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1、CADandCAMTheenginelathe,oneoftheoldestmetalremovalmachines,hasanumberofusefulandhighlydesirableattributes.Todaytheselathesareusedprimarilyinsmallshopswheresmallerquantitiesratherthanlargeproductionrunsareencountered.Tnthebeginning,CADsystemswerenomorethanagraphicseditorwithsomebuilt-inde
2、signsymbols.Thegeometryavailabletotheuserwaslimitedtolines,circulararcs,andthecombinationofthem.Thedevelopmentoffree-formcurvesandsurfaces,suchasCoon'spatch,Bezier'spatch,andB-spline,enablesaCADsystemsallowadesignertomoveintothethirddimension.Becauseathree-dimensionalmodelcontainsenoughi
3、nformationforNCcutter-pathprogramming,thelinkagebetweenCADandNCcanbedeveloped.SocalledturnkeyCAD/CAMsystemsweredevelopedbasedonthisconceptandbecamepopularinthe1970sand1980s.The1970smarkedthebeginningofanewerainCAD一theinventionofthree-dimensionalsolidmodeling.Inthepast,three-dimensional,w
4、ire-framemodelsrepresentedanobjectonlybyitsboundingedges.Theyareambiguousinthesensethatseveralinterpretationsmightbepossibleforasinglemodel.Thereisalsonowaytofindthevolumetricinformationofamodel.Solidmodelscontaincompleteinformation;therefore,notonlycantheybeusedtoproduceengineeringdrawi
5、ng,butengineeringanalysiscanbeperformedonthesamemodelaswell.Later,manycommercialsystemsandresearchsystemsweredeveloped.QuiteafewofthesesystemswerebasedonthePADLandBUILDsystems.Althoughtheyarepowerfulinrepresentation,manydeficienciesstillexist.Forexample,suchsystemshaveextremecomputationa
6、ndresource(memory)requirements,anunconventionalwayofmodelingobjectsandalackoftolerancecapabilityhaveallhinderedCADapplications.Ttwasnotuntilthemid-1980sthatsolidmodelersmadetheirwayintothedesignenvironment.Today,theiruseisascommonasdraftingandwire-framemodelapplication.CADimplementations
7、onpersonalcomputers(PCs)havebroughtCADtothemasses.ThisdevelopmenthasmadeCADavailableandaffordable.CADoriginallywasatoolusedonlybyaerospaceandothermajorindustrialcorporation.TheintroductionofPCCADpackages,suchasAutoCAD,VersaCAD,CADKEYsystems,madesmallcompanies,evenindividu
