FMEA潛在失效模式及后果分析(英文版)

FailureMode&EffectAnalysisExplanationandUseofFMEAWhatisFMEA?FMEAisaproblemsolvingprocessadoptedbySnap-onasakeycomponentoftheQualityForwardSystem.Generally,FMEAisdonebyanon-sitemultifunctionalteamfacilitatedlocallyorbyanSEQGroupAdvancedQualityEngineer.Objectiveistoidentifyallofthereasonswhyqualityofaprocessorproductdoesnotmeetexpectations.Usesseverity,occurrenceanddetectionratingstodeterminecorrectiveactionpriorityforeachpossiblefailurereason.WhenshouldaFMEAstudybeconducted?AspartofaDesign/Developmentphase.Whencorrectiveactionisneededduetounfavorableperformancedata–(performancebasedonQFSmetricsdoesnotmeetgoals).WhenaneedtomakeincrementalimprovementisidentifiedbyfacilitymanagementortheSEQGroup.FMEATeamStart-UpTeamSelection–donebylocalqualitycoordinator,businessunitmanageror,onrequest,SEQGroupAdvancedQualityEngineer.ProblemStatement–Aconciseandfocuseddescriptionofthequalityproblemoropportunityforimprovement,“whatwentwrong”or“whatneedsfixing”.GoalStatement–adescriptionofwhatistobeaccomplishedbytheteam,inquantifiableterms“reduceby”,“increaseby”,“eliminate”,etc.Goodmetricstouseincludescrapcost,reworkcost,orDefectsPerMillionOpportunities(DPMO),etc.Forexample,agoalstatementcouldbe“ToreduceDPMOonproductfamilyXfrom3000to2000byyearend”.CompleteFMEATeamStart-UpWorksheet(examplelocatedinprocedureSEQ80.10,Figure1).ProblemStatement&GoalStatementProblemStatementandGoalStatementshouldconsider:Whatwentwrong?Whatisthegapbetweenthedesiredqualitylevelandtheactualqualitylevel?Whichprocessorprocessesareinvolved?Whichdepartmentorcellisthedeficiencyoccurringin?Istheproblemcyclic,canitbeattributedtospecificevents?Whataretheappropriatemetricstomeasure?Whatistheimpactonoperationalfitnessandprofitability?Whatistheimpactonthebottomline(reduced,increased,eliminated)?Arethereconstraintsrecognizedearlyintheprocess?Ifso,havetheybeenexploredandclarifiedwiththeappropriatemanagementlevelFMEAProcessFMEA’suncoverprocessproblemsrelatedtothemanufactureofproduct.Examples:apieceofautomatedassemblyequipmentmaymisfeedpartsresultinginproductsnotbeingassembledcorrectly,or,inachemicalmanufacturingprocess,temperatureormixingtimecouldbesourcesofpotentialfailuresresultinginunusableproduct.Thinkintermsofthefiveelementsofaprocess:people,materials,equipment,methodsandenvironment.Withthesefiveelementsinmind,ask“Howcanprocessfailureaffecttheproduct,processingefficiencyorsafety?”NinestepsinFMEAprocess.Step#1-ReviewtheProcessEnsurethateveryoneontheFMEAteamhasthesameunderstandingoftheprocessbeingworkedon.Reviewblueprint/engineeringdrawingofproduct(ifconductingFMEAonproduct)and/oradetailedflowchartoftheprocess.Ifthesearenotavailable,theteamwillneedtocreateone.Usingtheblueprintand/orflowchart,teammembersshouldfamiliarizethemselveswiththeproductorprocess.Theyshouldphysicallyseetheproductoraprototypeoftheproduct,andphysicallywalkthroughtheprocessexactlyastheprocessflows.Itishelpfultohavean“expert”ontheproductorprocessavailabletoansweranyquestionstheteammighthave.Step#2–BrainstormPotentialFailureModesMethodofgeneratinganddocumentingideasofpotentialfailuremodes.Ifproductorprocessiscomplex,aseriesofbrainstormingsessions,eachfocusedonadifferentelement(i.e.people,methods,equipment,materials,environment),maybeneededtogenerateamorethoroughlistofpotentialfailuremodes.Facilitatorshouldwritedownallideasgeneratedinbrainstormingsessions.Oncebrainstormingiscomplete,ideasshouldbegroupedintolikecategories(asdeterminedbytheteam).Groupscanbetypeoffailure,whereontheproductfailureoccurred,estimatedseriousnessofthefailure,etc.Failuremodesmayalsobecombinediftheyarethesameorverysimilar.Oncefailuremodeshavebeengrouped/combined,theyshouldbetransferredtothePotentialFailureModeandEffectAnalysisSheet(exampleinSEQ80.10,Figure2).Step#2(continued)–

Brainstorming

GuidelinesDonotmakeanyjudgmentonideas.Teammembersshouldnotcommentonwhetheranideaisgoodorbad.Thinkingshouldbeunconventional,imaginative,orevenoutrageous.Aimforalargenumberofideasintheshortestpossibletime.Teammembersshould“hitchhike”onotherideas,byexpandingthem,modifyingthem,orproducingnewonesbyassociation.Allteammembersshouldparticipateinbrainstormingprocess.Step#3–ListPotentialEffectsofEachFailureModeAfterthefailuremodesarelistedontheFMEAworksheetform,theFMEAteamneedstorevieweachfailuremodeandidentifythepotentialeffectsofthefailureshoulditoccur.Forsomefailuremodes,theremaybeonlyoneeffect,whileotherfailuremodesmayhaveseveraleffects.Thisstepmustbethorough–thisinformationwilldetermineassignmentofriskratingsforeachofthefailures.Itishelpfultothinkofthisstepasanif-thenprocess:Ifthefailureoccurs,thenwhataretheconsequences.Step#4–AssignSeverityRatingTheseverityratingisanestimateofhowserioustheeffectswouldbeifagivenfailuredidoccur.Maybebasedonpastexperience,oranestimatebasedontheknowledgeandexpertiseoftheteammembers.Becauseeachfailuremayhaveseveraldifferenteffects,andeacheffectmayhaveadifferentlevelofseverity,theeffect,notthefailure,mustberated.Eacheffectshouldbegivenitsownseverityrating.Ratingsbasedon10-pointscale,with1beingthelowestratingand10beingthehighest.Generalexampleonnextpage–maybecustomizedbyteamfortheirspecificFMEAproject.Step#4continued–SeverityRatingScaleExampleRatingDescriptionDefinition10DangerouslyHighFailurecouldinjurethecustomeroranemployee9ExtremelyHighFailurewouldcreatenoncompliancewithfederalregulations8VeryHighFailurerenderstheunitinoperableorunfitforuse7HighFailurecausesahighdegreeofcustomerdissatisfaction6ModerateFailureresultsinasubsystemorpartialmalfunctionoftheproduct5LowFailurecreatesenoughofaperformancelosstocausethecustomertocomplain4VeryLowFailurecanbeovercomewithmodificationstothecustomer’sprocessorproduct,butthereisminorperformanceloss3MinorFailurewouldcreateaminornuisancetothecustomer,butthecustomercanovercomeitintheprocessorproductwithoutperformanceloss.2VeryMinorFailurewouldnotbereadilyapparenttothecustomer,butwouldhaveminoreffectsonthecustomer’sprocessorproduct1NoneFailurewouldnotbenoticeabletothecustomerandwouldnotaffectthecustomer’sprocessorproduct.Step#5–AssignOccurrenceRatingTheoccurrenceratingisameasureofhowoftenanfailuremodemayoccur.Bestmethodfordetermineoccurrenceratingistouseactualdatafromtheprocess(forexample,failurelogsorprocesscapabilitydata).Ifactualdataisnotavailable,theteamneedstoestimatehowoftenafailuremodecouldoccur.Teamcanmakeabetterestimateofhowlikelyafailuremodeistooccurandatwhatfrequencybyknowingthepotentialcausesoffailure.Ratingsbasedon10-pointscale,with1beingthelowestratingand10beingthehighest.Generalexampleonnextpage–maybecustomizedbyteamfortheirspecificFMEAproject.Step#5continued–OccurrenceRatingScaleExampleRatingDescriptionPotentialFailureRate10VeryHigh–FailureisalmostinevitableMorethanoneoccurrenceperdayoraprobabilityofmorethanthreeoccurrencesin10events(Cpk<0.33).9Oneoccurrenceeverythreetofourdaysoraprobabilityofthreeoccurrencesin10events(Cpkapproximatelyequalto0.33).8High–RepeatedfailuresOneoccurrenceperweekoraprobabilityof5occurrencesin100events(Cpkapproximatelyequalto0.67).7Oneoccurrenceeverymonthoroneoccurrencein100events(Cpkapproximatelyequalto0.83)6Moderate–OccasionalfailuresOneoccurrenceeverythreemonthsorthreeoccurrencesin1,000events(Cpkapproximatelyequalto1.00)5Oneoccurrenceeverysixmonthstooneyearoroneoccurrencein10,000events(Cpkapproximatelyequalto1.17)4Oneoccurrenceperyearorsixoccurrencesin100,000events(Cpkapproximatelyequalto1.33)3Low–RelativelyfewfailuresOneoccurrenceeveryonetothreeyearsorsixoccurrencesin10millionevents(Cpkapproximatelyequalto1.67)2Oneoccurrenceeverythreetofiveyearsortwooccurrencesinonebillionevents(Cpkapproximatelyequalto2.00)1Remote–FailureisunlikelyOneoccurrenceingreaterthanfiveyearsorlessthantwooccurrencesinonebillionevents(Cpkgreaterthan2.00)Step#6–AssignDetectionRatingThedetectionratinglooksathowlikelyitisthatafailureortheeffectofafailurewillbedetected.Startbyidentifyingcurrentcontrolsthatmaydetectafailureoreffectofafailure(example–SPCorin-processchecks).Morecontrolsinplacegeneratesalownumber(better)rating;nocurrentcontrolsmeansthelikelihoodofdetectionislowandthereforetheitemwouldreceiveahighnumber(worse)rating.Ratingsbasedon10-pointscale,with1beingthelowestratingand10beingthehighest.Generalexampleonnextpage–maybecustomizedbyteamfortheirspecificFMEAproject.Step#6continued–DetectionRatingScaleExampleRatingDescriptionDefinition10AbsoluteUncertaintyTheproductisnotinspectedorthedefectcausedbyfailureisnotdetectable.9VeryRemoteProductissampled,inspectedandreleasedbasedonAcceptableQualityLevel(AQL)samplingplans.8RemoteProductisacceptedbasedonnewdefectivesinasample.7VeryLowProductis100%manuallyinspectedintheprocess.6LowProductis100%manuallyinspectedusinggo/nogoorothermistake-proofinggages5ModerateSomeStatisticalProcessControl(SPC)isusedinprocessandproductisfinalinspectedoff-line4ModeratelyHighSPCisusedandthereisimmediatereactiontoout-of-controlconditions3HighAneffectiveSPCprogramisinplacewithprocesscapabilities(Cpk)greaterthan1.332VeryHighAllproductis100%automaticallyinspected.1AlmostCertainThedefectisobviousorthereis100%automaticinspectionwithregularcalibrationandpreventivemaintenanceoftheinspectionequipment.Step#7–CalculateRiskPriorityNumberTheriskprioritynumber(RPN)iscalculatedbymultiplyingtheseverityratingtimestheoccurrenceratingtimesthedetectionratingforalloftheitems.RPN=SeverityXOccurrenceXDetectionTotalRPNiscalculatedbyaddin