生產運營課件

CHAPTER10QualityControlMcGraw-Hill/IrwinOperationsManagement,EighthEdition,byWilliamJ.StevensonCopyright?2005byTheMcGraw-HillCompanies,Inc.Allrightsreserved.PhasesofQualityAssuranceAcceptancesamplingProcesscontrolContinuousimprovementInspectionbefore/afterproductionInspectionandcorrectiveactionduringproductionQualitybuiltintotheprocessTheleastprogressiveThemostprogressiveFigure10.1InspectionHowMuch/HowOftenWhere/WhenCentralizedvs.On-siteInputsTransformationOutputsAcceptancesamplingProcesscontrolAcceptancesamplingFigure10.2CostOptimalAmountofInspectionInspectionCostsCostof

inspectionCostof

passingdefectivesTotalCostFigure10.3WheretoInspectintheProcessRawmaterialsandpurchasedpartsFinishedproductsBeforeacostlyoperationBeforeanirreversibleprocessBeforeacoveringprocessExamplesofInspectionPointsTable10.1StatisticalProcessControl:

StatisticalevaluationoftheoutputofaprocessduringproductionQualityofConformance:

AproductorserviceconformstospecificationsControlChartControlChartPurpose:tomonitorprocessoutputtoseeifitisrandomAtimeorderedplotrepresentativesamplestatisticsobtainedfromanongoingprocess(e.g.samplemeans)UpperandlowercontrollimitsdefinetherangeofacceptablevariationControlChart0123456789101112131415UCLLCLSamplenumberMeanOutof

controlNormalvariation

duetochanceAbnormalvariation

duetoassignablesourcesAbnormalvariation

duetoassignablesourcesFigure10.4StatisticalProcessControlTheessenceofstatisticalprocesscontrolistoassurethattheoutputofaprocessisrandomsothatfutureoutputwillberandom.StatisticalProcessControlTheControlProcessDefineMeasureCompareEvaluateCorrectMonitorresultsStatisticalProcessControlVariationsandControlRandomvariation:Naturalvariationsintheoutputofaprocess,createdbycountlessminorfactorsAssignablevariation:AvariationwhosesourcecanbeidentifiedSamplingDistributionSampling

distributionProcess

distributionMeanFigure10.5NormalDistributionMean

95.44%99.74%

StandarddeviationFigure10.6ControlLimitsSampling

distributionProcess

distributionMeanLower

control

limitUpper

control

limitFigure10.7SPCErrorsTypeIerrorConcludingaprocessisnotincontrolwhenitactuallyis.TypeIIerrorConcludingaprocessisincontrolwhenitisnot.TypeIErrorMeanLCLUCL

/2

/2

Probability

ofTypeIerrorFigure10.8ObservationsfromSampleDistributionSamplenumberUCLLCL1234Figure10.9ControlChartsforVariablesMeancontrolchartsUsedtomonitorthecentraltendencyofaprocess.XbarchartsRangecontrolchartsUsedtomonitortheprocessdispersionRchartsVariablesgeneratedatathataremeasured.MeanandRangeChartsUCLLCLUCLLCLR-chartx-ChartDetectsshiftDoesnot

detectshiftFigure10.10A(processmeanisshiftingupward)SamplingDistributionx-ChartUCLDoesnot

revealincreaseMeanandRangeChartsUCLLCLLCLR-chartRevealsincreaseFigure10.10B(processvariabilityisincreasing)SamplingDistributionControlChartforAttributesp-Chart-Controlchartusedtomonitortheproportionofdefectivesinaprocessc-Chart-ControlchartusedtomonitorthenumberofdefectsperunitAttributesgeneratedatathatarecounted.Useofp-ChartsWhenobservationscanbeplacedintotwocategories.GoodorbadPassorfailOperateordon’toperateWhenthedataconsistsofmultiplesamplesofseveralobservationseachTable10.3Useofc-ChartsUseonlywhenthenumberofoccurrencesperunitofmeasurecanbecounted;non-occurrencescannotbecounted.Scratches,chips,dents,orerrorsperitemCracksorfaultsperunitofdistanceBreaksorTearsperunitofareaBacteriaorpollutantsperunitofvolumeCalls,complaints,failuresperunitoftimeTable10.3UseofControlChartsAtwhatpointintheprocesstousecontrolchartsWhatsizesamplestotakeWhattypeofcontrolcharttouseVariablesAttributesRunTestsRuntest–atestforrandomnessAnysortofpatterninthedatawouldsuggestanon-randomprocessAllpointsarewithinthecontrollimits-theprocessmaynotberandomNonrandomPatternsinControlchartsTrendCyclesBiasMeanshiftToomuchdispersionFigure10.11CountingAbove/BelowMedianRuns (7runs)CountingUp/DownRuns (8runs)UUD

UDUDUUDBAABABBBAABFigure10.12Figure10.13

CountingRunsTolerancesorspecificationsRangeofacceptablevaluesestablishedbyengineeringdesignorcustomerrequirementsProcessvariabilityNaturalvariabilityinaprocessProcesscapabilityProcessvariabilityrelativetospecification

ProcessCapability

ProcessCapabilityLower

SpecificationUpper

SpecificationA.Processvariability

matchesspecificationsLower

SpecificationUpper

SpecificationB.Processvariability

wellwithinspecificationsLower

SpecificationUpper

SpecificationC.Processvariability

exceedsspecificationsFigure10.15ProcessCapabilityRatioProcesscapabilityratio,Cp=specificationwidthprocesswidthUpperspecification–lowerspecification6

Cp=Process

meanLower

specificationUpper

specification1350ppm1350ppm1.7ppm1.7ppm+/-3Sigma+/-6Sigma3Sigmaand6SigmaQualityImprovingProcessCapabilitySimplifyStandardizeMistake-proofUpgradeequipmentAutomateTaguchiLossFunctionCostTargetLower

specUpper

specTraditional

costfunctionTaguchi

costfunctionFigure10.17LimitationsofCapabilityIndexesProcessmaynotbestableProcessoutputmaynotbenormallydistributedProcessnotcenteredbutCpisusedAdditionalPowerPointslides

contributedby

GeoffWillis,

UniversityofCentralOklahoma.CHAPTER10StatisticalProcessControl(SPC)InventedbyWalterShewhartatWesternElectricDistinguishesbetweencommoncausevariability(random)specialcausevariability(assignable)BasedonrepeatedsamplesfromaprocessEmpiricalRule-3

-1

-2

+1

+2

+3

68%95%99.7%ControlChartsinGeneralArenamedaccordingtothestatisticsbeingplotted,i.e.,Xbar,R,p,andcHaveacenterlinethatistheoverallaverageHavelimitsaboveandbelowthecenterlineat±3standarddeviations(usually)CenterlineLowerControlLimit(LCL)UpperControlLimit(UCL)VariablesDataChartsProcessCenteringXbarchartXbarisasamplemeanProcessDispersion(consistency)RchartRisasamplerangeXbarchartsCenterlineisthegran