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ANOVELINTEGRATEDSYSTEMFORRAPIDPRODUCTDEVELOPMENT

Thispaperpresentsanovelintegratedsystemofrapidproductdevelopmentforreducingthetimeandcostofproductdevelopment.Thesystemiscomposedoffourbuildingblocks—digitalprototype,virtualprototype,physicalprototypeandrapidtoolingmanufacturingsystem.Itcanaideffectivelyinproductdesign,analysis,prototype,mould,andmanufacturingprocessdevelopmentbyintegratingcloselythevariousadvancedmanufacturingtechnologieswhichinvolvethe3DCAD,CAE,reverseengineering,rapidprototypingandrapidtooling.Furthermore,twoactualexamplesareprovidedtoillustratetheapplicationofthisintegratedsystem.Theresultsindicatethatthesystemhasahighpotentialtoreducefurtherthecycleandcostofproductdevelopment.

Keywords:Rapidproductdevelopment;rapidprototyping;integratedsystem.

1.Introduction

Duetothepressureofinternationalcompetitionandmarketglobalizationinthe21stcentury,therecontinuestobestrongdrivingforcesinindustrytocompeteeffectivelybyreducingmanufacturingtimesandcostswhileassuringhighqualityproductsandservices.Currentindustriesarefacingthenewchallenges:quickresponsetobusinessopportunityhasbeenconsideredasoneofthemostimportantfactorstoensurecompanycompetitiveness;manufacturingindustryisevolvingtowarddigitalization,networkandglobalization.Therefore,newproductsmustbemorequicklyandcheaplydeveloped,manufacturedandintroducedtothemarket.Inordertomeetthedemandofrapidproductdevelopment,thevariousnewtechnologiessuchasreverseengineering(RE),3DCAD,rapidprototyping(RP),andrapidtooling(RT)haveemergedandareregardedaskeyenablingtoolswiththeabilitytoshortentheproductdevelopmentandmanufacturingtime.Forexample,ithasbeenclaimedthatRPcancutnewproductdevelopmentcostsbyupto70%andthetimetomarketby90%.1Intheformofabetterdesign,moredesignpossibilities,a3DCADmodelcanbeshowntothecustomerforapprovalandpreventsmisunderstandings.Avirtualprototypingisemployedtoguideinoptimizationoftheproductdesignandmanufacturingprocessplanning,whichmayresultintheaccuratedeterminationoftheprocessparameters,andreducethenumberofcostlyphysicalprototypeiterations.Rapidtoolingtechniqueoffersafastandlowcostmethodtoproducemoulds,andshowsahighpotentialforfasterresponsetomarketdemands.Whenproperlyintegratedamong3DCAD,CAE,RE,RPandRT,thesetechnologieswillplayamuchmoreimportantroletoreducefurtherthedevelopmentcycleandcostoftheproductproduction.Onthebasisofabovetechnologies,anovelintegratedsystemofrapidproductdevelopmentistobefoundedsoastomeettherequirementofrapidproductdevelopment.

2.ArchitectureoftheIntegratedDevelopmentSystem

Thedevelopmentprocessfrominitialconceptualdesigntocommercialproductisaniterativeprocesswhichincludes:productdesign;analysisofperformance,safetyandreliability;productprototypingforexperimentalevaluation;anddesignmodification.Therefore,anystepofthenewproductdevelopmentprocesshasadirectandstronginfluenceontime-to-marketinshortorder.Agoodproductdevelopmentsystemmustenabledesignersordesignteamstoconsiderallaspectsofproductdesign,manufacturing,sellingandrecyclingattheearlystageofthedesigncycle.Sothatdesigniterationandchangescanbemadeeasilyandeffectively.Themorefluentthefeedbackisthehigherpossibilityofsuccessthesystemhas.Designformanufacturing(DFM)andconcurrentengineering(CE)necessitatethatproductandprocessdesignbedevelopedsimultaneouslyratherthansequentially.

Theintegratedsystemofrapidproductdevelopmentiscomposedoffourmodules:digitalprototype,virtualprototype,physicalprototypeandrapidtooling.Theproductdevelopmentstartsfromthecreationofa3DCADmodelusingaCADsoftwarepackage.Atthatstage,theproductgeometryisdefinedanditsaestheticanddimensionalcharacteristicsareverified.Themainfunctionofdigitalprototypeistoperform3DCADmodelling.TheCADmodelisregardedasacentralcomponentofthewholesystemorprojectinformationbasewhichmeansthatinalldesign,analysisandmanufacturingactivitiesthesamedataisutilized.Theproductanditscomponentsaredirectlydesignedona3DCADsystem(e.g.Pro/Engineer,Unigraphics,CATIA,IDEAS,etc.)duringthecreativedesign.Ifaphysicalpartisready,themodelcanbeconstructedbythereverseengineeringtechnique.REisamethodologyforconstructingCADmodelsofphysicalpartsbydigitizinganexistingpart,creatingadigitalmodelandthenusingittomanufacturecomponents.REcanreducethedevelopmentcyclewhenredesignsbecomenecessaryforimprovedproductquality.Preexistingpartswithfeaturesforimprovedperformancecanbereadilyincorporatedintothedesiredpartdesign.Therefore,itisveryusefulincreatingtheCADmodelofanexistingpartwhentheengineeringdesignislostorhasgonethroughmanydesignchanges.Whenadesignercreatesanewdesignusingmock-up,itisalsonecessarytoconstructtheCADmodelofthemock-upforfurtheruseofthedesigndatainanalysisandmanufacturing.ThethreeprimarystepsinREprocessarepartdigitization,featuresextraction,andCADmodelling.Partdigitizationisaccomplishedbyavarietyofcontactornon-contactdigitizers.Therearevariouscommercialsystemsavailableforpartdigitization.Thesesystemsrangefromcoordinatemeasuringmachine(CMM),laserscannerstoultrasonicdigitizers.Theycanbeclassifiedintotwobroadcategories:contactandnon-contact.Lasertriangulationscanner(LTS),magneticresonanceimages(MRI),andcomputertomography(CT)arecommonlyusedasnon-contactdevices.ContactdigitizersmainlyhaveCMMandcross-sectionalimagingmeasurement(CIM).Featureextractionisnormallyachievedbysegmentingthedigitizeddataandcapturingsurfacefeaturessuchasedges.Partmodellingisfulfiledthroughfittingavarietyofsurfacestothesegmenteddatapoints.

Inordertoreducetheiterationsofdesign-prototype-testcycles,increasetheproductprocessandmanufacturingreliability,itisnecessarytoguideinoptimizingtheproductdesignandmanufacturingprocessthroughvirtualprototype(VP).VPisaprocessofusing3DCADmodel,inlieuofaphysicalprototype,fortestingandevaluationofspecificcharacteristicsofaproductoramanufacturingprocess.ItisoftencarriedoutbyCAEandvirtualmanufacturingsystem.Computeraidedengineering(CAE)analysisisanintegralpartoftime-compressiontechnologies.Varioussoftwaretoolsavailable(i.e.ANSYS,MARC,I-DEAS,AUTOFORM,DYNAFORM,etc.)canspeedupthedevelopmentofnewproductsbyinitiatingdesignoptimizationbeforephysicalprototypesarebuilt.TheCADmodelscanbetransferredtoaCAEenvironmentforananalysisoftheproductfunctionalperformanceandofthemanufacturingprocessesforproducingtheproduct’scomponents.Ithasalsoproventobeofgreatvalueinthedesignoptimizationofpartgeometry,todetermineitsdimensionsandtocontrolwarpageandshrinkagewhileminimizingprocess-inducedresidualstressesanddeformations.Virtualmanufacturingsystem(VM)isthenaturalextensionofCAE.Itsimulatestheproductfunctionalityandtheprocessesforproducingitpriortothedevelopmentofphysicalprototypes.VMenablesadesignertovisualizeandoptimizeaproductprocesswithasetofprocessparameters.Thevisualizationofavirtuallysimulatedpartpriortophysicalfabricationhelpstoreduceunwantedprototypeiterations.Therefore,aproductvirtualmanufacturingsystemmayresultinaccuratedeterminationoftheprocessparameters,andreducethenumberofcostlyphysicalprototypeiterations.3DCADmodelandVPallowmostproblemswithunfittingtobecomeobviousearlyintheproductdevelopmentprocess.AssembliescanbeverifiedforinterferenceasVPcanbeexercisedthrougharangeoftasks.StructureandthermalanalysiscanbeperformedonthesamemodelemployingCAEapplicationsaswellassimulatingdown-streammanufacturingprocesses.ItisclearthatVPincreasesprocessandproductreliability.AlthoughVPisintendedtoensurethatunsuitabledesignsarerejectedormodified,inmanycases,avisualandphysicalevaluationoftherealcomponentisneeded.Thisoftenrequiresphysicalprototypetobeproduced.Hence,oncetheVPisfinished,themodelmayoftenbesentdirectlytophysicalfabrication.

TheCADmodelcanbedirectlyconvertedtothephysicalprototypeusingaRPtechniqueorhigh-speedmachining(HSM)process.The3DCADmodelistobeexportednotonlyintheSTLformatwhichisconsideredthedefactostandardforinterfacingCADandRPsystems,butalsointheNCcodingwhichcanbeusedbyHSM.HSMhasapotentialforrapidproducingplasterorwoodenpatternforRT.RPisanewformingprocesswhichfabricatesphysicalpartslayerbylayerundercomputercontroldirectlyfrom3DCADmodelsinaveryshorttime.Incontrasttotraditionalmachiningmethods,themajorityofrapidprototypingsystemstendtofabricatepartsbasedonadditivemanufacturingprocess,ratherthansubtractionorremovalofmaterial.Therefore,thistypeoffabricationisunconstrainedbythelimitationsattributedtoconventionalmachiningapproaches.TheapplicationofRPtechniqueasausefultoolcanprovidebenefitsthroughouttheprocessofdevelopingnewproducts.Specifically,thereareseriousbenefitsthatRPcanbringintheareasofmarketresearch,salessupport,promotionalmaterial,andtheever-importantproductlaunch.PhysicalRPcanalsobecomeapowerfulcommunicationstooltoensurethateveryoneinvolvedinthedevelopmentprocessfullyunderstandsandappreciatestheproductbeingdeveloped.Hence,itcanhelptoreducesubstantiallytheinevitablerisksintheroutefromproductconcepttocommercialsuccess,andhelpshortentime-to-market,improvequalityandreducecost.Overthelast20years,RPmachineshavebeenwidelyusedinindustry.TheRPmethodscommerciallyavailableincludeStereolithgraphy(SLA),SelectiveLaserSintering(SLS),FusedDepositionManufacturing(FDM),LaminatedObjectManufacturing(LOM),BallisticParticleManufacturing(BMP),andThree-DimensionalPrinting(3Dprinting),etc.

Oncethedesignhasbeenaccepted,therealizationoftheproductionlinerepresentsamajortaskwithalongleadtimebeforeanyproductcanbeputtothemarket.Inparticular,thepreparationofcomplextoolingisusuallyinthecriticalpathofaprojectandhasthereforeadirectandstronginfluenceontime-to-market.Inordertoreducetheproductdevelopmenttimeandcost,thenewtechniqueofRThasbeendeveloped.RTisatechniquethatcantransformtheRPpatternsintofunctionalparts,especiallymetalparts.Itoffersafastandlowcostmethodtoproducemouldsandfunctionalparts.Furthermore,theintegrationofbothRPandRTindevelopmentstrategypromotestheimplementationofconcurrentengineeringincompanies.NumerousprocesseshavebeendevelopedforproducingdiesfromRPsystem.TheRTmethodscangenerallybedividedintodirectandindirecttoolingcategories,andalsosoft(firm)andhardtoolingsubgroups.IndirectRTrequiressomekindsofmasterpatterns,whichcanbemadebyconventionalmethods(e.g.HSM),ormorecommonlybyanRPprocesssuchasSLAorSLS.DirectRT,asthenamesuggests,involvesthemanufacturingofatoolcavitydirectlyonaRPsystem,henceeliminatingtheintermediatestepofgeneratingapattern.Softtoolingcanbeobtainedviareplicationfromapositivepatternormaster.Softtoolingisassociatedwithlowcosts;usedforlowvolumeproductionandusesmaterialsthathavelowhardnesslevelssuchassilicones,epoxies,lowmeltingpointalloys,etc.RTVsiliconerubbermoulds,epoxymoulds,metalsprayingmoulds,etc.aresomeofthesetypicalsoftmoldings.Hardtoolingisassociatedwithhighervolumeofproduction,andtheuseofmaterialsofgreaterhardness.Keltoolprocess,Quickcastprocess,andtheExpressToolprocessaresomeofthesehardtoolings.Electricaldischargemachining(EDM)seemstobeaninterestingareainwhichrapidtoolingfindsapotentialapplication.SomemethodsofmakingEDMelectrodesbasedonRPtechniquehavedeveloped,suchasabradingprocess,copperelectroformingandnetshapecasting,etc.Onthebasisoftheabovetechniques,anovelintegratedsystemofrapidproductdevelopmentistobeproposed.ItsoverallarchitectureisshowninFig.1.

3.CaseStudies

3.1.Casestudy1:Impeller

Atotalofthirtyplasticimpellers,witharelativelycomplexgeometry,wererequiredbyacustomerwithinfifteenworkingdaysfromthereceiptofa2DCADmodel.Thereweremanyfactorstobeconsideredindecidingthemostappropriaterouteforproducingtheimpellers.Thesefactorsmainlyinvolvedcost,lead-time,thenumberofpartsrequired,thefinalmaterialfortheparts,andthepartgeometry.Inordertomaximizethebenefitsintermsoftimeandcostreductionfortheparts,itwasdecidedtousesiliconrubbermouldandthepartswereeventuallyproducedbyvacuumcastingprocess.Siliconrubbermouldisaneasy,relativelyinexpensiveandfastwaytofabricateprototypeorpre-productiontools.Itcanbeutilizedformouldingpartsinwax,polyurethane,ABS,andafewepoxymaterials.Theprocessisbestsuitedforprojectswhereform,fit,orfunctionaltestingcanbedonewithamaterialwhichmimicsthecharacteristicsoftheproductionmaterial.Thecastingpartswithfinedetailsandverythinwallscanbeeasilyandrapidlyproduced.Thewholeprocessflowinvolvedthe3DCADmodelling,producingmasterpattern(RPprototype),siliconrubbermould,andcastinggreenparts.Thetimesequenceforthefabricationofimpellerswasdescribedasfollows.Duetothecomplexityoftheimpeller,thetaskofgeneratingthe3DCADmodelusingPro/Engineersoftwarepackagetookalmost3calendardays.ThemasterpatternforthisprojectwasbuiltonaSPS600machinein2calendardays.SLprocesswaschosenbecauseitwascosteffectiveandthesurfacefinishwasgood.Thenextstepinvolvedcreatingaroomtemperaturevulcanized(RTV)siliconerubbermoldwhichwascompletedwithinanadditional3calendardays.Finally,theABSmaterialswerecastintosiliconrubbermouldunderthevacuumcastingcondition,andthegreenpartswereachievedin4calendardays.Therequired30componentswereproducedsuccessfullyandcompletedin12calendardays.TheprimaryprocessstagesareillustratedinFig.2.Theseimpellersonlycostabout5thousandRMBandtook12workingdays.Consequently,incontrasttothetraditionaldevelopmentmode,theimpellersdevelopedusingtheintegratedsystemcancutcostbyupto50%andthetime-to-marketby75%.Whenevaluatedagainstsatisfyingurgentrequirementwithrespecttotime,theprocedureisclearlyworthpursuing,asindicatedbythecasestudydescribedabove.Gongfroma3DCADsolidmodelingtofullyfunctionalproductionimpellersinlessthan12workingdaysiscertainlyextraordinary.Withproperimplementationoftheprocessbyqualifiedpersonnel,workingwithinthescopeoftheconstraintsnoted,theacceptanceandadvancementoftheintegratedmanufacturingmethodislikelytogrow.

3.2.Casestudy2:Mannequin

Tenplasticmannequinswererequiredbyaclientinthreemonthsfromthereceiptoftheplastermodeloftheemulationalbody.Thiscomponentwasanidealcandidateforusingintegratedsystemtodevelopment,withaverycomplexsurfaceandarequirementforonly10parts.Inordertoproducetheplasticmannequin,thevarioustechnologiesincludingreverseengineering,3DCAD,rapidprototypingandrapidtoolingwereusedtocompletemodelmeasuring,surfacesreconstructing,3DCADmodelling,prototypeandmouldbuilding.Thewholedevelopmentworkwaspresentedbelow.ThefirststepoftheprojectwastoconstructaCADmodeloftheemulationalbodybyREprocess.ATOSmeasuringequipmentmadeinGOMInc.whichhasahighscanning(10,000points/sec)andcanmeasuremodelsinawiderangefrom500mmto10mm,wasemployedtocapturethedigitizeddataoftheplastermold.Figure3(a)showsthepointcloudsofthebodymodel.Thesubsequentprocesswastoperformsurfacesreconstructing.Tospeedthisprocess,aspecialreverseengineeringprogram,calledCopyCAD(DelcamInc.),wasusedtocreatequicklyandeasilytheCADsurfacesfromthedigitizeddata.Aftersurfaces

reconstructing,manyerrorsintheoriginalmodelandthejointsmustbemodifiedbyPowerShapesoftwarepackage(anothersoftwareofDelcamInc.).ThesurfacesmodelofthebodyisrepresentedinFig.3(b).Tofabricateeasily,thesurfacemodelwasdividedinto11individualcomponentswhichincludedthehead,body,upperarms,forearms,tights,shanksandfeetusingPro/Engineersoftwarepackage.Subsequently,everysurfacemodelwasconvertedtoasolidmodel,andmanyholesandslotsneededtobedesignedforfixingjointssuchasshoulder,knees,etc.Then,thesolidpartsandjointswereassembledtoformthesolidmodeloftheemulationalbody.Figure3(c)illustratesthecompletedCADsolidmodel.TheRPprototypesofthesecomponentswerebuiltonaLPS600machine.TheassemblyRPbodymodelisshowninFig.3(d).Inaddition,siliconrubbermouldsofthesecompon