GroupTechnologyGrouptechnology(GT)isaveryimportantmethodologyintodaysmanufacturingsignificant.Thereasonforthisisthatgrouptechnology,whenutilizedtoitsfullestextent,canaffectmostareasofmanufacturing,includingdesign,processplanning,scheduling,routing,factorylayout,procurement,qualityassurance,machinetoolutilization,tooldesign,producibilityengineering,andassembly.1IntroductionGrouptechnologyisasimpleconceptthatisusedwidelyinvariousforms.Foravarietyofreasons,itislogicaltocollectandassociatethingsbasedonfeaturesthattheyhaveincommon.Thisapproachisfamiliartoeveryoneforplants,animals,andchemicals.Suchorganizationalstructureshavealsobeenusedforhardwareandotherobviouslysimilarproductswithinthemanufacturingworld.Grouptechnologyrepresentsstructuredcategorizationofparticularvaluetothemanufacturingcommunity.Itisalreadywidelyused；perhaps50%ofmanufacturingcompaniesusesomeformofGT.Bathorlotproductionsuffersfrommanyinefficienciesduetopartvarietyandthegeneral-purposenature(flexibilityrequirements)ofmachinetoolsinuseontheshopfloor.Infact,aCincinnatiMilacronstudyshowedthat95%ofthetimeapartspendsontheshopfloorisidletime,theother5%isdividedbetweensetupandteardownofthemachinetool.Thefuturebreakdownofthe5%ofon-machinetimewasdevelopedbyDunlap.Basedonthisestimate,only24%ofthe5%istimewhichactuallyinvolvescutting；i.e.,partsarebeingmachinedduringonly1.2%ofthetotaltimespentinmanufacturing.Grouptechnologymakespossibletheapplicationofseveralmethodsofanalysiswhichassistinmakingbatchproductionmoreefficientbyreducingpartvarietyviapartfamiliesandimprovingthroughoutandwork-in-processinventory.Itisforthisreasonthatgrouptechnologyisbecomingakeyconceptinmanufacturing.2DefinitionManufacturingphilosophytosome,fundamentalbuildingblockformoreefficientproductiontomost,grouptechnologyisasimpleconceptwhichutilizes/exploitssimilaritiesformoreefficientproductioninbathmanufacturing.Grouptechnologyusuallyclassifiespartsintheformofacodewhichisassignedtoeachpartbasedonitsshapeorproductionprocessingcharacteristics.Inuse,codingpartsassistsinthecontrolofplanningandprocessing.Thisaddedcontrol,whichexploitssimilarities,leadstoeconomiesintheoverallmanufacturingprocess.Theactualoperatorontheshopfloormayneverknowthiscode,butdesigners,engineers,andplannersfinditaninvaluabletool,allowingthemtodomoreproductiveandusefulanalysis.3GeneralBenefitsInpractice,grouptechnologyisreallynothingmorethananinformation/indexingsystem.However,becauseofitsfocusonpartdesignandprocessingsimilarities,analysisispossiblewhichcreatesmanufacturingeconomiesofscale,encouragesstandardization,andeliminatesduplicationindesignandprocessplanning.Massproductionenjoysthebenefitsofwhatarecalledeconomiesofscale.Economiesofscaleachievedbyprocessingalargenumberofpartsoverthesameworkstationsorequipment.Thisresultinlesslaborperpart,moreefficientmachineutilization,andafasterturnoverofinventory.Batchproductioninthepasthasnotenjoyedeconomiesofscalebecauseoftheneedtoremainflexibleforchangingparttypesandproducts.However,bygroupingpartsintofamiliesbasedontheirsimilarities,muchofthemanufacturingprocessingofthesepartscanbedoneonentirefamilies.Thisincreasesthenumberofpartsprocessedwiththesameequipmentconditions,therebypermittingsomeoftheeconomiesofscaleofmassproduction.Standardizationisachievedinbothdesignandpartprocessplanning.Essentially,grouptechnologycreatesanefficientdesignretrievalsystemsincepartshavebeencodebasedonshape.Similardesignarelocatedquicklyandaspectssuchasparttolerancesandproducibilitycanbebetterunderstood,moreeasilyapplied,andkeptmoreconsistentfromdesigntodesign.Whenstandardizedprocessplanesaredevelopedandincludeinthegrouptechnologycode,newpartsandrepeatorderscanfollowsimilarprocessingroutesthroughtheshopfloor,simplifyingschedulingandflowthroughtheshop.Grouptechnologyeliminatesduplication.Inbothdesignandprocessplanning,thereismuchles“reinventingofthewheel”sincethereissufficientretrievalofstandarddesignsandprocessplans.4ApplicationofGTinProcessPlanningAlthoughmanyareasofbusinessoperationcanbenefitfromGT,manufacturing,theoriginalapplicationarea,continuestobetheplacewhereGTismostwidelypracticed.Twoimportanttasksinmanufacturingplanningandmanufacturingengineeringareschedulingandprocessplanning.Jobschedulingsetstheorderinwhichpartsshouldbeprocessedandcandetermineexpectedcompletiontimesforoperationandorders.Processplanning,ontheotherhand,decidesthesequenceofmachinestowhichapartshouldberoutedwhenitismanufacturedandtheoperationsthatshouldbeperformedateachmachine.Processplanningalsoencompassestool,jig,andfixtureselectionaswellasdocumentationofthetimestandards(runandsetuptime)associatedwitheachoperation.Processplanningcandirectlyaffectschedulingefficiencyand,thus,manyoftheperformancemeasuresnormallyassociatedwithmanufacturingplanningandcontrol.Someofthelargestproductivitygainshavebeenreportedinthecreationofprocessplansthatdeterminehowapartshouldbeproduced.Withcomputer-aidedprocessplanning(CAPP)andGTitispossibletostandardizesuchplans,reducethenumberofnewones,andstore,retrieve,edit,andprintthemoutveryefficiently.Processplanningnormallyisnotaformalprocedure.Eachtimeanewpartisdesigned,aprocessplannerwilllookatthedrawinganddecidewhichmachinetoolsshouldprocesstheparts,whichoperationsshouldbeperformed,andinwhatsequenceTherearetworeasonswhycompaniesoftengenerateexcessprocessplans.First,mostcompanieshaveseveralplanners,andeachmaycomeupwithadifferentprocessplanfortheverysamepart,Second,process；planningisdevelopedwiththeexistingconfigurationofmachinetoolsinmind.Overtime,theadditionofnewequipmentwillchangethesuitabilityofexistingplans.Rarelyarealterationstooldprocessplansmade.Onecompanyreportedlyhad477processplansdevelopedfor523differentgears.Acloselookrevealedthatmorethan400oftheplanscouldbeeliminated.ProcessplanningusingCAPPcanavoidtheseproblems.ProcessplanningwithCAPPtakestwodifferentforms；Withvariant-basedplanning,onestandardizedplan(andpossiblyoneormorealternateplans)iscreatedandstoredforeachpartfamily.WhentheplannerenterstheGTcodeforapart,thecomputerwillretrievethebestprocessplan.Ifnoneexists,thecomputerwillsearchforroutingsandoperationsforsimilarparts.TheplannercanedittheschemeontheCRTscreenbeforeprintout.Withgenerativeplanning,whichcanbutdoesnotnecessarilyrelyoncodedandclassifiedparts,thecomputerformstheprocessplanthroughaseriesofquestionsthecomputerposesonthescreen.Theendproductisalsoastandardizedprocessplan,whichisthebestplanforaparticularpart.Thevariant-basedapproachreliedonestablishedplansenteredintothecomputermemory,whilethegenerativetechniquecreatestheprocessplansinteractively,relyingonthesamelogicandknowledgethataplannerhas.Generativeprocessplanningismuchmorecomplexthanvariant-basedplanning；infact,itapproachestheartofartificialintelligence.Itisalsomuchmoreflexible；bysimplychangingtheplanninglogic,forinstance,engineerscanconsidertheacquisitionofanewmachinetool.Withthevariant-basedmethod,theengineersmustlookoverandpossiblycorrectallplansthatthenewtoolmightaffect.CAPPpermitscreationanddocumentationofprocessplansinafractionofthetimeitwouldtakeaplannertodotheworkmanuallyandvastlyreducesthenumberoferrorsandthenumberofnewplansthatmustbestored.Whenyouconsiderthatplansnormallyarehandwrittenandthatprocessplannersspendasmuchas30%oftheirtimepreparingthem,CAPPScontributionofstandardizedformatsforplansandmorereadabledocumentsisimportant.CAPP,ineffect,functionsasadvancedtexteditor.Furthermore,itcanbelinkedwithanautomatedstandarddatasystemthatwillcalculateandrecordtheruntimesandthesetuptimesforeachoperation.CAPPcanleadtolowerunitcoststhroughproductionofpartsinanoptimalway.Thatis,costsavingscomenotonlyviamoreefficientprocessplanningbutalsothroughreducedlabor,material,tooling,andinventorycosts.GTcanhelpinthecreationofprogramsthatoperatenumerically(NC)machinery,narearelatedtoprocessplanning.Forexample,aftertheengineersatOtisEngineeringhadformedpartfamiliesandcells,thetimetoproduceanewNCtapedroppedfrombetween4and8hoursto30minutes.ThecompanytherebyimprovedthepotentialforuseofNCequipmentonbatcheswithsmallmanufacturingquantities.編者：吳非曉等機械英語2外語教學(xué)與研究出版社2002.7成組技術(shù)在當(dāng)今的制造環(huán)境下，尤其是對批量生產(chǎn)來說，成組技術(shù)（GT）是一個很重要的生產(chǎn)方式而且它正變得越來越重要。其原因在于