171 DFMEA Presentation UWO 2012

11Devos AssociatesAdvisors to the Automotive IndustryAdvisors to the Automotive IndustryAdvisors to the Automotive IndustryAdvisors to the Automotive Industry

DESIGN FAILURE MODES

AND EFFECTS ANALYSIS(DFMEA)

PRESENTED BY

Denis J. Devos BA, BESc, MEng, PEng

Devos Associates Inc.

University of Western Ontario

October 17 2012


Setting the StageSetting the Stage

•• Design FMEADesign FMEA

Effects and SeverityEffects and Severity

Causes and ProbabilityCauses and Probability

Controls and EffectivenessControls and Effectiveness

•• Automotive S,O,D guidelinesAutomotive S,O,D guidelines

•• Special CharacteristicsSpecial Characteristics


• In today’s competitive environment, quality goods and services is not enough

• We must anticipate failure and nonconformance, and prevent these events before they occur.

IntroductionIntroduction

Studies of vehicle warrantee campaigns have shown that more disciplined use of the DFMEA would have prevented many of these campaigns


Lets RecapLets Recap

Potential Failure ModePotential Effects of the Failure Severity

Potential Causes/Mechanisms of the Failure Occurrence

Current Design ControlsPrevention, Detection Detection

Where S, O, D, numbers are unknown, estimate high". (also called “fear of the unknown!”)


Start the FMEA earlyStart the FMEA early

•• As soon as concepts are developed As soon as concepts are developed

•• Start from an existing DFMEA, and focus on Start from an existing DFMEA, and focus on

differences differences

•• Continually update as the design evolvesContinually update as the design evolves

•• Completed before drawings are releasedCompleted before drawings are released

DFMEA becomes an input to Process FMEA


Define the Subsystem

RISK Assessment

Reliability Tools/Analysis

Design Testing


• A tool to focus discussion within a team

• A graphical approach to collecting data

• A logical flow:

Failure Effect Cause Control

• A repository for corporate learning about a

process throughout the life cycle

What is an FMEA?What is an FMEA?


The lead design engineer is responsible to assemble a team from all disciplines (often a Core Team and Support Team):

The FMEA TeamThe FMEA Team

• Design engineers• Process engineers• Testing engineers• Purchasing• Suppliers

• QA • Sales• Field Service• Maintenance• Customers

The DFMEA is a catalyst to promote discussion and exchange of ideas among all stakeholders


Customer of the FMEACustomer of the FMEA

Design FMEA Design FMEA

•• Design engineers, other system design teamsDesign engineers, other system design teams

•• Manufacturing Process EngineersManufacturing Process Engineers

Process FMEAProcess FMEA

•• End UserEnd User

•• Downstream manufacturing operationsDownstream manufacturing operations

•• Service and maintenance operationsService and maintenance operations


Consider a Refrigerator as a SystemConsider a Refrigerator as a System

System System –– RefrigeratorRefrigerator

SubsystemSubsystem

•• Compressor SubsystemCompressor Subsystem

•• InsulationInsulation

•• Door SubsystemDoor Subsystem

•• IceIce--Maker SubsystemMaker Subsystem

Components (ice maker)Components (ice maker)

•• Plastic bucket in the doorPlastic bucket in the door

•• Plastic tube Plastic tube

•• Plastic push handlePlastic push handle


Column 1 Column 1 –– Process Function, Process Function,

RequirementsRequirements

•• Part Number, name and description of the Part Number, name and description of the

process stepprocess step

•• Include the function of the item which Include the function of the item which

meets the design intent. Include meets the design intent. Include

information relating to the environment information relating to the environment

where the item operates where the item operates


•• Describe in terms that can be measuredDescribe in terms that can be measured

•• Answer the question Answer the question ““what is this item what is this item

supposed to do?supposed to do?””

•• Functions:Functions:

•• Measureable, can be verified/validatedMeasureable, can be verified/validated

•• Includes additional constraints or design Includes additional constraints or design

parameters such as reliability specs, parameters such as reliability specs,

servicing specs, weight, size, locationservicing specs, weight, size, location

Column 1 Column 1 –– Process Function, Process Function, ReqtReqt’’ss


Process Function RequirementsProcess Function Requirements

•• Functions:Functions:

•• Describe functional intent or engineering Describe functional intent or engineering

requirementrequirement

•• Representation of all wants, needs, Representation of all wants, needs,

requirements, spoken and unspoken, for requirements, spoken and unspoken, for

all customers and systems.all customers and systems.

Remember: Functions cannot FAIL if they do not have measurable specifications



•• Describe in terms that can be measuredDescribe in terms that can be measured

•• Answer the question Answer the question ““what is this item what is this item

supposed to do?supposed to do?””

•• Written as VerbWritten as Verb--NounNoun--MeasureableMeasureable

““Store fluidStore fluid, , six six litreslitres, , withwith zerozero leaksleaks””

““Conduct current, 10 ampsConduct current, 10 amps””

““OpenOpen doordoor withwith 100 100 NewtonsNewtons of effortof effort””



•• (Gasket) (Gasket) SealSeal the the doordoor flush with flush with zero leakszero leaks

•• (Door Stop) (Door Stop) StopStop the the doordoor at at 120120°° openopen

•• ((LevellingLevelling Feet) Feet) LevelLevel the the RefrigeratorRefrigerator to a to a

frontfront--toto--back differential of back differential of 2 inches2 inches and a and a

sideside--toto--side differential of side differential of 1 inch.1 inch.

•• (compressor) (compressor) CoolCool the the compartment compartment to to 11°° CC

fully packed with 1.5 fully packed with 1.5 LitreLitre water bottles in an water bottles in an

ambient of ambient of 4545°° C, 80%C, 80% RH continuously for RH continuously for 10 10

years.years.


Column 2 Column 2 –– Potential Failure ModePotential Failure Mode

•• How could this component, subsystem fail How could this component, subsystem fail

to meet the design intent?to meet the design intent?

•• Describe the Describe the potentialpotential nonconformancesnonconformances

only for that function.only for that function.

•• A mode here can be the cause of a A mode here can be the cause of a

downstream process error, or the result of downstream process error, or the result of

an upstream process erroran upstream process error

•• Potential failure modes can occur only Potential failure modes can occur only

under certain operating conditions, and/or under certain operating conditions, and/or

certain customer situationscertain customer situations


•• How can the process fail to meet the intent How can the process fail to meet the intent

of the of the ““FunctionsFunctions”” column?column?

•• Typical ExamplesTypical Examples

•• No FunctionNo Function

•• Partial/Over Function/Degraded over timePartial/Over Function/Degraded over time

•• Intermittent FunctionIntermittent Function

•• Unintended FunctionUnintended Function

Column 2 Column 2 –– Potential Failure ModePotential Failure Mode


ExampleExample

Jack for changing a flat tire:

Raise vehicle to X feet above the ground, within Y

minutes, using Z maximum force, under all weather

conditions

No Function Does not raise the vehicle

Partial/Over/Degraded Does not raise to X, takes longer

than Y, uses more than Z force,

Intermittent function Inoperable in the rain

Unintended function None Known


ExampleExample

Windshield Wipers:

Return to the rest position and remain after being

switched off, within ± 5mm from the rest position

measured from the mid-point of the blade

No Function Switch doesn’t turn off the wiper

Wipers don’t remain in rest position

Partial/Over/Degraded Wipers rest off-location

Wipers drift their position over time

Intermittent function Wipers out of position below 0°C

Unintended function Wipers turn off when actuating turn signal


ExampleExample

Refrigerator Light:

Light turns off when the door is closed, for 10 years

No Function Door doesn’t engage the switch

Switch does not turn off the light

Partial/Over/Degraded Switch wears out before 10 years

Door partially engages the switch

Intermittent function Switch intermittently turns off the light

Unintended function Bulb overheats, melts the plastic cover


Column 3Column 3–– Potential Effects of FailurePotential Effects of Failure

•• Describe the failure as perceived by the customerDescribe the failure as perceived by the customer

•• State if the failure impacts on safety or product State if the failure impacts on safety or product

regulationsregulations

•• Express the effects in terms of the specific Express the effects in terms of the specific

component or subcomponent or sub--system being analyzedsystem being analyzed

A part can fracture, causing the assembly to vibrate, resulting in intermittent operation. This could cause degradation over time and premature failure.


Potential Effects of FailurePotential Effects of Failure

Ask: Ask: ““If this failure mode happens, what will be the If this failure mode happens, what will be the

effect oneffect onFF..””

•• Operation, function, of the items subOperation, function, of the items sub--components?components?

•• Operation, function, of the assembly Operation, function, of the assembly

•• Operation, function, of the subOperation, function, of the sub--system or systemsystem or system

•• Operation, safety, driveOperation, safety, drive--ability of the vehicleability of the vehicle

•• What will the customer see and experience?What will the customer see and experience?

•• Compliance with government regulations?Compliance with government regulations?


Potential Effects of the FailurePotential Effects of the Failure

• Effect on the (internal or external) customer.

• Assess if the failure could result in

noncompliance with safety, other regulations

• Remember relationships – a failure mode

could negatively impact subsequent

operations

Describe these modes in terms of what the customer perceives.


Sentencing TechniqueSentencing Technique

FAILURE

MODECAUSE

could

result in

due to

leads to

EFFECT

Remember: Relate cause back to

failure mode, not back to effect


Example Example –– Cold Air Leaking from the DoorCold Air Leaking from the Door

Q: What could “cold air leaking from the door” result in?

A: Increased energy consumption (effect)

Q: What could “cold air leaking from the door” be due to?

A: A kink or twist in the door seal

“Cold air leaking from the door” can result in “increased energy consumption” (effect)

“Cold air leaking from the door” can be due to “a kink or twist in the door seal” (cause)


Column 4 Column 4 –– Severity of the FailureSeverity of the Failure

•• How serious is the effect of the failure.How serious is the effect of the failure.

•• Use a 1 to 10 scaleUse a 1 to 10 scale

•• Use the voice of the customer to get as Use the voice of the customer to get as

accurate an assessment as possibleaccurate an assessment as possible

•• Design teams should customize its definitions Design teams should customize its definitions

of severity to best suit their needs, as long as of severity to best suit their needs, as long as

consistency is achievedconsistency is achieved

•• Severity can only be reduced through design Severity can only be reduced through design

changes. (process redesign is rare)changes. (process redesign is rare)


Column 5 Column 5 -- ClassificationClassification

•• Used to identify Special Characteristics which Used to identify Special Characteristics which

may require additional design controls and may require additional design controls and

validation testing, (and manufacturing controls)validation testing, (and manufacturing controls)

•• When Severity is 9 or 10, a When Severity is 9 or 10, a potential potential Critical Critical

Characteristic exists. Enter Characteristic exists. Enter ““pCCpCC”” herehere

•• Used to communicate Team assessment to the Used to communicate Team assessment to the

Product Designers for additional consideration Product Designers for additional consideration

and inclusion in design documentation and inclusion in design documentation


Column 6 Column 6 --Potential Causes of FailurePotential Causes of Failure

• What could cause the failure mode?

• What circumstances could cause the failure?

• How could the item fail to meet specifications?

• How could the item not deliver its function?

• How could item interactions be incompatible,

mismatched or unsynchronized?


Design Deficiency 1: The product is Design Deficiency 1: The product is

manufactured properly, but poor designmanufactured properly, but poor design

• Material specification unsuitable for application

• Material hardness specified too low

• Specified lubricant too thick

• Actual stresses higher than design loads

• Specified torque is too low, too high

• Inadequate design life assumption

• Excessive heat, vibration, noise


Design Deficiency 2: The product design Design Deficiency 2: The product design

leads to poor manufacturingleads to poor manufacturing

• Is orientation, alignment important to function?

• Can components be assembled upside-down

or backwards?

• Are engineering tolerances compatible with

manufacturing capabilities?

DesignDesign--forfor--AssemblyAssemblyDesignDesign--forfor--ManufacturabilityManufacturability


Design Deficiency 2: The product design Design Deficiency 2: The product design

leads to poor manufacturingleads to poor manufacturing

Examples:

• Specifying heat-treatment such that some lots

of steel cannot be properly machined

• Symmetrical Design that allows a part to be

installed backwards or upside down

• Wrong fastener used because the design is

too similar to a more standard fastener


Column 7 Column 7 –– Probability of OccurrenceProbability of Occurrence

• What is the service history, field experience with

similar components, subsystems, systems?

• Is the component a carry-over or similar to a past

design?

• Is the part very new or different from the past?

• Has the application of the part changed?

• Are there environmental, customer use changes?

• Have reliability studies been used to estimate the

expected failure rates for the application?


Overlaying ProbabilitiesOverlaying Probabilities

Often, a failure event does not necessarily cause Often, a failure event does not necessarily cause

the failure mode.the failure mode.

Example: leaving the refrigerator door open may Example: leaving the refrigerator door open may

lead to the overheating of the compressor, if itlead to the overheating of the compressor, if it’’s a s a

hot summer day (more than 30hot summer day (more than 30°°C)C)

Two Probabilities:Two Probabilities: Leave the door open Leave the door open –– 1%1%

It happens to be a hot summer day It happens to be a hot summer day –– 10%10%

What is the probability of the What is the probability of the ““failure modefailure mode””??

It is usually simpler to assume 1It is usually simpler to assume 1--toto--1 correlation1 correlation


Column 7 Column 7 –– Probability of OccurrenceProbability of Occurrence

• Use a consistent ranking chart

• The group decides the number, or rounds up

to the next higher number.

• Be careful assigning numbers 1,2,3. The

difference between 1 and 3 is a factor of 50.

• When Severity is between 5-8, and

Occurrence is between 4-8, a potential

Significant Characteristic exists. Use “pSC”


Column 8Column 8--9 9 -- Current Design ControlsCurrent Design Controls

Prevention Design Controls

• Product Design features that prevent the

Cause/Mechanism or Failure Mode from

occurring or reduce the rate of Occurrence

Detection Design Controls

• Product Testing and analysis to qualify a

product before it is released to production


Column 8 Column 8 –– Prevention Design ControlsPrevention Design Controls

Controls to prevent the failure, or lessen the Controls to prevent the failure, or lessen the

probability of occurrenceprobability of occurrence

•• Asymmetry in part design featuresAsymmetry in part design features

•• Special grades of raw materials, etc.Special grades of raw materials, etc.

•• RedundancyRedundancy

•• Vibration dampening materialsVibration dampening materials

•• Lubrication, feedback control systemsLubrication, feedback control systems

•• OneOne--part designs, combined functionspart designs, combined functions

•• Design Standards/Guides, Best PracticesDesign Standards/Guides, Best Practices


Column 9 Column 9 –– Detection Design ControlsDetection Design Controls

Controls to detect the failure during testing (DV Controls to detect the failure during testing (DV

controls), or mitigate the failure if it occurs in usecontrols), or mitigate the failure if it occurs in use

•• Design ReviewsDesign Reviews

•• Reliability AnalysisReliability Analysis

•• SimulationSimulation

•• Lab Testing, Accelerated Life TestingLab Testing, Accelerated Life Testing

•• Field TestingField Testing

•• Failsafe designs Failsafe designs –– pressure relief valvespressure relief valves

•• Feedback, faults, alarmsFeedback, faults, alarms


Watch Out!Watch Out!

If a potential cause is overlooked, a If a potential cause is overlooked, a

product with a design deficiency may product with a design deficiency may

go into production!go into production!

Look at all Failure Modes as a way of Look at all Failure Modes as a way of

detecting overlooked causesdetecting overlooked causes


Column 10 Column 10 –– Effectiveness of DetectionEffectiveness of Detection

Consider the effectiveness of analyses and tests:Consider the effectiveness of analyses and tests:

•• Design Analysis methodsDesign Analysis methods

•• Simulation, FEASimulation, FEA

•• Tolerance stackTolerance stack--up studiesup studies

•• Material StudiesMaterial Studies

•• Team design reviewsTeam design reviews

•• Design Development TestsDesign Development Tests

•• Experiments, Lab TestingExperiments, Lab Testing

•• Prototype TestingPrototype Testing

•• Durability, life cycle tests Durability, life cycle tests


(continued)(continued)

•• Experience with similar designsExperience with similar designs

•• Number of samples to be testedNumber of samples to be tested

•• Statistically significant samples sizesStatistically significant samples sizes

•• One prototype, because of cost and complexityOne prototype, because of cost and complexity

•• Timeliness of testing & evaluationTimeliness of testing & evaluation

•• Early in the concept stageEarly in the concept stage

•• At prototype stageAt prototype stage

•• Just prior to engineering Just prior to engineering

design freeze design freeze


Lets RecapLets Recap

Potential Failure ModePotential Effects of the Failure Severity

Potential Causes/Mechanisms of the Failure Occurrence

Current Design ControlsPrevention, Detection Detection

Where S, O, D, numbers are unknown, estimate high". (also called “fear of the unknown!”)


Column 13 Column 13 –– Responsibility & TimingResponsibility & Timing

• It is important that recommended actions

always be expressed as specific tasks, and

assigned to individuals with a specific time line.

•• The Design Team Leader or Product Engineer The Design Team Leader or Product Engineer

must ensure that all actions have been must ensure that all actions have been

implemented and properly addressed.implemented and properly addressed.

• Reconvene the team, and recalculate the new

RPN resultant from the process improvements.


• Team leader should ensure that all Recommended Actions are properly assigned, executed, and closed-out.

• After completion, FMEA should be compared to objectives for process, product, and organization.

• Results can be incorporated with APQP team sign off, or Management Review.

FMEA FollowFMEA Follow--UpUp


Appendix:Appendix:

Special CharacteristicsSpecial Characteristics


IntroductionIntroduction

• All products and processes have characteristics

that need to be controlled.

• Some Special Characteristics require extra

attention and control to prevent nonconformance

• Special Characteristics have high impact upon:

• Product & Process Safety

• Compliance with Regulations

• Customer Satisfaction


Special Characteristics Special Characteristics -- SymbolsSymbols

• Characteristics are Special or not

• Special Characteristics can be considered in two

categories:

• Safety or Regulatory – Critical Characteristics (CC)

• Critical to Function and

Customer Satisfaction – Significant Characteristics (SC)

• Special Characteristics are assigned symbols and

deployed down through drawings and other documents


EXAMPLEEXAMPLE

Routine Routine

controlcontrolNot a Special Not a Special

CharacteristicCharacteristic(blank)(blank)Mfg. / Mfg. /

AssemblyAssembly

Process Process

ControlsControlsSevSev: 9 : 9 -- 1010Impact on Impact on

Design SCDesign SCSCSCMfg. / Mfg. /

AssemblyAssembly

Process Process

ControlsControlsSevSev: 5 : 5 –– 88

Occur: 4Occur: 4--1010

Impact on Impact on

Design CCDesign CCCCCCMfg./ Mfg./

AssemblyAssembly

Special Special

ControlsControlsSevSev: 5 : 5 –– 88

Occur: 4Occur: 4--1010

Significant Significant

CharacteristicCharacteristicSCSCCustomer Customer

SatisfactionSatisfaction

Special Special

ControlsControlsSevSev: 9 : 9 -- 1010Critical Critical

CharacteristicCharacteristicCCCCSafety/ Safety/

RegulatoryRegulatory

Actions Actions

RequiredRequiredDFMEADFMEA

CriteriaCriteria

IndicatesIndicatesClassifiClassifi

--cationcationEffectEffect


Critical Characteristics Critical Characteristics -- CCCC

Critical Characteristics - CC

• Impact upon safe use and function

• Impact compliance with governmental regulations

Design Controls

• Special Materials

• Safety Factors

• Fail-safes

• Special Analysis

• Special Testing

Process Controls

• Special Tooling

• Materials Inspections

• Product Testing

• Product Inspections

• Special Torques

• Assembly Sequences


Significant Characteristics Significant Characteristics -- SCSC

Significant Characteristics - SC

• Critical to customer satisfaction

• Characteristics sensitive to manufacturing variation

• Special manufacturing controls required to

assure compliance

Design and Process Controls as for Critical Characteristics


• Significant to Customer Satisfaction

• Significant Sensitivity to Variation

σ

Significant Characteristics Significant Characteristics ––

Two ApproachesTwo Approaches

Design For Six Sigma


““Not SignificantNot Significant”” CharacteristicsCharacteristics

X

Target Value

Tolerance

Customer Dissatisfaction remains about constant over the design tolerances

Tolerance

Features are robust to manufacturing variation


There is an increasing “loss to society” as deviation from a target value increases

Taguchi Loss FunctionTaguchi Loss Function

Loss increases to the right and left of the target


Loss Function Loss Function –– Consider a Train Consider a Train

ScheduleSchedule

X

Published Train

Departure Time

Train Leaves earlier: people arrive on-time and miss the train

Train Leaves later: no one misses the train, but train arrives late and misses connections

Increasing “Loss to Society”


Significant CharacteristicsSignificant Characteristics

X

Target Value

Tolerance

Customer Dissatisfaction increases sharply as features depart from the designed target values

Tolerance

Features are sensitive to manufacturing variation


Special ControlsSpecial Controls

• Every effort must be made to eliminate Special

Characteristics through design actions to improve

product robustness.

• Special Characteristics are confirmed after all

design/process alternatives are exhausted and

when Special Controls have been identified

Documents

171 DFMEA Presentation UWO 2012