外文翻译--CADcam.doc

洛阳理工学院毕业论文第页1CAD/CAMComputertechnologyhasriseninanexponentialcurve.OnlyagenerationagocomputerswerenotreallyneededforNCcontrol.Exceptforrelativelyfewfive-axismachines.NCwaspointtopoint,whichwaseasilyaccomplishedwithmanualprogramming.Withtheadventoftwo-dimensionalprofiling,hower,aneedarosefornumerouscalculationstogeneratethecurvedprofile.Atthatpointthecomputerwaslookeduponasausefultoolinmanufacturingengineering.Aftersomedevelopment,itwasfoundthatpunchedormagnetictapecouldbedispensedwithentirelyinfavorofcomputerprogramsthatcontrolledthemachinesdirectly.Thencametheminicomputers,whichwhenoperatingwiththecentralprocessorbroughtaboutthefirstrealconceptoftheautomaticfactory.Allofthesedevelopmentswereimportantstepsintheadvanceoftechnology.Thecomputerisnolongerviewedasaremotepieceofhardwareusedprimarilyinaccountingandengineeringdepartments,butinsteadasanimportanttooltobeusedincreasinglyinCADandCAM.TodayCADandCAMhavebecomecloselylinkedforcompleteprocessingfromdesigntoproduction.ThedesinengineercannowcreatethedesireddesignonaCRTscreenthatislinkedtoacomputerizedgraphicsplotter.Thesamesystemcanbeusedtodeterminetheviabilityofthedesignbyanalyzingstressesanddeflectionsthatwilltakeplaceunderloadingconditions.Thefunctioningofmechanicallinkagesmayalsobechecked.Afterthedesigniscomplete,theproductiongroupcandrawontheinformationdevelopedinCADforcomputer-aidedmanufacture.ThustheunifiedCAD-CAMteamhasbeendevelopedtobringtheproductfromthedesignconcept洛阳理工学院毕业论文第页2throughmanufacture.CADFunctionsInitiallyCADsystemswereprimarilyautomateddraftingstationsinwhichcomputerplottersproducedengineeringdrawings.Thesystemswerelaterlinkedtographicdisplayterminals,whichallowedtheusertocommunicatewiththecomputerinpicturesinsteadofrawcolumnsofnumbers.Nowadvancedsystemshaveaddedanalyticalcapabilities.CADfunctionsmaybegroupedintofourmajorcategories:geometricmodeling,engineeringanalysis,kinematics,andautomateddrafting.GeometricModelingTraditionally,engineersdothesketchinganddrafts-menthedrafting.Engineersthendiscoverneededchangesorimprovementsanddraftsmendraftwhatisrequired.Movingabracket2in,totheleftcausesanentreechainreactionthroughoutacompletesetofdrawings.Nowthecomputerhasopenedupanewwaytomeetdesignengineeringneedswithspeedandreliabilityinproductsrangingfromhigh-performanceaircrafttocomplex,integratedcircuits.Thedesignercansketchdirectlyonthescreenofagraphicsterminal.Linesandcontoursaredefinedbypressingkeysandpositioningalightpen,andthecomputerdisplayswhatisexpressed.Curvefitting,orreducingthedesigntoasetofcontrolequationsisdoneattheterminal,eliminatingcoding,cardpunching,punching,andrepeatedcomputerbatchruns；thenCADconvertsthepreliminarydesigntoadimensionaldrawingwithauxiliaryviews.Ifthedrawingrevealsaproblemofcompatibilitywithasubassembly,thepiecescanbemovedaroundwiththelightpen.Thecomputerthenconvertsthispictorialrepresentationtoamathematicalmodelstoredinthecomputerdatabaseforlateruse.洛阳理工学院毕业论文第页3ThemodelmaybeusedorotherCADfuctionsoritmayberecalledandrefinedbytheengineeratanypointinthedesignprocess.GeometricmodelingisoftenconsideredtobethemostimportantfeatureofaCADsystembecausesomanyotherdesignfunctionsinthesystemdependheavilyonthemodel.Thegeometricmodelmaybeusedtocreateafiniteelementmodelofastructureforstressanalysis.Themodelmayalsoserveasaninputforautomateddraftingtoproduceengineeringdrawings.IfCAD/CAMsystemsareinterfaced,thegeometricmodelcanbeusedtocreateNCtapesforfabricatingthepart.Mostmodelingisdonewithawireframethatrepresentsthepartshapewithinterconnectedlineelements.AnalysisAfterthegeometricmodelingisdone,theCADsystemallowsthedesignertomovedirectlytoanalysis.Withsimplekeyboardinstructions,thecomputerisaskedtocalculateweight,volume,surfacearea,momenttoinertia,orcenterofgravityofapart.However,themostpowerfulmethodofanalyzingapartisbythefiniteelementmethod.Inthistechniquethestructureisbrokendownintoanetworkofsimpleelementthatthecomputerusestodeterminestresses,deflections,andotherstructuralcharacteristics.Suchanalysisrequiresthetremendouscomputationalpowerofamainframecomputer.KinematicsManyCADsystemhavekinematicfeaturesforplottingoranimatingthemotionofsimple,hingedpartssuchasdoorsorcranks.Suchanalysiscanensurethatmovingcomponentsdonotimpactonotherpartsofthestructure.Thedesignofanautomobilehoodlinkage,forexample,requiresonlyafewminutesofinteractionwithacomputer,whereashundredsofhoursofhourscanberequiredformanualdesignofthesamepart.洛阳理工学院毕业论文第页4Expertsbelievethatinthefuturecomputersandprogramswillbeavailabletocompletelysynthesizeacomplexmechanicalsystembasedsolelyonitsintendedfunction.DraftingWithautomateddrafting,detailedengineeringdrawingsmaybeproducedautomaticallyfromadatabase.Inaddition,mostdraftingsystemshaveautomaticscalinganddimensioningfeatures.AtypicalCADsystemwithautomateddraftingcangenerateuptosixviewsonthescreen.Anydesignchangemadeononeviewisautomaticallyaddedtotheothers.CAMFunctionsCAMfunctionscenteraroundfourmainareas:numericalcontrol,processplanning,robotics,andfactorymanagement.NumericalcontrolAsstatedpreviously,NCusescodedinformationtocontrolmachinetoolmovements.ThecomputercannowgenerateaNCprogramdirectlyfromageometricmodelofapart.Automaticcapillariesaregeneralitieslinkedtohighlysymmetricgeometricandotherspecializedshapes.ProcessPlanningProcessplanningisinvolvedwiththedetailedsequenceofproductionstepsfromstarttofinish.Essentially,theprocessplandescribesthestateoftheworkplaceateachworkstation.Theuseofcomputersasanaidtoprocessplanningiscomparativelyrecentand