Prof.RobLeachmanIEOR130Fall,2013

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Definition:FMEAisasystematicapproachtothemanagementofproductorprocessdevelopment.Itinvolves: Identifyingallpotentialwaysaproductorprocesscouldfail

Identifyingtheeffectsorconsequencesofsuchfailures

Identifyingandimplementingmethodsormeasurestoeliminateorreducethechanceofsuchfailuresoccurring

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FMEAgeneratesalivingdocumentfortheproductorprocessdelineatingallknownfailuremodes,theireffects,andthemitigationmeasuresimplementedtoprecludefailures.

Formalapplicationsbeganintheaerospaceindustryinthemid1960s.Subsequently,FMEAwasadoptedbymanyotherindustries(e.g.,automotive,semiconductors).

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Developmentofanewprocessflowtofabricateintegratedcircuitsisdividedintomodulescorrespondingtomajorprocesssteps(e.g.,aphotolithographystepmodule,aplasmaetchingstepmodule,andsoon).

Typically,eachmoduleincludesoneormoremeasurementsperformedasthelastsubstep(s)ofthemodulethatprovethatnoneofthefailuremodesarepresentbeforethesiliconwafersarepassedtothenextmodule.

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FMEAismosteffectivewhenperformedbeforeadesignisreleasedratherthanafterthefact Thefocusshouldbeonfailurepreventionratherthanjustfailuredetection

Assuch,FMEAisastandardengineeringmanagementpracticeusedinthedevelopmentofnewproducts

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DesignFMEA examinesthefunctionsofacomponent,subsystemormainsystem Potentialfailuresfromincorrectmaterialchoiceorinappropriatespecifications

Example:AirBag(excessiveairbaginflatorforce) ProcessFMEA examinestheprocessesusedtomakeacomponent,subsystemormainsystem Potentialfailuresfromincorrectassemblyorexcessprocessvariationresultinginoutofspecproduct

Example:AirBagassemblyprocess(carassemblylineoperatormightnotinstallairbagproperlysuchthatitmightnotengageduringimpact)

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BasicandSecondaryFunctions verbnoundescriptionsofwhatproduct(process)does. BasicFunction:ingresstoandegressfromvehicle Secondaryfunctions protectoccupantfromnoise

FailureMode physicaldescriptionofafailure. noiseentersatdoortoroofinterface

FailureEffects impactoffailureonpeople,equipment driverdissatisfaction

FailureCause referstocauseofthefailure insufficientdoorseal

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Identifypotentialfailuremode

Identifypotentialeffect(s)offailuremode

Identifypotentialcause(s)offailuremode

Evaluatecurrentcontrolsordesignverificationprocess

Determineseverity

Determineoccurrence

Determinedetectability

Determineriskprioritynumber(RPN)

Identifyactionsleadingtoimprovement

Severityisaratingcorrespondingtotheseriousnessofaneffectofapotentialfailuremode.(Scale:110.1:noeffectonoutput,5:moderateeffect,8:seriouseffect,10:hazardouseffect)

Occurrenceisaratingcorrespondingtotherateatwhichafirstlevelcauseanditsresultantfailuremodewilloccuroverthedesignlifeofthesystem,overthedesignlifeoftheproduct,orbeforeanyadditionalprocesscontrolsareapplied.(Scale:110.1:failureunlikely,5:occasionalfailure,8:high#offailureslikely,10:failurescertain)

Detectionisaratingcorrespondingtothelikelihoodthatthedetectionmethodsorcurrentcontrolswilldetectthepotentialfailuremodebeforetheproductisreleasedforproductionfordesign,orforprocessbeforeitleavestheproductionfacility.(Scale:110.1:willdetectfailure,5:mightdetectfailure,10:almostcertainnottodetectfailures)

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TheRPNidentifiesthegreatestareasofconcern.Itcombinestheassessmentsofthe

(1)Severityrating,(2)Occurrencerating,and(3)Detectionratingforapotentialfailuremode.

RPN=SeverityRatingxOccurrenceRatingxDetectionRating

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Theseverityis9or10(potentiallyhazardousfailures),OR

SeverityratingxOccurrenceratingishigh,OR RPN(severityxoccurrencexdetection)ishigh. NoabsoluterulesforwhatisahighRPNnumber.Rather,failuremodesoftenareviewedonarelativescale(i.e.,highestRPNisaddressedfirst).

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CompaniesoftenidentifyspecialproductcharacteristicswithanappropriatesymbolontheFMEAworksheet.

Thesespecialcriticalcharacteristics(CCs)aretypicallyitemswhichaffectregulatorycompliance,suchasitemswhichrequireawarninggiventoconsumersorspecialprocesscontrols.

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AsfirststepstowardgeneratinganFMEAdocument,itisoftenusefulto Performafunctionalanalysis,then GenerateFMEAcauseandeffectdiagrams.

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Identifythebasicandsecondaryfunction(s) ofproductsorprocessesusingverbnounrelationships.

Basicfunctions:specificfunctionswhichaproductorprocessisdesignedtodo. Mousetrapexample:basicfunctionistoKillMouseorCatchMouse.

Secondaryfunctions:allotherfunctionswhicharesubordinatetothebasicfunction(e.g.,closetrap).

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Afailuremodeistypicallyjusttheinabilitytoperformafunctionidentifiedinthefunctionalanalysis.

Example:Describefailuremodesforacardoor: Basicfunction:ingress/egressvehicle

Failuremodes:doordoesnotopen,doorsticks,doordoesnotopenwideenough

SecondaryFunction:protectoccupantfromnoise FailureMode:doordoesnotseal,doorheaderleaks

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Methods

Machinery

Material

People

Environment

FailureMode

DownstreamProcess

EndUserOperation

CustomerSafety

Causes Effects

Note:failuremodemayhavemultiplecausesand/ormultipleeffects

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Methods:Lackofproperwarnings

Machinery:Regulatornotfunctioning

Material:Bagmaterialtooabrasive

People:Passengertoosmall Environment:

Passengernotwearingseatbelt

FailureMode Injurelightweightpassenger

Bruisepassengerincrash

Killsmallchildren

Causes Effects

Occupantunabletoabsorbinflationforce

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PartorProcessNameAutomotivePassengerAirBagSystem

SuppliersandPlantsAffected

Design/MfgResponsibility

ModelDate

OtherAreasInvolved EngineeringChangeLevel

ProcessOperation,

ProductFunctionorPurpose

PotentialFailureMode

PotentialEffect(s)ofFailure

SEV

CC

PotentialCause(s)ofFailure

OCC

CurrentControlsEvaulationMethod

DET

S*O

RPN

RecommendedAction(s)

Inflateairbag Bagdoesnotopenonimpact InjurePassenger 8 *Sensorisnotfunctioningproperly

2Lighttonotifysystemismalfucntioning

6 16 96 Addredundantsensortomonitorimpact

Restrainpassenger

Occupantunabletowithstandinflationforce

Injurelightweightpassenger 8 *

Passengernotwearingseatbelt 4 None 10 32 320

1)Installswitchwhichdeactivatesairbagsystemunlessseatbeltisworn

2)Consumereducationofairbagsystempotentialfailures

Bruisepassengerincrash 3

Forceregulatornotworking 2

Repeatabilitytestsinlab 3 6 18

LastcolumnsofFMEAWorksheetareusedtoidentifyimprovementplan: Recommendedactions Identifyresponsibilitytocompleteactions Identifytargetdatestocompleteactions ListactionstakenandreassessRPN

LikeotherQualityControlmethodologies,FMEAusesaMeasureAnalyze ImproveControlcycle.

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