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1、沈陽(yáng)理工大學(xué)學(xué)位論文27附錄A英文原文A.1FORGINGBulkdefirnnationofmetalsreferstovariousprocesses,suchasforging,rolling,orextruding,wherethereisacontrolledplasticfloworworkingofmetalsintousefulshapes.Themostwellknownoftheseprocessesisforgingwheredeformationisaccomplishedbymeansofpressure,impactblows,oracombinationofbot
2、h.HammerForgingHanunerforgingconsistsofstrikingthehotmetalwithalargesemiautomatichammer.Ifnodiesareinvolved,theforgingwillbedependentmainlyontheskilloftheoperator.Ifclosedorimpressiondiesareused,oneblowisstruckforeachofseveral(liecavities.A-gain,productivityandqualitydependtoalargedegreeontheskillof
3、thehanimeroperatorandthetooling.PressForgingPressforgingischaracterizedbyaslowsqueezingaction.Again,openorcloseddiesmaybeused.Theopendiesareusedchieflyforlarge,simple-geometrypartsthatarelatermachinedtoshape.Closed-dieforgingrelieslessonoperatorskillawlmoreonthedesignofthepreformandforgingdies.2Asan
4、exampleoftheversatilityoftheprocess,newerdevelopmentshavemadeitpossibletoproducebevelgearswithstraightorhelicalteeth.Rotationofthedie(luringpenetrationwillpressbevelgearswithspiralteeth.Open-dieForgingOpen-dieforgingisdistinguishedbythefactthatthemetalisnevercompletelyconfinedasitisshapedbyvariousdi
5、es.Mostopen-dieforgingsareproducedonflat,V,orswagingdies.Roundswaging(liesandVdiesareusedinpairsorwithaflatdie.Thetop(lieisattachedtotheramofthepress,andthebottomdieisattachedtothehammeranvilor,inthecaseofpressopen-dieforging,tothepressbed.Astheworkpieceishammeredorpressed,itisrepeatedlymanipulatedb
6、etweenthediesuntilhotworkingforcesthemetaltothefinaldimensions,as-showninFig.1.Afterforging,thepartisrough-andfinished-machined.Asanexampleoftheamountofmaterialallowed沈陽(yáng)理工大學(xué)學(xué)位論文28formachining,a6.5in.diametershaftwouldhavetobeforgedto7.4in.dianieter.Inopen-dieforgingofsteel,aruleofthumbsaysthat50lbof
7、fallingweightisrequiredforeachsquareinchofcrosssection.Impression-dieForgingInthesimplestexampleofimpression-dieforging,twodiesarebroughttogether,andtheworkpieceundergoesplasticdeformationuntilitsenlargedsidestouchthesidewallsofthedie(Fig.2).Asmallamountofmaterialisforcedoutsidethedieimpression,form
8、ingflashthatisgraduallythinned.Theflashcoolsrapidlyandpresentsincreasedresistancetodeformation,effectivelybecomingapartofthetool,andhelpsbuildupl)ressUreinsidethebulkofthework-piecethataidsmaterialflowintounfilledimpressions.沈陽(yáng)理工大學(xué)學(xué)位論文29Closed-dieforgings,aspecialformofimpression-dieforging,doesnotd
9、ependontheformationofflashtoachievecompletefillingofthe(lie.Thusclosed-dieforgingisconsiderablymoredemandingondiedesign.Sincepressingisoftencompletedinonestroke,carefulcontroloftheworkpieeevolumeisnecessaiytoachievecompletefillingwithoutgeneratingextremepressuresinthediesfromoverfilling.ExtrusionFor
10、gingAswithupsetting,extrusionforgingisoftenaccomplishedbycoldworking.Threeprincipaltypesofmetaldisplacementbyplasticflowareinvolved.Backwardandforward,tube,andimpactextrusionareshowninFig.3.Themetalisplacedinacontainerandcorn-pressedbyarammovementuntilpressureinsidethemetalreachesflow-stresslevels.T
11、heworkpiececompletelyfillsthecontainer,andadditionalpressurecausesittoleavethroughanorificeandformtheextrudedproduct.Extrudedproductsmaybeeithersolidorhollowshapes.Tubeextrusionisusedtoproducehollowshapessuchascontainersandpipes.Reverse-impactextrusionisusedformassproductionofaluminumcans.Theramhits
12、aslugofmetalinthedieathighimpact,usually15timestheyieldstrengthofthemetal,whichcausesittoflowinstantaneouslyupthewallsofthedie.Othercommonhollowextrusionproductsareaerosolcans,lipstickcases,flashlightcases,andvacuumbottles.Secondaryoperations,suchasheading,threadrolling,dimpling,andmachining,areofte
13、nneededtocompletetheitems.沈陽(yáng)理工大學(xué)學(xué)位論文30Generallysteelimpactsarelimitedto2.5timesthepunchdiameter.Hydraulicpressesareusedforloadsofover2000tonsbecausetheyhaveagreatervariationinstrokelength,speed,andothereconomicadvantages.Tolerancesvarywithmaterialsariddesign,hutproductionrunscallingfor0.002-to0.005-
14、in,toleranceareregularlymade.RollForgingRollforginginitssimplestformconsistsofaheatedbilletpassingbetweenapairofrollsthatdeformitalongitslength(Fig.8-4).Comparedtoconventionalrollingprocesses,therollsarerelativelysmallindiameterandserveasanarborintowhichtheforgingtoolsaresecured.Theactivesurfaceofth
15、etooloccupiesonlyaportion(usuallyhalf)oftherollcircumferencetoaccommodatethefullcrosssectionofthestock.Thereductionofthecrosssectionobtainableinonepassislimitedbythetendencyofthematerialtospreadandformanundesirableflashthatmaybeforgedintothesurfaceasadefectinthesubsequentoperations.Theworkpieceisint
16、roducedrepeatedlywith90rota-tionbetweenpasses.RingRollingRingrollingoffersahomogeneouscircumferentialgrainflow,easeoffabricationandmachining,andversatilityofmaterialsize.Manu-factureofarolledringstartswithashearedblank,whichisforgedtoapancake,punched,andpierced.Thereisnolimittothesizeoftherolledrings,rangingfromroller-bearingsleevestoFig.4Rollforgingrings25ftindiameterwithfaceheightsof80in.Variousprofilesmayberolledbysuitablyshapingthedriven,idlingrolls.
機(jī)械外文翻譯--鍛造.doc
