171 dfmea presentation uwo 2012
DESCRIPTION
DFMEA Presentation with case study.TRANSCRIPT
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
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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
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• 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
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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!”)
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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
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Define the Subsystem
RISK Assessment
Reliability Tools/Analysis
Design Testing
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• 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?
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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
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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
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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
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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
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•• 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
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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
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Process Function RequirementsProcess Function Requirements
•• 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””
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Process Function RequirementsProcess Function Requirements
•• (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.
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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
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•• 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
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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
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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
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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
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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.
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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?
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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.
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Sentencing TechniqueSentencing Technique
FAILURE
MODECAUSE
could
result in
due to
leads to
EFFECT
Remember: Relate cause back to
failure mode, not back to effect
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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)
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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)
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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
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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?
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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
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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
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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
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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?
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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
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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”
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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
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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
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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
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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
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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
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(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
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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!”)
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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.
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• 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
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Appendix:Appendix:
Special CharacteristicsSpecial Characteristics
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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
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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
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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
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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
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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
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• Significant to Customer Satisfaction
• Significant Sensitivity to Variation
σ
Significant Characteristics Significant Characteristics ––
Two ApproachesTwo Approaches
Design For Six Sigma
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““Not SignificantNot Significant”” CharacteristicsCharacteristics
X
Target Value
Tolerance
Customer Dissatisfaction remains about constant over the design tolerances
Tolerance
Features are robust to manufacturing variation
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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
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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”
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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
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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