外文翻译实体自由成型制造与快速原型制造.doc
南通大学毕业设计附录(英文资料翻译)-1-SOUDFREEFORMFABRICATIONISFF)ANDRAPIDPROTOTYPING11SOUDFREEFORMFABRICATIONISFF)METHODSSeveralmanufacturingprocessesareavailabletomaketheimportanttransitionfromcomputeraideddesign(CAD)toaprototypepartSeveralnewtechnologiesbegantomaketheirappearanceafter1987Inthatyear,stereolithography(SLA)wasfirstintroducedbv3DSystemsInc,andoverthenextfiveyearsseveralrivalmethodsalsoappearedTllScreatedthefamilyofprocessesknownassolidfreeformfabricationfSFFlAswithmostnewtechnologiesatthebeginningofthe“marketadoptionSshapedcurves”inChapter2theSFFdomainiSaccompaniedbyarelativeamountofadvertising“hype”SFFprocessesaresometimesdescribedas:·Partsondemand·Fromarttopart·Desktopmanufacturing·RapidprototypingAtthetimeofthiswriting,stereolithography(SLA),selectivelasersintering(SLS),fuseddepositionmodeling(FDM),andlayeredobjectmodeling(LOM)arebeingusedonaday-to-daybasisbycommercialprototypingcompaniesThethree-dimensional(3一D)printingprocessincornstarch,plastic,andceramicsisalsobeingusedcommerciallyThemethodsloweronthelistshowpromisebutdonotseemtobeingreatusebythirdpartyprototypinghousestomaketheirdailyincomeCastingisaspecialcaseItisstillusedtomakeoneof-akindprototypesFurthermore,forbatchrunsinthe10to500categoryitisaverycosteffectivemethodtouseonceanoriginalmoldhasbeenmadebyaprocesssuchasstereolithographyMachiningisalsousedtomakeoneofakindorseveralprototypes111SummaryofSFFandRapidPrototypingProcessesIndailycommercialuse:·Stereolithography(SLA)·Selectivelasersintering(SIS)·Laminatedobjectmodeling(LOM)·Fuseddepositionmodeling(FDM)南通大学毕业设计附录(英文资料翻译)-2-Moreattheresearchanddevelopment(R&D)stage:·3-Dprintingincornstarch,plastic,orceramic·3-Dprintingwithplasticsfollowedbyplanarizationusingmachining·Solidgroundcuring(similartoSLA)·Shapedepositionmodelingracombinationofadditionandsubtraction)Non-SFF(traditional):·Machining·CastingComparisonsdoneintheearly1990sbytheChryslerCorporationrevealedthattheSLAprocesswasaheadofitsrivalnontraditionalprototypingmethodsintermsofcostandaccuracy(thesestudiesexcludedanevaluationofmachiningandcasting)FollowingthetechnicaldescriptionsinthischapteradditionalfiguresandtablesarethusincludedtocomparethesecostsandaccuraciesOverthelastdecade,SLAhasfurtheremergedasthemostusedSFFprocess,especiallyforthegenerationofthemasterpatternsforcastingandinjectionmoldingAtthetimeofthiswriting,SLS,FDMandLOMhavethemostvisibilityafterSLA112TheHistoryofSFFMethodsDuringthelate1970s,MeadandConway(1980)createdthegroundworkforthefastprototypingofverylargescaleintegrated(VLSllcircuitsDesignerswereencouragedtothinkintermsoffivetwo-dimensional(2D)patternsThesepatternsdefinedthreestackedinterconnectionlayersonametaloxidesemiconductorfMOSlwaferandtheirmutualconnectionsthroughholesThepatternsdescrybedtheactualgeometrvoftheconnectionrunsandviaholesthatonewouldseewhenlookingdownontothecircuitchip,regardlessoftheexactprocessandnumberofmaskingstepsthatwereusedtoimplementthechip(seeMOSIS,2000)Inspiredbythissuccess,beginninginthe1970s,severalcompaniestriedtocreatelayeredmanufacturingformechanicalpartsAISObythemid1980s,severaU.Sgovernmentstudiesanalyzedthepossibilitiesofa“mechanicalMOSIS”(ManufacturingStudiesBoard,1990;Bouldin,1994;NSFworkshopI,1994,andII,1995)TheprospectsforamechanicalMOSISwerethusfrequentlylinkedtothefabricationprocessesinthelistsmentioned(Ashley,1991,1998;Heller,1991;Kruth,1991;Woo,1992,1993;AuandWright,1993;Kochan,1993;Kai,1994;UCLA,1994;WleissandPrinz,南通大学毕业设计附录(英文资料翻译)-3-1995;Coheneta1,1995;Dutta,1995;Jacobs,1992,1996;Beamaneta1,1997;Kumareta1,1998;Sachseta1,2000)TheintroductionofthefirstcommercialSFFtechnology-stereolithography-wasaccompaniedbytheadventoftheSTereoLithography(STL)representationofaCADobiect“STUisamodifiedCADformatthatsuitsasubsequentslicingoperactionandthe“downstream”laserscanningpathsonaphysicalSLAFDMorSLSmachineIsasoccerballround?TheanswerdependsonhowcarefullythebalIismeasuredNominally,itisaperfectsphereHoweveroncloserinspectiontheleatherissewntogetherfromabout20littlehexagonalpatchesandafewpentagonalpatchestocreatethecurvatureInrealityitisanapproximationtoasphereLikewisethe“STLformatapproximatestheboundarysurfacesofaCADmodelbybreakingitdownintointerconnectedsmalltriangles-aprocesscalledtessellationEachtriangleisrepresentedbythexyzcoordinatesofeachofitsthreevertices,enumeratedbytherighthandrulethatisCounterclockwise(ccw)orderasviewedfromtheoutsideofthebodvThevectornormaltothesurfaeeofeachtriangleisalsospecified1histessellatedsurfaceisstoredasan“STLfile”thisfilePerhapscontainingupto200,000triangles,issentovertheInternettoaprototypingshopAsshowninFigure41thistessellatedCADmodelisthenslicedlikeastackofplayingcardsFor3DSystemsmachinesthisisknownastheSLIorslicedfileOtherrapidprototypingmachinesusetheslicingtechniquebuthavetheirownfilecreationdetailsandnamesEachslicefortheimaginarysoccerballwillthusbeacircleHoweverbecauseofthetessellationprocedureitwillnotbeaperfectcircleTheslicingactioncutsthroughthetrianglesontheboundaryThus,eachcircularslice(ordiscwillactuallybeamultisidedpolygonrunninginsidethe“boundingcircle”ThenumberofsidesonthisinnerpolygonisofcourserelatedtohowfinelydividedtheoriginaltessellationwasmadeInsidetheSLAmachinethelaserfirstcreatestheouterboundaryofeachsliceandthen“weaves”acrosseachsliceinahatchingpatterntocreatethelayerThenumberofslicesandthestyleoftheweavingpatternarechosenbyeachrapidproTotypingshopEspeciallyforSLAandSLSacertainamountoftrialanderrorOrcraftspersonship,beginstoplayaroleatthisstageThisisreviewedinmoredetailoverthenextfewpages“STL,isnowthestandardexchangeformatforSFFprocessesHoweveritisinadequate南通大学毕业设计附录(英文资料翻译)-4-formanyreasonsFirst,thefilesarelargeduetothetessellationmethodSecondthereareredundanciesinthe“STLformat0neexampleofredundancyisasfollows:thetrianglesarerepresentedbythe“counterclockwiserule”sothatitisclearinwhichdirectiontheouter-surfacenormalactsHoweverithasalsobecomecustomarytospecifythesurfacevectoraswellInconsistencycanbeintroducedasaresultofthisredundancy,andnorulesexistforresolvingitMcMains(1996)describeshow“STLdoesnotcapturetopologyorconnectivity,makingitdifficulttofixsomeofthecommonerrorsfoundinfilessuchascracks,penetratingorextraneousfaces,andinconsistentsurfacenormalswithoutresortingtoguessingthedesignersoriginalintentMoregeneraldigitalinterchangeformatshavealsobeenusedwithSFlFTheseincludeACIS(1993)andIGES(Heller,1991)However,asdescribedinNSF(1995),problemsarisewiththeseformats,tooOneaspectofongoingresearchisthustoimprovethisrepresentationlanguage(McMainseta1,1998)12CASTINGMETHODSFORRAPIDPROTOTYPING