文献翻译铸造及其他成形工艺.docx

文献翻译铸造及其他成形工艺.docx

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文献翻译铸造及其他成形工艺

附录

英文：

CastingandOtherFormingProcesses

DeGarmo,E.Pauletal.MaterialsandProcessesinManufacturintg.JohnWiley&Song,1998.P205-211

Casting

Castingistheintroductionofmoltenmetalintoacavityormoldwhere,uponsolidification,itbecomesanobjectwhoseshapeisdeterminedbymoldconfiguration.Castingoffersseveraladvantagesoverothermethodofmetalforming:

itisadaptabletointricateshapes,toextremelylargepieces,andtomassproduction;itcanprovidepartswithuniformphysicalandmechanicalpropertiesthroughoutand,dependingontheparticularmaterialbeingcast,thedesignofthepart,andthequantitybeingproduced,itseconomicadvantagescansurpassotherprocesses.

Categories

Twobroadcategoriesofmetal-castingprocessesexist:

ingotcasting（whichincludescontinuouscasting）andcastingtoshape.Ingotcastingsareproducedbypouringmoltenmetalintoapermanentorreusablemold.Followingsolidificationtheseingots（orbars,slabs,orbillets,asthecasemaybe）arethenfurtherprocessedmechanicallyintomanynewshapes.Castingtoshapeinvolvespouringmoltenmetalintomoldsinwhichthecavityprovidesthefinalusefulshape,followedonlybymachiningorweldingforthespecificapplication.

IngotcastingIngotcastingsmakeupthemajorityofallmetalcastingsandareseparatedintothreecategories:

staticcastingots,semi-continuousordirect-chillcastingots,andcontinuouscastingots.

StaticcastingotsStaticingotcastingsimplyinvolvespouringmoltenmetalintoapermanentmold.Aftersolidification,theingotiswithdrawnfromthemoldandthemoldcanbereused.Thismethodisusedtoproducemillionsoftonssteelannually.

Semi-continuouscastingotsAsemicontinuouscastingprocessisemployedinthealuminumindustrytoproducemostofthecastalloysfromwhichrod,sheet,strip,andplateconfigurationsaremade.Inthisprocessmoltenaluminumistransferredtoawater-cooledpermanentmoldwhichhasamovablebasemountedonalongpiston.Aftersolidificationhasprogressedfromthemoldsurfacesothatasolid"skin"isformed,thepistonismoveddown.Finallythepistonwillhavemoveditsentirelength,andtheprocessisstopped.Conventionalpracticeinthealuminumindustryutilizessuitablylubricatedmetalmolds.However,technologicaladvanceshaveallowedmajoraluminumalloyproducerstoreplacethemetalmold（atleastinpart）byanelectromagneticfieldsothatmoltenmetaltouchesthemetalmoldonlybriefly,therebymakingaproductwithamuchsmootherfinishthanthatproducedconventionally.

ContinuouscastingotsContinuouscastingprovidesamajorsourceofcastmaterial.Inthesteelandcopperindustryandisgrowingrapidlyinthealuminumindustry.Inthisprocessmoltenmetaldeliveredtoapermanentmold,andthecastingbeginsmuchinthesamewayasinsemicontinuouscasting.However,insteadoftheprocessceasingafteracertainlengthoftime,thesolidifiedingotiscontinuallyshearedorcutintolengthsandremovedduringcasting.Thustheprocessiscontinuous,thesolidifiedbarorstripbeingremovedasrapidlyasitisbeingcast.Thismethodhasmanyeconomicadvantagesoverthemoreconventionalcastingtechniques;asaresult,allmodemsteelmillsproducecontinuouscastproducts.

CastingtoshapeCastingtoshapeisgenerallyclassifiedaccordingtothemoldingprocess,moldingmaterialormethodoffeedingthemold.Therearefourbasictypesofthesecastingprocesses:

sand,permanent-mold,die,andcentrifugal

SandcastingThisisthetraditionalmethodwhichstillproducesthelargestvolumeofcast-to-shapepieces.Itutilizesamixtureofsandgrains,water,clay,andothermaterialstomakehigh-qualitymoldsforusewithmoltenmetal.This"greensand"mixtureiscompactedaroundapattern（wood,plaster,ormetal）,usuallybymachine,to20-80%ofitsbulkdensity.Thetwohalvesofthemold（thecopeanddrag）areclosedovercoresnecessarytoforminternalcavities,andthewholeassemblyisweightedordampedtopreventfloatingofthecopewhenthemetalispoured.

Othercastingprocesseswhichutilizesandsasabasiccomponentaretheshell,carbondioxide,investmentcasting,ceramicmoldingandplastermoldingprocesses.Inaddition,therearealargenumberofchemicallybondedsandswhicharebecomingincreasinglyimportant.

Permanent-moldcastingManyhigh-qualitycastingsareobtainedbypouringmoltenmetalintoamoldmadeofcastiron,steel,orbronze.Semipermanentmoldmaterialssuchasaluminum,siliconcarbide,andgraphitemayalsobeused.Themoldcavityandthegatingsystemaremachinedtothedesireddimensionsafterthemoldiscast:

thesmoothsurfacefrommachiningthusgivesagoodsurfacefinishanddimensionalaccuracytothecasting.Toincreasemoldlifeandtomakeejectionofthecastingeasier,thesurfaceofthemoldcavityisusuallycoatedwithcarbonsootorarefractoryslurry;thesealsoserveasheatbarriersandcontroltherateofcoolingofthecasting.Theprocessisusedforcastironandnonferrousalloyswithadvantagesoversandcastingsuchassmoothersurfacefinish,closertolerances,andhigherproductionrates.

DiecastingAfurtherdevelopmentofthepermanentmoldingprocessisdiecasting.Moltenmetalisforcedintoadiecavityunderpressuresof100-100,000psi.Twobasictypesofdie-castingmachinesarehot-chamberandcold-chamber.Inthehot-chambermachine,aportionofthemoltenmetalisforcedintothecavityatpressuresuptoabout2,000psi.Theprocessisusedforcastinglow-melting-pointalloyssuchaslead,zinc,andtin.

Inthecold-chamberprocessthemoltenmetalisladledintotheinjectioncylinderandforcedintothecavityunderpressureswhichareabout10timesthoseinthehot-chamberprocess.High-melting-pointalloyssuchasaluminum-,magnesium-,andcopper-basealloysareusedinthisprocess.Diecastinghastheadvantagesofhighproductionrates,highqualityandstrength,surfacefinishontheorderof40—100-microinchrms（rootmeansquare）,andclosetolerances,withthinsections.

Rheocastingisthecastingofamixtureofsolidandliquid.Inthisprocessthealloytobecastismeltedandthenallowedtocooluntilitisabout50%solidand50%liquid.Vigorousstirringpromotesliquidlikepropertiesofthismixturesothatitcanbeinjectedinadie-castingoperation.Amajoradvantageofthistypeofcastingprocessisexpectedtobemuchreduceddieerosionduetothelowercastingtemperatures.

CentrifugalcastingInertialforcesofrotationdistributemoltenmetalintothemoldcavitiesduringcentrifugalcasting,ofwhichtherearethreecategories:

truecentrifugalcasting,semicentrifugalcasting,andcentrifuging.Thefirsttwoprocessesproducehollowcylindricalshapesandpartswithrotationalsymmetryrespectively.Inthethirdprocess,themoldcavitiesarespunatacertainradiusfromtheaxisofrotation;thecentrifugalforcethusincreasesthepressureinthemoldcavity.

Therotationalspeedincentrifugalcastingischosentogivebetween40and60gacceleration.Diesmaybemadeofforgedsteelorcastiron.Colloidalgraphiteisusedonthediestofacilitateremovalofthecasting.

Successfuloperationofanymetal-castingprocessrequirescarefulconsiderationofmolddesignandmetallurgicalfactors.

SheetandPlateBending

Bendingisamethodofproducingshapesbystressingmetalbeyonditsyieldstrength,butnotpastitsultimatetensilestrength.Theforcesappliedduringbendingareinoppositedirections,justasinthecuttingofsheetmetal.Bendingforces,however,arespreadfartherapart,resultinginplasticdistortionofmetalwithoutfailure.

Thebendingprocessappearstobesimple;yet,inreality,itisarathercomplexprocessinvolvinganumberoftechnicalfactors.Includedarecharacteristicsoftheworkpiecematerialflowandreactionsduringvariousstagesofdeformation,theeffectoftoolingdesignonforcerequiredtoformthebend,andthetypeofequipmentused.

Inthelarge,variedfieldofsheetmetalandplatefabricating,severaltypesofbendingmachinesareused.Pressbrakespredominateinshopsthatprocessheavy-gagematerials,becausetheyarewellsuitedtosuchapplicationsandalsobecausetheyareadaptabletoothermetalworkingoperations,suchaspunching,piercing,blanking,notching,perforating,embossing,shearing,anddrawing.

Light-gagemetaltypicallyisformedwithspecializedbendingmachines,whicharealsodescribedasleaf,pan,orboxbrakes;aswingfolders;andasswivelbenders.Equipmentofthistypeisoftenmanuallyoperated.

Theprincipalkindsofequipmentusedtobendsheetmetalandplatecanbegroupedintothefollowingcategories:

Mechanicalpressbrakes—elongatedpresseswithnumeroustoolingoptions.Workisperformedbymeansofenergyreleasedfromamotor-drivenflywheel.Thesemachinesnormallyhavea3"or4"strokelength.

Hydraulicpressbrakes—stretchedC-framepressesthatarelikewisecompatiblewithawiderangeanddiversityoftooling.High-pressureoilinhydrauliccylinderssuppliestheforce,whichisdirecteddownwardinmostmodels.Thestrokinglengthusuallyexceeds6".

Hydraulic-mechanicalpressbrakes—presseswithdrivesthatcombinehydraulicandmechanicalprinciples.Inoperation,oilforcesapistontomovearmsthatpushtheramtowardthebed.

Pneumaticpressbrakes—low-tonnagebendingmachinesthatareavailablewithsuitabletoolingoptions.

Bendingbrakes—poweredormanualbrakescommonlyusedforbendinglight-gagesheetmetal.

Specialequipment—custom-builtbendersandpanelformersdesignedforspecificformingapplications.

Termsusedtodescribevariousaspectsofsheetmetalbendi