模具毕业设计论文外文翻译.doc

模具毕业设计论文外文翻译.doc

《模具毕业设计论文外文翻译.doc》由会员分享，可在线阅读，更多相关《模具毕业设计论文外文翻译.doc（6页珍藏版）》请在冰豆网上搜索。

InjectionMolding

Thebasicconceptofinjectionmoldingrevolvesaroundtheabilityofathermoplasticmaterialtobesoftenedbyheatandtohardenwhencooled.Inmostoperations,granularmaterial（theplasticresin）isfedintooneendofthecylinder（usuallythroughafeedingdeviceknownasahopper）,heated,andsoftened（plasticizedorplasticated）,forcedouttheotherendofthecylinder,whileitisstillintheformofamelt,throughanozzleintoarelativelycoolmoldheldclosedunderpressure.Here,themeltcoolsandhardensuntilfullyset-up.Themoldisthenopened,thepieceejected,andthesequencerepeated.

Thus,thesignificantelementsofaninjectionmoldingmachinebecome:

1）thewayinwhichthemeltisplasticized（softened）andforcedintothemold（calledtheinjectionunit）;2）thesystemforopeningthemoldandclosingitunderpressure（calledtheclampingunit）;3）thetypeofmoldused;4）themachinecontrols.

Thepartofaninjection-moldingmachine,whichconvertsaplasticmaterialfromasoldphasetohomogeneousseni-liguidphasebyraisingitstemperature.Thisunitmaintainsthematerialatapresenttemperatureandforceitthroughtheinjectionunitnozzleintoamold.Theplungerisacombinationoftheinjectionandplasticizingdeviceinwhichaheatingchamberismountedbetweentheplungerandmold.Thischamberheatstheplasticmaterialbyconduction.Theplunger,oneachstorke;pushesunmeltedplasticmaterialintothechamber,whichinturnforcesplasticmeltatthefrontofthechamberoutthroughthenozzle

Thepartofaninjectionmoldingmachineinwhichthemoldismounted,andwhichprovidesthemotionandforcetoopenandclosethemoldandtoholdthemoldclosewithforceduringinjection.Thisunitcanalsoprovideotherfeaturesnecessaryfortheeffectivefunctioningofthemoldingoperation.Movingplateisthememberoftheclampingunit,whichismovedtowardastationarymember.themovingsectionofthemoldisboltedtothismovingplate.Thismemberusuallyincludestheejectorholesandmoldmountingpatternofblotholesor“T”slots.Stationaryplateisthefixedmemberoftheclampingunitonwhichthestationarysectionofthemoldisbolted.Thismemberusuallyincludesamold-mountingpatternofbolesor“T”slots.Tierodsarememberoftheclampingforceactuatingmechanismthatserveasthetensionmemberoftheclampwhenitisholdingthemoldclosed.Theyalsoserveasagutdememberforthemovableplate.Ejectorisaprovisionintheclampingunitthatactuatesamechanismwithinthemoldtoejectthemoldedpart（s）fromthemold.Theejectionactuatingforcemaybeappliedhydraulicallyorpneumaticallybyacylinder（s）attachedtothemovingplate,ormechanicallybytheopeningstorkeofthemovingplate.

Methodsofmeltingandinjectingtheplasticdifferfromonemachinetoanotherandareconstantlybeingimprored.couventionalmachinesuseacylinderandpistontodobothjobs.Thismethodsimplifiesmachineconstructionbutmakescontrolofinjectiontemperaturesandpressuresaninherentlydifficultproblem.Othermachinesuseaplastcatingextrudertomelttheplasticandpistontoinjectitwhilesomeharebeendesignedtouseascrewforbothjobs:

Nowadays,sixtypercentofthemachinesuseareciprocatingscrew,35%aplunger（concentratedinthesmallermachinesize）,and5%ascrewpot.

Manyoftheproblemsconnectedwithinjectionmoldingarisesbecausethedensitiesofpolymerschangesomarkedlywithtemperatureandpressure.Athightemperatures,thedensityofapolymerisconsiderablycowerthanatroomtemperature,providedthepressureisthesame.Therefore,ifmodlswerefilledatatmosphericpressure,“shrinkage”wouldmakethemoldingdeviateformtheshapeofthemold.

Tocompensateforthispooreffect,moldsarefilledathighpressure.Thepressurecompressesthepolymerandallowsmorematerialstoflowintothemold,shrinkageisreducedandbetterqualitymoldingsareproduced.Cludesamold-mountingpatternofboltholesor“T”slots.Tierodsaremembersoftheclampingforceactuatingmachanismthatserveasthetensionmembersofclampwhenitisholdingthemoldclosed.Ejectorisaprovisionintheclamingunitthatactuatesamechanismwithinthemoldtoejectthemoldedpart（s）formthemold.Theejectionactuatingforcemaybeappliedhydraulicallyorpneumaticallybyacylinder（s）attachedtothemovingplate,ormechanicallybytheopeningstrokeofthemovingplate.

Thefunctionofamoldistwofold:

impartingthedesiredshapetotheplasticizedpolymerandcoolingtheinjectionmoldedpart.Itisbasicallymadeupoftwosetsofcomponents:

thecavitiesandcoresandthebaseinwhichthecavitiesandcoresaremounted.Themold,whichcontainsoneormorecavities,consistsoftwobasicparts:

（1）astationarymoldshalfonethesidewheretheplasticisinjected,

（2）Amovinghalf