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攀枝花学院本科毕业设计(论文)外文译文院(系)机电工程学院专业机械设计制造及其自动化姓名王中蔚学号ZJD02043指导教师评语签名年月日外语文献翻译摘自制造工程与技术(机加工)(英文版)ManufacturingEngineeringandTechnologyMachining机械工业出版社2004年3月第1版页564560P美s.卡尔帕基安Seropekalpakjians.r施密德StevenR.Schmid著原文20.9MACHINABILITYThemachinabilityofamaterialusuallydefinedintermsoffourfactors1、Surfacefinishandintegrityofthemachinedpart2、Toollifeobtained3、Forceandpowerrequirements4、Chipcontrol.Thus,goodmachinabilitygoodsurfacefinishandintegrity,longtoollife,andlowforceAndpowerrequirements.Asforchipcontrol,longandthinstringycuredchips,ifnotbrokenup,canseverelyinterferewiththecuttingoperationbybecomingentangledinthecuttingzone.Becauseofthecomplexnatureofcuttingoperations,itisdifficulttoestablishrelationshipsthatquantitativelydefinethemachinabilityofamaterial.Inmanufacturingplants,toollifeandsurfaceroughnessaregenerallyconsideredtobethemostimportantfactorsinmachinability.Althoughnotusedmuchanymore,approximatemachinabilityratingsareavailableintheexamplebelow.20.9.1MachinabilityOfSteelsBecausesteelsareamongthemostimportantengineeringmaterialsasnotedinChapter5,theirmachinabilityhasbeenstudiedextensively.Themachinabilityofsteelshasbeenmainlyimprovedbyaddingleadandsulfurtoobtainsocalledfreemachiningsteels.ResulfurizedandRephosphorizedsteels.Sulfurinsteelsformsmanganesesulfideinclusionssecondphaseparticles,whichactasstressraisersintheprimaryshearzone.Asaresult,thechipsproducedbreakupeasilyandaresmallthisimprovesmachinability.Thesize,shape,distribution,andconcentrationoftheseinclusionssignificantlyinfluencemachinability.Elementssuchastelluriumandselenium,whicharebothchemicallysimilartosulfur,actasinclusionmodifiersinresulfurizedsteels.Phosphorusinsteelshastwomajoreffects.Itstrengthenstheferrite,causingincreasedhardness.Hardersteelsresultinbetterchipformationandsurfacefinish.Notethatsoftsteelscanbedifficulttomachine,withbuiltupedgeformationandpoorsurfacefinish.Thesecondeffectisthatincreasedhardnesscausestheformationofshortchipsinsteadofcontinuousstringyones,therebyimprovingmachinability.LeadedSteels.Ahighpercentageofleadinsteelssolidifiesatthetipofmanganesesulfideinclusions.Innonresulfurizedgradesofsteel,leadtakestheformofdispersedfineparticles.Leadisinsolubleiniron,copper,andaluminumandtheiralloys.Becauseofitslowshearstrength,therefore,leadactsasasolidlubricantSection32.11andissmearedoverthetoolchipinterfaceduringcutting.Thisbehaviorhasbeenverifiedbythepresenceofhighconcentrationsofleadonthetoolsidefaceofchipswhenmachiningleadedsteels.Whenthetemperatureissufficientlyhighforinstance,athighcuttingspeedsandfeedsSection20.6theleadmeltsdirectlyinfrontofthetool,actingasaliquidlubricant.Inadditiontothiseffect,leadlowerstheshearstressintheprimaryshearzone,reducingcuttingforcesandpowerconsumption.Leadcanbeusedineverygradeofsteel,suchas10xx,11xx,12xx,41xx,etc.LeadedsteelsareidentifiedbytheletterLbetweenthesecondandthirdnumeralsforexample,10L45.Notethatinstainlesssteels,similaruseoftheletterLmeanslowcarbon,aconditionthatimprovestheircorrosionresistance.However,becauseleadisawellknowntoxinandapollutant,thereareseriousenvironmentalconcernsaboutitsuseinsteelsestimatedat4500tonsofleadconsumptioneveryyearintheproductionofsteels.Consequently,thereisacontinuingtrendtowardeliminatingtheuseofleadinsteelsleadfreesteels.Bismuthandtinarenowbeinginvestigatedaspossiblesubstitutesforleadinsteels.CalciumDeoxidizedSteels.Animportantdevelopmentiscalciumdeoxidizedsteels,inwhichoxideflakesofcalciumsilicatesCaSoareformed.Theseflakes,inturn,reducethestrengthofthesecondaryshearzone,decreasingtoolchipinterfaceandwear.Temperatureiscorrespondinglyreduced.Consequently,thesesteelsproducelesscraterwear,especiallyathighcuttingspeeds.StainlessSteels.Austenitic300seriessteelsaregenerallydifficulttomachine.Chattercanbesproblem,necessitatingmachinetoolswithhighstiffness.However,ferriticstainlesssteelsalso300serieshavegoodmachinability.Martensitic400seriessteelsareabrasive,tendtoformabuiltupedge,andrequiretoolmaterialswithhighhothardnessandcraterwearresistance.Precipitationhardeningstainlesssteelsarestrongandabrasive,requiringhardandabrasionresistanttoolmaterials.TheEffectsofOtherElementsinSteelsonMachinability.Thepresenceofaluminumandsiliconinsteelsisalwaysharmfulbecausetheseelementscombinewithoxygentoformaluminumoxideandsilicates,whicharehardandabrasive.Thesecompoundsincreasetoolwearandreducemachinability.Itisessentialtoproduceandusecleansteels.Carbonandmanganesehavevariouseffectsonthemachinabilityofsteels,dependingontheircomposition.Plainlowcarbonsteelslessthan0.15Ccanproducepoorsurfacefinishbyformingabuiltupedge.Caststeelsaremoreabrasive,althoughtheirmachinabilityissimilartothatofwroughtsteels.Toolanddiesteelsareverydifficulttomachineandusuallyrequireannealingpriortomachining.Machinabilityofmoststeelsisimprovedbycoldworking,whichhardensthematerialandreducesthetendencyforbuiltupedgeformation.Otheralloyingelements,suchasnickel,chromium,molybdenum,andvanadium,whichimprovethepropertiesofsteels,generallyreducemachinability.Theeffectofboronisnegligible.Gaseouselementssuchashydrogenandnitrogencanhaveparticularlydetrimentaleffectsonthepropertiesofsteel.Oxygenhasbeenshowntohaveastrongeffectontheaspectratioofthemanganesesulfideinclusionsthehighertheoxygencontent,thelowertheaspectratioandthehigherthemachinability.Inselectingvariouselementstoimprovemachinability,weshouldconsiderthepossibledetrimentaleffectsoftheseelementsonthepropertiesandstrengthofthemachinedpartinservice.Atelevatedtemperatures,forexample,leadcausesembrittlementofsteelsliquidmetalembrittlement,hotshortnessseeSection1.4.3,althoughatroomtemperatureithasnoeffectonmechanicalproperties.Sulfurcanseverelyreducethehotworkabilityofsteels,becauseoftheformationofironsulfide,unlesssufficientmanganeseispresenttopreventsuchformation.At
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