sc统计过程控制简介英文

StatisticalProcessControlStatisticalProcessControlVariabilityexistsineverything-people,machinesandnaturePurpose-tobesurethatprocessesareperforminginanacceptablemannermonitorovertimeforecastifwillstillbewellinfuturedeterminefactorsthatmakeitoutofcontrolStatisticalProcessControlDesignqualitychecksintotheprocess-eliminateneedforinspectionbuildbetterproductduringdesignmakeproductwithstandvariation-TaguchiMethodHistoryPriortoIRcraftsmenwereresponsibleforentireprocess-prideofworkmanshipDuring1920’sW.ShewartofBellLabsbuildControlCharts-ASQformedDuring1950’sDemingintroducedQCtechniquestoJapanese1961FeigenbaumwroteTotalQualityControlStatisticalProcessControlTwomainsubjectsAcceptanceSampling-testrandomsamplesoffinishedgoodsandacceptorrejectwholelotProcessControl-sampleprocessoutputatdifferentpointsintime-seeifprocessisincontrol-determinecauseofout-of-controlbehaviorStatisticalProcessControlMonitortheproductionprocessinoneofthreeplaces-before,duringorafterPhysicallyexaminesomeoftheunitsBasicissues;wheredoweinspecthowmuchandhowoftendoweinspectdoweinspectvariablesorattributesBalancetwocosts:inspectionandserviceRulesofthumbforwheretoinspect;1.Inputs-donotpayforgoodsthatdonotmeetstandards2.FinishedGoods-protectyourreputation3.Beforeacostlyoperation-donotwastetimeandlabor4.Beforeanirreversibleoperation-reworkonlyuptoacertain point5.Beforeacoveringoperation-paintingorassemblyTypesofSamplingDefn:AttributeSampling-checkforthepresenceorabsenceofaproductcharacteristicDefn:VariableSampling-productcharacteristicsthatcanbemeasuredonacontinuousscaleStatisticalProcessControlusedtoevaluatetheoutputofaprocessmostprocessesexhibitsomekindofvariationrandomvariation-naturalvariation,uncontrollableassignablevariation-canidentifycausedeterminewhethernon-randomsourcesofvariationareresponsibleforproblemsControlChartsPreventproductionofexcessivenumberofdefects-lookforcausesofvariabilityAtime-orderedplotofsamplestatisticsControllimits-determinethedifferencebetweenrandomandassignablevariation-usually3

EachnewsamplestatisticisplottedandcomparedtothecontrollimitsStatisticalProcessControlTypesofControlCharts1.VariableControlchartsA.MeansChart-monitorscentraltendencyB.RangeChart-monitorsdispersion-bothcanbeusedtomonitorsameprocess-use20-25samplestobuildinitiallimits-takesamplesof5-9observations-reasonableamountoftimeandcostslessTypesofControlCharts(cont)2.AttributesControlChartsA.P-Chart-countnumberofdefectsinsampleB.C-Chart-countnumberofdefectsperunit-buildingcontrolchartsaddstothetimeandcostofproduction-attributesamplingiseasierthanvariable-needlargersamplesizesProcessCapabilitySpecifyrangesforcertainproductdimensionsduringdesignTolerancesMaxandminacceptablelevelofoutputBearingforrotatingshaft-diameteris1.25inches0.005Processhas=0.02inches-a3-controlchartlimitsarewiderthantolerancesCapabilityIndexShowshowwellpartsfitintotherangespecifiedbydesignlimitsIfdesignlimitsarewiderthanprocesslimits,theprocesscanshiftandstillproducegoodpartsCpk=CapabilityIndexExample-lightbulbsareproducedwithanaveragelifeof90hours.Thetargetdesignlifeis100hours.TheUTL=120andtheLTL=80hours.If=4.8whatistheCpk?4AcceptanceSamplingPurposesDeterminepolicyforacceptingorrejectingaproductionlotofmaterialsorcomponentsSamplequalityisusedtomakedecisionAdvantagesLesshandlingdamageFewerinspectorsApplicabilitytodestructivetestingEntirelotrejection(motivationforimprovement)5AcceptanceSamplingDisadvantagesRisksofaccepting“bad”lotsandrejecting““good”lotsAddedplanninganddocumentationSampleprovideslessinformationthan100-percentinspectionAcceptancePlans1.Single-SamplePlans-onlyonesampledefinenandcOperatingCharacteristicCurve-graphstheperformanceofplanAcceptableQualityLevel-definesgoodlotsLotTolerancePercentDefective-definesbadlotsAverageOutgoingQuality-thepercentdefectsinlotsleavinginspectionAcceptancePlans(cont)-Producer’’sRisk()-probabilityofrejectinggoodlot-Consumer’’sRisk()-probabilityofacceptingabadlot-canreduceerrorsbynotbiasingthesampleandtakingalargerone-usethePoissondistributiontocomputeprobabilityofacceptance9OperatingCharacteristicCurven=99c=4AQLLTPD01123456789101112PercentdefectiveProbabilityofacceptanceB=.10(consumer’srisk)a=.05(producer’srisk)AcceptancePlansPlansconsiderstheinteractionamongtheabovecriteria-itconsiderstheobjectivesofthesupplierandconsumerTheproducerwouldlikelowprobabilityofrejectingagoodlotandconsumerwantstonotacceptabadlotHPandJapanesevendorAcceptancePlans(cont)2.Double-SamplePlansA.DrawonesampleB.ifnumberofdefectsislessthanalowerlimit,accept