机械类文献翻译CADCAM的发展.docx

机械类文献翻译CADCAM的发展.docx

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机械类文献翻译CADCAM的发展

TheEvolutionofCAD/CAM

Introduction

Giventhefactmachinetoolautomationreallybeganonlywiththedevelopmentofnumericalinthe1950s-lessthan40yearsage-itisamazingthatthereexisttodaymanufacturingplantsthatarealmostcompletelyautomated.Granted,theseinstallationsproducerelativelyfewvarietiesofproduct,butitisclearthatthephysicalcomponentsforasophisticatedautomatedenterpriseareavailable.

Beforebeginningtodiscussthesecapabilities,wemustidentifywhatwewillmeanby“manufacturingplants”inthisbook,sincethereareseveralcategoriesofmanufacturing（orproduction）thatcouldbeconsidered.Wewillconsidermanufacturinginthreebroadareas

（1）continuous-processproduction,

（2）massproduction,and（3）job-shopproduction.Inanevenbroaderclassification,thelattertwocategoriescouldbeconsideredasdiscrete-itemproduction.

Continuous-processProductionproductthatflowsinacontinuousstreamfallsintothismanufacturingcategory.Typicalprocessesincludepetroleum,cement,steelrolling,petrochemical,andpaperproduction,aswellasmanyothers.Anobviousattributeoftheseisthattheproductionequipmentisutilizedforarelativelysmallgroupofsimilarproducts.Combiningthisattributewiththecontinuous-flowcharacteristicallowedinvestmentinautomatedequipmentthatrealizedbenefitswellbeforesuchadvantageswereseenintheothertwocategoriesofproduction.Thistextwillnotbeorientedtowardcontinuous-processproduction,though.Thistextwillnotbeorientedtowardcontinuous-processproduction,thoughmanyofthetopicswillbeasgermanetothiscategoryastoothertwo.

MassproductionThisentailstheproductionofdiscreteunitsofproductionatveryhighratesofspeed.Discrete-itemproductionisusedforsuchgoodsasautomobiles,televisionsets,refrigerators,electroniccomponents,andsoon.Massproductionattemptstoemulatethecharacteristicsofcontinuous-flowproductionfordiscreteproductsthatareproducedinhighvolumeswithrelativelysmallvariationsinproduct.Asaresult,massproductionhashistoricallyrealizedmanybenefitsfrommechanizationandautomation.

Job-shopProductionAmanufacturingfacilitythatproducesalargenumberofdifferentdiscreteitemsthatrequiredifferentsequencesthroughtheproductionequipmentisusuallycalledajobshop.Becauseofthelargenumberofdifferentproductsanddemandsforthoseproducts,schedulingandroutingproblemsareenormous.Asaresult,automationhasatbestbeenrestrictedtoindividualcomponentsofthejobshop（someonereferredtoasislandsofautomation），andtherehavebeenfewattemptstoautomatetheentirefacilitybyintegrationtheislandsofautomation.

Nowwecanclarifywhatmeantearlierwhenwesaidthatthephysicalcomponentsforanautomatedmanufacturingsystemexistalthoughlittleautomationofcompletemanufacturingfacilitieshasactuallybeenaccomplished.First,wedonotincludecontinuous-flowsprocesses,whichcomprisearelativelysmallpercentageofmanufacturing.Wedoinclude,however,massproductionofdiscreteitems,wheresegmentsoftheproductionlineareoftenquiteautomated,butnottheentireline.Forexample,spotweldingandpaintinginautomobilelinemaybecompletelyautomatedusingrobotics,butmuchassemblyworkisaccomplishedbyhumanlabor.Similarly,job-shopfacilitieshavelongusedautomatedmachinetools,butonlyrarelyhastransferofworkinprogressamongthesemachinesbeenhandledautomatically.Otherthansomephysicalequipmentthatmightbeneededtocompletelyautomateaspecificdiscrete-itemfacility,amajorproblemistheonealludedtointheintroductoryquotationforthischapterThesoftwareneededtointegrateinformationhasnotevolvedtotheleveloftheavailablephysicalhardware.

Inlinewiththisobservation,amajorcomponentofautomatedinformationthatneedstobemadeavailabletothemanufacturingoperationinordertoallowplantautomation/integrationmustcomefromproductdesign.However,informationonmanufacturingcapabilityisfrequentlynotavailabletotheproductdesigndepartment,leadingtowhathasoftenbeencalledthe“wall”betweendesignandmanufacturing.Manufacturingismoreconcernedwithprocessdesignthanproductdesign.

TheEvolutionofCAD/CAM

Itisfuntoattempttotraceeventsthatledtoamajorscientificdiscovery.Infact,apopularrecenttelevisionseriestracedsuchconnectionsformanysuchdiscoveries.Thedigitalcomputer’sroots,forexample,weretracedbacktotheStoneAgeandcountingonnotchedsticks.Wewillnotattemptsuchaninterestingtaskasshowingthattypeofevolutionbutwilllimitourselvestoprovensteppingstones.

TheEvolutionofCADTherootsofCAMhavebeenmoreclearlydelineatedinrecentyearsthanhavethoseofCADLogically,CAD’sdevelopmenthascomethroughtheevolutionofcomputergraphicsandcomputer-aideddrawinganddrafting,oftencalledCADD.Perhapsamomentshouldbetakennowtodefinewhatthesetermsmean:

Computergraphicsreferstotheusedofcomputertoassistinthegenerationofpictorialrepresentations.Thesemayrangefrombusinessapplicationsgeneratingpieandbarchartstocomplexartrepresentationsthatsimulatepaintingsbytheoldmasters.

Computer-aideddrawinganddraftingusesthecomputertoassistinthegenerationofblueprint-typedata.Thisisusuallyintheformoftwo-dimensionalrepresentationsofapartwithassociateddimensionaldataaswellasothermanufacturinginformation.

Computer-aideddesigngoesfarbeyondCADD,allowingforanalysisaswellasgraphicalrepresentation.Forexample,anautomobilesuspensionsystemmaybedesignedusingCADprogramsfrequentlyincorporatecomplexengineeringanalysisroutines.Forexample,anarchitecturallayoutforanofficebuildingmightbeconsideredasCADDifnoanalysisisincluded.However,ifthecomputerpackageincludesthecapabilityofinsuringthatfederalstandardsaremaintainedasregardsmaximumdistancetorestrooms,humanfactorcharacteristicsoftheofficelayout,andsoon,thenCADisrealized.

BesantcreditsworkbyIvanSutherlandattheMassachusettsInstituteofTechnologyasbeingthefirstmajorstepintheevolutionofcomputergraphicsandthustheevolutionofcomputer-aideddesign.Thiswork,whichproducedSKETCHPAD,wasaccomplishedin1963.Acathode-rayoscilloscopewasdrivenbyaLincolnTX2computertoallowgraphicalinformationtobedisplayedonascreen.Picturescouldbedrawnonthescreenandthenmanipulatedusingglightpen.BesantcallsthisinceptionofinteractivegraphicsandIvanSutherlandthefatherofcomputergraphics.

Attheandofthe1960stherewerethan200CADworkstationsinthUnitedStates,primarilyintheaerospaceandautomotiveindustries.Thenextdecadesawthistosome12000workstations,withindustrialapplicationmuchwiderthanthepreviousdecade’snarrowspectrum.Amajorimpetusforthisproliferationwastheadventoftheminicomputerandthedevelopmentofdisplayunitsthatweremuchbetterforrepresentinggraphicalinformationthantheoriginaloscilloscopes.Extremelycomplexcomputer-aideddesignsoftwarepackagescannowberesidentinmicrocomputers,realizingsignificantcostadvantagesthatallowengineeringstudentsthepossibilityofhavingtheirownpackageintheirhome.

TheEvolutionofCAMTherootstheautomationofacompletefactorycouldbeshowntohavecomefrommanydifferentsources,thoughithasbeenclaimedthatamechanicalflourmillpatentedbyOliverEvansofPhiladelphiain1975wastheworld’sfirstautomaticfactory.This,ofcourse,fallsinthecontinuous-productionclassification.

Therootsforautomationofdiscrete-itemproductionarefirmlyembeddedinthemassproductionconceptsdevelopedbyHenryFordearlyinthetwentiethcentury.Therateofproduction（cycletime）forandautomobilemightbesuchthatafinishedautomobilecomesoffthelineeveryminuteandahalf.Thelengthoftimerequiredforactualassemblyofanautomobileis,ofcourse,muchlonger.Assemblytasksarecombinedsotthatgroupsoftaskscanbeaccomplishedinlessthanthecycletime.Suchgroupingsareoftencalledstations,andmanystationsarerequiredalongtheline.Thisgroupingoftasksifanalogoustogrouptechnologyasbeingthekeytorealizingmanyofcomputer-aidedmanufacturing’sobjectivesforjob-shopproduction.

Logically,thedigitalcomputeristhekeytocomputer-aidedmanufacturingaswellascomputer-aideddesign.Digitalcomputershavebeenusedtocontrolmanufacturingfunctionsofmorethan30years.Forexample,itwasreportedin1973thatadiversegroupingofcomputercontrolapplicationsincluded:

●Automobiletrafficcontrol

●Producttestingandqualitycontrol

●Foundrycontrol

●Numericalcontrolequipment

●Spaceengineeringresearch

●Neurologicalandbiomedicalresearch

●Railroadfreight-carmonitoring

●Deep-seadatalogging

●Cementplantblendingcontrol

●Utilityplantstartupandcontrol

●Hot-striproughing-millcontrol

●Oxygenfurnaceapplications

●Blastfurnaceapplications

●Nylonplantprocesscontrol

●Ethyleneplantcontrol

●Oilrefinerycat-crackeroperation

Thereisanobviousreasonforamajorityoftheapplicationsfallingintotheprocessindustrycategory.Anyformofcontrolrequiredisinformationtobegatheredfromwhatisbeingcontrolled-say,theprocess;theinformationgatheredhastobeanalyzedtodetermineifcorrectiveactionisneeded;theprocesshastobeadjustedifcorrectiveactionisneeded；theprocesshastobeadjustedifcorrectiveactionisneeded.Thisthree-stagecontrolsequencecomprisessensing→analysis→actuation.Automaticsensingandaut