ie工业工程_工程能力

ProcessCapability 工程能力 Sept 16 2003SEQ Contents DefinitionObjectiveDesignforPCSPopulationandSampleHowtoperformaPCSHowtointerpretaPCS Definition MachineCapability Variationcausedbythemachineandnotthevariationcausedbyotherpartsoftheprocess ProcessCapability Variationcausedbyallthesourcesofvariation themachine thematerialused themethodsemployed theoperators involved andtheenvironmentasitaffectstheproducts Definition Include Changesinincomingshipmentsofmaterials Shiftsintemperatures Toolwear Useofdifferentoperators Smallchangesinmethods Objective OldProcessesNewProcessesNewMaterialEvaluationProductSpecificationsProcessManagementProductDesignProblemSolving DesignforPCS Terminology SubgroupWindow TimeBetweenSubgroups Specimen Sample SampleSize Thedurationofeach sampling periodThedurationofeach nosampling periodAnindividualunitofproductThecollectionofSpecimensgatheredduringasubgroupwindowThenumberofspecimensinthesample DesignforPCS DesignforPCS StandardDeviations Sigma isusedtorepresentstandarddeviation s Specimen to specimenstandarddeviation w Window to windowstandarddeviation h Historicalstandarddeviation DesignforPCS ProcessVariation ThetotalamountofprocessVariation h isacombinationof sand w h s w PopulationandSample PopulationandSample Process Lot Sample Lot Sample Data Data Sampling Action Measurement Sampling Action Measurement HowtoperformaPCS DefiningtheObjectiveofthePCSExaminationofprocessstabilityLookingforaCPKvalueEstimationofthesteady stateprocessvariationMaintainingcontrolchartsafterthePCS HowtoperformaPCS 2 SettingOperatingConditionsTheconditionswillvaryfromstudytostudydependingontheobjectives Machineadjustments Operatingcrewschange Rawmaterialslotchange Linespeedchange HowtoperformaPCS 3 DesigningthePCSSubgroupwindowThedecisiononhowlargetomakethesubgroupwindowdependsontheobjectiveofthePCS Ex Iftheobjectiveistostudytheextremeshorttermvariationoftheprocess thesubgroupwindowwouldbechosentobeassmallaspossible Thespecimensgatheredduringeachsubgroupwindowmustbedrawnatrandom HowtoperformaPCS 3 DesigningthePCS2 SampleSizeAlargesamplesizeprovidesmoresensitivityfordetectingshiftsinmeanandstandarddeviation Samplesizedeterminationisastatisticalandeconomicissue Reasonablesamplesize 4 5 HowtoperformaPCS 3 DesigningthePCSNumberofSubgroupsTheremustbeenoughsubgroupstoproperlyestimatethecontrolchartparameters Minimumsubgroups 20ThenumberofsubgroupstogetherwiththesubgroupwindowdeterminesthelengthofthePCS HowtoperformaPCS 3 DesigningthePCSTimeBetweenSubgroupsThetimesbetweensubgroupsshouldbeofvaryinglengthtoavoidpossiblecoincidencewithaprocesscycle T WST WS S 1 BB S 1T ThetotaldurationofthePCSW ThesubgroupwindowS ThenumberofsubgroupsB Thetimebetweensubgroups HowtoperformaPCS HowtoperformaPCS 4 PerformingthePCS1 ThemeasurementofeachspecimenEachspecimengatheredduringthePCSismeasuredforaspecificsetofproperties EachspecimenmustretainitsidentitythroughoutthePCS SpecimensshouldbetestedinrandomorderVariationofrecalibration differentinstrumentsand ortechnicians HowtoperformaPCS 4 PerformingthePCS2 ProcessCapability 6 Processcapabilityisameasurablepropertyoftheprocess Theresultingmeasureisexpressedintermsof6 ofvariation thestandarddeviationoftheprocessunderastateofstatisticalcontrol Thestandarddeviationmeasuresthedistanceonthehorizontalscaleassociatedwiththe68 26 95 46 and99 7 HowtoperformaPCS X N Xisnormallydistributedwithmean andvariance HowtoperformaPCS 4 PerformingthePCS3 ProcessCapabilityMeasurementOneofmethodsformeasuringprocesscapabilityisthecontrolchartmethod X Rcontrolchartsforvariablessuchaslengthorwidth temperatureandvolume Theprocesscapabilityiscomputedas6 whichincludes99 73 ofthedata HowtoperformaPCS 4 PerformingthePCS4 StatisticalBasisoftheChartsIfx x xnisasampleofsizen thentheaverageofthissampleisx x xnx nTheprocessaverageisthegrandaveragex x xmx mxwouldbeusedasthecenterlineonthexchart HowtoperformaPCS Xisnormallydistributedwithmean andstandarddeviation x n Subgroup n 9 n 4 n 1 HowtoperformaPCS 4 PerformingthePCS4 StatisticalBasisoftheChartsIfx x xnisasampleofsizen thentherangeofthesampleisthedifferencebetweenthelargestandsmallestobservations R xmax xminLetR R Rmbetherangeofthemsamples R R RmR m HowtoperformaPCS 4 PerformingthePCS4 StatisticalBasisoftheChartsControlLimitsforthexchartUCL x A RCL xLCL x A RTheconstantA istabulatedforvarioussamplesizesinTableVI HowtoperformaPCS 4 PerformingthePCS4 StatisticalBasisoftheChartsControlLimitsfortheRchartUCL D RCL RLCL D RTheconstantD andD aretabulatedforvariousvaluesofninTableVI HowtoperformaPCS 4 PerformingthePCS4 StatisticalBasisoftheChartsThepurposeofacontrolchartistodeterminewhetherornotaprocessisinastateofstatisticalcontrol andifnot Discardthedata trytoeliminatethecauseoftheout of controlcondition andrepeatthePCS Acceptthecomputationasagoodapproximationofprocesscapability HowtoperformaPCS 4 PerformingthePCS3 ProcessCapabilityMeasurement Method R6 6S 6 d S ThecalculatedstandarddeviationofthesampleR Theaveragerangeofthesubgroupsd Theconstantforconvertingrangesintostandarddeviations fortheparticularsubgroupsizeValuesofd forvarioussamplesizesaregiveninTableVI HowtoperformaPCS 4 PerformingthePCS5 ProcessCapabilityMeasurement Method PreparationAssureyourselfthattheprocessyouwanttostudyisinDesignState useNormalMaterialsandNormalOperators TakeasmuchtimeasthePCS sclientwillpermit PerformanceCollect50pairsofsamplesovertheallottedtimeperiodandmeasuretheproductvariableofinterest pairmeansconsecutivesamples HowtoperformaPCS 4 PerformingthePCS5 ProcessCapabilityMeasurement Method UseoftheRangetoestimate cThedifferenceinthemeasurementbetweeneachpairgivesavaluecalledRange R CalculatetheaverageRange R ofthe50pairs Estimatethestandarddeviationoftheprocess scapability c as RR c d 1 128 HowtoperformaPCS 4 PerformingthePCS5 ProcessCapabilityMeasurement Method UseoftheRangetoestimate cAssurethateachRcollectedwasincontrol DothisbycalculatinganduppercontrollimitontheindividualR sbyUCL D R 3 268RIfanyrangevalueisgreaterthan3 268R discardthisvalue recalculateRandrepeatprocedure HowtoperformaPCS 4 PerformingthePCS5 ProcessCapabilityMeasurement Method xand hObtaintheaverage x andthestandarddeviation h oftheprocess shistorybyusingalltheindividualmeasurementsandcalculatingtheaverageandthestandarddeviationintheconventionalmanner HowtoperformaPCS 4 PerformingthePCS5 ProcessCapabilityMeasurement Method h CalculationS x x orS n x x n 1n n 1 S samplestandarddeviation sumofx observedvaluesx arithmeticmeann numberofobservations HowtointerpretaPCS 1 DrawingConclusions1 InterpretingtheresultsofaPCSProcessCapability x currentcapabilityx 3 cx 3 htypicalhistoryProductARequirementCapableBmostlikelycapital Notcapablere