制造工程与技术12MetalCasting课件

Chapter12MetalCasting:Design,MaterialsandEconomics12章金属铸件：设计、材料和经济性Content12.1Introduction简介

12.2DesignConsiderations设计考虑

12.3CastingAlloys铸造合金

12.4TheEconomicsofCasting铸件经济性12.1IntroductionIntheprecedingtwochapters,itwasnotedthatsuccessfulcastingpracticerequirescarefullycontrolofallargenumberofvariables.Thesevariablespertain(属于)totheparticularcharacteristicsofthemetalsandalloyscast,themethodofcasting,themoldanddiematerials,themolddesignandvariousprocessparameters.Theflowofthemoltenmetalinthemoldcavities,thegatingsystems,therateofcooling,andthegasesevolvedallinfluencethequalityofacasting.从前两章中的介绍中，我们知道了只有对大量的变量进行仔细的控制才能获得成功的铸造生产。这些变量与金属和合金的铸造特性、铸造方法、铸型设计以及各种工艺参数相关。金属液在型腔中的流动、浇注系统、冷却率和卷入气体等都影响铸件质量。

12.2DesignConsiderationsTheseprinciples（原则）wereestablishedprimarilythroughpracticalexperience,butnewanalyticalmethods,processmodeling,andcomputer-aideddesignandmanufacturingtechniquesarenowcomingintowideruse,improvingproductivity(生产力)andthequalityofcastingsandresultinginsignificantcostsavings.

12.2.1Designforexpendable-moldcasting(一次性模铸造的设计)

1.

Corners,anglesandsectionthickness.Sharpcorners(方角),angles(倒角)andfillets(肩角)shouldbeavoided(Fig.12.1),becausetheyactasstressraisersandmaycausecrackingandtearingofthemetals(aswellasofthedies)duringsolidification.Filletradiishouldbeselectedtoreducestressconcentrationsandtoensureproperliquid-metalflowduringthepouringprocess.Filletradiiusuallyrangefrom3mmto25mm,althoughsmallerradiimaybepermissible(容许的)insmallcastingsandinlimitedapplications.Ontheotherhand,ifthefilletradiiaretoolarge,thevolumeofthematerialsinthoseregionsisalsolargeand,consequently,therateofcoolingislower.

Themostsignificantconsiderationsareidentified(标示)andaddressed(强调).Fig.12.1Suggesteddesignmodificationstoavoiddefectsincastings.Notethatsharpcornersareavoidedtoreducestressconcentrations.Sectionchangesincastingsshouldbesmoothlyblendedintoeachother.Becausethecoolingrateinregionswithlargethicknessislower,theyarecalledhotspots(热节),whichcanbedevelopedtoshrinkagecavitiesandporosity(缩孔和疏松).Itisimportanttomaintain(保持),asmuchaspossible,uniformcross-sectionsandwallthicknessesthroughoutthecastingtoavoidshrinkagecavities.

Fig.12.2Examplesofdesignsshowingtheimportanceofmaintaininguniformcross-sectionsincastingstoavoidhotspotsandshrinkagecavities2.Flatareas(平面面积).Largeflatareas(plainsurfaces)shouldbeavoided,becausetheymaywarp(翘曲)duringcoolingbecauseoftemperaturegradientsordeveloppoorsurfacefinish.Flatsurfacescanbebrokenupwithribs(肋条)andserrations.3.Shrinkage.Thereshouldbeallowancesforshrinkageduringsolidification.Stagger:错开排列,intersectiongeometry:横截面几何形状.Patterndimensionsshouldalsoprovideforshrinkageofthemetalduringsolidificationandcooling.Patternmaker’sshrinkageallowances:模型制作的收缩允许率,usuallyrangefromabout10mm/mto20mm/m.4.Partingline.Tobealongaflatplane,ratherthancontoured,locatedatthecornersoredgesofcastings.Itisimportantformolddesignandaffectsmanyfactors.Fig.12.5Redesignofacastingbymakingthepartinglinestraighttoavoiddefects5.Draft(减面率).Toenableremovalofthepatternwithoutdamagingthemold.Rangingfrom5mm/mmto15mm/m,angles:0.5oto2o,forinsideangles,1oto4o.6.Dimensionaltolerance(尺寸公差).Aswideaspossible,withinthelimitsofgoodpartperformance,usually±0.8to±6mmforsmallandlargecastings.7.MachiningAllowance.Allowancesusuallyrangefromabout2mmto5mmforsmallcastingstomorethan25mmforlargecastings.8.Residualstress(残余应力).Thedifferentcoolingrateswiththebodyofacastingcauseresidualstress.Stressrelievingmaythusbenecessarytoavoiddistortionsincriticalapplications.12.2.3.DesignforPermanent-MoldCasting:永久型模铸设计Itissimilarwithexpendable-moldcasting,exceptdraftanglesreduceto1/2to1/4o.galling:咬住Fig.12.7Examplesofundesirableanddesirabledesignpracticesfordie-castparts.Notethatsection-thicknessuniformityismaintainedthroughoutthepart.Fig.12.8Mechanicalpropertiesforvariousgroupsofcastalloys.Notethatgrayironhasverylittleductilityandtoughness.Comparedwithmostothercastalloys,someofwhichundergoconsiderableelongationandreductionofareaintension.Notealsothatevenwithinthesamegroup,thepropertiesofcastalloysvaryoverwiderange,particularlyforcaststeels.12.3.1.Nonferrouscastingalloys:非铁磁性铸造合金1.Aluminum-basedalloys(铝合金)havehighelectricalconductivity(电导率)andgenerallygoodatmosphericcorrosionresistance.Nontoxic(非毒性)andgoodmachinability.Application:architecturalanddecorativeuse,automobilecomponents.Fig.12.8Mechanicalpropertiesforvariousgroupsofcastalloys.Notethatgrayironhasverylittleductilityandtoughness.Comparedwithmostothercastalloys,someofwhichundergoconsiderableelongationandreductionofareaintension.Notealsothatevenwithinthesamegroup,thepropertiesofcastalloysvaryoverwiderange,particularlyforcaststeels.

PartsmadeofAl-andMg-basedalloysareknownaslight-metalcasting.

2.Magnesium-basedalloyswithlowestdensityofallcommercialcastingalloys,goodcorrosionresistanceandmoderatestrength.3.Copper-basedalloys,goodelectricalandthermalconductivity,corrosionresistanceandnontoxicity,wearproperties,suitableforbearingmaterials.4.Zinc-basedalloys,goodfluidityandsufficientstrengthforstructuralapplications,commonuseindiecasting.5.High-temperaturealloys,Titaniumalloysandsuperalloys,meltingtemperatureupto1650oC;specialtechniquesareusedtocastthesealloysintojet-androcket-enginecomponents.Ductile(nodular)castiron,typicallyusedformachineparts,andcrankshafts,specifiedbytwo-digitnumbers,poordampingandthermalconductivity,hightensilestrengthandfatigueresistance..Whitecastironusedmainlyinlinersformachinerytoprocessabrasivematerialsrollsforrollingmills,andrailroad-carbrakesbecauseofitsextremehardnessandwearresistance.Malleableiron.Usedforrailroadequipmentandvarioustypesofhardware.Specifiedbyafive-digitdesignation(命名).Compactedgraphiteiron.Firstproducedcommerciallyin1976,withpropertiesthatfallbetweenthoseofgrayandductileirons.2.Caststeels.Thehightemperaturesinvolvedpresentdifficultiesintheselectionofmoldmaterials,particularlyinviewofthehighreactivityofsteelswithoxygen,inmeltingandpouringthemetal.Itpossessesmoreuniform(isotropic)thanthosemadebymechanicalworkingpossessing.Bewelded,butaffectingthemicrostr