Lesson 5 Statistical Process Control (SPC) Reading Assignment

It is the variation that is inherent in a process that is operating as designed. Assignable cause variation is unnatural variation in a process. It should be ... Lesson5StatisticalProcessControl(SPC) ReadingAssignment: Downloadandread Chapter10inEssentialsofQualityWithCasesandExperientialExercises. ReviewtheDiscussionQuestionsattheendofthechapter tobesurethatyouunderstandwhatyouhaveread. Discussion--StatisticalProcessControl(SPC)Defined: SPCisconcernedwithqualityofconformance.SPCisdefined as"theapplicationofstatisticaltechniquestocontrolaprocess."SPC canbedividedintocontrolchartingandprocesscapabilitystudy.Control chartsprovideameansofdeterminingthetypeofvariation(commoncause orassignablecause)thatispresentinaprocess.Processcapabilitystudy determinestheabilityofthe"incontrol"processtoproduceproductwhich meetsspecifications. Considerthatyouaremanagerofanoperationthatconsistsof oneprocess. Theprocessproducesproductswhichyouselltocustomers.  Whatwouldbeimportanttoyourelativetothatprocess? Onepoint mightbethepredictabilityoftheprocess. Itwouldbeniceifthe processbehavedthesamewaydayinanddayout. Being"incontrol" meansthattheprocessispredictable. Controlchartspermitusto determinethestateofcontrolofaprocess. Asecondimportantpointwouldbetheabilityofthepredictableprocess toproduceproductswhichmeetspecificationrequirements. Itisquite possibleforaprocesstobepredictabally"bad"--thatis,theprocessconsistently producesproductswhichfailtoconformtothespecifications. Theappropriate actionstotakewouldbetorecentertheprocessonthetargetvalueifnecessary, andthendeterminethesourcesofthecommoncausevariationinthesystem withthepurposeofminimizingthatvariation(commoncausevariationcan neverbeeliminated). Areductioninthevariationofaproperlycentered processwillmaketheprocessmorecapableofproducingproductswhichmeet specifications. Analternativewaytoimprovethecapabilityofaprocess wouldbetoexpandthespecificationlimits. Oftenyouwillbeconstrained fromdoingthisbycustomerrequirements. Discussion--Variation: Variationistheenemyofquality.Itcanbepartitionedbetween "commoncauses"and"assignablecauses."Commoncausevariationexistsin everyprocess--itcanbereducedbyprocessimprovementactivities,butnot eliminated.Itisthevariationthatisinherentinaprocessthatisoperating asdesigned.Assignablecausevariationisunnaturalvariationinaprocess. Itshouldbeidentifiedandaddressed. Controlchartsenableustodetermine thetypeofvariationthatexistsinaprocess. Acommonprobleminbusinessismanagerswhotreatallvariationas ifitwereduetoassignablecauses. Thisleadstotheoveradjustment ofprocesses(whichincreasesvariation),criticismofemployeesforvariation thatisoutoftheircontrol,andrewardofemployeesforbeingthe"best" whenthatdistinctionistheresultofjustcommoncausevariation.  Deming'sRedBeadExperimentprovidesgraphicproofofthefollyoftreating allvariationasifithadanassignablecause. TheFunnelExperiment showstheresultofoveradjustmentofaprocess. AProcessControlAnecdote(courtesyofG.Ferguson, QualityDigest,Dec.1999,pp.22-23) AqualityengineernoticesapatternontheX-barchartofaturning process. Thepointrepresentingthemeasurementtakenaround12:30 isalwaysabovetheUCL. AlltheotherpointsarewithintheUCL.  Realizingthatproductionoperatorsareusuallyaninvaluablesourceofinformation, thequalityengineerheadstotheproductionfloor. Aninterviewwith Charlie,thelatheoperator,revealsthatareliefoperator,Bill,takesover at12:00toallowCharlietotakealunchbreak. Billsayshenever hastoadjusttheprocessbecauseitisalwaysrunningfinewhenhetakes overfromCharlie. So,youhavetwooperatorsmakingthesamepart onthesamemachinewiththesameset-upandmaterials,buttheirpartsare different. TheengineerasksCharlietodemonstratehowhemakesa part. Bill,watching,sayshedoesitexactlythesameway. The engineerasksBilltodemonstrate. Ashesetsuptheworkinthechuck, Charliesays,"Woah! Whatareyoudoing? That'swaytoomuch pressure. Ifyouclampitdownlikethatyou'llmaketheTeflondistort."  Billreplies,"I'vebeenrunninglathesallmylife. That'stheway Ialwaysdoit." "Yeah,"saysCharlie,"butthatwaswithsteelparts.  Teflonpartsaredifferent. It'seasytodistort. Nowonderyou weregettingscrewyreadingsontheOD." Problemsolved! WritingAssignment: AnswerDiscussionQuestion1attheendof Chapter10ofthetext. Clickhere tobeginLessonFivePresentation.