NOKIA内部资料：制程能力控制

ProcessCapability(Cp/Cpk/Pp/Ppk)

GlobalTrainingMaterialCreator :GlobalMechanicsProcessManagerFunction :MechanicsApprover :GaryBradley/GlobalProcessTeamDocumentID :DMT00018-ENVersion/Status :V.1.0/ApprovedLocation :Notes:\\…\NMP\DOCMANR4\PCP\PCProcessLibraryDocManChangeHistory:Issue Date HandledBy Comments1.0 21stDec’01 JimChristy&SørenLundsfryd ApprovedforGlobalUseNOTE–Allcommentsandimprovementsshouldbeaddressedtothecreatorofthisdocument.第一页，共五十六页。ContentsSection Heading/Description Page1 Variation,TolerancesandDimensionalControl 4 2 Population,SampleandNormalDistribution 153 CpandCpkConcept 284 UseoftheNMPDataCollectionSpreadsheet 445 ConfidenceofCpk 52 第二页，共五十六页。ProcessCapability-EvaluatingManufacturingVariationAcknowledgementsBennyMatthiassen (NMPCMT,Copenhagen,Denmark)FrankAdler (NMPAlliance,Dallas,USA)JoniLaakso (NMPR&D,Salo,Finland)JimChristy (NMPSRC,Southwood,UK)第三页，共五十六页。Section1Variation,TolerancesandDimensionalControl第四页，共五十六页。TwoTypesofProductCharacteristicsVariable:Acharacteristicmeasuredinphysicalunits,limetres,volts,amps,decibelandseconds.ONOFFAttribute:Acharacteristicthatbycomparisontosomestandardisjudged“good”or“bad”,e.g.freefromscratches(visualquality).Inthistrainingwedealwithvariablesonly第五页，共五十六页。TheSourcesofProcess/SystemVariationMethodsOperatorsCustomerSatisfactionMaterialEnvironmentEquipmentProcess第六页，共五十六页。TwoTypesofProcessesAllprocesseshave:Natural(random)variability

=>duetocommoncausesStableProcess:

AprocessinwhichvariationinoutcomesarisesonlyfromcommoncausesUnstableProcess:

AprocessinwhichvariationisaresultofbothcommonandspecialcausesUSLLSLnominalvalueDefectUSLLSLnominalvalue

Unnaturalvariability=>duetospecialcauses第七页，共五十六页。Shewhart(1931)TheTwoCausesofVariationCommonCauses:Causesthatareimplementedintheprocessduetothedesignoftheprocess,andaffectalloutcomesoftheprocessIdentifyingthesetypesofcausesrequiresmethodssuchasDesignofExperiment(DOE),etc.

SpecialCauses:Causesthatarenotpresentintheprocessallthetimeanddonotaffectalloutcomes,butarisebecauseofspecificcircumstancesSpecialcausescanbeidentifiedusingStatisticalProcessControl(SPC)USLLSLNominal

valueDefectUSLLSLnominal

value第八页，共五十六页。TolerancesLSL(lowerspecificationlimit)10,7USL(upperspecificationlimit)10,9AcceptablepartRejectedPartRejectedProductNominal10,80,1RejectedPartAtoleranceisaallowedmaximumvariationofadimension.第九页，共五十六页。MeasurementReportInmostcaseswemeasureonlyonepartpercavityformeasurementreport第十页，共五十六页。ExampleofCapabilityAnalysisDataForsomecriticaldimensionsweneedtomeasuremorethan1partForcapabilitydataweusuallymeasure5pcs2times/hour=100pcs(butsamplingplanneedstobemadeonthebasisofproductionquantity,rundurationandcycletime)第十一页，共五十六页。ProcessCapability-Whatisit?ProcessCapabilityisameasureoftheinherent

capabilityofamanufacturingprocesstobeabletoconsistentlyproducecomponentsthatmeettherequireddesignspecificationsProcessCapabilityisdesignatedbyCpandCpkProcessPerformanceisameasureoftheperformanceofaprocesstobeabletoconsistentlyproducecomponentsthatmeettherequireddesignspecifications.ProcessPerformanceincludesspecialcausesofvariationnotpresentinProcessCapabilityProcessPerformanceisdesignatedPpandPpk第十二页，共五十六页。WhyMakeProcessCapabilityStudiesLSL(lowerspecificationlimit)10,7USL(upperspecificationlimit)10,9Nominal10,80,1Thispartiswithinspec.ThetoolwouldbeapprovedifonlythispartwasmeasuredThesepartsareoutofspecandcouldbeapprovedifonlyonegoodpartwasmeasuredAprocesscapabilitystudywouldrevealthatthetoolshouldnotbeacceptedWhenadimensionneedstobekeptproperlywithinspec,wemuststudytheprocesscapability….butstillthisisnoguaranteefortheactualperformanceoftheprocessasitisonlyaninitialcapabilitystudy第十三页，共五十六页。E1.5

E1

E2

E3

E4

E5TheNokiaProcessVerificationProcessBlackdiamondstobefixedbyE3(oftenachangeofawhitediamond)ProposalforblackdiamondstobediscussedwithSupplier.Max:105,85OngoingProcessControl(SPC)TolerancesappliedtodrawingType1FunctionalCharacteristics-1part/cavitymeasuredformeasurementreportWhitediamonds(s)tobeagreedWhitediamonds(s)tobediscussedwithsupplier10parts/cavitymeasuredformeasurementreportCapabilitystudy:Requirement:CpandCpk>1.67byE3.Quantitiestobeagreedwithsupplier.Minimum5partspr1/2hourin10hoursmeasuredforeachcavity=100parts.Canvarydependingontoolcapacity,e.g.stampedparts(seeDMY00019-EN)第十四页，共五十六页。Section2.Population,SampleandNormalDistribution第十五页，共五十六页。TheBellShaped(Normal)DistributionSymmetricalshapewithapeakinthemiddleoftherangeofthedata.Indicatesthattheinputvariables(X's)totheprocessarerandomlyinfluenced.第十六页，共五十六页。“PopulationParameters”

=Populationmean

=PopulationstandarddeviationPopulationversusSamplePopulationAnentiregroupofobjectsthathavebeenmadeorwillbemadecontainingacharacteristicofinterestSampleThegroupofobjectsactuallymeasuredinastatisticalstudyAsampleisusuallyasubsetofthepopulationofinterestPopulationSample“SampleStatistics” x=Samplemean s=Samplestandarddeviation第十七页，共五十六页。TheNormalDistribution第十八页，共五十六页。WhatMeasurementsCanBeUsedtoDescribeaProcessorSystem?Example:1

=52

=73

=44

=25

=6mean(average)ordescribesthelocationofthedistributionµ(mü),ameasureofcentraltendency,isthemeanoraverageofallvaluesinthepopulation.Whenonlyasampleofthepopulationisbeingdescribed,meanismoreproperlydenotedas

(x-bar):第十九页，共五十六页。Example:1

=52

=73

=44

=25

=6Themostsimplemeasureofvariabilityistherange.Therangeofasampleisdefinedbyasthedifferencebetweenthelargestandthesmallestobservationfromsamplesinasub-group,e.g.5consecutivepartsfromthemanufacturingprocess.WhatMeasurementsCanBeUsedtoDescribeProcessvariation?第二十页，共五十六页。sST-oftennotatedasorsigma,isanothermeasureofdispersionorvariabilityandstandsfor“short-termstandarddeviation”,whichmeasuresthevariabilityofaprocessorsystemusing“rational”sub-grouping.where

istherangeofsubgroupj,Nthenumberofsubgroups,andd2*dependsonthenumberNofsubgroupsandthesizenofasubgroup(seenextslide)WhatMeasurementsCanBeUsedtoDescribeProcessvariation?第二十一页，共五十六页。d2*valuesforSSTWhere:N=no.ofsub-groups,n=no.ofsamplesineachsub-groupd2*d2Typical:N=20&n=5第二十二页，共五十六页。

x3

x2

x1

x10x_tExample:WhatMeasurementsCanBeUsedtoDescribeProcessvariation?第二十三页，共五十六页。TheDifferenceBetweenSSTandsLT!!meanTimeDimensionShorttermStandardDeviationLongtermStandardDeviationSubgroupsizen=5NumberofsubgroupsN=7TRENDSubgroupNo.1第二十四页，共五十六页。ThedifferencebetweenthestandarddeviationssLTandsSTgivesanindicationofhowmuchbetteronecandowhenusingappropriateproductioncontrol,likeStatisticalProcessControl(SPC).Short-termstandarddeviation:Long-termstandarddeviation

:ThedifferencebetweensSTandsLT第二十五页，共五十六页。ThedifferencebetweensSTandsLTThedifferencebetweensLTandsST

isonlyinthewaythatthestandarddeviationiscalculatedsLTisalwaysthesameorlargerthansSTIfsLTequalssST,thentheprocesscontroloverthelonger-termisthesameastheshort-term,andtheprocesswouldnotbenefitfromSPCIfsLTislargerthansST,thentheprocesshaslostcontroloverthelonger-term,andtheprocesswouldbenefitfromSPCThereliabilityofsLTisimprovedifthedataistakenoveralongerperiodoftime.AlternativelysLTcanbecalculatedonseveraloccasionsseparatedbytimeandtheresultscomparedtoseewhethersLTisstable第二十六页，共五十六页。Exercise1:SampleDistributions1.InExcelfile"Dataexercise1.xls"

youfind100measurementsbeingtheresultofacapabilitystudy.Thespecificationforthedimensionis15,16,01

2.Howwelldoesthesamplepopulationfitthespecification,e.g.shouldweexpectanypartsoutsidespec?3.Mentionpossibleconsequencesofhavingapartoutsidespec.4.Mentionpossiblecausesofvariationforparts.5. Calculatethesamplemeanandsamplestandarddeviationforthe100measurements.UsetheaverageandstdevfunctionsExcel.第二十七页，共五十六页。Section3.CpandCpkConcept第二十八页，共五十六页。DefiningCpandPpSamplemeanProcessvariation6*sUSL-LSLLSLUSLNominaldimThetoleranceareadividedbythetotalprocessvariation,irrespectiveofprocesscentring.第二十九页，共五十六页。DefiningCpkandPpkSamplemeanProcessvariation3sProcessvariation3sMean-LSLUSL-MeanLSLUSLNominaldimCpkandPpkIndexesaccountalsoforprocesscentring.第三十页，共五十六页。WhatistheDifferenceBetweenCpandCpk?TheCpindexonlyaccountsforprocessvariabilityTheCpkIndexaccountsforprocessvariabilityandcenteringoftheprocessmeantothedesignnominalTherefore,CpCpkNOTE:SameappliesalsoforPpandPpkCp=Cpk(bothlow)LSLUSLMean=NominalRejectpartsRejectpartsCphigh,Cpklow

Processshouldbeoptimized!NominalLSLMeanUSLRejectparts第三十一页，共五十六页。WhatDoTheseIndexesTellUs??Simplenumericalvaluestodescribethequalityoftheprocess>>ThehigherthenumberthebetterRequirementforCpandCpkis1.67min.RecommendationforPpandPpkis1.33min.Thisleavesussomespaceforthevariation,i.e.asafetymarginAreweabletoimproveourprocessbyusingSPC?Ifindexislow,followingthingsshouldbegivenathought:IstheproductdesignOK?Aretolerancelimitssetcorrectly?Tootight?Istheprocesscapableofproducinggoodqualityproducts?Processvariation?DOErequired?Isthemeasuringsystemcapable?(SeeGageR&R)第三十二页，共五十六页。Cpk-Witha2-sigmasafetymargin-3sST+3sSTLCLUCLLSLUSLMeanvalue=NominalvalueorTargetRequirementforCpandCpkis

1.67min.1.67isaratioof=5/3or10/6.6*standarddeviation10*standarddeviation2*standarddeviation2*standarddeviation第三十三页，共五十六页。Cpk<1.67theprocessNOTCAPABLEAcceptabilityofCpkIndex

Cpk>=1.67theprocessisCAPABLECpk>=2.0theprocesshasreachedSixSigmalevel第三十四页，共五十六页。WhatDoTheseIndexesTellUs??IfCp=Cpk,IfPp=Ppk,IfCpk<Cp,IfPpk<Pp,IfCp=Pp,IfCpk=Ppk,IfPp<Cp,IfPpk<Cpk,…thenprocessisaffectedbyspecialcauses.InvestigateX-bar/R-chartforout-of-controlconditions.SPCmaybeeffective…thenprocessisnotaffectedbyspecialcausesduringthestudyrun.SPCwouldnotbeeffectiveinthiscase…thenprocessperfectlycentred…thenprocessnotcentred(checkprocessmeanagainstdesignnominal)第三十五页，共五十六页。CpandCpkIndicesandDefects

(bothtailsofthenormaldistribution)Pp=Ppk=1,3363ppmdefects=0,006%Cp=Cpk=1,670,6ppmdefects=0,00006%Note:PpmrejectratescalculatedfromCp&Cpkarebasedontheshorttermvariationwhichmaynotrepresentthelongtermrejectrate第三十六页，共五十六页。TheEffectsofCpkandCponFFR第三十七页，共五十六页。Exercise2:CpandCpkCalculateCpandCpkforthe100measurementsinthefile"Dataexercise1.xls"DeterminetheapproximateCpandCpkforthe4samplepopulationsonthefollowingpageShouldactionsbemadetoimprovetheseprocesses.Ifyes,which?第三十八页，共五十六页。EstimateCpandCpk?Thewidthofthenormaldistributionsshowninclude±3*sLSLUSLA)LSLUSLB)LSLUSLC)USLLSLD)第三十九页，共五十六页。EstimateCpandCpk?-A)LSLUSLA)MeanandnominalUSL-LSL6*sUSL-MeanMean-LSL3*s第四十页，共五十六页。EstimateCpandCpk?-B)LSLUSLB)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3*s第四十一页，共五十六页。EstimateCpandCpk?-C)LSLUSLC)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3*s第四十二页，共五十六页。EstimateCpandCpk?-DUSLLSLD)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3*s第四十三页，共五十六页。Section4.UseoftheNMPDataCollectionSpreadsheet第四十四页，共五十六页。ExampleofhowtoCollectData

1. Runinandstabiliseprocess2. Notethemainparametersforreference3. Whentheprocessisstablerunthetoolfor10hours3. Take5partsoutfromeachcavityeveryhalfhourandmarkthemwithtime,dateandcavity.Total20setsof5partsfromeachcavitymustbemade,oraccordingtoagreement.4. Afterthelastsamplelotnotethemainprocessparametersforreference5. Measureandrecordthemainfunctionalcharacteristics(whitediamonds)6. FilldataintotheNMPdatacollectionspreadsheet7. Analyse!SeeDMY00019-ENClassificationandMarkingofFunctionalCharacteristicsTimeDimensionSubgroupsizen=5NumberofsubgroupsN=200,5hoursbetweensamplestakenNote:Forclarity,only6subgroupsareshown第四十五页，共五十六页。DataCollectionSheet(DMM00024-EN-5.0)第四十六页，共五十六页。DataCollectionSheet(DMM00024-EN-5.0)第四十七页，共五十六页。Gra