Failure Modes and Effects Analysis (FMEA)

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Transcript of Failure Modes and Effects Analysis (FMEA)

  • Prof.RobLeachmanIEOR130Fall,2013

    9/3/13 FMEA Rob Leachman 1

  • Definition:FMEAisasystematicapproachtothemanagementofproductorprocessdevelopment.Itinvolves: Identifyingallpotentialwaysaproductorprocesscouldfail

    Identifyingtheeffectsorconsequencesofsuchfailures

    Identifyingandimplementingmethodsormeasurestoeliminateorreducethechanceofsuchfailuresoccurring

    9/3/13 FMEA Rob Leachman 2

  • FMEAgeneratesalivingdocumentfortheproductorprocessdelineatingallknownfailuremodes,theireffects,andthemitigationmeasuresimplementedtoprecludefailures.

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

    9/3/13 FMEA Rob Leachman 3

  • 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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  • 9/3/13 FMEA Rob Leachman 8

    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)

    9/3/13 FMEA Rob Leachman 9

  • 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).

    9/3/13 FMEA Rob Leachman 14

  • Afailuremodeistypicallyjusttheinabilitytoperformafunctionidentifiedinthefunctionalanalysis.

    Example:Describefailuremodesforacardoor: Basicfunction:ingress/egressvehicle

    Failuremodes:doordoesnotopen,doorsticks,doordoesnotopenwideenough

    SecondaryFunction:protectoccupantfromnoise FailureMode:doordoesnotseal,doorheaderleaks

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  • 9/3/13 FMEA Rob Leachman 16

    Methods

    Machinery

    Material

    People

    Environment

    FailureMode

    DownstreamProcess

    EndUserOperation

    CustomerSafety

    Causes Effects

    Note:failuremodemayhavemultiplecausesand/ormultipleeffects

  • 9/3/13 FMEA Rob Leachman 17

    Methods:Lackofproperwarnings

    Machinery:Regulatornotfunctioning

    Material:Bagmaterialtooabrasive

    People:Passengertoosmall Environment:

    Passengernotwearingseatbelt

    FailureMode Injurelightweightpassenger

    Bruisepassengerincrash

    Killsmallchildren

    Causes Effects

    Occupantunabletoabsorbinflationforce

  • 9/3/13 FMEA Rob Leachman 18

    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.

    9/3/13 FMEA Rob Leachman 19