外文翻译铸造及其他成形工艺.docx
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外文翻译铸造及其他成形工艺.docx
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外文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
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