外文翻譯--超輕車輛設(shè)計(jì) 采用先進(jìn)的汽車合成技術(shù)克服設(shè)計(jì)阻礙英文版.pdf

ULTRALIGHT-HYBRIDVEHICLEDESIGN:OVERCOMINGTHEBARRIERSTOUSINGADVANCEDCOMPOSITESINTHEAUTOMOTIVEINDUSTRY1.INTRODUCTIONAdvancedpolymericcompositeshaveseveraladvantagesincludingpartsconsolidation,highspecificstrengthandenergyabsorption,stylingflexibility,goodnoise/vibration/harshness(NVH)characteristics,andexcellentcorrosionresistancethatsuitthemtoautomobiles.Furthermore,technologicaladvancesinprocessingandmaterialsappeartomakeadvancedcompositessuitableforhigh-volumeapplications:low-pressurefabricationprocessessuchasresintransfermolding(RTM)couldrequireverylowinvestmentcostsand,dependingonthechoiceofresinandtoolingmaterial,offerfastcycletimes,whilenewversionsofresinsandfiberspromiselowcostandhighperformance.Inaddition,recentdevelopmentsinautomotivedesigndrivetheneedforwhatispotentiallyadvancedcompositesbiggestadvantage:massreduction.Ultralight-hybridvehicledesigns,suchasRockyMountainInstitutes“hypercar”concept,necessitatestringentmass-optimizationparticularlyforthebody-in-white1,theautomotivetermfortheunfinishedbodyanditsframeorchassis.Advancedcompositebodies-in-whitehavethepotentialtobeupto67%lighterthanaconventionalsteelunibodyforequivalentsizeandsafety.However,aquicklookattheuseofadvancedcompositesintheautomotiveindustryraisesanobviousquestion:Ifadvancedcompositesaresuchwonderfulmaterials,whyaretheynotbeingused?Asidefromafewspecialtycomponentsfornichevehicles,suchasonepartintheDodgeViper,andevenfewerwhole-systemapplicationssuchGMs1991Ultraliteconceptcar,theautoindustryhasshunnedtheuseofadvancedcomposites.Evenregularstructuralcomposites,usinglow-performancereinforcementsinquasi-isotropicarrangements,arebeingappliedinlower-than-expectedquantities.Inresponse,organizationstargetingtheautomotiveindustry,suchastheAutomotiveCompositesConsortium(ACC),andcompositeproducers,includingsomeinNISTsAdvancedTechnologyProgram(ATP),areambitiouslyimplementingstrategiestospeedtheintegrationofstructuralandadvancedcompositesintotheautomobile.ButtheACCsfocusoncomponentapplicationssuchasacompositepickuptruckbox,liketheATPsfundingofmanufacturingprocessimprovementswithoutaccompanyingdesignchanges,indicateastrategyofevolutionaryintegration.Whileanevolutionaryapproachminimizesriskintheshortterm,itmaynotbetheoptimallong-termstrategytoovercomethebarrierstoputtingadvancedcompositesintocars.Justasthecombinationofanultralightbodywithahybriddrivelineprovidesa“l(fā)eapfrog”approachtoincreasingfuelefficiencyanddecreasingemissions,sothewhole-systemapplicationofcompositestoanultralightmonocoqueBIWisthebestwayfortheadvancedmaterialsandautomotiveindustriesto“tunnelthrough”thebarrierstolarge-scaleimplementation.Toanautomaker,aleapfrogapproachtocompositeintegrationcouldprovidebenefitsfarout-weighingtherisksanduncertaintiesofworkingwithunfamiliarmaterialsandtechnologies.Toanadvancedmaterialssupplier,aleapfrogapproachcanpreventthe“setuptofail”scenarioexperiencedinmanyautomotivecomponentapplicationsbyoptimallyexploitingthenewmaterialsintrinsicadvantages.Inaddition,aleapfrogapproachcouldpotentiallyexpandtheadvancedmaterialsmarketbyseveralfoldormore,achievingvolumeswhichcouldlowertheirproductscosts.ThusanadvancedmaterialspushintotheBIWshouldnotbesimplyanissueofmaterialsubstitutiononepartatatime:itneedstosubstitutematerialsusingawhole-platformdesignthatmaximizesthematerialsbenefitswhileminimizingandpotentially1eliminatingmanyoftheircosts.2.TECHNOLOGIESFORVOLUMEPRODUCTIONHowcouldpolymericcompositeBIWsbecompetitivelymadeinhighvolume?Thereisnodefinitiveanswer；theslateofpotentialtechnologiesforfabricatingandassemblinganadvanced-materials-basedBIWislargeandgrowingrapidly.Thediversityoftechnologicaloptionsaddsbothuncertaintyandrobustness.Also,whileadvancedpolymericcompositesrequiresophisticateddesigntotakeadvantageofuniquepropertiessuchasanisotropy,theirhigh-volumemanufacturingandassemblytechniquesareconceptuallysimple.Themostpromisingoff-the-shelfornear-termtechnologiesforBIWmanufacturingarebrieflylistednext；afullersurveyisin.2.1RawMaterialsPolymericcompositesincorporatefibrousreinforcementinaresinmatrix.Issuesimportantforrawmaterialselectionincludecost,compatibilitywithfabricationtechnologies,mechanicalandenvironmentalperformance,andrecyclability.2.2MoldingInthevariousmoldingoperations,theintermediatefiberformandresin,combinedeitherpreviouslyordirectlyinthemold,areshapedandhardenedintotheformofthemoldingcavity.Foranall-compositeBIW,liquidcompositemolding(LCM)eitherresintransfermolding(RTM)orstructuralreaction-injectionmolding(SRIM)isgenerallyconsideredtobethemostpromisingprocess.BothRTMandSRIMutilizethermosetresinsbecauseoftheirlowviscosity,althoughcyclicthermoplasticsmaybeadaptable.LCMrequiresapreform,whichcancompriseavarietyofintermediatefiberforms.Asmentionedabove,anadvanced-compositeBIWwouldprobablyuseamorecomplexpreformwithhigher-performancefibers.Compressionmolding,normallydonewithSheetMoldingCompound(SMC),isahigh-pressureprocesswithalowercycletimeandgenerallyabettersurfacefinishthanLCM,suitingittoBIWapplicationswithinthecurrentsteelinfrastructure.However,likeglass,afullycompression-moldedBIW,duetoitsweight,maynotbeabletoreapadequatesynergieswithahybriddrive,norhaveadequatecrashworthiness.BIWdesigns,lessmaturebuthigher-performancemanufacturingtechnologiessuchasRTMorSRIMappeartobemoreapplicabletoanall-compositeBIW.2.3TechnologicalBarriersUnliketheoveralldesignstrategyforcompositeBIWs,noneofthecompositetechnologieslistedaboverequirefundamentaladvancestopermitvolumeBIWmanufacturing.Eachneedsvaryingdegreesofrefinementbutseemstofacenointractabletechnologicalbarriers:implementationrequirestechnologyoptimizationandintegrationratherthaninvention.Someofthekeytechno-economicbarriersaredescribednext.2.3.1Carbon-FiberCostThecostofcarbonfiberisoftencitedasthemostformidablebarriertocommercialapplicationsforcarbon-fibercomposites.ForPAN-basedcarbonfiber,thecombinationofexpensiveprecursorandlow-volume,specializedequipmenthasledtoitshighcost.However,twoenterprisingdomesticmanufacturers,ZoltekandAkzoNobel,offerlow-cost,hightowcommodity-gradecarbonfiber.Bulkcreelpricesfortheircontinuousfiberarecurrentlyaslowas$17.60/kg.Centraltofurtherdecreasesinpricearecheaperversionsoftheprecursor,whichhas“nocostcontrollingdifferences”fromthecommodity-gradeacrylicfiberthatcosts$3.00/kg.toproduce.Inaddition,highervolumesofproductionareneededtolowerunitcapitalandlaborcosts.High-volumemanufacturingcouldsoonberealized:ZoltekandAkzoplannear-termexpansion.Theirstrategycouldovercomethecostbarrierforadvanced2compositeswithasupply-pushoflow-costfiberintothetransportationmarket.2.3.2PreformingThedifficultyofproducingcomplexpreformsatreasonablecostiscitedalmostasoftenascarbon-fibercostasthechieftechnicalbarriertohigh-volumeadvancedcompositesmanufacturing.PrincetonsConferenceonBasicResearchNeedsforVehiclesoftheFuturerecentlygavepreformingthehighestpriorityamongneededresearchandinnovation.Currently,automakersfavorquasi-isotropicchoppedorcontinuousmatpreformsofglassfiber,which,aswasmentionedabove,aretooweak,isotropic,andhenceheavyforamass-optimizedBIW.Theanisotropicstrategiescommoninaerospaceapplications,suchasprepregtapesandhandlay-upwithautoclaving,aretooslowandcostlyforcars.Fortunately,theproblemofcreatinglow-costcomplexpreformsmaynotbeintractable:severalinnovativetechnologiescouldpermittherapidandinexpensivefabricationofcomplex,net-shapepreforms.FabricssuchasCOTECHarenon-crimp,stitch-bondedlayersofunidirectionalcontinuousfiberthat,accordingtotheirmanufacturer,canbecheaperthanrandommatyetperformaboutaswellasunidirectionaltape.Astitch-bondingprocesscaninexpensivelycreatecomplexpreformsbycombiningaquasi-isotropicbaseoffabricwithstrategicallyplacedinsertsofunidirectionalfabricorrovingatmaximumloadpoints.Alternatively,theCompFormprocessclaimsevencheaperandfastercomplexpreformingpotential,substitutingUV-curablebindersforfabricstitchesalthoughthisprocesscannotbeusedwithacarbon-intensivepreform.Forcreatingnet-shapepreforms,fastultrasoniccutting,usingnestingpatternstominimizewaste,couldbeagoodcomplementtostitch-bonding.Obviously,complexpreformsrequireheavyfront-endengineeringtoavoidresinflowproblemssuchasracetrackingandunexpectedfibermovements.Nevertheless,theseprocesseshavereal-worldvalidity:bothUVstitchingandultrasoniccuttingwereusedtocreateacomplexpreformforaBuickRivierabumperbeam.2.3.4SurfaceQualityBecausecompositemonocoquesrequirestructuralcompositeswithClassAsurfaces,asignificantbarrierisproducingcomponentswithbothhighfiber-volumefractionsandsmooth,porosity-freeexteriors.IfsofttoolingisusedtocapturestrategicadvantagesortoensurecompatibilitywithE-beamcuringforcycle-timereductions,thechallengeofobtainingClassAsurfacesbecomesmorecomplexandimportant.WhileClassAsurfacescouldbedifficultforstructuralcomposites,theyarebynomeansimpossible.Thestitch-bondedfabricdescribedaboveforcomplexpreformswetsouteasilyandhasasurprisinglysmoothsurface,asitismadeupofunidirectionallayers,sosubjecttoresinconsistencyandtoolingsurfacequality,itcouldsimplybesurface-finishedwithaClassAmoldandpainted,savingtheinvestmentandoperationcostsofconventionalsteelfinishingprerequisitetopaintingexteriorBIWparts.Anevensimplerapproachcouldalsoavoidpaintingbyapplyingoneofseveralproprietarylay-in-the-moldClassAcolorcoatpolymerproducts,orperhapsinjectathermoplasticcolorcoatintoaClassAmoldandthenlayinthestructuralelementsbehinditusingacompatibleresinsystem.3.OVERCOMINGTHEBARRIERSTheresultsofthesesurveysledonesetofinterviewerstoconcludethatsince“theadoptionofstructuralcompositesfacesmultiplebarriers,noonesimplequickfixwillrapidlyacceleratetheirdeployment.”Yetdespitecompleximplementationdetails,thereisarelativelysimpleifun-expectedconceptualframeworktointegrateadvancedcompositesintoautomaking.Themosteffectivewaytoovercomethebarriersappearstobereplacingtodaysdominantstrategyofincremental,part-by-partmaterialssubstitutionwithawhole-system-designed,all-advanced-compositeBIW.This“l(fā)eapfrog”approachintegratesaclean-sheetdesign,high-performancerawmaterials,3existingmanufacturingmethods,andaradicallysimplerandsmallerassemblyprocess.Itholdspromiseofbypassingmanybarriersandofchangingautomakersattitudetowardadvancedcompositesfroma“necessaryevil”orindefinitelypostponableinconvenienceintoapromptandlucrativeopportunity.Waystocircumventmajorbarriersaresurveyednext.3.1CostComponent-by-componentsubstitutionofcompositesforsteelcannotoccuruntilmarket-determinedmaterialpricesjustifysubstitutiononasingle-partbasis,eitherthroughcheapermanufacturingorthroughsavedgasoline,withlittleifanycreditformassdecompoundingandevenforthesavedsteelitself.Thesubstitutedmaterialsremaincostly,however,becauseonlysmallvolumesarebeingbought.Creditshouldbe,butisnotalways,takenforthemodestreductionsinpartscount；asaresult,thinkingincomponentterms-makesithardorimpossibletoquantifysavedassemblycosts.Finally,integrationofacompositecomponentwithinasteelBIWcanraiseoverallassemblycosts,especiallyifthecompositepartscycletimesarelongerortheirdimensionsandotherpropertiesaremorevariable.Asaresult,integrationrequirementsofteneconomicallyfavorcompressionmoldingoverRTM,leadingtopartswithsuboptimalperformancefordemandingstructuralapplications.Incontrast,clean-sheetwhole-platformredesigncanyieldradicalreductionsinpartscount,size,andcomplexity:thetypicalBIWwouldhaveonlyafewparts,andassemblyeffortwoulddropbyanorderofmagnitude.Buyingthespecialmaterialsinbulkshouldyielddiscountsand,throughincreasingproductionvolumes,cutmarketprices.Productionvolumescouldbeoptimizedforconvenienceandmarketdemand,ratherthanartificiallyinflatedtomeetamortizationrequirementsforsteeltoolsandpresses.Productionflexibilitycouldberetainednotonlyinvolumebutalsoinstyling.Finally,savingscouldaccumulate“downstream”fromBIWmanufacturingthroughamuchsmallerandsimplerdrivelineandothercomponents,shorterproductcycletimes,andgreaterproductionflexibility.3.2SafetyAdvancedcompositeshavefundamentallydifferentenergyabsorptioncharacteristicsandfailuremodesthansteel.Theyfituncomfortablyintothetraditionalsafety-designparadigm,especiallywhenappliedbysteel-orienteddesignerswhotreatadvancedcompositesas“blackstee