英文模具论文_A NOVEL INTEGRATED SYSTEM FOR RAPID PRODUCT DEVELOPMENT

一种快速成型的新系统

JournalofAdvancedManufacturingSystems

Vol.3,No.2(2004)141–150

cWorldScienti cPublishingCompany

ANOVELINTEGRATEDSYSTEMFORRAPIDPRODUCT

DEVELOPMENT

HONGBOLAN , ,YUCHENGDING,JUNHONGandDIANLIANGWU

SchoolofMechanicalEngineering,Xi’anJiaotongUniversity

Xi’an710049,People’sRepublicofChina Tel.:+86-29-82663202 lanhb@

Thispaperpresentsanovelintegratedsystemofrapidproductdevelopmentforreduc-ingthetimeandcostofproductdevelopment.Thesystemiscomposedoffourbuildingblocks—digitalprototype,virtualprototype,physicalprototypeandrapidtoolingman-ufacturingsystem.Itcanaide ectivelyinproductdesign,analysis,prototype,mould,andmanufacturingprocessdevelopmentbyintegratingcloselythevariousadvancedmanufacturingtechnologieswhichinvolvethe3DCAD,CAE,reverseengineering,rapidprototypingandrapidtooling.Furthermore,twoactualexamplesareprovidedtoillus-tratetheapplicationofthisintegratedsystem.Theresultsindicatethatthesystemhasahighpotentialtoreducefurtherthecycleandcostofproductdevelopment.

Keywords:Rapidproductdevelopment;rapidprototyping;integratedsystem.

1.Introduction

Duetothepressureofinternationalcompetitionandmarketglobalizationinthe21stcentury,therecontinuestobestrongdrivingforcesinindustrytocompetee ectivelybyreducingmanufacturingtimesandcostswhileassuringhighqual-ityproductsandservices.Currentindustriesarefacingthenewchallenges:quickresponsetobusinessopportunityhasbeenconsideredasoneofthemostimpor-tantfactorstoensurecompanycompetitiveness;manufacturingindustryisevolvingtowarddigitalization,networkandglobalization.Therefore,newproductsmustbemorequicklyandcheaplydeveloped,manufacturedandintroducedtothemarket.Inordertomeetthedemandofrapidproductdevelopment,thevariousnewtech-nologiessuchasreverseengineering(RE),3DCAD,rapidprototyping(RP),andrapidtooling(RT)haveemergedandareregardedaskeyenablingtoolswiththeabilitytoshortentheproductdevelopmentandmanufacturingtime.Forexample,ithasbeenclaimedthatRPcancutnewproductdevelopmentcostsbyupto70%andthetimetomarketby90%.1Intheformofabetterdesign,moredesignpossi-bilities,a3DCADmodelcanbeshowntothecustomerforapprovalandprevents Correspondingauthor.

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misunderstandings.Avirtualprototypingisemployedtoguideinoptimizationoftheproductdesignandmanufacturingprocessplanning,whichmayresultintheaccuratedeterminationoftheprocessparameters,andreducethenumberofcostlyphysicalprototypeiterations.Rapidtoolingtechniqueo ersafastandlowcostmethodtoproducemoulds,andshowsahighpotentialforfasterresponsetomarketdemands.Whenproperlyintegratedamong3DCAD,CAE,RE,RPandRT,thesetechnologieswillplayamuchmoreimportantroletoreducefurtherthedevelopmentcycleandcostoftheproductproduction.Onthebasisofabovetech-nologies,anovelintegratedsystemofrapidproductdevelopmentistobefoundedsoastomeettherequirementofrapidproductdevelopment.

2.ArchitectureoftheIntegratedDevelopmentSystem

Thedevelopmentprocessfrominitialconceptualdesigntocommercialproductisaniterativeprocesswhichincludes:productdesign;analysisofperformance,safetyandreliability;productprototypingforexperimentalevaluation;anddesignmodi ca-tion.Therefore,anystepofthenewproductdevelopmentprocesshasadirectandstrongin uenceontime-to-marketinshortorder.Agoodproductdevelopmentsystemmustenabledesignersordesignteamstoconsiderallaspectsofproductdesign,manufacturing,sellingandrecyclingattheearlystageofthedesigncycle.Sothatdesigniterationandchangescanbemadeeasilyande ectively.Themore uentthefeedbackisthehigherpossibilityofsuccessthesystemhas.Designformanufacturing(DFM)andconcurrentengineering(CE)necessitatethatproductandprocessdesignbedevelopedsimultaneouslyratherthansequentially.2

Theintegratedsystemofrapidproductdevelopmentiscomposedoffourmod-ules:digitalprototype,virtualprototype,physicalprototypeandrapidtooling.Theproductdevelopmentstartsfromthecreationofa3DCADmodelusingaCADsoftwarepackage.Atthatstage,theproductgeometryisde nedanditsaestheticanddimensionalcharacteristicsareveri ed.Themainfunctionofdigi-talprototypeistoperform3DCADmodelling.TheCADmodelisregardedasacentralcomponentofthewholesystemorprojectinformationbasewhichmeansthatinalldesign,analysisandmanufacturingactivitiesthesamedataisutilized.Theproductanditscomponentsaredirectlydesignedona3DCADsystem(e.g.Pro/Engineer,Unigraphics,CATIA,IDEAS,etc.)duringthecreativedesign.Ifaphysicalpartisready,themodelcanbeconstructedbythereverseengineeringtechnique.REisamethodologyforconstructingCADmodelsofphysicalpartsbydigitizinganexistingpart,creatingadigitalmodelandthenusingittomanufacturecomponents.3REcanreducethedevelopmentcyclewhenredesignsbecomenec-essaryforimprovedproductquality.Preexistingpartswithfeaturesforimprovedperformancecanbereadilyincorporatedintothedesiredpartdesign.Therefore,itisveryusefulincreatingtheCADmodelofanexistingpartwhentheengineeringdesignislostorhasgonethroughmanydesignchanges.Whenadesignercre-atesanewdesignusingmock-up,itisalsonecessarytoconstructtheCADmodel

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ofthemock-upforfurtheruseofthedesigndatainanalysisandmanufacturing.ThethreeprimarystepsinREprocessarepartdigitization,featuresextraction,andCADmodelling.Partdigitizationisaccomplishedbyavarietyofcontactornon-contactdigitizers.Therearevariouscommercialsystemsavailableforpartdig-itization.Thesesystemsrangefromcoordinatemeasuringmachine(CMM),laserscannerstoultrasonicdigitizers.Theycanbeclassi edintotwobroadcategories:sertriangulationscanner(LTS),magneticresonanceimages(MRI),andcomputertomography(CT)arecommonlyusedasnon-contactdevices.ContactdigitizersmainlyhaveCMMandcross-sectionalimagingmeasure-ment(CIM).Featureextractionisnormallyachievedbysegmentingthedigitizeddataandcapturingsurfacefeaturessuchasedges.Partmodellingisful ledthrough ttingavarietyofsurfacestothesegmenteddatapoints.4

Inordertoreducetheiterationsofdesign-prototype-testcycles,increasetheproductprocessandmanufacturingreliability,itisnecessarytoguideinoptimiz-ingtheproductdesignandmanufacturingprocessthroughvirtualprototype(VP).VPisaprocessofusing3DCADmodel,inlieuofaphysicalprototype,fortestingandevaluationofspeci puteraidedengineering(CAE)analysisisanintegralpartoftime-compressiontechnologies.Varioussoftwaretoolsavailable(i.e.ANSYS,MARC,I-DEAS,AUTOFORM,DYNAFORM,etc.)canspeedupthedevelopmentofnewproductsbyinitiatingdesignoptimizationbeforephysicalprototypesarebuilt.TheCADmodelscanbetransferredtoaCAEenvironmentforananalysisoftheproductfunctionalperfor-manceandofthemanufacturingprocessesforproducingtheproduct’scomponents.Ithasalsoproventobeofgreatvalueinthedesignoptimizationofpartgeometry,todetermineitsdimensionsandtocontrolwarpageandshrinkagewhileminimizingprocess-inducedresidualstressesanddeformations.6Virtualmanufacturingsystem(VM)isthenaturalextensionofCAE.Itsimulatestheproductfunctionalityandtheprocessesforproducingitpriortothedevelopmentofphysicalprototypes.VMenablesadesignertovisualizeandoptimizeaproductprocesswithasetofprocessparameters.Thevisualizationofavirtuallysimulatedpartpriortophysi-calfabricationhelpstoreduceunwantedprototypeiterations.Therefore,aproductvirtualmanufacturingsystemmayresultinaccuratedeterminationoftheprocessparameters,andreducethenumberofcostlyphysicalprototypeiterations.3DCADmodelandVPallowmostproblemswithun ttingtobecomeobviousearlyintheproductdevelopmentprocess.Assembliescanbeveri edforinterferenceasVPcanbeexercisedthrougharangeoftasks.StructureandthermalanalysiscanbeperformedonthesamemodelemployingCAEapplicationsaswellassimulatingdown-streammanufacturingprocesses.7ItisclearthatVPincreasesprocessandproductreliability.AlthoughVPisintendedtoensurethatunsuitabledesignsarerejectedormodi ed,inmanycases,avisualandphysicalevaluationoftherealcom-ponentisneeded.Thisoftenrequiresphysicalprototypetobeproduced.Hence,oncetheVPis nished,themodelmayoftenbesentdirectlytophysicalfabrication.

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TheCADmodelcanbedirectlyconvertedtothephysicalprototypeusingaRPtechniqueorhigh-speedmachining(HSM)process.The3DCADmodelistobeexportednotonlyintheSTLformatwhichisconsideredthedefactostandardforinterfacingCADandRPsystems,butalsointheNCcodingwhichcanbeusedbyHSM.HSMhasapotentialforrapidproducingplasterorwoodenpatternforRT.RPisanewformingprocesswhichfabricatesphysicalpartslayerbylayerundercomputercontroldirectlyfrom3DCADmodelsinaveryshorttime.Incontrasttotraditionalmachiningmethods,themajorityofrapidprototypingsystemstendtofabricatepartsbasedonadditivemanufacturingprocess,ratherthansubtractionorremovalofmaterial.Therefore,thistypeoffabricationisunconstrainedbythelim-itationsattributedtoconventionalmachiningapproaches.8TheapplicationofRPtechniqueasausefultoolcanprovidebene tsthroughouttheprocessofdevelopingnewproducts.Speci cally,thereareseriousbene tsthatRPcanbringintheareasofmarketresearch,salessupport,promotionalmaterial,andtheever-importantproductlaunch.PhysicalRPcanalsobecomeapowerfulcommunicationstooltoensurethateveryoneinvolvedinthedevelopmentprocessfullyunderstandsandappreciatestheproductbeingdeveloped.Hence,itcanhelptoreducesubstan-tiallytheinevitablerisksintheroutefromproductconcepttocommercialsuc-cess,andhelpshortentime-to-market,improvequalityandreducecost.Overthelast20years,RPmachineshavebeenwidelyusedinindustry.TheRPmethodscommerciallyavailableincludeStereolithgraphy(SLA),SelectiveLaserSintering(SLS),FusedDepositionManufacturing(FDM),LaminatedObjectManufacturing(LOM),BallisticParticleManufacturing(BMP),andThree-DimensionalPrinting(3Dprinting),9etc.

Oncethedesignhasbeenaccepted,therealizationoftheproductionlinerep-resentsamajortaskwithalongleadtimebeforeanyproductcanbeputtothemarket.Inparticular,thepreparationofcomplextoolingisusuallyinthecriticalpathofaprojectandhasthereforeadirectandstrongin uenceontime-to-market.Inordertoreducetheproductdevelopmenttimeandcost,thenewtechniqueofRThasbeendeveloped.RTisatechniquethatcantransformtheRPpatternsintofunctionalparts,especiallymetalparts.Ito ersafastandlowcostmethodtopro-ducemouldsandfunctionalparts.Furthermore,theintegrationofbothRPandRTindevelopmentstrategypromotestheimplementationofconcurrentengineeringincompanies.NumerousprocesseshavebeendevelopedforproducingdiesfromRPsystem.TheRTmethodscangenerallybedividedintodirectandindirecttoolingcategories,andalsosoft( rm)andhardtoolingsubgroups.IndirectRTrequiressomekindsofmasterpatterns,whichcanbemadebyconventionalmethods(e.g.HSM),ormorecommonlybyanRPprocesssuchasSLAorSLS.DirectRT,asthenamesuggests,involvesthemanufacturingofatoolcavitydirectlyonaRPsys-tem,henceeliminatingtheintermediatestepofgeneratingapattern.Softtoolingcanbeobtainedviareplicationfromapositivepatternormaster.Softtoolingisassociatedwithlowcosts;usedforlowvolumeproductionandusesmaterialsthathavelowhardnesslevelssuchassilicones,epoxies,lowmeltingpointalloys,etc.10

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RTVsiliconerubbermoulds,epoxymoulds,metalsprayingmoulds,etc.aresomeofthesetypicalsoftmoldings.Hardtoolingisassociatedwithhighervolumeofpro-duction,andtheuseofmaterialsofgreaterhardness.Keltoolprocess,Quickcastprocess,andtheExpressToolprocessaresomeofthesehardtoolings.Electricaldischargemachining(EDM)seemstobeaninterestingareainwhichrapidtooling ndsapotentialapplication.SomemethodsofmakingEDMelectrodesbasedonRPtechniquehavedeveloped,suchasabradingprocess,copperelectroformingandnetshapecasting,etc.Onthebasisoftheabovetechniques,anovelintegratedsystemofrapidproductdevelopmentistobeproposed.ItsoverallarchitectureisshowninFig.1.

3.CaseStudies

3.1.Casestudy1:Impeller

Atotalofthirtyplasticimpellers,witharelativelycomplexgeometry,wererequiredbyacustomerwithin fteenworkingdaysfromthereceiptofa2DCADmodel.Thereweremanyfactorstobeconsideredindecidingthemostappropriaterouteforproducingtheimpellers.Thesefactorsmainlyinvolvedcost,lead-time,thenum-berofpartsrequired,the nalmaterialfortheparts,andthepartgeometry.Inordertomaximizethebene tsintermsoftimeandcostreductionfortheparts,itwasdecidedtousesiliconrubbermouldandthepartswereeventuallyproducedbyvacuumcastingprocess.Siliconrubbermouldisaneasy,relativelyinexpensiveandfastwaytofabricateprototypeorpre-productiontools.Itcanbeutilizedformouldingpartsinwax,polyurethane,ABS,andafewepoxymaterials.Theprocessisbestsuitedforprojectswhereform, t,orfunctionaltestingcanbedonewithamaterialwhichmimicsthecharacteristicsoftheproductionmaterial.Thecast-ingpartswith nedetailsandverythinwallscanbeeasilyandrapidlyproduced.Thewholeprocess owinvolvedthe3DCADmodelling,producingmasterpattern(RPprototype),siliconrubbermould,andcastinggreenparts.Thetimesequenceforthefabricationofimpellerswasdescribedasfollows.Duetothecomplexityoftheimpeller,thetaskofgeneratingthe3DCADmodelusingPro/Engineersoftwarepackagetookalmost3calendardays.ThemasterpatternforthisprojectwasbuiltonaSPS600machinein2calendardays.SLprocesswaschosenbecauseitwascoste ectiveandthesurface nishwasgood.Thenextstepinvolvedcreatingaroom-temperaturevulcanized(RTV)siliconerubbermoldwhichwascompletedwithinanadditional3calendardays.Finally,theABSmaterialswerecastintosiliconrub-bermouldunderthevacuumcastingcondition,andthegreenpartswereachievedin4calendardays.Therequired30componentswereproducedsuccessfullyandcompletedin12calendardays.TheprimaryprocessstagesareillustratedinFig.2.Theseimpellersonlycostabout5thousandRMBandtook12workingdays.Con-sequently,incontrasttothetraditionaldevelopmentmode,theimpellersdevelopedusingtheintegratedsystemcancutcostbyupto50%andthetime-to-marketby

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Fig.1.Architectureoftheintegrateddevelopmentsystem.

75%.Whenevaluatedagainstsatisfyingurgentrequirementwithrespecttotime,theprocedureisclearlyworthpursuing,asindicatedbythecasestudydescribedabove.Gongfroma3DCADsolidmodelingtofullyfunctionalproductionimpellersinlessthan12workingdaysiscertainlyextraordinary.Withproperimplementationoftheprocessbyquali edpersonnel,workingwithinthescopeoftheconstraints

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(a) CAD model

(b) RP prototype

(d) Plastic impellers

Fig.2.(c) Silicon rubber mould

Developmentprocedureoftheplasticimpellersbasedontheintegratedsystem.noted,theacceptanceandadvancementoftheintegratedmanufacturingmethodislikelytogrow.

3.2.Casestudy2:Mannequin

Tenplasticmannequinswererequiredbyaclientinthreemonthsfromthereceiptoftheplastermodeloftheemulationalbody.Thiscomponentwasanidealcan-didateforusingintegratedsystemtodevelopment,withaverycomplexsurfaceandarequirementforonly10parts.Inordertoproducetheplasticmannequin,thevarioustechnologiesincludingreverseengineering,3DCAD,rapidprototypingandrapidtoolingwereusedtocompletemodelmeasuring,surfacesreconstruct-ing,3DCADmodelling,prototypeandmouldbuilding.Thewholedevelopmentworkwaspresentedbelow.The rststepoftheprojectwastoconstructaCADmodeloftheemulationalbodybyREprocess.ATOSmeasuringequipmentmadeinGOMInc.whichhasahighscanning(10,000points/sec)andcanmeasuremodels

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(a) Point clouds of the

body model(b) Surface model ofthe body (c) The complete CAD

solid model

(f) The plastic mannequin

Fig.3.(e) The silicone rubbermould of the head(d) RP pattern Development owoftheplasticmannequinsbasedontheintegratedsystem.

inawiderangefrom500mmto10mm,wasemployedtocapturethedigitizeddataoftheplastermold.Figure3(a)showsthepointcloudsofthebodymodel.Thesubsequentprocesswastoperformsurfacesreconstructing.Tospeedthisprocess,aspecialreverseengineeringprogram,calledCopyCAD(DelcamInc.),wasusedtocreatequicklyandeasilytheCADsurfacesfromthedigitizeddata.Aftersurfacesreconstructing,manyerrorsintheoriginalmodelandthejointsmustbemodi edbyPowerShapesoftwarepackage(anothersoftwareofDelcamInc.).ThesurfacesmodelofthebodyisrepresentedinFig.3(b).Tofabricateeasily,thesurfacemodelwasdividedinto11individualcomponentswhichincludedthehead,body,upperarms,forearms,tights,shanksandfeetusingPro/Engineersoftwarepackage.Sub-sequently,everysurfacemodelwasconvertedtoasolidmodel,andmanyholesandslotsneededtobedesignedfor xingjointssuchasshoulder,knees,etc.Then,thesolidpartsandjointswereassembledtoformthesolidmodeloftheemulationalbody.Figure3(c)illustratesthecompletedCADsolidmodel.TheRPprototypesofthesecomponentswerebuiltonaLPS600machine.TheassemblyRPbodymodelisshowninFig.3(d).Inaddition,siliconrubbermouldsofthesecompo-nentswerefabricatedforproducingthegreenparts.Finally,therequired10plastic

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mannequinswereproducedsuccessfullyandtheprojectwascompletedinabout12weeks.Figures3(e)and(f)describerespectivelythesiliconrubbermouldofhalfheadandthegreenproduct.Thecaseindicatestherapiddevelopmentoflargeproductandcomplexsurfacescanberealizedquicklyfollowingtheintegrateddevel-opmentmode.

4.Conclusion

Inthispaper,wehavepresentedanintegratedsystembasedonRPforrapidproductdeveloping.Thesystemconsistsoffourmodules:digitalprototype,virtualproto-type,physicalprototypeandrapidtooling.Itemploysfullyandintegratescloselythevariousadvancedmanufacturingtechnologieswhichinvolvethe3DCAD,RE,CAE,RP,andRT.Inthissystem,theprocedureofdevelopmentfromdesigntoendproductisworkedstepbystep:design,analysis,rapidprototypeandtooling.Byevaluatingthewholeprocessanditsvariouscomponents,andcomparingthemwithtraditionalprocess,ithasbeenclearthatonecanreapbene tsinvariousways.Thesystemcane ectivelycompressthedesignandmanufacturingcycletimeandreducethedevelopmentcost,ingthisintegratedsystemtodevelopnewproductshowsahighpotentialforfasterresponsetomarketandcustomers’demands.Asaresult,itwillplayamoreandmoreimportantroletoreducethemanufacturingcycleandcostofproductdevel-opmentinthefuture.

Acknowledgements

ThisresearchwassupportedbyTheNationalHighTechnologyResearchandDevelopmentProgram(863Program)undertheproject“Theintegratedman-ufacturingtechnologyandequipmentsofrapidtoolingforrapidproductdevel-opment”(No.2001AA421270),and“TenthFive-Year”NationalKeyTechnologiesR&DProgramofChinaundertheproject“Researchanddemonstratorofrapidmanufacturingintegratedsystembasedonrapidprototyping”(No.2001BA205B10-CMTT1001).

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