铸造技术动态建模过程和模具设计中英文对照外文翻译文献.docx

铸造技术动态建模过程和模具设计中英文对照外文翻译文献.docx

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铸造技术动态建模过程和模具设计中英文对照外文翻译文献

中英文对照外文翻译

（文档含英文原文和中文翻译）

原文：

《Modellingthedynamicsofthetilt-castingprocessandtheeffectofthemoulddesignonthecastingquality》

Received29June2010

Revised9November2010

Accepted12November2010

Availableonline21November2010

Abstract

Alltitaniumalloysarehighlyreactiveinthemoltenconditionandsoareusuallymeltedinawater-cooledcoppercrucibletoavoidcontaminationusingprocessessuchasInductionSkullMelting（ISM）.Theseprovideonlylimitedsuperheatwhich,coupledwiththesurfaceturbulenceinherentinmostconventionalmouldfillingprocesses,resultsinentrainmentdefectssuchasbubblesinthecastings.Toovercometheseproblems,anoveltilt-castingprocesshasbeendevelopedinwhichthemouldisattacheddirectlytotheISMcrucibleholdingthemeltandthetwoarethenrotatedtogethertoachieveatranquiltransferofthemetalintothemould.Fromthemodellingpointofview,thisprocessinvolvescomplexthree-phaseflow,heattransferandsolidification.Inthispaper,thedevelopmentofanumericalmodelofthetilt-castingprocessispresentedfeaturingseveralnovelalgorithmdevelopmentsintroducedintoageneralCFDpackage（PHYSICA）tomodelthecomplexdynamicinteractionoftheliquidmetalandmeltingatmosphere.Thesedevelopmentsrelatetothefronttrackingandheattransferrepresentationsandtoacasting-specificadaptationoftheturbulencemodeltoaccountforanadvancingsolidfront.Calculationshavebeenperformedfora0.4 mlongturbinebladecastinatitaniumaluminidealloyusingdifferentmoulddesigns.Itisshownthatthefeeder/basinconfigurationhasacrucialinfluenceonthecastingquality.Thecomputationalresultsarevalidatedagainstactualcastingsandareusedtosupportanexperimentalprogramme.Althoughfluidflowandheattransferareinseparableinacasting,theemphasisinthispaperwillbeonthefluiddynamicsofmouldfillinganditsinfluenceoncastqualityratherthanheattransferandsolidificationwhichhasbeenreportedelsewhere.

Keywords

Tilt-casting;Moulddesign;3-Dcomputationalmodel;Castingprocess；

1.Introduction

Thecastingprocessisalreadymanycenturiesold,yetmanyresearchersarestilldevotedtoitsstudy.Netshapecastingisveryattractivefromthecostpointofviewcomparedtoalternativecomponentmanufacturingmethodssuchasforgingormachining.However,reproduciblequalityisstillanissue;theeliminationofdefectsandcontrolofmicrostructuredriveresearch.Castinginvolvesfirstthefillingofthemouldandsubsequentlythesolidificationofthemelt.Fromthenumericalmodellingpointofview,thissimplesequenceresultsinaverycomplexthree-phaseproblemtosimulate.Arangeofinteractionsofphysicalphenomenaareinvolvedincludingfreesurfacefluidflowasthemouldfills,heterogeneousheattransferfromthemetaltothemould,solidificationofthemoltenmetalasitcools,andthedevelopmentofresidualstressesanddeformationofthesolidifiedcomponent.

Inindustrytherearemanyvariantsofthecastingprocesssuchassandcasting,investmentcasting,gravity,andlowandhighpressurediecasting.Inthisstudy,theinvestmentcastingprocess,alsocalledlost-waxcasting,hasbeeninvestigated.Oneoftheadvantagesofthisprocessisthatitiscapableofproducing（near）netshapeparts,whichisparticularlyimportantforgeometricallycomplexanddifficult-to-machinecomponents.Thisprocessstartswithmakingaceramicmouldwhichinvolvesthreemainsteps:

injectingwaxintoadietomakeareplicaofthecomponentandattachingthistoapouringbasinandrunningsystem;buildingaceramicshellbytheapplicationofseverallayersofaceramicslurryandceramicstuccotothewaxassembly;de-waxingandmouldfiring.Thepouringofthecastingisperformedeithersimplyundergravity（nocontrol）,orusingarapidcentrifugalaction[1]（dangerofmacro-segregationplushighlyturbulentfilling）,orbysuctionasincounter-gravitycasting（e.g.theHitchinerprocess[2]）,orbytilt-casting.Inthisstudy,tilt-castingwaschoseninanattempttoachievetranquilmouldfilling.Tilt-castingwaspatentedin1919byDurville[3]andhasbeensuccessfullyusedwithsandcastings[4]andaluminiumdiecastings[5].IntheIMPRESSproject[6],anovelprocesshasbeenproposedandsuccessfullydevelopedtocombineInductionSkullMelting（ISM）ofreactivealloyswithtilt-casting[7],[8],[9] and [10],withaparticularapplicationtotheproductionofturbinebladesintitaniumaluminidealloys.AsshowninFig.1,thisiscarriedoutinsideavacuumchamberandthemouldispre-heatedinsitutoavoidmisruns（incompletemouldfillingduetoprematuresolidification）andmouldcrackingduetothermalshock.

Tilt-castingprocess:

（a）experimentalequipment;（b）schematicviewoftheISMcrucibleandmould,showingthedomedshapeacquiredbythemoltenmetal;（c）differentstagesofmouldfillingshowingtheprogressivereplacementofgasbythemetal.Thecomponent（s）tobecastareattachedtoapouringbasinwhichalsodoublesasasourceofmetaltofeedthesolidificationshrinkage.Thecomponentsareangledonthebasintopromotetheprogressiveuni-directionalflowofmetalintothemould.Asthemetalentersthemoulditdisplacesthegasandanescaperoutehastobeincludedinthedesignsothatthetwocounter-flowingstreamsarenotmixedleadingtobubblestrappedinthemetal.Ventsarealsousedtoenableanytrappedgastoescape.The‘feeder’usedtoconnectthemouldtothecrucibleisnormallyinanycastingthelastportionofmetaltosolidify,sosupplyingmetaltothemouldtocountertheeffectsofsolidificationshrinkage.Intilt-casting,thefeederisalsotheconduitforthetranquilflowofmetalintothemouldandalsofortheunhinderedescapeofgas.Forthisreason,thefluiddynamicsofthemouldfeederinterfacemeritdetailedstudy.

Aswellasthemould/feederdesign,theproductionofcastingsinvolvesseveralotherkeyparameters,suchasthemetalpouringtemperature,initialmouldtemperature,selectivemouldinsulationandthetiltcycletiming.Alltheseparametershaveaninfluenceontheeventualqualityofthecastingleadingtoaverylargematrixofexperiments.Modelling（oncevalidated）iscrucialinreducingtheamountofphysicalexperimentsrequired.Asmentionedabove,themathematicalmodelsarecomplexduetothefactthatthisisathree-phaseproblemwithtworapidlydevelopingphasefronts（liquid/gasandsolid/liquid）.Inthispaper,a3-Dcomputationalmodelisusedtosimulatethetilt-castingprocessandtoinvestigatetheeffectofthedesignofthebasin/feederontheflowdynamicsduringmouldfillingandeventuallyoncastingquality.

2.Experimentaldescription

Detailsoftheexperimentalsetuphavebeenpublishedelsewhere[11],butforcompletenessasummarydescriptionisgivenhere.Fig.1ashowsanoverallviewoftheequipmentusedtoperformthecasting.TheInductionSkullMelting（ISM）coppercrucibleisinstalledinsideavacuumchamber.Toenablerotation,itisattachedtoaco-axialpowerfeed,whichalsoallowscoolingwatercontainingethyleneglycoltobesuppliedtotheISMcrucibleandtheinductioncoil.Thecoilsuppliesamaximumof8 kAatafrequencyof∼6 kHz.Thecruciblewallissegmented,sothattheinductionfieldpenetratesthroughtheslots（byinducingeddycurrentsintoeachfingersegment）tomeltthechargeandatthesametimerepeltheliquidmetalawayfromthesidewalltominimisethelossofsuperheat.AbilletofTiAlalloyisloadedintothecruciblebeforeclampingontheceramicshellmould.Themouldissurroundedbyalowthermalmasssplit-mouldheater.Afterevacuatingthevacuumchamber,themouldisheatedtotherequiredtemperature（1200 °Cmaximum）andthevesselback-filledwithargontoapartialpressureof20 kPapriortomelting.Thispressuresignificantlyreducestheevaporativelossofthevolatilealuminiumcontainedinthealloy.Thepowerappliedtotheinductioncoilisincreasedaccordingtoapre-determinedpowervs.timeschedulesothatareproduciblefinalmetaltemperatureisachieved.Attheendofmelting（7–8 min）,themouldheaterisopenedandmovedaway.Theinductionmeltingpowerisrampeddownand,simultaneously,theISMcrucibleandmouldarerotatedby180°usingaprogrammablecontrollertotransferthemetalintothemould.Themouldcontainingthecastingisheldverticallyasthemetalsolidifiesandcoolsdown.

3.Mathematicalmodel

3.1.Fluidflowequations

Themodellingofthecastingprocesshasinvolvedanumberofcomplexcomputationaltechniquessincetherearearangeofphysicalinteractionstoaccountfor:

freesurfacefluidflow,turbulence,heattransferandsolidification,andsoon.ThefluidflowdynamicsofthemoltenmetalandthegasfillingtherestofthespacearegovernedbytheNavier–Stokesequations,anda3Dmodelisusedtosolvetheincompressibletime-dependentflow:

（1）

（2）

whereuisthefluidvelocityvector;ρisthedensity;μisthefluidviscosity;Suisasourcetermwhichcontainsbodyforces（suchasgravitationalforce,aresistiveforce（Darcyterm）[12]）andtheinfluenceofboundaries.Thereisasharp,rapidlyevolving,propertyinterfaceseparatingmetalandgasregionsintheseequationsasexplainedbelow.

3.2.Freesurface:

counterdiffusionmethod（CDM）

Oneofthedifficultiesofthesimulationarisesfromthefactthattwofluidmediaarepresentduringfilling:

liquidmetalandresidentgasandtheirdensityratioisashighas10,000:

1.Notonlydoesthefluidflowproblemneedtobesolvedoverthedomain,butthemodelalsohastotracktheevolutionoftheinte