材料成型铸造专业毕业设计英文文献原文

Castinganditsprocesses1.1IntroductionManufacturingprocesscanbeclassifiedintotwogeneralgroupsknownasprimaryandsecondaryprocesses.Theprimaryprocesses,namely,casting,forging,coldheading,coldextruding,brakeforming,andsoon,arethosethatconvertrawmaterialintoshapes.Theseformingmethodsincludebothhotandcoldworkingprocessesand,ingeneral,willstillrequirefurtherfinishingoperationsinordertoobtainanendproduct.Thesecondaryprocessesarethosethatbringtheparttothedimensionsandsurfacefinishspecified.Onemayalsoincludeinthesecondaryprocessessuchoperationsasheattreatingandsurfacetreatmentsforcorrosionresistance,hardness,andappearance.Secondaryprocessesareplanning,turning,milling,drilling,boring,reaming,broaching,grinding,honing,lapping,polishing,andspecialmethodsofmetalremovalsuchaselectrochemicalmachining.Operationslikescrewcutting,tapping,threadmilling,gearcutting,andsoon,aresecondaryprocessesthataremerelyadaptationsofoneoftheaforementionedprocessesthataremerelyadaptionofoneoftheaforementionedprocesses.Acompletediscussionoftheseproceduresisbeyondthescopeofthistext.Therefore,wewillconfineourselvestosuccinctdescriptionsofthemostprominenttechniques.1.2CastingsCastingsareidentifiedbythetypeofmoldortheforcerequiredtoyfillthemold.Moldsareeitherpermanentorexpendable.Thepatternofsand,shell,andplastermolds,however,canbeusedrepeatedlyformakingnewmolds.Asthemetalcools,ittakestheshapeofthecavity.Thebasiccastingmethodsaredescribedbelow.Sandcastings.1.Thegreensandprocessisoneinwhichmost,bondedsandspackedaroundawoodormetalpattern.Thepatternisthenremovedandmoltenmetalispouredintothecavity.Whenthemetalsolidifies,themoldisbrokenandthecastingisremoved.Almostanymetalcanbeused,withvirtuallynolimitastothesizeorshapeofthepart.Themethodpermitscastingcomplexcomponentsatalowtoolingcostandisthemostdirectroutefrompatterntocasting.Somemachiningisalwaysnecessarywiththegreensandprocess,andlargecastingshaveroughsurfacefinish.Closetolerancesaredifficulttoachieve,andlong,thinprojectionsshouldnotbecast.Itispossible,however,todesignforbosses,undercutsandinserts.Theminimumcoreholediameteradvisablearealuminum,3|16—1|4in.;andtheminimumsectionthicknessesadvisablearealuminum,3|16in.;cooper,3|32in.;iron,3|32in.;magnesium,5|332in;andsteel,1|4—1|2in.2.Thedrysandprocessissimilartothegreensandprocessexceptthatcoreboxesareusedinplaceofpatterns.Thismethodisusuallylimitedtosmallerpartsthanmethod1.Thesandisbondedwithasettingbinder,andthecoreisthenovenbakedat300—400toremovethemoisture.3.Thecarbendioxidesandprocessisoneinwhichthesandmoldsarebondedwhitsodiumsilicatesolutionsandsetbyforcingcarbondioxidegasthroughthesand.Thistypeofmoldisstrongandpermitstheproductionofbetterdimensionallycontrolledcastingsthaneithermethod1or2.4.Thecore—sandmoldprocessisonewherethemoldsareputtogethercompletelyfromovenbakedcoressetwithorganicbinderssuchasoilordextrines.ShellMoldCasting.Thisisaprocesswherethemoldsaremadebycoatingthesandwithathermosettingplastic.Themoldisthensupportedontheoutsaidbysandorshot,andmoltenmetalispoured.Whenthemetalhassolidified,themoldisbrokenawayfromthefinishedcasting.Shellmoldingproducescastingwithsmoothsurfaces,uniformgrainstructure,highdimensionalaccuracy,rapidproductionrateandminimalamountoffinishingoperations.Theminimumsectionthicknisscastableis1|16—1|4in.butsectiondifferenceswherethemaximum–minimumratioisgreaterthan5to1shouldbeavoided.Bosses,undercutsandinsertsareeasilycastandtheminimumcoredholediameteris1|8—1|4in.Themethodisrelativelycostlyislimitedtofewmetals.Full-MoldCasting.Aprocessinwhichagreensandorcold-settingresinbondedispackedaroundafoamedplasticpattern(forexample,polystyrene).Theplasticpatternisvaporizedwiththepouringofthemoltenmetalintothemold.Animprovedcastingsurfacecanbeobtainedbyputtingarefractorytypeofcoatingonthepatternsurfacebeforesandpacking.Thepatterncanbeonepieceorseveralpieces,dependinguponthecomplexityoftheparttobecast.Theplasticpatternsarehandledeasily.Theydonotrequireanydraft,andproducenoflashonthecasting.Forsmallquantityproductionthismethodcanbeexpensive,dependinguponthesizeandcomplexityofthecasting.Theminimumrecommendedsectionthicknessis0.1in.,andthemaximumsectionthicknessisunlimited.Bosses,undercuts,andinsertspresentnoprobleminthistypeofcasting.Theminimumcoredholediameteris1|4in.PermanentMoldCastings.Theseareformedbyamoldthatcanbeusedrepeatedly.Someapplicationshavereportedasmanyas25000castingsbeingmadefromthesamemold.Usually,themoldrequiressomeredressingafterabout3000uses.Themoldsaremachinedofmetal(forexample,grayiron)forcastingnonferrousmetalsandcastitons.Machinedgraphitemoldsareusedtocaststeel.Thismethodproducescastingsthathaveagoodsurfacefinishaswellasagoodgrainstructure,lowporosity,andhighdimensionalaccuracy.Theinitialmoldcostisrelativelyexpensive,butcastingsweighingaslittleasseveralouncestocastingsarelimitedtorelativelysimpleshapesandforms.Themaximumrecommendedsectionthicknessisabout2.0in.Theminimumthickness,however,dependsuoonthematerialbeingcastasfollows:3|16in.foriton,3|32—1|8in.foraluminum,5|32in.formagnesium,and3|32–5|16in.forcopper