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GroupTechnologyGrouptechnologyGTisaveryimportantmethodologyintodaysmanufacturingsignificant.Thereasonforthisisthatgrouptechnology,whenutilizedtoitsfullestextent,canaffectmostareasofmanufacturing,includingdesign,processplanning,scheduling,routing,factorylayout,procurement,qualityassurance,machinetoolutilization,tooldesign,producibilityengineering,andassembly.1IntroductionGrouptechnologyisasimpleconceptthatisusedwidelyinvariousforms.Foravarietyofreasons,itislogicaltocollectandassociatethingsbasedonfeaturesthattheyhaveincommon.Thisapproachisfamiliartoeveryoneforplants,animals,andchemicals.Suchorganizationalstructureshavealsobeenusedforhardwareandotherobviouslysimilarproductswithinthemanufacturingworld.Grouptechnologyrepresentsstructuredcategorizationofparticularvaluetothemanufacturingcommunity.Itisalreadywidelyusedperhaps50ofmanufacturingcompaniesusesomeformofGT.Bathorlotproductionsuffersfrommanyinefficienciesduetopartvarietyandthegeneralpurposenatureflexibilityrequirementsofmachinetoolsinuseontheshopfloor.Infact,aCincinnatiMilacronstudyshowedthat95ofthetimeapartspendsontheshopfloorisidletime,theother5isdividedbetweensetupandteardownofthemachinetool.Thefuturebreakdownofthe5ofonmachinetimewasdevelopedbyDunlap.Basedonthisestimate,only24ofthe5istimewhichactuallyinvolvescuttingi.e.,partsarebeingmachinedduringonly1.2ofthetotaltimespentinmanufacturing.Grouptechnologymakespossibletheapplicationofseveralmethodsofanalysiswhichassistinmakingbatchproductionmoreefficientbyreducingpartvarietyviapartfamiliesandimprovingthroughoutandworkinprocessinventory.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,thereismuchlesreinventingofthewheelsincethereissufficientretrievalofstandarddesignsandprocessplans.4ApplicationofGTinProcessPlanningAlthoughmanyareasofbusinessoperationcanbenefitfromGT,manufacturing,theoriginalapplicationarea,continuestobetheplacewhereGTismostwidelypracticed.Twoimportanttasksinmanufacturingplanningandmanufacturingengineeringareschedulingandprocessplanning.Jobschedulingsetstheorderinwhichpartsshouldbeprocessedandcandetermineexpectedcompletiontimesforoperationandorders.Processplanning,ontheotherhand,decidesthesequenceofmachinestowhichapartshouldberoutedwhenitismanufacturedandtheoperationsthatshouldbeperformedateachmachine.Processplanningalsoencompassestool,jig,andfixtureselectionaswellasdocumentationofthetimestandardsrunandsetuptimeassociatedwitheachoperation.Processplanningcandirectlyaffectschedulingefficiencyand,thus,manyoftheperformancemeasuresnormallyassociatedwithmanufacturingplanningandcontrol.Someofthelargestproductivitygainshavebeenreportedinthecreationofprocessplansthatdeterminehowapartshouldbeproduced.WithcomputeraidedprocessplanningCAPPandGTitispossibletostandardizesuchplans,reducethenumberofnewones,andstore,retrieve,edit,andprintthemoutveryefficiently.Processplanningnormallyisnotaformalprocedure.Eachtimeanewpartisdesigned,aprocessplannerwilllookatthedrawinganddecidewhichmachinetoolsshouldprocesstheparts,whichoperationsshouldbeperformed,andinwhatsequenceTherearetworeasonswhycompaniesoftengenerateexcessprocessplans.First,mostcompanieshaveseveralplanners,andeachmaycomeupwithadifferentprocessplanfortheverysamepart,Second,processplanningisdevelopedwiththeexistingconfigurationofmachinetoolsinmind.Overtime,theadditionofnewequipmentwillchangethesuitabilityofexistingplans.Rarelyarealterationstooldprocessplansmade.Onecompanyreportedlyhad477processplansdevelopedfor523differentgears.Acloselookrevealedthatmorethan400oftheplanscouldbeeliminated.ProcessplanningusingCAPPcanavoidtheseproblems.ProcessplanningwithCAPPtakestwodifferentformsWithvariantbasedplanning,onestandardizedplanandpossiblyoneormorealternateplansiscreatedandstoredforeachpartfamily.WhentheplannerenterstheGTcodeforapart,thecomputerwillretrievethebestprocessplan.Ifnoneexists,thecomputerwillsearchforroutingsandoperationsforsimilarparts.TheplannercanedittheschemeontheCRTscreenbeforeprintout.Withgenerativeplanning,whichcanbutdoesnotnecessarilyrelyoncodedandclassifiedparts,thecomputerformstheprocessplanthroughaseriesofquestionsthecomputerposesonthescreen.Theendproductisalsoastandardizedprocessplan,whichisthebestplanforaparticularpart.Thevariantbasedapproachreliedonestablishedplansenteredintothecomputermemory,whilethegenerativetechniquecreatestheprocessplansinteractively,relyingonthesamelogicandknowledgethataplannerhas.Generativeprocessplanningismuchmorecomplexthanvariantbasedplanninginfact,itapproachestheartofartificialintelligence.Itisalsomuchmoreflexiblebysimplychangingtheplanninglogic,forinstance,engineerscanconsidertheacquisitionofanewmachinetool.Withthevariantbasedmethod,theengineersmustlookoverandpossiblycorrectallplansthatthenewtoolmightaffect.CAPPpermitscreationanddocumentationofprocessplansinafractionofthetimeitwouldtakeaplannertodotheworkmanuallyandvastlyreducesthenumberoferrorsandthenumberofnewplansthatmustbestored.Whenyouconsiderthatplansnormallyarehandwrittenandthatprocessplannersspendasmuchas30oftheirtimepreparingthem,CAPPScontributionofstandardizedformatsforplansandmorereadabledocumentsisimportant.CAPP,ineffect,functionsasadvancedtexteditor.Furthermore,itcanbelinkedwithanautomatedstandarddatasystemthatwillcalculateandrecordtheruntimesandthesetuptimesforeachoperation.CAPPcanleadtolowerunitcoststhroughproductionofpartsinanoptimalway.Thatis,costsavingscomenotonlyviamoreefficientprocessplanningbutalsothroughreducedlabor,material,tooling,andinventorycosts.GTcanhelpinthecreationofprogramsthatoperatenumericallyNCmachinery,narearelatedtoprocessplanning.Forexample,aftertheengineersatOtisEngineeringhadformedpartfamiliesandcells,thetimetoproduceanewNCtapedroppedfrombetween4and8hoursto30minutes.ThecompanytherebyimprovedthepotentialforuseofNCequipmentonbatcheswithsmallmanufacturingquantities.编者吴非晓等机械英语2外语教学与研究出版社2002.7成组技术在当今的制造环境下,尤其是对批量生产来说,成组技术(GT)是一个很重要的生产方式而且它正变得越来越重要。其原因在于,当成组技术发挥最大作用的时候,能够影响大多数的制造领域,其中包括设计、工艺规划、调度、路线、工厂布局、采购、质量保证、车床应用、刀具设计、生产能力设计及组装。1简介成组技术是一个以各种形式广泛应用的简单概念。基于各种原因,我们有理由根据事物的共同特征把它们收集并联系在一起。对于植物、动物和化合物来说,每个人都很熟悉这种方法。在制造业内,这种组织结构也被用于硬件和其它明显相似的产品中。成组技术对于生产团体来说,代表着具有具体价值的组织分类。它早就被广泛应用,大约有50的生产企业在使用某种形式的成组技术。由于零件多种多样以及生产车间使用的车床的通用特性(灵活性要求),造成了批量和规模生产效率差的情况很多。一份辛辛那提麦尔克伦的研究表明,实际上一个零件花费在生产车间的时间有95是闲置的,另外5的时间在车床的装配和拆卸之间进行分配。Dunlap对这5的机上时间进一步的分解进行了研究。据此估计,5的机上时间中只有24的时间用于切割。也就是说,只有1.2的总时间用于零部件的加工。成组技术能够利用几中不同分析的方法,通过零件族来减少零件的种类,从而使批量生产更具有效率,提高生产能力并缓解加工过程的库存问题。正是由于这个原因,成组技术才在生产中成为一个至关重要的概念。2定义成组技术在某种程度上是一种生产观念,而在很大程度上是高效率生产的基本构件,它是一个简单的概念,它在批量生产过程中利用或使用相似性提高制造效率。成组技术通常利用代码将零件分类。代码是根据零件的形状或生产过程的特征分配给每个零件的。使用中,代码零件有助于对规划和加工的控制。这种利用相似性的附加控制能给整个生产过程带来许多经济效益。车间里的实际操作者可能永远也不知道这个代码,但是设计者、工程师和规划人员把它当成一种最宝贵的工具,能够使他们进行更加有用和富有成效的分析。3益处实际上,成组技术其实就是一个信息或索引系统。然而,由于它着眼于零件设计和加工的相似性就有可能进行分析,规模生产的经济效益,促进标准化并避免重复设计和工艺规划。批量生产有利于规模经济。规模经济效益通过用同一车间或设备加工大量零
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