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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,oneblowisstruckforeachofseveralliecavities.Again,productivityandqualitydependtoalargedegreeontheskillofthehanimeroperatorandthetooling.PressForgingPressforgingischaracterizedbyaslowsqueezingaction.Again,openorcloseddiesmaybeused.Theopendiesareusedchieflyforlarge,simplegeometrypartsthatarelatermachinedtoshape.Closeddieforgingrelieslessonoperatorskillawlmoreonthedesignofthepreformandforgingdies.2Asanexampleoftheversatilityoftheprocess,newerdevelopmentshavemadeitpossibletoproducebevelgearswithstraightorhelicalteeth.Rotationofthedieluringpenetrationwillpressbevelgearswithspiralteeth.OpendieForgingOpendieforgingisdistinguishedbythefactthatthemetalisnevercompletelyconfinedasitisshapedbyvariousdies.Mostopendieforgingsareproducedonflat,V,orswagingdies.RoundswagingliesandVdiesareusedinpairsorwithaflatdie.Thetoplieisattachedtotheramofthepress,andthebottomdieisattachedtothehammeranvilor,inthecaseofpressopendieforging,tothepressbed.Astheworkpieceishammeredorpressed,itisrepeatedlymanipulatedbetweenthediesuntilhotworkingforcesthemetaltothefinaldimensions,asshowninFig.1.Afterforging,thepartisroughandfinishedmachined.Asanexampleoftheamountofmaterialallowed沈阳理工大学学位论文28formachining,a6.5in.diametershaftwouldhavetobeforgedto7.4in.dianieter.Inopendieforgingofsteel,aruleofthumbsaysthat50lboffallingweightisrequiredforeachsquareinchofcrosssection.ImpressiondieForgingInthesimplestexampleofimpressiondieforging,twodiesarebroughttogether,andtheworkpieceundergoesplasticdeformationuntilitsenlargedsidestouchthesidewallsofthedieFig.2.Asmallamountofmaterialisforcedoutsidethedieimpression,formingflashthatisgraduallythinned.Theflashcoolsrapidlyandpresentsincreasedresistancetodeformation,effectivelybecomingapartofthetool,andhelpsbuilduplressUreinsidethebulkoftheworkpiecethataidsmaterialflowintounfilledimpressions.沈阳理工大学学位论文29Closeddieforgings,aspecialformofimpressiondieforging,doesnotdependontheformationofflashtoachievecompletefillingofthelie.Thuscloseddieforgingisconsiderablymoredemandingondiedesign.Sincepressingisoftencompletedinonestroke,carefulcontroloftheworkpieeevolumeisnecessaiytoachievecompletefillingwithoutgeneratingextremepressuresinthediesfromoverfilling.ExtrusionForgingAswithupsetting,extrusionforgingisoftenaccomplishedbycoldworking.Threeprincipaltypesofmetaldisplacementbyplasticflowareinvolved.Backwardandforward,tube,andimpactextrusionareshowninFig.3.Themetalisplacedinacontainerandcornpressedbyarammovementuntilpressureinsidethemetalreachesflowstresslevels.Theworkpiececompletelyfillsthecontainer,andadditionalpressurecausesittoleavethroughanorificeandformtheextrudedproduct.Extrudedproductsmaybeeithersolidorhollowshapes.Tubeextrusionisusedtoproducehollowshapessuchascontainersandpipes.Reverseimpactextrusionisusedformassproductionofaluminumcans.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,hutproductionrunscallingfor0.002to0.005in,toleranceareregularlymade.RollForgingRollforginginitssimplestformconsistsofaheatedbilletpassingbetweenapairofrollsthatdeformitalongitslengthFig.84.Comparedtoconventionalrollingprocesses,therollsarerelativelysmallindiameterandserveasanarborintowhichtheforgingtoolsaresecured.Theactivesurfaceofthetooloccupiesonlyaportionusuallyhalfoftherollcircumferencetoaccommodatethefullcrosssectionofthestock.Thereductionofthecrosssectionobtainableinonepassislimitedbythetendencyofthematerialtospreadandformanundesirableflashthatmaybeforgedintothesurfaceasadefectinthesubsequentoperations.Theworkpieceisintroducedrepeatedlywith90rotationbetweenpasses.RingRollingRingrollingoffersahomogeneouscircumferentialgrainflow,easeoffabricationandmachining,andversatilityofmaterialsize.Manufactureofarolledringstartswithashearedblank,whichisforgedtoapancake,punched,andpierced.Thereisnolimittothesizeoftherolledrings,rangingfromrollerbearingsleevestoFig.4Rollforgingrings25ftindiameterwithfaceheightsof80in.Variousprofilesmayberolledbysuitablyshapingthedriven,idlingrolls.
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