BasicSPC(Attribute)-.ppt

AttributeControlCharts LearningObjectives DefectivevsDefectBinomialandPoissonDistributionpChartnpChartcChartuChartTestsforInstability ShewhartControlCharts Overview DefectiveandDefect DefectiveAunitofproductthatdoesnotmeetcustomer srequirementorspecification Alsoknownasanon conformingunit ExampleAbasecastingthatfailsporosityspecificationisadefective Adiscclampthatdoesnotmeettheparallelismspecificationisadefective DefectAflaworasinglequalitycharacteristicthatdoesnotmeetcustomer srequirementorspecification Alsoknownasanon conformity Therecanbeoneormoredefectsinadefective ExampleAdentonaVCMpolethatfailscustomer sspecificationisadefect Astainonacoverthatfailscustomer sspecificationisadefect DefectiveandDefect ShewhartControlChartsforAttributeData Thereare4typesofAttributeControlCharts 43 np c p u Defects PoissonDistribution Defectives BinomialDistribution TypesofDataandDistributions DiscreteData Attribute BinomialPoissonContinuousData Variable NormalExponentialWeibullLognormaltc2F DiscreteDistributions ContinuousDistributions TypesofDistributions NormalDistribution ExponentialDistribution UniformDistribution BinomialDistribution DiscreteDistributions ContinuousDistributions BinomialDistributionUsefulforattributedata orbinarydata Resultfrominspectioncriteriawhicharebinaryinnature e g pass fail go nogo accept reject etc Datageneratedfromcountingofdefectives DiscreteDistributions PlotisknownasProbabilityMassFunctionofX BinomialDistributionIfaprocesstypicallygives10 rejectrate p 0 10 whatisthechanceoffinding0 1 2or3defectiveswithinasampleof20units n 20 DiscreteDistributions CommonlyusedinAcceptanceSampling Thelocation dispersionandshapeofabinomialdistributionareaffectedbythesamplesize n anddefectiverate p BinomialDistribution DiscreteDistributions JamesBernoulli BinomialDistribution DiscreteDistributions PoissonDistributionUsefulfordiscretedatainvolvingerrorrate defectrate dpu dpmo particlecountrate etc Datageneratedfromcountingofdefects DiscreteDistributions PoissonDistributionIfaprocesstypicallygives4 0defectrate l 4dpu whatisthechanceoffinding0 1 2or3defectsperunit DiscreteDistributions Commonlyusedasanapproximationofthebinomialdistributionwhen p 0 1 10 nislarge Thelocation dispersionandshapeofaPoissondistributionareaffectedbythemean l PoissonDistribution DiscreteDistributions SimeonDPoisson PoissonDistribution DiscreteDistributions pChart FractionNon ConformingRejectRate DefectiveRatePercentFallout 2 0 1 0 0 0 5 0 4 0 3 0 2 0 1 0 0 S a m p l e N u m b e r P r o p o r t i o n 1 P 0 2 1 4 0 3 0 S L 0 3 8 8 0 3 0 S L 0 0 4 0 0 0 pChart Fractionnon conforming p Ratioofnumberofdefectives ornon conformingitems inapopulationtothenumberofitemsinthatpopulation Samplefractionnon conforming p Ratioofnumberofdefectives d inasampletothesamplesize n i e Is p asamplestatistic Theunderlyingprinciplesofthepchartarebasedonthebinomialdistribution Thismeansthatifaprocesshasatypicalfractionnon conforming p themeanandvarianceofthedistributionforp sarecomputedfromthebinomialequation giving pChart k numberofsubgroup shouldbebetween20to25beforeconstructingcontrollimits Xi numberofdefectiveunitinsubgroupiwhichhasatotalsamplesizeofniunits Thepchartalsoassumesasymmetricalbell shapedistribution withsymmetricalcontrollimitsoneachsideofthecenterline Thisimpliesthatthebinomialdistributionisapproximatelyclosetotheshapeofthenormaldistribution whichcanhappenundercertainconditionsofpandn p 1 2andn 10implyingnp 5Forothervaluesofp thegeneralguidelineistohavenp 10togetasatisfactoryapproximationofthenormaltothebinomial pChart pChart FollowingShewhart sprinciple theCenterLineandControlLimitsofapchartare Ifthesamplesizeisnotconstant thentheControlLimitsofapchartmaybecomputedbyeithermethod a VariableControlLimitswhereniistheactualsamplesizeofeachsamplingib ControlLimitsBasedonAverageSampleSizewherenistheaverage ortypical samplesizeofallthesamples pChart WhentoUseControlLimitsBasedonAverageSampleSizeinsteadofVariableControlLimitsSmallestsubgroupsize nmin isatleast30 ofthelargestsubgroupsize nmax Futuresamplesizeswillnotdiffergreatlyfromthosepreviouslyobserved WhenusingControlLimitsBasedonAverageSampleSize theexactcontrollimitsofapointshouldbedeterminedandexaminedrelativetothatvalueif ThereisanunusuallylargevariationinthesizeofaparticularsampleThereisapointwhichisnearthecontrollimits pChart Example1 pChart S NSampledRejects1501225015350845010550465077501685099501410501011505125061350171450121550221650817501018505195013205011 Frozenorangejuiceconcentrateispackedin6 ozcardboardcans Ametalbottompanelisattachedtothecardboardbody Thecansareinspectedforpossibleleak 20samplingsofdifferentsamplingsizewereobtained Verifyiftheprocessisincontrol ThedataarefoundinSPCCharts MTW MiniTab sStat ControlCharts P Example1 pChart Example1 pChart Example1 pChart Example1 pChart MinitaballowsdifferencesetofcontrolchartstobeplottedononechartMiniTab sStat ControlCharts P Example1 pChart npChart Ifthesamplesizeisconstant itispossibletobaseacontrolchartonthenumbernonconforming np ratherthanthefractionnonconforming p TheCenterLineandControlLimitsofannpchartare Example2 npChart S NSampledRejects1501225015350845010550465077501685099501410501011505125061350171450121550221650817501018505195013205011 Frozenorangejuiceconcentrateispackedin6 ozcardboardcans Ametalbottompanelisattachedtothecardboardbody Thecansareinspectedforpossibleleak 20samplingsof50cans samplingwereobtained Verifyiftheprocessisincontrol ThedataarefoundinSPCCharts MTW Example2 npChart MiniTab sStat ControlCharts NP Example2 npChart pChartvsnpChart Foreaseofrecording thenpchartispreferred Thepchartoffersthefollowingadvantages accommodationforvariablesamplesizeprovidesinformationaboutprocesscapability SampleSizeforpandnpCharts SampleSizeisdeterminedbasedonthe2criteria AssumptiontoapproximateBinomialDistributiontoaNormalDistributionToensurethattheLCLisgreaterthanzero Forp 0 5 Forp othervalues cChart DefectsperUnit DPU ErrorRate DefectRateDefectsperOpportunity 2 0 1 0 0 2 0 1 0 0 S a m p l e N u m b e r S a m p l e C o u n t C 9 6 5 0 3 0 S L 1 8 9 7 3 0 S L 0 3 3 0 7 cChart Eachspecificpointatwhichaspecificationisnotsatisfiedresultsinadefectornonconformity ThecchartisacontrolchartforthetotalnumberofdefectsinaninspectionunitbasedonthenormaldistributionasanapproximationforthePoissondistribution whichcanhappenwhen cor 15 cChart InspectionUnitTheareaofopportunityfortheoccurrenceofnonconformities e g aHSA amedia aPCBAThisisanentitychosenforconvenienceofrecord keeping Itmayconstitutemorethan1unitofproduct e g aHSA bothsurfacesofamedia 10piecesofPCBA cChart Ifthenumberofnonconformities defects perinspectionunitisdenotedbyc then TheCenterLineandControlLimitsofacchartare uChart Incaseswherethenumberofinspectionunitsisnotconstant theuchartmaybeusedinstead with Iftheaveragenumberofdefectsperinspectionunitisdenotedbyu then Whereciisthecountofthenumberofdefectsinnumberofinspectionunits ai uChart TheCenterLineandControlLimitsofauchartare Example3 canduCharts S NUnitsDefects1510251235845145510651675118579510105151159125513571451115512165617581851019572055 Apersonalcomputermanufacturerplanstoestablishacontrolchartfornonconformitiesatthefinalassemblyline Thenumberofnonconformitiesin20samplesof5PCsareshownhere Verifyiftheprocessisin control Example3 canduCharts MiniTab sStat ControlCharts C Example3 canduCharts MiniTab sStat ControlCharts U Example3 canduCharts u orc Chartvsp np Chart Theu orc chartoffersthefollowingadvantages Moreinformativeasthetypeofnonconformityisnoted FacilitatesParetoanalysis FacilitatesCause EffectAnalysis c ChartMeasuresthetotalnumberofdefectsinasubgroupThesubgroupsizecanbe1unitofproductifweexpecttohavearelativelylargenumberofdefects unitRequiresaconstantsubgroupsizeu ChartMeasuresthenumberofdefects unitofproduct dpu Thesubgroupsizecanbeconstantorvariablep ChartMeasurestheproportionofdefectiveunitsinasubgroupThesubgroupsizecanbeconstantorvariablenp ChartMeasuresthenumberofdefectiveitemsinasubgroupRequiresaconstantsubgroupsize SelectingtheAppropriateChart Exercise 1 Strengthof5testpiecessampledeveryhourNumberofdefectivesin100partsNumberofsolderdefectsinaprintedcircuitboardassemblyDiameterof40unitsofproductssa