC on crit dim., new s/r frame I;VI VII I I I VII I

(assumptions above) d) BIW stiffness degradation x BII Reinforce BIWe) vehicle interior trim fatique (fixing) x BII Upgrade interior trim fixings I;VIf) paint surface wear x BII Use harder paint VI

30 NOISE 3: DUTY CYCLE / CUSTOMER USAGE -- over Useful Life Period

31 "Typical" a) high frequency use x x BII using SDS instead of ES spec I;VI I ICustomer usage b) vehicle speed x x C,A SPC on crit dim., new s/r frame VII III VIIover Useful Life Period c) sunroof misuse (override), only on mechanical system x BII using SDS instead of ES spec I(assumptions above) d) external roof load x BII Change anti trap parametrisat. III

e) road profile x x A new s/r frame tech. VI IIIanti trap usage x x BII WDS instead of EWG74/60 I;III

32 Transport, storage, dewaxingf) non-usage N/A33 High pressure cleaning g) cleaning water / chemicals, high pressure jet x BII using SDS instead of ES spec IV;V35 Customer misuse/abuse i) neglect poor service, uncontrolled fluids N/A No service necessary

40 NOISE 4: EXTERNAL ENVIRONMENT

41 Climatic conditions, Typical territory Condition 1 Condition 2geographic conditions, a) Canada, Scandinavia cold dry x x x x BII using SDS instead of ES spec I;IV;VI I III Ilocal environment, b) Britain, Germany cold humid x x x x x BII using SDS instead of ES spec I;IV;VI I I III Isurfaces or obstacles, c) Arizona, Florida, AUS sunload dry BII using SDS instead of ES spec I III Iramps and curbs, d) Taiwan hot wet x x x BII using SDS instead of ES spec I;VI I I III Iindustrial fall-out, e) Nova Scottia salt x BII using SDS instead of ES spec I I I IIIinsects, trees... droppings, f) Pikes Peak, GGlockner high altitude long downhillmarten bite etc. g) industrial fall out, trees dropping, dust, dirt, BII using SDS instead of ES spec I;IV

50 NOISE 5: IN-VEHICLE SYSTEMS ENVIRONMENT -- over Useful Life Period

51 Physical interfaces a) generic passenger compartment seal conditions x BII Change winddeflector design VII VIIwith associated systems b) torsional stiffnes of different body styles x BII Reinforce weakest BIWor mating components c) suspension type/ tires of different derivatives x BII Increase sunroof S&R robust.over Useful Life Period d) passenger comp. volume of different body styles x BII Change winddeflector design VII

52 Loads from or f) vibration x x BII using SDS instead of ES spec I;VI IIIinteraction with g) EDS voltage variation x BII using SDS instead of ES spec I III I Ineighboring systems h) electromagnetic field BII using SDS instead of ES spec III

Design Controls, CAD / CAE ... Component => Subsystem ==> System ===> Vehicle Tests

Useful L ife Period Target

10 Years or 240,000 km (or 13,000

cyc les)

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Failure mode to test traceability and

Noise factor to test traceability leading to ...

Reliability & Robustness Demonstration

“In the development of robustness, it is essential to provide one noise condition for each failure mode”. Don Clausing, Professor of Engineering, MIT.

Robustness Assessment and Noise Factor Management Matrix

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Reliability Demonstration Matrix

1000 10000Failure cycles

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Robustness Demonstration

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2. Analyze Noise Factors

• Inner Noises• Wear-out or fatigue• Piece-to-piece variation • Interfaces with neighboring

subsystems• Outer Noises

• External Operating Environment (e.g., climate, road conditions, etc.)

• Customer usage / duty cycle

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2. Reduce Sensitivity to Noise Factors

1. Change the design concept2. Make basic current design

assumptions insensitive to the noises – design out failure

• Parameter Design• Beef Up Design

3. Insert a compensation device4. Disguise the effect - Send the error

state/noise where it will do less harm

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2. Noise Factor Management 1. 2. 3. 4. 5.Change (i)Parameter (ii)Beef-up Reduce Comp- DisguiseConcept Design. Design Noise ensate

Piece-to-piece x x x

Wear Out x x x

Customer Use x x x

External Environment x x x

System Interactions x x x x

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3. Test for Reliability• How robust are the products?

– Test to Bogey: assessing performance at a predetermined time, cycle or number of miles. It estimates the proportion of failures at a particular time. pass/fail

– Test to Failure: shows when a component or system can no longer perform at a specified level

– Degradation Testing: focuses on the key stresses associated with real world uses – for example - increasing the tire load to create a tire failure

• How can you shorten the reliability test time for new designs?– Key Life Test/Accelerated Test

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3. Example – Testing for Reliability• Proportional Hazard Model to Tire Design

Analysis– Perform Root cause analysis

• Consists of laboratory tests aimed to duplicate field failures

• Tire geometry and physical properties are selected as variables that potentially affect the tire

• Survival data is analyzed by a proportional hazard model

– The adequacy is assessed by the chi-square goodness- of fit test and the Cox-Snell residual analysis

• Identify elements of a tire design that affect the probability of tire failure due to failure mode in question.

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3. Example - Testing for Reliability Cont’d

• Type of failure mode analyzed – tread and belt separation

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• Tread and belt separation can be considered a sequence of two events:– Failure crack initiation in the wedge area– Crack propagation between the belts

• Design characteristics that could be variables:– Tire age– Wedge gauge– Interbelt gauge – End of belt # 2 to buttress– Peel force– Percent of carbon black (chemical in rubber)

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• Testing procedure– Dyno testing

• Warm up over 2 hours at 50 mph• Cool down over 2 hour at full stop• At 1300 lbs of load: speed steps starting at 75

mph and increasing by 5 mph every half hour till 90 mph and then every hour till failure

• At 1500 lbs of load: all the above speed steps are half-hour duration

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• Test speed profile

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• Vibration and sound pattern of tire before tread and belt separation failure

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• Test data set used in proportional hazard analysis

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• Estimates of proportional hazard model with covariates identified

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• Estimates of Proportional Hazard Model with statistically significant covariates

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• Exponential probability plot of Cox-Snell Residuals

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• Cumulative Hazard function predicted from the estimated model based on some typical values of covariates for “poor” and “good” tires

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• Conclusion– Wedge and interbelt gauges as well as the

peel force are significant factors affecting hazard rate of tire and belt separation failures in an inversely proportional way

– Agree with hypothesis

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• Component design and manufacturing technologies are becoming increasingly complex.

• As geometries shrink and development cycles shorten, opportunities for defects increase.

• Testing for Reliability is becoming increasingly important.

3. Test for Reliability

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• This process involves:• Data collection and selection

• Set up databases for tracking failures• Warranty, Early Warranty, Things Gone Wrong

• Analyzing trends

• Performing closed loop analysis/corrective action

• Calculating observed reliability parameters

• Assessing reliability growth.


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• Brake warranty is on track with targets and achieves more than 60% warranty CPU reduction since 1994

• Brake health charts were instituted in 1995 to monitor key performance index and drive design competency

• Supplier business unit reviews (BURS) quarterly to address key quality and manufacturing issues

$52

$14 Target

$38

$75

$18

$28

$31

$35

$75

$25 Target

$0

$25

$50

$75

$100

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Model Year

$(CPU)

TargetActions Implemented And/ Or ApprovedOld Target

BrakeHealthChart

Created

BrakeQuartback

TeamStarted

FirstFSS/SI

ProgramLaunched

NA 3/36 Combined Car & Truck Brake Warranty CPU Reduction

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• Time-to-Failure Curve


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Challenges in DFR

• Many CAE models have limited capability to represent real-world noise; therefore, surrogate noise based on engineering knowledge is required.

• Precise reliability estimates require precise knowledge of statistical distributions of noise factors.

– As a contrast, comparative reliability assessments and robust design require only approximate knowledge of statistical distributions.

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Challenges in DFR

• Many CAE models are computationally expensive – preparation time to set up the model – computing time

• Many CAE models focus on “error states” (e.g., fatigue, vibration, noise); therefore, a multi-objective optimization is often needed.

• In early product development, when the impact of robust design can be greatest, design objectives and constraints are still imprecise.

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References

• Reliability - Ford Design Institute• Ford Reliability Class – T. P. Davis, V. Krivtsov/

VKRIVTSO• http://www.reliabilityanalysislab.com/

ReliabilityServices.asp

• U.S.: R.L. Polk Vehicles in Operation Report June, 1997 Europe: New Car Buyer StudyEuropean Buyer - Big Five Survey 1995

• Ford's Strategy in Reliability (Prof. Tim Davis)

• http://pms401.pd9.ford.com:8080/arr/concept.htm

mpd 575 design for reliability jonathan weaver. 2 dreliability development history originally...

Documents

reliability slide

high reliability

reliability failure

useful life slide

low reliability

optimal component design

conceptual product design

mistakefree slide