process-capabilityPPT课件

ProcessCapabilityStudyPurposeTounderstandcapabilityconceptandhowtostudyprocesscapability;Tounderstandrelationbetweenprocesscapabilitystudyandgagestudy,SPC,DOE.Whatiscapabilityofaprocess?TerminologyWhytodoprocesscapabilitystudy?GagestudyandcapabilitystudySPCandcapabilitystudyDOEandcapabilitystudyHowtodoprocesscapabilitystudy?ContentWhatiscapabilityofaprocess?Capabilityistheextenttowhichastableprocessisabletomeetspecifications.Aprocessissaidtobestableifitonlyexhibitscommoncausevariation.(Controlchartshownopointsoutofcontrol)Terminology(1)DOE-DesignOfExperiment,synonymouswithdesignedexperiments,orstatisticallydesignedexperiments,itisamethodicalprocessthateffectivelyusesresourcestostudytheimpactofvariousfactorsonaprocess;VariableData-Quantitativedatathatcanbemeasuredandcanvaryfrompiecetopiece;AttributeData-Qualitativeorcategoricaldatacanbecounted.Attributedataischaracteristiccounts.Terminology(2)Mean-Ameasureofthecentraltendency;StandardDeviation-Ameasureofspread(variability).USL-UpperSpecificationLimit.Thenumericalvalue,abovewhichdefectsoccur.LSL-LowerSpecificationLimit.Thenumericalvalue,belowwhichdefectsoccur.Terminology(3)SpecialCause-Atypeofvariationthatisshownbyanoutofcontrolsituationfromacontrolchart.Itsuggestssomethingspecialhashappenedtocreateachangeintheprocess.CommonCause-Anaturaltypeofvariationthatcomesfromthenormaloperatingconditionsofaprocess.GageStudy-Astudytoquantifythedifferenttypesofmeasurementerrorassociatedwithagageormeasurementsystem.Whytodocapabilitystudy?Capabilitystudiesgiveanestimateoftheexpecteddefectrateforaprocessthatisincontrol;Itshouldbeperformedtoevaluatenewequipment,comparedifferentmachines;Itcanalsobeperformedonanongoingbasis.GagestudyandcapabilitystudyAllmeasurementdevicesusedtocollectdataforacapabilitystudyshouldhaveacceptablegageerror;Gagestudyincludingbias,linearity,stability,repeatabilityandreproducibility;Otherwise,thestudyisinvalid.SPCandcapabilitystudyAcapabilitystudycanonlybeperformedonastableprocessthatisincontrol;Suitablecontrolchartshouldbeusedtomonitorstabilityofprocessanalyzed.DOEandcapabilitystudyCapabilitystudycanbeconductedtoprioritizewhereexperimentationshouldbeperformed,tobestutilizeresources;Capabilitystudiesperformedbothbeforeandafterexperimentationcanbeusedtoquantifyanyimprovementmadeintheprocess.Howtodocapabilitystudy?(1)Capabilitystudywithvariabledata.Capabilitystudywithattributedata;Capabilitystudycanbecategorizedbydatatype.CapabilityStudyWithVaraibles(Cp,Cpk,Pp,Ppk)Capabilitystudywithvariables(1)Anormaldistributionorclosetoitbeingassumedwithparametersstudied;Priortocapabilitystudy,anormalitystudyshouldbeconducted;Avariablecontrolchartshouldbeusedduringcapabilitystudy.Capabilitystudywithvariables(2)Cp&Cpk-commoncapabilityindexforvariabledata,whichbeingusedtoevaluatethestatisticalstableprocess’scapability.TheyusethewithingroupsigmatoestimatethetotalgroupsigmaCp=(USL-LSL)/6SCapabilitystudywithvariables(3)Cpk-Themostcommoncapabilityindexforvariabledata,whichbeingusedtoevaluateprocess’sstatisticalstablecapability.it’sconsiderthedeviationofprocessCpk=minimum((USL-X)/3S,(X-LSL)/3S)Capabilitystudywithvariables(4)TheCpisequaltotheCpkwhenandonlywhentheprocessiscenteredbetweenitsspecificationlimits.DynamicProcessUSLLSLShort-termcapabilityLong-termcapabilityLSLnX-X)j2j=1g(Time1Time2Time3Time4NaturalprocesscharacteristicUSLContinuousprocesscharacteristicTotalSTD短期及长期能力工艺的短期能力分析需获取短期内(数天或数星期)一组30~50个数据.工艺的长期能力分析需获取长期内(数个月)一组100~200个数据.3Sigma工艺中值无漂移65554535UpperSpecLowerSpec0.400.110.000.10Obs%USLExpCpk1.0Cp1.03Sigma工艺中值漂移1.5Sigma0.000.006.605.89Obs%USLExpCpkCp0.51.007565554535LowerSpecUpperSpec6Sigma工艺中值无漂移80706050403020UpperSpecLowerSpec0.000.000.000.00Obs%USLExpCpkCp2.02.06Sigma工艺中值漂移1.5Sigma80706050403020UpperSpecLowerSpec0.000.000.000.00Obs%USLExpCpkCp1.52.0Capabilitystudywithvariables(5)Pp-Acommoncapabilityindexforvariabledata,whichbeingusedtoevaluateprocess’sperformance;ThecalculationformulaissameasCpexceptdifferentderivingofS.theSisdirectlyderivedfromallthedataofthegroupCapabilitystudywithvariables(6)Ppk-Anothercommoncapabilityindexforvariabledata,whichbeingusedtoevaluateprocess’sperformance.ThecalculationissameasCpkexceptdifferentderivingofS.Capabilitystudywithvariables(7)CpandCpkonlyincludescommoncausevariation,stableprocessisrequired;PpandPpkincludesbothcommoncausevariationandspecialcausevariation,sounstableprocessisapplicable.Capabilitystudywithvariables(8)Cpk1.67excellentcapability1.67>Cpk1.33Sufficientcapability1.33>Cpk1.0Passablecapability1.0>Cpk0.67Insufficientcapability0.67