搜索
ManufacturingEngineering&TechnologyPrefaceManufacturing---makingproductThebookdealswiththemethodsandtechnologiesoffabricatingmetallicworkpieces.Generalprocessoffabricatingametallicworkpiece:selectingsuitablematerials→hotworking(casting,forging,welding,etc.)toformroughworkpiece→finishedworkpiecebymachining(turning,grinding,planing,milling,etc.)Theknowledgeshouldbemastered1Generalprocessingmethodsandproceduresofmetalparts2Thestructuraltechnologyofaworkpiecefabricatedbyacertainprocessingmethod3TheprofessionalwordsandphrasescommonlyusedinthetextbookChapter1FundamentalsofMetalCastingThecastingprocessbasicallyinvolvespouringmoltenmetalintoamoldpatternedaftertheparttobemanufactured,allowingittosolidifyandremovingthepartfromthemold.Thedefectssuchasshrinkages,porosities,cracks,etc.willtakeplaceduringsolidification,whichisdeterminedbythetypeofmetal,thethermalpropertiesofboththemetalandthemold,andtheshapeofthecasting.1.1SolidificationofPureMetalsBecauseapuremetalhasaclearlydefinedmelting(orfreezing)point,itsolidifiesataconstanttemperature.Afterthetemperatureofthemoltenmetaldropstoitsfreezingpoint,itstemperatureremainsconstantwhilethelatentheatoffusionisgivenoff.Thesolidificationfront(solid-liquidinterface)movesthroughthemoltenmetalfromthemoldwallsintowardthecenter.Mainpoints：1.纯金属的凝固特点2.过冷现象和过冷度3.冷却速度对晶粒尺寸的影响1.2SolidificationofAlloysSolidificationinalloysbeginswhenthetemperaturedropsbelowtheliquidus,TL,andiscompletewhenitreachesthesolidus,TS.Withinthistemperaturerange,thealloyisinamushyorpastystateconsistingofcolumnardendrites.Thewidthofthemushyzone(wherebothliquidandsolidphasesarepresent)isanimportantfactorduringsolidification.Thiszoneisdescribedintermsofatemperaturedifference,knownasthefreezingrange:Freezingrange=TL–TSMainpoints：1.合金的凝固特点2.相图的特性点、线、区3.凝固区间的大小对合金组织性能的影响Coolingrateversusthewidthofmushyzone1.3FluidflowincastingWhenmoltenmetalispouredthroughapouringbasinorcup;itthenflowsthroughthegatingsystem(consistingofsprue,runners,andgates)intothemoldcavity.Thesprueisataperedverticalchannelthroughwhichthemoltenmetalflowsdownwardinthemold.Runnersarethechannelsthatcarrythemoltenmetalfromthesprueintothemoldcavityorconnectthespruetothegate(thatportionoftherunnerthroughwhichthemoltenmetalentersthemoldcavity).Risers(alsocalledfeeders)serveasreservoirsofmoltenmetaltosupplyanymoltenmetalnecessarytopreventporosityduetoshrinkageduringsolidification.Mainpoints：浇注系统的组成和作用直浇道：充型压力横浇道：档渣内浇道：调节液流冒口：补缩1.4GrainstructureincastingsAtthemoldwalls,whichareatambienttemperatureortypicallyaremuchcoolerthanthemoltenmetal,themetalcoolsrapidlyandproducesasolidifiedskin,orshell,offineequiaxedgrains.Thegrainsgenerallygrowinadirectionoppositetothatoftheheattransferoutthroughthemold.Thosegrainsthathavefavorableorientationgrowpreferentiallyandarecalledcolumnargrains.Thosegrainsthathavesubstantiallydifferentorientationsareblockedfromfurthergrowth.Asthedrivingforceoftheheattransferisreducedawayfromthemoldwalls,thegrainsbecomeequiaxedandcoarse.equiaxedgrains等轴晶Mainpoints：铸件的组织特点及性能表层：细晶中间：柱状晶心部：等轴晶1.5ShrinkageBecauseoftheirthermalexpansioncharacteristics,metalsusuallyshrink(contract)duringsolidificationandwhilecoolingtoroomtemperature.Shrinkageistheresultofthefollowingthreesequentialevents:1）Contractionofthemoltenmetalasitcoolspriortoitssolidification.2）Contractionofthemetalduringphasechangefromliquidtosolid.3）Contractionofthesolidifiedmetal(casting)asitstemperaturedropstoambienttemperature.Shrinkagecancausedimensionalchangesandassociatedporosityandleadtowarpingandcracking,whichcaninturncompromisethemechanicalpropertiesofthecasting.Mainpoints：收缩造成缺陷：缩孔、应力、变形、开裂1.6PorosityPorosityinacastingmaybecausedbyshrinkage,entrainedordissolvedgases,orboth.Porousregionscandevelopincastingsbecauseofshrinkageofthesolidifiedmetal.Thinsectionsinacastingsolidifysoonerthanthickerregions;asaresult,moltenmetalflowsintothethickerregionsthathavenotyetsolidified.Porousregionsmaydevelopattheircentersbecauseofcontractionasthesurfacesofthethickerregionbegintosolidifyfirst.Microporosityalsocandevelopwhentheliquidmetalsolidifiesandshrinksbetweendendritesandbetweendendritebranches.Mainpoints：孔的形成因素及防止措施防止措施：顺序凝固1.7ThedevelopmentofthermalstressMainpoints：了解热应力的形成应力方向：快（慢）冷部位形成压（拉）应力防止措施：同时凝固1.8OtherDefectsChapter2MetalCastingProcessesandEquipmentCastingProcessesPatternPatternsareusedtomoldthesandmixtureintotheshapeofthecastingandmaybemadeofwood,plastic,ormetal.Theselectionofapatternmaterialdependsonthesizeandshapeofthecasting,thedimensionalaccuracyandthequantityofcastingsrequired,andthemoldingprocess.Category:1)Onepiecepattern2)Splitpattern•3)Match-platepatternMainpoint：了解模板的特点和用途2.1Expendable-mold,Permanent-patterncastingprocessAtypicalsandmoldconsistsof90%sand,7%clay,and3%Water.Themoldisproducedfromapattern;insomeprocesses,suchassandandshellcasting,themoldisexpendable,butthepatternisreusedtoproduceseveralmolds.Suchprocessesarereferredtoasexpendable-mold,permanent-patterncastingprocesses.Mainpoints：了解铸型的购造和一次性铸型、永久性模样的铸造特点VacuumCastingThepatterniscoveredtightlywithathinsheetofpla