制造工程与技术chapter 10

ManufacturingEngineeringandTechnologyHotProcess(制造工程与技术-热加工）,主讲人：张新房H.P-mail:teaoren,Preface（前言）,1st、PropertyandObjective(课程性质及目的)2nd、Maincontentandrequirement(主要内容及要求)3rd、Textbookandmainreferencebooks(教材及主要参考书)4th、Examination(本课程的考核),1st、PropertyandObjective,本课程是为材料加工专业本科生开设的专业课其目的在于使学生掌握一些基本的材料加工专业英语词汇，能够从事材料、机械类的英文文献的阅读翻译工作，了解材料加工制造行业的先进技术、加工工艺及最新技术动态。,2nd、MainContentandRequirement,1.MainContent:Metal-CastingProcessesandEquipments)。Including:Chapter10:FundamentalsofMetal-CastingChapter11:Metal-CastingProcessesChapter12:Metal-Casting:Design,MaterialsandEconomics,MainContentsandRequirements,2.Fromstudyingthiscourse,YoushouldremembertheusualmaterialsmanufacturingwordsandcanreadandtranslateprofessionalpapersandreferencesinEnglishedition.(通过本课程的学习，使学生能够掌握一些常见到的材料加工专业英文词汇，能够顺利地阅读翻译相关的专业英文文献资料。),3rd、TextbookandReferenceBook,Textbook：SeropeKalpakjianandStevenR.Schmind,(制造工程与技术-热加工）机械工业出版社，2007.ReferenceBook：全燕鸣主编，制造工程与技术-热加工及学习辅导，机械工业出版社，2007.,4th、Examination,考查：以上课、回答问题、作业完成和出勤情况为依据进行考查，考查合格者方能参加考试。考试：闭卷考试，百分制计分。,PartIIMetal-CastingProcessesandEquipments,Severaldifferentmethods,suchascasting,molding(造型),forming(成型),powdermetallurgy(粉末冶金),andmachining(机加工）,areavailabletoshapemetalsintousefulproducts.Oneoftheoldestprocessesiscasting,whichbasicallyinvolvespouring（浇注）metalintoamoldcavitywhere,uponsolidification,ittakestheshapeofthecavity.,Thecastingprocessiscapableofproducingintricate(复杂的）shapesinonepieces,includingthosewithinternalcavities,suchasengineblocks（发动机壳体).,Waterpump:水泵Pulley:滑轮Grill:栅栏Intakeandexhaustmanifold:进气和排气管Diskbrake:刹车片Brakedrum:制动鼓Brakecylinder:闸缸Lettering:编字码Differentialhousing:差速机壳Transmissionhousing:变速机壳Engineblock:汽缸体Carburetor:化油器Piston:阳模Alternatorhousing:同步发电机壳,Fig.II.1Castpartsinatypicalautomobile,图一个典型的汽车中的铸造部件,Castingprocessesaremostoftenselectedoverothermanufacturingmethods,forthefollowingreasons:Castingcanproducecomplexshapeswithinternalcavitiesorhollow(中空的)sections.Itcanproduceverylargeparts;Itcanutilize(利用)workpiece(工件)materialsthataredifficultoruneconomicaltoprocessbyothermeans;Castingiscompetitivewithotherprocesses.Almostallmetalscanbecastin,ornearlyin,thefinalshapedesired,oftenwithonlyminorfinishingoperationrequired.Thiscapabilityplacescastingamongthemostimportantnet-shapemanufacturing(近成型制造）technologies,alongwithnet-shapeforging（锻造）,stampingofsheetmetal（薄板冲压）,andpowdermetallurgyandmetal-injectionmolding（金属注塑成型）.,Fig.II.2Outlineofmetal-castingprocessesdescribedinPartII.图II.2.在第二部分中所描述的金属铸造工艺概要,Chapter10FundamentalofMetalCasting(金属铸造基础),Introduction:简介Solidificationofmetals:金属的凝固Fluidflow:流体流动Fluidityofmoltenmetal:熔融金属的流动性Heattransfer:热传递Defects:缺陷,1.Introduction,Thecastingprocessbasicallyinvolvesthreesteps:(a)pouringmoltenmetalintoamoldpatternedaftertheparttobemanufactured;(b)allowingittocoolandsolidify(c)removingthemetalfromthemold.Aswithothermanufacturingprocesses,anunderstandingorthefundamentalsisessential-bothfortheproductionofgoodqualityandeconomiccasting,andtoestablishpropertechniquesformolddesignandcastingpractice.Importantconsiderationsincastingoperationsareasfollows:theflowofthemoltenmetalintothemoldcavity;FluidityThesolidificationandcoolingofthemetalinthemold;HeattransferTheinfluencesofthetypeofmoldmaterial.Differentheattransferabilityfordifferentmoldmaterial,10.2SOLIDIFICATIONOFMETALS(金属的凝固),Aftermoltenmetalispouredintoamold,aseriesofevents(变化）takeplaceduringthesolidificationofthecastinganditscoolingtoambienttemperature（室温）.Theseeventsgreatlyinfluencethesize（尺寸、大小）,shape（形状）,uniformity（均匀性）,andchemicalcompositionofthegrainsformedthroughoutthecasting,whichinturn（依次）influenceitsoverallproperties.Thesignificantfactorsaffectingtheseeventsarethetypeofmetal(金属种类);thethermalproperties(热性能)ofthebothmetalandthemold;thegeometricrelationship(几何关系)betweenvolumeandsurfaceareaofthecasting;andtheshapeofthemold.,10.2.1Puremetals(纯金属),Forpuremetal,themeltingpointisconstant,so,thesolidificationislikethisone:,AfterreachingfreezingpointTl,Releaseoflatentheatoffusion(融化潜热),solidificationfrommoldwallintowardthecenterwithdifferentgraintypeandsizeformation,ThegrainstructureofapuremetalcastinasquaremoldisshowninFig.10.1a.Rapidcoolingrateatthemoldwallproducesasolidifiedskin(表层),orshell(壳体),offineequiaxedgrains(等轴晶).Thegrainsgrowinadirectionofoppositetothatoftheheattransferoutthroughthemold.Thesegrainshavefavorableorientation(取向)willgrowpreferentiallyandarecalledcolumnargrains(柱状晶).,Fig.10.1.Schematicillustrationofthreecasterstructureofmetalssolidifiedinasquaremold;a,puremetals;b,solid-solutionalloys;c,structuredobtainedbyusingnucleatingagents(孕育剂).,Chillzone:极冷区，白口区，grainsizeduetoveryhighcoolingrate.Columnarzone:柱状区，largegrainsizeduetolowercoolingrateandheterogeneousnucleation.Equiaxedzone:等轴晶区，homogeneousnucleation.,Fig.10.2.Developmentofapreferredtexture(择优质构)atacoolmoldwall.Notethatonlyfavorablyorientedgrainsgrowawayfromthesurfaceofthemold。,Asthedrivingforceoftheheattransferisreducedawayfrothemoldwalls,thegrainsbecomeequiaxedandcoarse.Thosegrainsthathavesubstantiallydifferentorientationsareblockedfromfurthergrowth.Suchgraindevelopmentisknownashomogeneousnucleation(均匀形核),meaningthatthegrains(crystals)growuponthemselves,startingatthemoldwall.,10.2.2Alloys(合金),ThesolidificationprocessofalloyscanbeschematicallyillustratedfromFig.10.3.,Fig.10.3.Schematicillustrationofalloysolidificationandtemperaturedistributioninthesolidifyingmetal.Notetheformationofdendritesinthemushyzone(多空隙的区域).,Fromthisfigure,wecansee,thesolidificationtakesplaceinatemperaturerange,TlandTs.Thesolidificationprocessofthistypealloycanbeillustratedasfollow:,BelowTl,Solidificationstart,Chillzoneformation,Dendriteformation,Finish,BelowTs,BetweenTlandTs,Forthistypedendrite,itcanbenamedascolumnardendrite(枝晶),withthree-dimensionalarmsandbranches.Thestructureofdendriteinfluencesthepropertiesofcastingseriously,soitisessentialtofindandstudytheeffectorsonitsstructure.,Fig.10.4(a)Solidificationpatternsforgraycastironina180mmsquarecasting.Notethatafter11min.ofcooling,dendritesreacheachother,butthecastingisstillmushythroughout.(b)Solidificationofcarbonsteelinsandandchill(metal)molds.Notethedifferenceinsolidificationpatternsasthecarboncontentincreases,Thestructureofdendritecanbedescribedasdifferentmushyzoneduringsolidification,andthemushyzonecanbenamedasfreezingrange,asthis:Freezingrange=Tl-Ts,thetemperaturedifferencebetweenTlandTsduringsolidification.Eutectic:共晶的,symmetricalphasediagram:对称相图,lamellar:层、片状的,fibrous:针状的、纤维状的,castiron:铸铁Forexample:Forpuremetalsandeutecticalloys,freezingrange=0,so,nomushyzone,nodendriteformation.Usually,theshortfreezingrange110oC,example,AlandMg-basealloys,andthesealloysareinamushystatethroughoutmostofsolidificationprocess.,Effectofcoolingrate(冷却速度的影响),Thecastingstructureisaffectedseriouslybythecoolingrate:Usually,forslowcoolingrate(102K/s),coarsedendriteformation;Fastercoolingrate(ontheorderof104K/s),finerdendriteformation;Highercoolingrate(106108K/s),amorphousformation.Ascoolingrateincreases,thegrainsizedecreases,sostrengthandductilityenhanced,thatishall-petchformula.Microporosity:显微疏松,interdendriticshrinkagevoid:枝晶间疏松、空洞,anisotropic:各向异性的,Columndendritic,equaixeddendritic,equaixednondendritic,Forthesolidifiedstructure,itcanbecertifiedbytheratioofG/R,whereGisthermalgradient(热梯度)attheinterfaceofliquidandsolid,andRistherateatwhichtheliquid-solidinterfacemoves.TypicalvaluesforGrangefrom102to103K/mandforRfrom10-3to10-4m/s.Dendritictypestructures(Figs.105.5aandb)typicallyhaveanratiointherangeof105to107,whereasratiosof1010to1012produceaplane-front,nondendriticliquid-solidinterface(Fig.10.6).,Fig.10.6.Schematicofcaststructuresin(a)planefront,singlephase,and(b)planefront,twophases.,10.2.3Structure-PropertyRelationships(结构性能关系),Allcastingsarehopedtomeetdesignandservicerequirements.Usually,thepropertyisuptostructure.Thecompositionsofdendritesandtheliquidmetalaregivenbythephasediagramsofparticularalloys,usuallybinaryalloys.Ascoolingrateverylow,dendritewithuniformcompositiondevelops.Normal(fast)coolingrate,core(中心、核心)dendritesdevelopwithdifferentcompositionatsurfaceandcenter,knownasconcentrationgradient(浓度梯度):highercontentofalloyingelementinthesurfacelayerthanthatofcenter.Thatisduetosoluterejectionduringsolidifiedprocess,resultinginmicrosegregation(微观偏析).,Macrosegregation(宏观偏析)involvesdifferencesincompositionthroughoutthecasting.Normalsegregation(正常偏析),versesegeration(反向偏析),thereasonisthatliquidmetal(havingahigherconcentrationofalloyingelements)entersthecavitiesdevelopedfromsolidificationshrinkage(收缩)inthedendriticarmswhichsolidifiedsooner.Gravitysegregation(重力偏析)describestheprocesswherebyhigher-densityinclusions(夹杂)orcompositionssink(下沉)andlighterelements(suchasantimonyinantimony-leadalloy(锑-铅)float(上浮)tosurface.Inoculants(孕育剂)inducethenucleationofthegrainsthroughouttheliquidinducedheterogeneousnucleation(非均匀形核).Convection(对流)promotestheformationofanouterchillzone,refinesgrainsizeandacceleratesthetransitionfromcolumnartoequiaxedgrains.Dendritemultiplication:枝晶增殖,rheocasting:流变铸造,microgravity:微重力,10.3FLUIDFLOW(流体流动）,Thefluidflowismostimportantfactorincasting.Asshowninfig.10.7,thecastingprocessisdescribedas:themoltenmetalispouredthroughapouringbasin(转包，浇注槽)orcup.Itthenflowsthroughthegatingsystem(浇注系统)(sprue,runnersandgates,注流口,流道,内浇道)intothemoldcavity.Sprueisaverticalchannelthroughwhichmoltenmetalflowsdownwardinthemold.Runnersarethechannelsthatcarrythemoltenmetalfromthespruetothemoldcavity,orconnectthespruetothegate.Thegateisthatportionoftherunnerthroughwhichthemoltenmetalentersthemoldcavity.Risers(冒口)serveasreservoirs(储液槽)tosupplythemoltenmetalnecessarytopreventshrinkageduringsolidification,asshowninFig.10.7.,Fig.10.7.Schematicillustrationofatypicalriser-gatedcasting(冒口-浇口铸造).Risers(冒口)serveasreservoirs(储液槽),supplyingmoltenmetaltothecastingasitshrinksduringsolidification.Trapcontaminant:捕获杂质,prematurecooling:过早冷却,gasentrapment:夹气Gatingsystemdesignisthemostimportantparttogethighqualitycastings.,Twobasicprinciplesoffluidflowarerelevanttogatingdesign:Bernoullistheoremandlawofmasscontinuity.Bernoullistheorem:百努利定律(10.2)Where:h:theelevation(高度)aboveacertainplane,p:pressureatthatelevation,v:velocityoftheliquidatatelevation,:thedensityofthefluid,g:gravitationalconstant.Conservationofenergyrequiresthat,ataparticularlocation,inthissystem,therelationshipissatisfied:,(10.3),Where,subscripts(下标)1and2representtwodifferentelevations,andfrepresentsthefrictional(非粘结性的)lossintheliquidasittravelsdownwardthroughthesystem.Continuity(连续性)Thelawofmasscontinuity(质量连续性)statesthatforincompressible(不可压缩的)liquidandinasystemwithimpermeable(不可渗透的)wall,therateofflowisconstant:,(10.4),WhereQ:therateofflow,A:thecross-sectionalareaoftheliquid,andv:theaveragevelocityoftheliquidinthatcross-sectional(横截面的)location.Thedescription1and2refertotwodifferentlocationsinthesystem.,Forexample,forsprue(流道)design:,(10.5),So,theareaofthebottominthesprueissmallerthanthatoftop,thatmeanstaperedsprue(圆锥型流道).,Aspiration:吸出,choke:节流口，缩颈Recallthatinafree-fallingliquid(suchaswaterfromafaucet:水龙头)thecross-sectionareaofthestreamdecreasesasitgainsvelocitydownward.Ifwedesignaspruewithaconstantcross-sectionareaandpourthemoltenmetalintoit,regionsmaydevelopwheretheliquidlosscontactwiththespruewalls.Asaresultaspiration（抽吸),aprocesswherebyairissuckedinorentrappedintheliquid,maytakeplace.Ontheotherhand,taperedspruesarenowreplacedinmanysystemsbystraight-sidedsprueswithachoketoallowthemetaltoflowsmoothly.,Flowcharacteristics:(流体性质),Animportantconsiderationinthefluidflowingatingsystemsisthepresenceofturbulence(湍流)asopposedtothelaminarflow(层流).WeusetheReynoldsnumber(雷诺系数),Re,toquantify(定量)thisaspect(方面)offluidflow;Itrepresentstherationtheinertia(惯性)totheviscousforces(粘滞力)influidflow,andisdefinedas:,(10.6),Where,v:velocity,D:diameterofthechannel;anddensityandviscosity(粘度).Re200000,severeturbulentflow,resultinginairentrainmentandtheformationdross(熔渣)(thescum(浮渣)thatformsonthesurfaceofthemoltenmetal)fromthereactionoftheliquidmetalwithairandothergases.Techniquesforminimizingturbulencegenerallyinvolveavoidanceofsuddenchangesinflowdirectionandinthegeometryofchannelcross-sectionsingatingsystemdesign.Mitigate:缓和，减小Skimming:挡渣Filter:过滤器,10.4Fluidityofmoltenmetal(熔融金属的流动性),Thecapability(能力，本领)ofthemoltenmetaltofill(充填)moldcavitiesiscalledfluidity(流动性);itconsists(包括)oftwobasicfactors:(1)characteristicsofthemoltenmetal,and(2)castingparameters.Thefollowingcharacteristicsofmoltenmetalinfluencefluidity:a,viscosity(粘度)increasing,fluiditydecreasing;b,surfacetension(表面张力)increasing,fluiditydecreasing;c,inclusion(夹杂)increasing,fluiditydecreasing;d,solidificationpatternofthealloy,freezingrangeincreasing,fluiditydecreasing.,Thefollowingcastingparametersinfluencefluidityandalsoinfluencethefluidflowandthermalcharacteristicsofthesystem:Molddesign,thedesignanddimensionsofsprue,runnerandrisersallinfluencefluidity;Moldmaterialsanditssurfacecharacteristics:thermalconductivityandsurfaceroughincreasing,fluiditydecreasing;Degreeofsuperheat(过热)increasing,fluidityincreasing;Rateofpouringdecreasing,fluiditydecreasing;Heattransfer.Thisfactordirectlyaffectstheviscosityoftheliquidmetal.,Castabilty(可铸性):theeasewithwhichametalcanbecasttoobtainapartwithgoodquality,includesnotonlyfluiditybutalsocastingparametersaswell.,10.4.1Testsforfluidity(流动性测试）,Fig.10.8Atestmethodforfluidityusingaspiralmold(螺旋模).Thefluidityindex(流动性指数)isthelengthofthesolidifiedmetalinthespiralpassage(通道，通路).Thegreaterthelengthofthesolidifiedmetal,thegreaterisitsfluidity.,10.5Heattransfer(热传导）,Animportantconsiderationincastingistheheattransferduringthecompletecyclefrompouringtosolidificationandcoolingtoroomtemperature.Forinstance,incastingthinsections,themetalflowratesmustbehighenoughtoavoidpremature(早期的)chillingandsolidification.However,theflowratemustnotbesohighastocauseexcessive(过多的)turbulencewithitsdetrimental(有害的)effectsonthecastingprocess.,Fig.10.9.Temperaturedistributionattheinterfaceofthemoldwallandtheliquidmetalduringsolidificationofmetalsincasting.Theshapeofthecurvedependsonthethermalpropertiesofthemoltenmetalandthemold.,Fig.10.9Temperaturedistributionattheinterfaceofthemoldwallandtheliquidmetalduringsolidificationofmetalsincasting.,10.5.1.Solidificationtime(凝固时间),Duringearlystagesofsolidification,athin,solidifiedskinbeginstoformatthecoolmoldwallsand,astimepasses,theskinthickens.Withflatmoldwall,thisthicknessisproportionaltothesquarerootoftime.Thesolidificationtimeisafunctionofthevolumeofacastinganditssurfacearea(Chvorinovsrule);thatis,Solidificationtime=,(10.7),Where,C:aconstantthatreflects(反映)moldmaterial,metalproperties(includelatentheat),andtemperature.Thatmeans,thesolidificationtimeisinverse(反比于)proportionaltospecificarea(比表面积).,Cube:三次方，square:平方、二次方,Fig.10.10Solidifiedskinonasteelcasting,Notethattheskinthicknessincreaseswithelapsedtime,butthattheskinisthinneratinternalangel(内切角)thanatexternalangels(外切角).Thislatterconditioniscausedbyslowercoolingatinternalangelsthanatexternalangels.,Forexample,samevolumeforsphere,cubeandcylinder,thesequenceofsurfaceareais:spherecylindercube,sospherehaslowestsolidificationrate.,10.5.2.Shrinkage(收缩),Shrinkageistheresultofthefollowingthreeevents:Contraction(收缩)ofthemoltenmetalasitcoolspriortoitssolidification;Contractionofthemetalduringphasechangefromliquidtosolid(latentheatoffusion);Contractionofthesolidifiedmetal(thecasting)asitstemperaturedropstoambienttemperature.（largest),TABLE10.1SolidificationContractionforvariousCastMetals,Notethatgraycastiron(灰铸铁)expands,duetothatgraphitehasarelativelyhighspecificvolume,andwhenitprecipitatesasgraphite(石墨)flakes(薄片，片状的)duringsolidification,itcausesanetexpansionofthemetal.,10.6Defects(缺陷),Sevenbasiccategories(类)ofcastingdefectsnamedbytheInternationalcommitteeofFoundryTechnicalAssociationsareshownasfollows:,Metallicprojection(突出，隆起),consistingoffins(毛刺),flash(飞刺),ormassiveprojectionsasswells(隆起)androughsurface(粗燥表面，铸疵);Cavities(空洞，凹起),consistingofrounded(滚圆的)orrough(粗燥的)orexposed(外露的)cavities,includingblow-holes(砂眼),pinholes(引孔线,针孔，气孔),andshrinkagecavities(收缩孔),hottear(热撕裂),exothermicpadding(发热贴片).,Fig.1o.11Examplesofhottears.Thesedefectsoccurbecausethecastingcannotshrinkfreelyduringcooling,owingtoconstraintsinvariousportionsofthemoldsandcores.Exothermic(heatproduction)compoundsmaybeused(asexothermicpadding)tocontrolcoolingatcriticalsectiontoavoidhottearing.,Discontinuities(不连续性，间断),suchascracks,coldorhottearing,andcoldshuts(冷疤);Defectivesurface,suchassurfacefolds(表面褶皱),laps(褶皮),scars(疤痕),adheringsandlayers(粘沙层）,andoxidescale(氧化皮);Incompletecasting,suchasmisruns(铸件不满),insufficientvolumeofthemetalpouredandrunout,Reason:moltenmetalwithlowtemperatureorlowspeedofpour;Incorrectdimensionsorshape,owingtofactorssuchasimpropershrinkageallowance,patternmountingerror,irregularcontraction,definedpattern,orwarpedcasting(翅曲的，凹凸的);Inclusion(夹杂),whichformduringmelting,solidificationandmolding,spalling(涨裂，剥落).,疤痕,吹坑,泡疤,粘砂,积痕,未充满,冷疤,Fig.10.12Examplesofcommondefectsincastings.Thesedefectscanbeminimizedoreliminatedbyproperdesignandpreparationofmoldsandcontrolofpouringprocedures.,10.6.1.Porosity(气孔，孔隙),Porosityinacastingmaybecausedbyshrinkageorgasesorboth,itdeducesthestrengthandductilityofthecastingorevenfailed.Porositycausedbyshrinkagecanbereducedoreliminatedbyvariousmeans.Adequateliquidmetalshouldbeprovidedtoavoidcavitiescausedbyshrinkage.Internalorexternalchills(冷铁，冷模,冷却片),arealsoeffectivemeanstoreduceshrinkageporosity.Thefunctionofchillsistoincreasetherateofsolidificationincriticalregions.Withalloys,porositycanbereducedoreliminatedbymakingthetemperaturegradientsteep(陡的).Subjectingthecastingtohotisostaticpressing(热等静压）isanothermethodofreducingporosity.,Fig.10.13Varioustypesof(a)internaland(b)externalchills,usedincastingstoeliminateporositycausedbyshrinkage.Chillsareplacedinregionswherethereisalargervolumeofmetal,asshownin(c),Fig.10.14Solubilityofhydrogen(H)inaluminum(Al).Notethesharpdecreaseinsolubilityasthemoltenmetalbeginstosolidify.,Liquidmetalshavemuchgreatersolubility(溶解度)forgasesthandosolidmetals,asshowninFig.10.14.Whenametalbeginstosolidify,thedissolved(溶入的)gasesareexpelled(挤出)fromthesolut