The evolution of six sigma

heSixSigmamethodologyisnotarevolutionarywayofthinking,anditdoesnotprovidearadicallynewsetofqualitytools.Itismoreofanevolutionarydevelopmentinthescienceofcontinuousimprovementthatcombinesthebestelementsfrommanyearlierqualityinitiatives.AlthoughsomeofthetoolsusedinSixSigma,suchasqualityfunctiondeploy-ment(QFD),arerelativelynew,most,suchasthefishbonediagram,dateback50yearsormore.ThephilosophiesrelatedtoSixSigmahaveexistedinoneformoranotherevenlongerthanthat(seeFigure1).Customerfocus,datadrivendecisionmaking,businessresultsfocusandprocessunderstandingarenotnewapproachestobusinesssuccess.Whatisnew,andwhatmakesSixSigmasopowerful,isthecombinationoftheseelementswitharigorous,disciplinedapproachandwell-publicized,provenbusinesssuccesses.GeneralGeorgePattonwasagreatstudentofhistory.Hebelievedthosewhodidnotlearnfrompastmistakesweredoomedtorepeatthem.Thisistrueinthefieldofqualityandcontinuousimprovement,aswell.Understandingquality’srootsandthereasonsbehindthemethodswillallowpractitionerstobebetterpreparedtolaunchsuccessfulprojectsorlargescaleinitiatives.1798:EliWhitney,MassProductionandInterchangeablePartsBestknownforhisinventionofthecottonginin1787,EliWhitneyhadagreaterimpactonmodernmanufacturingwiththeintroductionofhisrevo-lutionaryuniformitysystem.1In1798,Whitneywasawardedagovernmentcontracttoproduce10,000muskets.Heproveditwaspossibletoproduceinterchangeablepartsthatweresimilarenoughinfitandfunctiontoallowforrandomselectionofpartsintheassemblyofthemuskets.Throughoutthenextcentury,qualityinvolveddefiningwaystoobjectivelyverifythenewpartswouldmatchtheoriginalpartsordesign.Exactreplica-tionwasnotalwaysnecessary,practical,costeffectiveormeasurable.Objectivemethodsofmeasuringandassuringdimensionalconsistencyevolvedinthemid-1800swiththeintroductionanduseofgogagesthatveri-fiedtheminimumdimensionofthenewpart.2Correctreplicationofthemax-imumdimensionwasassuredbyusingthenogogagesthatwereintroducedabout30yearslater.Minimumandmaximumtolerancelimits,asmeasuredbytheuseofthesegages,providedsomeofthefirstobjectivemeasuresofsimi-larityamongparts.Thesemeasureseventuallyevolvedintospecifications.SeeFigure2(p.41)foralistofsomeoftheeras’contributionstoSixSigma.1913:HenryFordandtheMovingAssemblyLineWiththeintroductionofHenryFord’smovingautomobileassemblylinein1913,theneedforpredeterminedpartconsistencybecamemoreacute.ItwasHISTORYTheEvolutionofSixSigmaALOOKATTHEINNOVATIONSTHATCONTRIBUTEDTOTHEMETHODOLOGYWECALLSIXSIGMAANDAGLIMPSEINTOITSFUTURE.TByJimFolaron,J.P.MorganChase&Co.38IAUGUST2003I:WalterShewhartTheWesternElectricmanufacturingplantinHawthorne,IL,isnoteworthybecauseitwasthebreedinggroundformanyqualityleaders,includingJosephM.Juran,W.EdwardsDemingandWalterA.Shewhart.Juranworkedattheplantfor17years,Demingworkedthereasaninternduringtwosum-mers,andShewhartworkedintheresearchlabsthatsupportedtheplant.OnMay16,1924,Shewhartintroducedanewdatacollection,displayandanalysisform.3Itcontainedthefirstknownexampleofaprocesscontrolchartandsig-naledthebeginningoftheageofstatisticalqualitycontrol.Theoriginalcontrolchartformallowedaninspectortodocumentthepercentageofdefectiveproductinbothatabularandatimeorderedgraphicformat.Asdatacollectionprogressed,statisticallycomputedlimitsweredrawntoidentifytheexpectedrangeofdefectiveproducts.Thishelpedalerttheoperatortochangesintheprocess.Theabilitytousestatisticallybasedcontrolchartschangedtheroleofthequalityinspectorfromoneofidentifyingandsortingdefectiveproducttooneofmonitoringthestabilityoftheprocessandidentifyingwhenithadchanged.Earlydetectionbytheinspectororworkerhelpedidentifythecausesofthechangeandtargetimprovements.Improvedproductqualityresultedthroughplanningandtimely,appropriatecorrectiveaction.Asproductionlotsgrewlargerandmorecomplexthroughouttheremainderofthe1920sand1930s,theneedforsophisticatedqualityassuranceandcontrolgavebirthtolargequalitycontrolfunctions.Qualitycontroldepartmentscametoincludeinspectors,chiefinspectors,supervisors,engineersandmanagers.4Theuseofstatisticsgrew,andin1950,theU.S.gov-ernmentrequiredstatisticallybasedlevelsofproductqualityfromitsvendors.ThemilitarystandardMIL-STD-105Awasadoptedandusedbycontractingoffi-cersandpurchasingagentstodefinecontractuallyrequiredsamplesizesandmaximumtolerabledefectrates.Thisvalidatedtheneedforlargeseparatequali-tyfunct