6SIGMA、精益生产与约束理论的比较

ITHINTHEAMERICANbusinesscommunityamultitudeofprocessimprovementchampionsarevyingforleadershipattention.Eachchampionadvocatestheadoptionofhisorherimprove-mentmethodologyinyourorganization.Almostallpleadthatifyouadopttheirspecifictoolsorfollowaspecificwayofthinking,allyourbusinessprob-lemswillbesolved.Afterlisteningtomultiplechampionsadvocatetheirspecialmethodology,howdoyouchoosewhatwillbebestforyoursituation?Whatmethod-ologyfitsthecultureofyourorganization?Manyprocessimprovementmethodologiesappeartoconflictwitheachotheroratleastdown-playthecontributionofothermethodologies.Thismontageoftoolsandphilosophiescreatestheillusionofconflictingstrategies.Inthisarticle,Iwilldiscussthebasicsofthethreeimprovementmethodologiesandpresentamodeltohelpyouunderstandtheircon-ceptsandeffectsandsimilaritiesanddifferences.Table1describestheessenceofeachmethodology.QUALITYPROGRESSIMARCH2002I73HowToCompareSixSigma,LeanandtheTheoryofConstraintsAframeworkforchoosingwhat’sbestforyourorganizationbyDaveNavePROCESSIMPROVEMENTSixSigmaSixSigmaclaimsthatfocusingonreductionofvariationwillsolveprocessandbusinessproblems.Byusingasetofstatisticaltoolstounderstandthefluctuationofaprocess,managementcanbegintopredicttheexpectedoutcomeofthatprocess.Iftheoutcomeisnotsatisfactory,associatedtoolscanbeusedtofurtherunderstandtheelementsinfluenc-ingthatprocess.Througharigidandstructuredinvestigationmethodology,theprocesselementsaremorecom-pletelyunderstood.Theassumptionistheoutcomeoftheentireprocesswillbeimprovedbyreducingthevariationofmultipleelements.SixSigmaincludesfivesteps:define,measure,WImprovementProgramsTABLE1ProgramSixSigmaLeanthinkingTheoryofconstraintsTheoryReducevariationRemovewasteManageconstraintsApplication1.Define.1.Identifyvalue.1.Identifyconstraint.guidelines2.Measure.2.Identifyvaluestream.2.Exploitconstraint.3.Analyze.3.Flow.3.Subordinateprocesses.4.Improve.4.Pull.4.Elevateconstraint.5.Control.5.Perfection.5.Repeatcycle.FocusProblemfocusedFlowfocusedSystemsconstraintsanalyze,improveandcontrol(commonlyknownasDMAIC):•Define.Practitionersbeginbydefiningtheprocess.Theyaskwhothecustomersareandwhattheirproblemsare.Theyidentifythekeycharacteristicsimportanttothecustomeralongwiththeprocessesthatsupportthosekeycharacteris-tics.Theythenidentifyexist-ingoutputconditionsalongwiththeprocesselements.•Measure.Nextthefocusisonmeasuringtheprocess.Keycharacteristicsarecategorized,measurementsystemsareveri-fiedanddataarecollected.•Analyze.Oncedataarecol-lected,itisanalyzed.Theintentistoconverttherawdataintoinformationthatpro-videsinsightsintotheprocess.Theseinsightsincludeidenti-fyingthefundamentalandmostimportantcausesofthedefectsorproblems.•Improve.Thefourthstepistoimprovetheprocess.Solutionstotheproblemaredeveloped,andchangesaremadetotheprocess.Resultsofprocesschangesareseeninthemeasurements.Inthisstep,thecompanycanjudgewhetherthechangesarebeneficial,orifanothersetofchangesisnecessary.•Control.Iftheprocessisperformingatadesiredandpredictablelevel,itisputundercontrol.ThislaststepisthesustainingportionoftheSixSigmamethodology.Theprocessismonitoredtoassurenounexpectedchangesoccur.Focusingontheprimaryareaofvariationreductionproducesothersecondaryeffects,too.Qualityisimproved.Processinvestigationproducesthere-eval-uationofthevalueaddedstatusofmanyelements.Someelementsaremodified,whileothersarediscon-tinued.Elementsarerefinedandimproved.Mistakesandopportunitiesformistakesarereduced.SomeelementsdiscoveredduringtheSixSigmainvestigationconstraintheflowofproductsorser-vicesthroughthesystem.Flowisdefinedasthetimefromtheinputofrawmaterialtotheoutputofasal-ableitem.Improvementofaprocessthatwasrestrict-ingflowresultsinreducedvariation,betterqualityandimprovementinthevolumeoftheprocessout-put.Thustheorganizationhaslessmoneytiedupinin-processinventory.Thetimefrompayingforinputmaterialtoseeingaprofitisreduced,andtheorgani-zationcanrespondtocus-tomerneedsmorequickly.SixSigmaisfoundedontwomainassumptions.First,peopleinanorgani-zationunderstandandappreciatethefactthatnumberscanrepresentfeaturesandcharacteris-ticsofaprocess.Theyappreciatethatadeeperunderstandingofdataanddataanalysiscanbeusedtoproduceimprovements,andgraphicalrepresenta-tionsofdatacanprovidenewanddifferentper-spectivesoftheprocess.Analyticaltypes,suchasengineersandscientists,generallyrespectthisapproach.Anotherassumptionisthatthroughthereductionofvariationofalltheprocesses,theoverallperfor-manceoftheorganizationwillbeimproved.Butwhileitishardtoargueagainstimprovement,theeconomicrealityofbusinessiswewantthemostimprovementfortheleastinvestment.Improvingallofanorganiza-tion’sindividualprocessescouldactuallyhaveadetri-mentaleffectonthecompany’sabilitytosatisfythecustomer’sneedsandprovideproductandservicesattherighttimeatthelowestcost.Therealizedsavingstothesystemmightbelessthanthecostofalltheimprovements.So,anorganizationthatimprovesthingsjustbecauseitcanmaybeimprovingthewrongthingsforthebusiness.LeanthinkingLeanthinkingissometimescalledleanmanufactur-ing,theToyotaproductionsystemorothernames.Leanfocusesonther