LEAN_Just-in-time (JIT) production and process unr

~UST-IN--TI~(JI~)PRODOCY~$OMPROCESSUNRELIAEILI~YMenberuLuluUniversityofSouthFloridaABSTRACT.Theeffectsofprocessunreliab{,l,~tyontheperformanceofasimula-tionmode~ofaJust-in-TimeProductionandManufacturingSystem(J!TMPS)isin-vestigated.Inamulti-component-fabricationandproduct-assemblyenvironment,arelativelylowe~]~e~e~offabricationprocessunreliabilityresultsinapro-nou~cedlevelofloweredsy~e~utilization.Work-in-Processinventory-inducedgainsinp~o.d~tionratesin~he:JI~PSa~re~tassi~mi~_~a~a~ma~ee~-~.is-io~ed~i~~r~dit/uD~alprod~cti~systemsthates~em~-~e~ra~e~der~as~INTRODUCTIONTheo~erationalobjectiveoftheJust-in-TimeM~£ac~[i~a~Pr~l~ctionSystem[3~T~P~]!~stopr~d~c~thek~dofunitsn~ee~ed,attheti~eneeded[i.e.Hu:st-in-Time(JIT)],andinthequantitiesneeded.Thisproductionsystemisd%ep~Kooted'i~Westernconceptsofqualityimprovementtechnique~~ra~nandDenning-USA)andinsystems-based(GroupTechnoIogy)rat~o.al~zationofbatchprod~ction--cellularmanufacturing(mostnotably:Kaling-Sweden,Mirofanov-USS~and,O~itz-Germany).~he~ITMPSemploysthePuIlSystemofprod~ctiomcontr~Ithat~asi~-%egzated~mporta~functionsoftheproductioncontrolsystemwiththatofthemanufacturingsystem.Qualitycontrol,inventorycontrolandshort-%~r~produc-tioncontrolhavetraditionallybeenstafffunctio,s.F~KtheJ[TMP$,thesearenewlinefunctions.Thepned~t~worker's~obisenlargedtoincluderespon-s~bil%tyfor~roductqualityassurance.Thelineforeman's~ob~semIar~edtoincludeinve~tor~cmntrolandshort-termproductionpl~ninga~c~erol.TheJITMPSmanagementapproachandthecellularstructureof~tsmanufacturingsys-temshauegeneratednewformsofworkerorganization,suchasQualityCirclesthathaveledtD~inm~vationsinproductdesign,machinedesigne~q~salityim-provements[5].AnnualSimulationSymposinm/~2'3T238LULUInthePullSystemofproductioncontrol,thefinalassemblygoestotheprecedingprocesstoobtainthenecessaryparts,atthenecessarytime,foraspecificproductassembly.Thissignalstheprecedingprocesstoproduce(i.e.,toreplace)thepartswithdrawnbythefollowingprocess.Fortheproductionoftheseparts,theprecedingprocessobtainsthenecessarypartsfromtheprocessfurtherprecedingit.TheKanbansystemisamanual(nonautomated)implementa-tionofthepul!systemofproductioncontrol.AKanbanisacardusuallyputinarectangularvinylsackandattachedtoapartcontainer(cart).ThetwoprimarykindsofKanbansaretheConveyanceKanbanthatisutilizedbyasucceedingprocesstowithdrawpartsfromapreced-ingprocess,andtheProductionKanbanthatisutilizedtoorderproductionoftheportionwithdrawnbythesucceedingprocess.Seereferences[3,5,7]fordetailedexplanationoftheKanbansystem.UsingKanbansbetweenalltheprocesseslinkstheactivitiesofthefinalprocesstotheremainingprecedingprocesses.Thischain-linkingisthemechanismforsynchronizingJITproduction.KimuraandTerada[2]utilizedsimulationtoshowthatdemandfluctuationatthefinalproductionstagedoesnotinduceamplificationinproductionandinven-torylevelsinprecedingproductionstages.Theleveloffluctuationineachoftheprecedingn-iproductionstagesequalsthatofthelaststage.Kim[i]analyzedanoperatingpolicyforJITproductioncalledPeriodicPullSystem(PPS).TheessenceofPPSistoreviewthestatusofmaterialflowatallproductionstagesatregularintervals.Consequently,onlytheexactamountofmaterialthathasbeenconsumedatasucceedingstagesincethelastreviewtimeisallowedtobeWithdrawn.PPSreducesproductionleadtimebyreplacingmanualprocessingofinformation(Kanbans)withcomputerinformationprocessing.RESEARCHOBJECTIVEANDMETHODOLOGYPROBLEMDESCRIPTIONInaKanban-linkedJITMPS,whenabreakdownoccursataprecedingcell(process),theconveyanceofworkpartstotheinputstockpointofasucceedingcellisdelayedduetolackofworkparts.Asaconsequence,thesucceedingcellisstarvedandproductionhalts.Furthermore,allthedownstreamprocesseseventuallyhaltduetosubsequentstarving.Similarly,abreakdownatasucceed-ingstagedelaysmovementofconveyanceKanbanstotheoutputstockpointofaprecedingcell.This,inturn,delaysproductionKanbanmovementinthepreced-ingcell.ThenetresultisthattheprecedingcellispreventedfromfurtherAnnualSimulationSymposiumJUST-IN-TIMEPRODUCTIONANDPROCESSUNRELIABILITY239productionduetoblockingbythesucceedingcell.TheeventualabsenceofconveyanceKanbanmovementsbetweentheupstreamprocesseswillinduceacor-respondingabsenceofproductionKanbanmovements.Hence,alltheupstreamprocesseswillbepreventedfromfurtherproduction.Westernproductionmanagershaveapolicyofinsertingbufferstocksbetweenproductionstagestoprotectagainstproductionirregularitythatiscausedbyprocessunreliability[6].Whiletheirapproachguaranteesthemaintenanceofhigherproductionrates,itneverthelessresultsinhigherWIPinventory.Insteadofaddingbufferstocksatpointsofirregularity,JITproductionmanagersdeliberatelyexposetheworkforcetotheconsequencesofproductionirregularity.Eachtimeworkerscorrectthecausesofarecentirregularity,themanagersremovemoreinventory.Theworkersareneverallowedtosettleintoacomfortablepatternofthestatusguo;orrather,thepatternbecomesoneofcontinuallyperfectingtheproductionprocess.ThethesisforsuchanapproachisthatWIPinventoryhidesproblemswhichcancauseproductionirregularity.Thispaperfocusesoninvestigatingtheimpactofprocessunreliability