快速成型与虚拟成型在产品设计和制造中的应用毕业课程设计外文文献翻译.docx
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快速成型与虚拟成型在产品设计和制造中的应用毕业课程设计外文文献翻译.docx
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快速成型与虚拟成型在产品设计和制造中的应用毕业课程设计外文文献翻译
RapidPrototypingVersusVirtualPrototypinginProductDesignandManufacturing
C.K.Chua1,S.H.Teh1andR.K.L.Gay2
SchoolofMechanical&ProductionEngineering;and2GinticInstituteofManufacturingTechnology,NanyangTechnologicalUniversity,Singapore
Abstract
Rapidprototyping(RP)istheproductionofaphysicalmodelfromacomputermodelwithouttheneedforanyjigorfixtureornumericallycontrolled(NC)programming.Thistechnologyhasalsobeenreferredtoaslayermanufacturing,materialdepositmanufacturing,materialadditionmanufacturing,solidfreeformmanufacturingandthree-dimensionalprinting.Inthelastdecade,anumberofRPtechniqueshasbeendeveloped.Thesetechniquesusedifferentapproachesormaterialsinproducingprototypesandtheygivevaryingshrinkage,surfacefinishandaccuracy.Virtualprototyping(VP)istheanalysisandsimulationcarriedoutonafullydevelopedcomputermodel,thereforeperformingthesametestsasthoseonthephysicalprototypes.Itisalsosometimesreferredtoascomputer-aidedengineering(CAE)orengineeringanalysissimulation.Thispaperdescribesacomparativestudyofthetwoprototypingtechnologieswithrespecttotheirrelevanceinproductdesignandmanufacture.Thestudyinvestigatesthesuitabilityandeffectivenessofbothtechnologiesinthevariousaspectsofprototyping,whichispartandparcelofanoveralldesignandmanufacturingcycle.
Keywords:
Productdesign;Rapidprototyping;Virtualprototyping
1.Introduction
Rapidprototyping(RP)isemergingasakeyprototypingtechnologywithitsabilitytoproduceevencomplicatedpartsvirtuallyovernight.Itenablesproductdesignerstoshortentheproductdesignanddevelopmentprocess.Thecoming-of-ageofthistechnologyisclearlyreflectedintheinclusionofastereolithography(STL)filegeneratorinmost,ifnotall,CAD.systemstoday.TheSTLfileisthedefactostandardusedbyRPsystemsintherepresentationofthesolid3DCADmodels.
WhileRPisarelativelyyoungtechnology,virtualprototyping(VP)hasbeeninsteadydevelopmentsincethe1970sinmanyguises.Virtualprototypingistakentomeanthetestingandanalysisof3Dsolidmodelsoncomputingplatforms.Today,VPisoftentightlyintegratedwithCAD/CAMsoftwareandsometimesreferredtoasCAEpackages.Itprovidestheabilitytotestpartbehaviourinasimulatedcontextwithouttheneedtomanufacturethepartfirst[1].
2.DefinitionsofRPandVP
Rapidprototyping(RP)isawidelyusedterminengineering,particularlyinthecomputersoftwareindustrywhereitwasfirstcoinedtodescriberapidsoftwaredevelopment.
Thistermhasalsobeenadoptedbythemanufacturingindustrytocharacterisetheconstructionofphysicalprototypesfromasolid,powder,orliquidinashortperiodoftimewhencomparedto“traditional”subtractivemachiningmethods.Thistechnologyhasalsobeenvariouslyreferredtoaslayermanufacturing,materialdepositmanufacturing,materialadditionmanufacturing,solidfreeformmanufacturingandthreedimensionalprinting[2].
Virtualprototyping(VP)referstothecreationofamodelinthecomputer,oftenreferredtoasCAD/CAM/CAE.Virtualorcomputationalprototypingisgenerallyunderstoodtobetheconstructionmodelsofproductsforthepurposeofrealisticgraphicalsimulation[1].Inthispaper,VPwillrefertothesimulation,virtualrealityandmanufacturingprocessdesigndomains[3].
Nevertheless,therearemanyareaswherethedistinctionbetweenRPandVPisblurred.AsRPsystemsrelyonCADsystemstogeneratethefilesneededtoproducetheprototype,itwouldseemthatRPisadownstreamprocessfromVPintheproductorpartdevelopmentcycle.Indeed,Pratt’sdefinitionofVPrevealsthefactthatVPisatermwhichislooselyusedintheprototypingcommunity.Assuch,itwouldbeappropriatetoclearlydefinebothRPandVP.
Rapidprototypingwillbetakentomean,asabove,theproductionofaphysicalmodelfromacomputermodelwithouttheneedofanyjigorfixtureorNCprogramming.ThisalsoincludesotherrelatedprocessesandapplicationswhichuseRP-producedobjects,suchasrapidtooling.
Similarly,VPisdefinedasthesubsequentmanipulationofasolidCADmodelasasubstituteforaphysicalprototypeforthepurposesofsimulationandanalysis,andisnotinclusiveoftheconstructionofthesolid3Dmodel.VPincludesthefollowingfunctions:
1.Finiteelementanalysis.
2.Mechanicalform,fitandinterferencechecking.
3.Mechanicalsimulation.
4.Virtualrealityapplications.
5.Cosmeticmodelling.
6.Assemblability.
TherelationshipsbetweenRPandVPareshowninFig.1.
Fig.1.ClassificationofRPandVP
3.PrototypinginSingapore
Twoselectedmulti-nationalcompanies(oneAmericanandoneFrench)basedinSingaporewithsignificantproductdevelopmentactivitiesshoweddifferingapproachestobothRPandVP.BothuseRPintheirprototypingactivities.
Thefirstcompany,B,placedmoreemphasisonvirtualprototyping.Itmanufacturestelecommunicationsequipmentsuchaspagersandhandphones.Itismovingallprototypingapplicationsupstream,whichistomoveprototypingfromRPtoVP.Atpresent,theirRPmodelsareusedonlyforproofofconceptandmarketingpurposes.OtherprototypingactivitiesarebeingcarriedoutwithVP.
Thesecondcompany,C,manufacturesconsumerelectronicsproductssuchastelevisionsets,videocassetterecordersandtelephones.ItusesVPonlyasatooltocreateasolid3Dmodel.Fromthesolid3Dmodel,CgeneratestheSTLfileneededtoproducetheRPprototype.CompanyCthenusestheRPpartasamasterforsiliconerubbermouldstoproducealimitednumberofphysicalABS(polyacrylonitritebutadienestyrene)prototypesforthevariousprototypingtestsandsimulation.
CompanyBintendstomovemoreprototypingtoVP,ratherthanusingphysicalmodels.Virtualprototypingallowsforimprovementsinreliabilityandqualityaswellasreducingcosts.ManipulationofvirtualprototypesmakesiteasierforBtoimplementdesignimprovementscomparedtoaniterativecycleusingphysicalprototypes.
CompanyBdraftstheCADmodelsinPro/ENGINEER,thenusesPatrantopre-processthemodels.Staticfinite-elementanalysis(FEA)iscarriedoutwithABAQUSStandardwhereasdynamicscenariosareanalysedwithABAQUSExplicit.ALIAS/Wavefrontisusedforcosmeticmodellingwhenpresentingdifferentconceptualandactualdesigns.
ThebulkoftheVPcarriedoutbyBusesFEA,whichtypicallytakes4–6weeksforapagerdesign.OfalltheFEAcarriedout,themajorityareconcentratedonstructuralstrength(static)analysisanddroptest(dynamic)analysis.Vibrationtestsareoccasionallycarriedout.Somecosmeticmodellingiscarriedout,butusuallyonlyforpresentationpurposes.
Finite-elementanalysisisusedtoinvestigatethefollowingproblems:
Relativecomparisonofdifferentdesignoptions;toseehowonedesigncomparestoanother.Possiblefailuremodesare:
1.Toevaluateadesignchangeordesigncorrection.
2.Toassessthepossibilityoffailure,basedonpastexperience.
3.Tomakesomeeducated-guesscorrelationwithphysicaltesting.
4.Totrytoidentifywhatinitiatedafailure.
AccordingtoB,thedrawbackofVPisthatitcannotsimulateprocessproblemsefficientlyandeffectively.TheaccuracyofFEAisalsolimitedbecauseoftheinconsistentbehaviourof
material.TheamountofcomputingpoweralsodeterminestheaccuracyofFEA.
TheapplicationofRPisratherlimitedinB.Thein-houselaminatedobjectmanufacturing(LOM)RPsystemisusedtoproducedesignprototypesforproofofconceptonly,andnot
geometricalprototypes.
CompanyCusesRPheavily,buthasverylittleVP.ThepartsproducedusingRPrangefromaudioproductsto29-in.televisioncasings.Typically,ittakes1yearfromtheconceptionoftheproducttothesaleoftheproduct.CompanyCaimstoprototypeall(mostlyplastic)partsbyRP.Acomparisonbetweennumericallycontrolled(NC)machiningofprototypesfromABSagainstRPisshowninTable1.CompanyCprojected50%savingsusinganin-houseRPsystemversusanNCmachiningsystem.
CADmodelsarecreatedusingI-DEAS.The.STLformatisthencreatedforproductionoftheRPpart.ThemainpurposeoftheRPpartsistoverifythedesign.Rapidprototypingpartsareusedforthefollowingfunctions:
1.Formfitting.
2.Ergonomicscheck.
3.Proofofconcept(toconfirmdesignwithindustrial
designers).
4.Manufacturability(designfortooling,designforassemblability).
5.Reliabilitycheck(whetherpartdislodgesorbreakswhenforceapplied,especiallysnap-oncovers).
6.Kinematiccheck.
CompanyCofferssomeinsightintothelimitationsofVP,inthatVPisunabletomodel:
1.Tactilefeeling(forbuttons)notquantified;maybeabletoVPifabletoquantify“pressing”force.
2.Assemblability(e.g.PCBsinsertedatanangle,difficulttovisualise).
4.CaseStudy1:
PrototypingofaTelephoneHandset
Thiscasestudyinvestigatesthedesignverification,assembly,interferencecheckandformfittingaspectsofboththeRPandVPmodel.TheproductionABS,RPandVPpartsormodelswereevaluatedintheaboveaspects.TheRPsystemusedhereisthestereolithographyapparatus(SLA).BoththeABSandRPpartsareshowninFig.2.InspectionoftheRPpartsrevealthat:
1.ThesurfacefinishwasmuchpoorerthanintheABSpart.
2.Warpagewasclearlyevident(seeFig.3).
4.1DesignVerification
Asatruedimensionalphysicalpart,theRPmodelisabletogivethedesignerasenseofsizeestimation.ThejudgementofaVPpartcanbeerroneousbecausepartsareoftenautomaticallysizedtofittheviewingwindow.Anotheradvantage
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