机械外文翻译--锻造.doc

沈阳理工大学学位论文27附录A英文原文A.1FORGINGBulkdefirnnationofmetalsreferstovariousprocesses,suchasforging,rolling,orextruding,wherethereisacontrolledplasticfloworworkingofmetalsintousefulshapes.Themostwellknownoftheseprocessesisforgingwheredeformationisaccomplishedbymeansofpressure,impactblows,oracombinationofboth.HammerForgingHanunerforgingconsistsofstrikingthehotmetalwithalargesemiautomatichammer.Ifnodiesareinvolved,theforgingwillbedependentmainlyontheskilloftheoperator.Ifclosedorimpressiondiesareused,oneblowisstruckforeachofseveral(liecavities.A-gain,productivityandqualitydependtoalargedegreeontheskillofthehanimeroperatorandthetooling.PressForgingPressforgingischaracterizedbyaslowsqueezingaction.Again,openorcloseddiesmaybeused.Theopendiesareusedchieflyforlarge,simple-geometrypartsthatarelatermachinedtoshape.Closed-dieforgingrelieslessonoperatorskillawlmoreonthedesignofthepreformandforgingdies.2Asanexampleoftheversatilityoftheprocess,newerdevelopmentshavemadeitpossibletoproducebevelgearswithstraightorhelicalteeth.Rotationofthedie(luringpenetrationwillpressbevelgearswithspiralteeth.Open-dieForgingOpen-dieforgingisdistinguishedbythefactthatthemetalisnevercompletelyconfinedasitisshapedbyvariousdies.Mostopen-dieforgingsareproducedonflat,V,orswagingdies.Roundswaging(liesandVdiesareusedinpairsorwithaflatdie.Thetop(lieisattachedtotheramofthepress,andthebottomdieisattachedtothehammeranvilor,inthecaseofpressopen-dieforging,tothepressbed.Astheworkpieceishammeredorpressed,itisrepeatedlymanipulatedbetweenthediesuntilhotworkingforcesthemetaltothefinaldimensions,as-showninFig.1.Afterforging,thepartisrough-andfinished-machined.Asanexampleoftheamountofmaterialallowed沈阳理工大学学位论文28formachining,a6.5in.diametershaftwouldhavetobeforgedto7.4in.dianieter.Inopen-dieforgingofsteel,aruleofthumbsaysthat50lboffallingweightisrequiredforeachsquareinchofcrosssection.Impression-dieForgingInthesimplestexampleofimpression-dieforging,twodiesarebroughttogether,andtheworkpieceundergoesplasticdeformationuntilitsenlargedsidestouchthesidewallsofthedie(Fig.2).Asmallamountofmaterialisforcedoutsidethedieimpression,formingflashthatisgraduallythinned.Theflashcoolsrapidlyandpresentsincreasedresistancetodeformation,effectivelybecomingapartofthetool,andhelpsbuildupl)ressUreinsidethebulkofthework-piecethataidsmaterialflowintounfilledimpressions.沈阳理工大学学位论文29Closed-dieforgings,aspecialformofimpression-dieforging,doesnotdependontheformationofflashtoachievecompletefillingofthe(lie.Thusclosed-dieforgingisconsiderablymoredemandingondiedesign.Sincepressingisoftencompletedinonestroke,carefulcontroloftheworkpieeevolumeisnecessaiytoachievecompletefillingwithoutgeneratingextremepressuresinthediesfromoverfilling.ExtrusionForgingAswithupsetting,extrusionforgingisoftenaccomplishedbycoldworking.Threeprincipaltypesofmetaldisplacementbyplasticflowareinvolved.Backwardandforward,tube,andimpactextrusionareshowninFig.3.Themetalisplacedinacontainerandcorn-pressedbyarammovementuntilpressureinsidethemetalreachesflow-stresslevels.Theworkpiececompletelyfillsthecontainer,andadditionalpressurecausesittoleavethroughanorificeandformtheextrudedproduct.Extrudedproductsmaybeeithersolidorhollowshapes.Tubeextrusionisusedtoproducehollowshapessuchascontainersandpipes.Reverse-impactextrusionisusedformassproductionofaluminumcans.Theramhitsaslugofmetalinthedieathighimpact,usually15timestheyieldstrengthofthemetal,whichcausesittoflowinstantaneouslyupthewallsofthedie.Othercommonhollowextrusionproductsareaerosolcans,lipstickcases,flashlightcases,andvacuumbottles.Secondaryoperations,suchasheading,threadrolling,dimpling,andmachining,areoftenneededtocompletetheitems.沈阳理工大学学位论文30Generallysteelimpactsarelimitedto2.5timesthepunchdiameter.Hydraulicpressesareusedforloadsofover2000tonsbecausetheyhaveagreatervariationinstrokelength,speed,andothereconomicadvantages.Tolerancesvarywithmaterialsariddesign,hutproductionrunscallingfor0.002-to0.005-in,toleranceareregularlymade.RollForgingRollforginginitssimplestformconsistsofaheatedbilletpassingbetweenapairofrollsthatdeformitalongitslength(Fig.8-4).Comparedtoconventionalrollingprocesses,therollsarerelativelysmallindiameterandserveasanarborintowhichtheforgingtoolsaresecured.Theactivesurfaceofthetooloccupiesonlyaportion(usuallyhalf)oftherollcircumferencetoaccommodatethefullcrosssectionofthestock.Thereductionofthecrosssectionobtainableinonepassislimitedbythetendencyofthematerialtospreadandformanundesirableflashthatmaybeforgedintothesurfaceasadefectinthesubsequentoperations.Theworkpieceisintroducedrepeatedlywith90rota-tionbetweenpasses.RingRollingRingrollingoffersahomogeneouscircumferentialgrainflow,easeoffabricationandmachining,andversatilityofmaterialsize.Manu-factureofarolledringstartswithashear