Statistical Process Control(英文版)(ppt 23页).PPT

1、StatisticalProcessControl,StatisticalProcessControl,Variabilityexistsineverything-people,machinesandnaturePurpose-tobesurethatprocessesareperforminginanacceptablemannermonitorovertimeforecastifwillstillbewellinfuturedeterminefactorsthatmakeitoutofcontrol,StatisticalProcessControl,Designqualitychecks

2、intotheprocess-eliminateneedforinspectionbuildbetterproductduringdesignmakeproductwithstandvariation-TaguchiMethod,History,PriortoIRcraftsmenwereresponsibleforentireprocess-prideofworkmanshipDuring1920sW.ShewartofBellLabsbuildControlCharts-ASQformedDuring1950sDemingintroducedQCtechniquestoJapanese19

3、61FeigenbaumwroteTotalQualityControl,StatisticalProcessControl,TwomainsubjectsAcceptanceSampling-testrandomsamplesoffinishedgoodsandacceptorrejectwholelotProcessControl-sampleprocessoutputatdifferentpointsintime-seeifprocessisincontrol-determinecauseofout-of-controlbehavior,StatisticalProcessControl

4、,Monitortheproductionprocessinoneofthreeplaces-before,duringorafterPhysicallyexaminesomeoftheunitsBasicissues;wheredoweinspecthowmuchandhowoftendoweinspectdoweinspectvariablesorattributesBalancetwocosts:inspectionandservice,Rulesofthumbforwheretoinspect;,1.Inputs-donotpayforgoodsthatdonotmeetstandar

5、ds2.FinishedGoods-protectyourreputation3.Beforeacostlyoperation-donotwastetimeandlabor4.Beforeanirreversibleoperation-reworkonlyuptoacertainpoint5.Beforeacoveringoperation-paintingorassembly,TypesofSampling,Defn:AttributeSampling-checkforthepresenceorabsenceofaproductcharacteristicDefn:VariableSampl

6、ing-productcharacteristicsthatcanbemeasuredonacontinuousscale,StatisticalProcessControl,usedtoevaluatetheoutputofaprocessmostprocessesexhibitsomekindofvariationrandomvariation-naturalvariation,uncontrollableassignablevariation-canidentifycausedeterminewhethernon-randomsourcesofvariationareresponsibl

7、eforproblems,ControlCharts,Preventproductionofexcessivenumberofdefects-lookforcausesofvariabilityAtime-orderedplotofsamplestatisticsControllimits-determinethedifferencebetweenrandomandassignablevariation-usually3Eachnewsamplestatisticisplottedandcomparedtothecontrollimits,StatisticalProcessControl,T

8、ypesofControlCharts,1.VariableControlchartsA.MeansChart-monitorscentraltendencyB.RangeChart-monitorsdispersion-bothcanbeusedtomonitorsameprocess-use20-25samplestobuildinitiallimits-takesamplesof5-9observations-reasonableamountoftimeandcostsless,TypesofControlCharts(cont),2.AttributesControlChartsA.P

9、-Chart-countnumberofdefectsinsampleB.C-Chart-countnumberofdefectsperunit-buildingcontrolchartsaddstothetimeandcostofproduction-attributesamplingiseasierthanvariable-needlargersamplesizes,ProcessCapability,SpecifyrangesforcertainproductdimensionsduringdesignTolerancesMaxandminacceptablelevelofoutputB

10、earingforrotatingshaft-diameteris1.25inches0.005Processhas=0.02inches-a3-controlchartlimitsarewiderthantolerances,CapabilityIndex,ShowshowwellpartsfitintotherangespecifiedbydesignlimitsIfdesignlimitsarewiderthanprocesslimits,theprocesscanshiftandstillproducegoodpartsCpk=,CapabilityIndex,Example-ligh

11、tbulbsareproducedwithanaveragelifeof90hours.Thetargetdesignlifeis100hours.TheUTL=120andtheLTL=80hours.If=4.8whatistheCpk?,4,AcceptanceSampling,PurposesDeterminepolicyforacceptingorrejectingaproductionlotofmaterialsorcomponentsSamplequalityisusedtomakedecisionAdvantagesLesshandlingdamageFewerinspecto

12、rsApplicabilitytodestructivetestingEntirelotrejection(motivationforimprovement),5,AcceptanceSampling,DisadvantagesRisksofaccepting“bad”lotsandrejecting“good”lotsAddedplanninganddocumentationSampleprovideslessinformationthan100-percentinspection,AcceptancePlans,1.Single-SamplePlans-onlyonesampledefin

13、enandcOperatingCharacteristicCurve-graphstheperformanceofplanAcceptableQualityLevel-definesgoodlotsLotTolerancePercentDefective-definesbadlotsAverageOutgoingQuality-thepercentdefectsinlotsleavinginspection,AcceptancePlans(cont),-ProducersRisk()-probabilityofrejectinggoodlot-ConsumersRisk()-probabili

14、tyofacceptingabadlot-canreduceerrorsbynotbiasingthesampleandtakingalargerone-usethePoissondistributiontocomputeprobabilityofacceptance,9,OperatingCharacteristicCurve,AcceptancePlans,Plansconsiderstheinteractionamongtheabovecriteria-itconsiderstheobjectivesofthesupplierandconsumerTheproducerwouldlikelowprobabilityofrejectingagoodlotandconsumerwantstonotacceptabadlotHPandJapane