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Cpk知識(shí)資料香港新科、光寶課件1Cpk知識(shí)資料香港新科、光寶課件2DefinitionofTermsCapability-Theabilityofaprocesstoproducepartswithinspecification.Aprocessissaidtobecapablewhennearlyallpartsproducedbytheprocessarewithinspecification.ProcessCapabilityIndices-Measuresofthecapabilityofaprocess.X-Theaverageofasampleofdata,-ThesamplestandarddeviationSUSL,LSL=UpperandLowerspecificationxxni=?sxxni=-?-()21Cp

-

=USLLSLs6CpkXsXs=é?êù?úminimum,USL-

3-LSL3DefinitionofTermsCapability3Cpk知識(shí)資料香港新科、光寶課件4Cpk知識(shí)資料香港新科、光寶課件5WhyuseCpk?Cpk.1.151.301.331.523%orppm13%2.4%0.7%2700ppm561ppm96ppm66ppm7ppm2"ppb">>1"ppb"Singlenumbersummaryofprocessperformance.

CancomparePerformanceacrossProcessesMotivatesvariancereductionandprocesscentering.Distinguishesamong"in-spec"processes.Cpkcanbeconvertedtoanestimateddefectratefornormallydistributedprocesses.

(Thesenumbersassumeastable,centeredprocess)WhyuseCpk?Cpk.1.1516ProperUseofCpkAssumptions1.Theprocessisstatisticallystable2.Dataisdistributedapproximatelynormally.3.Specificationsrepresentcustomerneeds.4.Processtargetiscenteredbetweenspecs.5.Measurementvariationissmall.ProperUseofCpkAssumptions1.7MoreOnAssumptions

1. -Thedatacollectedshouldexhibitstabilitywhenplottedonacontrolchart -Cpkoftheunstableprocessmayberepresentativeofthehistoricalperformanceoftheprocessandnotnecessarilyindicativeoftheabilityofteprocesstomeetthespecsinthelongerterm2.Because-Cpkforthenonnormalprocessmisrepresentstheprocessduetotheeffectthatnonnormalityhassomeestimation3.SpecificationlimitsusedforcalculatingCpkmaybearbitraryCpkmaybegood,qualityofproductcouldbebadCpkmaybebad,qualityofproductcouldbegoodSpecsmaybe“bestguesses”orbasedonprocessChangingspecscausesCpktochange,whiletheperformanceoftheprocessinunchanged.MoreOnAssumptions1. -Theda8MoreonAssumptions4.Thetargetneedstobethecenterofthespeclimits Ifthetargetisnotthecenterofthespeclimits,thentheprocessmeanmustbelocatedintheinterval{target-(specrange)/6}to{target+(specrange)/6}5. ThemeasurementsvariationinthevaluesusedforcalculatingtheCpkmustbesmallrelativetothespecificprocesscapabilityfortheparameterbeingmeasured.Ifthemeasurementvariationiscomparativelylarge,thentheCpkmaynotbeindicative.BecauseCpkwillbeincludingthisvariation,whichisnotrelatedtotheabilityofthewprocesstomeetthespecificationsMoreonAssumptions4.Thetarg9ProperUseofCpkCalculatingandInterpretingCpkCollectatleast100measurementsoveranextendedtimeperiod,(2-4weeksormore).Validatetheassumptions(above).CalculateCpkusingtheoverallstandarddeviationoftheindividualdata.Don'tusesubgroupaveragesorpooledstandarddeviation!CalculateaconfidenceintervalforCpk(especiallyifn<100).Makeacapabilityplot(histogramwithoverlaidspeclimits).Resolveanydifferences.ProperUseofCpkCalculatinga10Top10ListofMisuseandConfusion1.PeoplethinkCpkistheonlymeasurethatmatters!2.ThereisnoagreementonwhichCpkvalueis"good"...(1,1.15,1.33,1.5,2,etc.).3.SpecificationlimitsusedforCpkmaybearbitrary.4.TherearetoomanyvariationsontheCpk"theme".5.Peopledon'tgraphtheirdatawheninterpretingCpk.6.ThescaleofCpkisnon-characteristic.7.Cpkisinappropriatelyusedasacontrolparameter.8.TheCpkestimateforsmallsamplesisregardedasthe"truth".9.Cpkmisrepresentsnon-normalorunstableprocesses.10.TheuseofCpkismandatedwithoutpropertraining.Top10ListofMisuseandConf11Reason#10TheuseofCpkismandatedwithoutpropertraining.Usedinsituationswhereitdoesn'tfit.Calculatedjustformanagementwithoutanybenefittothosewhomanagetheprocess.Reason#10TheuseofCpkis12Cpk知識(shí)資料香港新科、光寶課件13Cpk知識(shí)資料香港新科、光寶課件14Cpk知識(shí)資料香港新科、光寶課件15Reason#6ThescaleofCpkisnon-intuitive.01.51.3PoorAcceptableExcellent2.0CpkScaleReason#6ThescaleofCpkisn16Cpk知識(shí)資料香港新科、光寶課件17Cpk知識(shí)資料香港新科、光寶課件18Cpk知識(shí)資料香港新科、光寶課件19Cpk知識(shí)資料香港新科、光寶課件20Cpk知識(shí)資料香港新科、光寶課件21Remainanimportanttoolforsummarizingprocessperformanceandcommunicatingwithmanagement.Expectmoreconfusionasalternatedefinitionsareproposed.AttemptstosimplifyCpk(includingthispresentation)willcauseshorttermconfusion.ExternaltrainingofferingswillcontinuethetrendtowardcomplicatingCpkFutureofCpkRemainanimportanttoolfors22Cpk知識(shí)資料香港新科、光寶課件23Cpk知識(shí)資料香港新科、光寶課件24DefinitionofTermsCapability-Theabilityofaprocesstoproducepartswithinspecification.Aprocessissaidtobecapablewhennearlyallpartsproducedbytheprocessarewithinspecification.ProcessCapabilityIndices-Measuresofthecapabilityofaprocess.X-Theaverageofasampleofdata,-ThesamplestandarddeviationSUSL,LSL=UpperandLowerspecificationxxni=?sxxni=-?-()21Cp

-

=USLLSLs6CpkXsXs=é?êù?úminimum,USL-

3-LSL3DefinitionofTermsCapability25Cpk知識(shí)資料香港新科、光寶課件26Cpk知識(shí)資料香港新科、光寶課件27WhyuseCpk?Cpk.1.151.301.331.523%orppm13%2.4%0.7%2700ppm561ppm96ppm66ppm7ppm2"ppb">>1"ppb"Singlenumbersummaryofprocessperformance.

CancomparePerformanceacrossProcessesMotivatesvariancereductionandprocesscentering.Distinguishesamong"in-spec"processes.Cpkcanbeconvertedtoanestimateddefectratefornormallydistributedprocesses.

(Thesenumbersassumeastable,centeredprocess)WhyuseCpk?Cpk.1.15128ProperUseofCpkAssumptions1.Theprocessisstatisticallystable2.Dataisdistributedapproximatelynormally.3.Specificationsrepresentcustomerneeds.4.Processtargetiscenteredbetweenspecs.5.Measurementvariationissmall.ProperUseofCpkAssumptions1.29MoreOnAssumptions

1. -Thedatacollectedshouldexhibitstabilitywhenplottedonacontrolchart -Cpkoftheunstableprocessmayberepresentativeofthehistoricalperformanceoftheprocessandnotnecessarilyindicativeoftheabilityofteprocesstomeetthespecsinthelongerterm2.Because-Cpkforthenonnormalprocessmisrepresentstheprocessduetotheeffectthatnonnormalityhassomeestimation3.SpecificationlimitsusedforcalculatingCpkmaybearbitraryCpkmaybegood,qualityofproductcouldbebadCpkmaybebad,qualityofproductcouldbegoodSpecsmaybe“bestguesses”orbasedonprocessChangingspecscausesCpktochange,whiletheperformanceoftheprocessinunchanged.MoreOnAssumptions1. -Theda30MoreonAssumptions4.Thetargetneedstobethecenterofthespeclimits Ifthetargetisnotthecenterofthespeclimits,thentheprocessmeanmustbelocatedintheinterval{target-(specrange)/6}to{target+(specrange)/6}5. ThemeasurementsvariationinthevaluesusedforcalculatingtheCpkmustbesmallrelativetothespecificprocesscapabilityfortheparameterbeingmeasured.Ifthemeasurementvariationiscomparativelylarge,thentheCpkmaynotbeindicative.BecauseCpkwillbeincludingthisvariation,whichisnotrelatedtotheabilityofthewprocesstomeetthespecificationsMoreonAssumptions4.Thetarg31ProperUseofCpkCalculatingandInterpretingCpkCollectatleast100measurementsoveranextendedtimeperiod,(2-4weeksormore).Validatetheassumptions(above).CalculateCpkusingtheoverallstandarddeviationoftheindividualdata.Don'tusesubgroupaveragesorpooledstandarddeviation!CalculateaconfidenceintervalforCpk(especiallyifn<100).Makeacapabilityplot(histogramwithoverlaidspeclimits).Resolveanydifferences.ProperUseofCpkCalculatinga32Top10ListofMisuseandConfusion1.PeoplethinkCpkistheonlymeasurethatmatters!2.ThereisnoagreementonwhichCpkvalueis"good"...(1,1.15,1.33,1.5,2,etc.).3.SpecificationlimitsusedforCpkmaybearbitrary.4.TherearetoomanyvariationsontheCpk"theme".5.Peopledon'tgraphtheirdatawheninterpretingCpk.6.ThescaleofCpkisnon-characteristic.7.Cpkisinappropriatelyusedasacontrolparameter.8.TheCpkestimateforsmallsamplesisregardedasthe"truth".9.Cpkmisrepresentsnon-normalorunstableprocesses.10.TheuseofCpk

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