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洛阳理工学院毕业论文第页1CAD/CAMComputertechnologyhasriseninanexponentialcurve.OnlyagenerationagocomputerswerenotreallyneededforNCcontrol.Exceptforrelativelyfewfiveaxismachines.NCwaspointtopoint,whichwaseasilyaccomplishedwithmanualprogramming.Withtheadventoftwodimensionalprofiling,hower,aneedarosefornumerouscalculationstogeneratethecurvedprofile.Atthatpointthecomputerwaslookeduponasausefultoolinmanufacturingengineering.Aftersomedevelopment,itwasfoundthatpunchedormagnetictapecouldbedispensedwithentirelyinfavorofcomputerprogramsthatcontrolledthemachinesdirectly.Thencametheminicomputers,whichwhenoperatingwiththecentralprocessorbroughtaboutthefirstrealconceptoftheautomaticfactory.Allofthesedevelopmentswereimportantstepsintheadvanceoftechnology.Thecomputerisnolongerviewedasaremotepieceofhardwareusedprimarilyinaccountingandengineeringdepartments,butinsteadasanimportanttooltobeusedincreasinglyinCADandCAM.TodayCADandCAMhavebecomecloselylinkedforcompleteprocessingfromdesigntoproduction.ThedesinengineercannowcreatethedesireddesignonaCRTscreenthatislinkedtoacomputerizedgraphicsplotter.Thesamesystemcanbeusedtodeterminetheviabilityofthedesignbyanalyzingstressesanddeflectionsthatwilltakeplaceunderloadingconditions.Thefunctioningofmechanicallinkagesmayalsobechecked.Afterthedesigniscomplete,theproductiongroupcandrawontheinformationdevelopedinCADforcomputeraidedmanufacture.ThustheunifiedCADCAMteamhasbeendevelopedtobringtheproductfromthedesignconcept洛阳理工学院毕业论文第页2throughmanufacture.CADFunctionsInitiallyCADsystemswereprimarilyautomateddraftingstationsinwhichcomputerplottersproducedengineeringdrawings.Thesystemswerelaterlinkedtographicdisplayterminals,whichallowedtheusertocommunicatewiththecomputerinpicturesinsteadofrawcolumnsofnumbers.Nowadvancedsystemshaveaddedanalyticalcapabilities.CADfunctionsmaybegroupedintofourmajorcategoriesgeometricmodeling,engineeringanalysis,kinematics,andautomateddrafting.GeometricModelingTraditionally,engineersdothesketchinganddraftsmenthedrafting.Engineersthendiscoverneededchangesorimprovementsanddraftsmendraftwhatisrequired.Movingabracket2in,totheleftcausesanentreechainreactionthroughoutacompletesetofdrawings.Nowthecomputerhasopenedupanewwaytomeetdesignengineeringneedswithspeedandreliabilityinproductsrangingfromhighperformanceaircrafttocomplex,integratedcircuits.Thedesignercansketchdirectlyonthescreenofagraphicsterminal.Linesandcontoursaredefinedbypressingkeysandpositioningalightpen,andthecomputerdisplayswhatisexpressed.Curvefitting,orreducingthedesigntoasetofcontrolequationsisdoneattheterminal,eliminatingcoding,cardpunching,punching,andrepeatedcomputerbatchrunsthenCADconvertsthepreliminarydesigntoadimensionaldrawingwithauxiliaryviews.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.CAMFunctionsCAMfunctionscenteraroundfourmainareasnumericalcontrol,processplanning,robotics,andfactorymanagement.NumericalcontrolAsstatedpreviously,NCusescodedinformationtocontrolmachinetoolmovements.ThecomputercannowgenerateaNCprogramdirectlyfromageometricmodelofapart.Automaticcapillariesaregeneralitieslinkedtohighlysymmetricgeometricandotherspecializedshapes.ProcessPlanningProcessplanningisinvolvedwiththedetailedsequenceofproductionstepsfromstarttofinish.Essentially,theprocessplandescribesthestateoftheworkplaceateachworkstation.TheuseofcomputersasanaidtoprocessplanningiscomparativelyrecentandhasledtoarebirthofwhatisknownasgrouptechnologyGT.Grouptechnologyisbasedonorganizingallsimilarpartsintofamiliestoallowstandardizationoffabricatingsteps.Currentlyunderdevelopmentisprocessplanningsystemthatisabletoproduceprocessplansdirectlyfromthegeometricmodeldatabasewithalmostnohuman
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