Introduction to Six Sigma rev.ppt - UC Berkeley ieor130/Introduction to Six Sigma rev.pdf9/11/2014 Rob Leachman Intro to Six Sigma 1 Six Sigma is an engineering ... 1980s 1990s TQM and 6 ... Introduction to Six Sigma rev.ppt ...

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  • Prof.RobLeachmanIEOR130Fall,2014

    9/11/2014 1RobLeachmanIntrotoSixSigma

  • SixSigmaisanengineeringmanagementparadigmoriginallydevelopedatMotorola.Itsapplicationhasspreadfromhitechmanufacturingtogeneralbusinessprocessesinmanyindustries.

    SixSigmaseekstoimprovethequalityofprocessoutputsbyidentifyingandremovingthecausesofdefects (errors)andvariability. Itinvolvesstatisticalmethodsandusuallyreliesonaspecialinfrastructureofpeoplewithintheorganizationwhoareexpertsinthesemethods.

    ASixSigmaprojecttypicallyhasspecificfinancialgoalsforcostreductionorprofitgain.9/11/2014 2RobLeachmanIntrotoSixSigma

  • FirstwrittenformulationbyBillSmithofMotorolain1986.

    BUT,SixSigmadrawsheavilyonthepreviouslypublishedqualityparadigmsandmethodologies(statisticalqualitycontrol,TQM,ZeroDefects,etc.)developedbyShewart,Deming,Juran,Ishikawa,Taguchiandothersfromthe1930suptothe1980s.

    9/11/2014 3RobLeachmanIntrotoSixSigma

  • Adefectisanythingthatcouldleadtocustomerdissatisfaction.Defectsareverycostly.

    Theremustbecontinuousefforttoachievestableandpredictableprocessresults(i.e.,toreduceprocessvariationandhencedefects).

    Processeshavecharacteristicsthatcanbemeasured,analyzed,improvedandcontrolled.

    Achievingsustainedqualityimprovementrequirescommitmentfromtheentireorganization.

    9/11/2014 4RobLeachmanIntrotoSixSigma

  • Consideraprocessgeneratinganongoingstreamofoutput.

    Ifonanongoingbasisweplottheaveragesofparametermeasurementsforgroupsoffiveormoreoutputunitsoftheprocess,thenbytheCentralLimitTheoremofstatistics,weshouldseeanormaldistribution .

    PROVIDEDTHATtheprocessisstable,i.e.,providedthatconsecutivemeasurementsareindependentandidenticallydistributed(IID)randomvariables. IfnotIID,thentheprocessisnotinstatisticalcontrol andissaidtobeoutofcontrol(OOC).

    9/11/2014 5RobLeachmanIntrotoSixSigma

  • Foranormaldistribution,99.9%ofthemassliesbetween[3,+3],where denotesthemean and denotesthestandarddeviation.Thus,aspreadof6 containsvirtuallyalltheoutputoftheprocess:

    9/11/2014 6RobLeachmanIntrotoSixSigma

  • Weassumeforeachimportantprocessparameterthattheengineersdefinespecificationlimits,wherebyiftheparameterfallsbelowthelowerspecificationlimit(LSL) orabovetheupperspecificationlimit(USL),thentheoutputunitisdefectiveandnogoodforthecustomer.

    Howmanydefectsweexperiencecanbecharacterizedbycomparingthespeclimitstothe6spreadofthenormaldistributionfortheprocess

    9/11/2014 RobLeachmanIntrotoSixSigma 7

  • Averywellcontrolledprocess.Thedistributioniswellcenteredbetweenthespeclimits,andthe6 spreadishalfthe12 spreadofthespeclimits.

    9/11/2014 8RobLeachmanIntrotoSixSigma

  • Processcapabilityconcernstheabilityoftheprocesstogenerateoutputwithinthespeclimits.Motoroladevelopedsomemetricsforthispurpose:

    Cp ={USL LSL}/6 istermedtheprocesscapabilityindex,whereUSLdenotestheupperspecificationlimitandLSLdenotesthelowerspecificationlimit. Cp >>1meansgoodprocesscapability.Cp

  • Cp =1mightseemliketherewouldbelittlescrap.Butthatwouldonlybethecaseiftheprocesswasperfectlycentered(i.e.,themeanliesexactlyhalfwaybetweenLSLandUSL).

    Toallowforthefactthataprocessmightnotbewellcentered,anewmetricwasdeveloped:

    Cpk =Min{(LSL)/3,(USL)/3 }iscalledtheprocessperformanceindex.

    Cpk >1indicatesthemeanismorethan3 awayfromthenearestspeclimit,i.e.,thereislittleornoscrap.

    9/11/2014 10RobLeachmanIntrotoSixSigma

  • Itisfoundinpracticethattheprocessmeanisoftennotstationarybuttendstodrift overtime.

    ThusCpk =1doesnotimplyqualityisreallygreat,becauseiftheprocessdriftsunfavorablywewillstartgettingscrap.

    AcommonindustrygoalistoraiseCpk forallimportantprocessparameterstoatleast1.5,i.e.,thenearestspeclimitshouldbeatleast4.5awayfromtheprocessmean.

    9/11/2014 11RobLeachmanIntrotoSixSigma

  • Identifytheoccurrencesofprocessvariationandestablishcontainmentmeasures Addinspectionsormeasurements(e.g.,SPCcharts)todetectoutofcontrolexcursions

    Engineerfixestoeliminaterootcausesofexcursions,OR:

    Reengineertheproductsothatthespeclimitscanbewideryetthecustomerwillbejustashappy

    9/11/2014 12RobLeachmanIntrotoSixSigma

  • DMAIC (forexistingprocesses) Definehighlevelgoalsanddefinetheexistingprocess. Measurekeyaspectsoftheprocessandsetupdatacollectionsystems.

    Analyzethedatatoverifycauseandeffectrelationships.Determinethoserelationships.

    Improveoroptimizetheprocessbasedonapplicationoftechniqueslikedesignofexperiments.

    Controltoensurethatanydeviationsfromtargetsarecorrectedbeforetheyresultindefects.

    9/11/2014 13RobLeachmanIntrotoSixSigma

  • DMADV (fornewproductsorprocesses) Definedesigngoalsconsistentwithcustomerdesiresandenterprisestrategy.

    MeasureandidentifyCTQs(criticaltoqualitycharacteristics),productcapabilities,productionprocesscapability,andrisks.

    Analyzetodevelopanddesignalternatives,createahighleveldesignandevaluatedesigncapabilitytoselectbestdesign.

    Designdetails,optimizethedesign,andplanfordesignverification.(Mayrequiresimulation.)

    Verifythedesign,setuppilotruns,implementtheproductionprocess,handovertoprocessowners.9/11/2014 14RobLeachmanIntrotoSixSigma

  • Statisticalprocesscontrolcharts(AKAShewartcontrolcharts,SPCcharts)

    Ishikawadiagrams(AKAFishbonediagrams) Designofexperiments(DOE) Failuremodesandeffectsanalysis(FMEA) Faultdetectionandclassification(FDC) Regressionanalysis,Analysisofvariance Taguchimethods,TaguchiLossFunction Manyothers

    9/11/2014 15RobLeachmanIntrotoSixSigma

  • Continuousprocessparameter Xbarchart trackmeanoffixedsizesamples LCL=,UCL= isprocessmean, isprocessstandarddeviation,nissamplesize

    Rchart trackrangeoffiveunitsamples LCL=d3R,UCL=d4R,Risaveragerangeofsample,d3andd4areconstantsfromstatisticaltables

    =R/d2,d2isconstantfromstatisticaltable (canusethisinXbarchart)

    9/11/2014 RobLeachmanIntrotoSixSigma 16

    n/3 n/3

  • Countableparameter(e.g.,particlesonwafer) Cchart LCL=,UCL= c istheaveragecountforafixedsizesample

    9/11/2014 RobLeachmanIntrotoSixSigma 17

    cc 3 cc 3

    nppp /)1(3 nppp /)1(3

    Binaryparameter(e.g.,goodornotgood) Pchart

    LCL=,UCL= pistheaveragefractionbad,nisthesamplesize

  • 1930s ShewhartinventscontrolchartsatBellLabsandimplementstheminWesternElectric(AT&Tsmanufacturingarm)

    1940sWesternElectricandafewothersmakegooduseofSPC,butmostcompaniesresistit

    1950s DeminggoestoJapan;SPCisembracedthere

    1970s&1980s ManyAmericanindustriesaredecimatedbyJapanesecompetition

    1980s&1990sTQMand6movementsinUSA9/11/2014 RobLeachmanIntrotoSixSigma 18

  • Introducequalitymanagementprofessionalsthatcutacrosstraditionaldept.boundaries ExecutiveLeadership definevision,empowerroleholderswithfreedomandresources

    Champions responsibleforimplementation,mentortheBlackBelts

    MasterBlackBelt Fulltime,inhousecoaches,ensureconsistentapplicationacrossfunctionsanddepartments

    BlackBelt Fulltime,applymethodologytospecificprojects

    GreenBelt handleimplementationunderguidanceofBlackBeltsalongwithotherjobduties

    YellowBelt trainedinbasicapplicationoftools,workwithBlackBelts,closesttothework9/11/2014 19RobLeachmanIntrotoSixSigma

  • Fortheperiod1986 2006,MotorolaclaimsitsSixSigmaprogramsachieved$17billioninsavings.

    Startinginthe1990s,GeneralElectricunderJackWelchbecameastrongdiscipleofSixSigma,andGEclaimsmajorsuccessesfromit. Subsequently,SixSigmabecameamanagementcraze.Success

    atothercompanieshasbeenmixed.

    SixSigmaisnotapanacea. Itisnosubstituteforinventingandmarketinggreatproducts. Itisanincrementalimprovementonpreviousqualitytheories.

    Ontheotherhand,thereisnosubstituteforgreatquality,andthemethodologiesembracedbySixSigmaembodythebestknowledgewehaveonthesubject.

    9/11/2014 RobLeachmanIntrotoSixSigma 20

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