外文翻译--机械加工及其加工工具.doc

MachiningTechniquesAndToolDrillingandDrillsDrillinginvolvesproducingthroughorblindholesinaworkpiecebyforcingatool,whichrotatesarounditsaxis,againsttheworkpiece.Consequently,therangeofcuttingfromthataxisofrotationisequaltotheradiusoftherequiredhole.Inpractice,twosymmetricalcuttingedgesthatrotateaboutthesameaxisareemployed.Drillingoperationscanbecarriedoutbyusingeitherhanddrillsordrillingmachines.Thelatterdifferinsizeandconstruction.Nevertheless,thetoolalwaysrotatesarounditsaxiswhiletheworkpieceiskeptfirmlyfixed.Thisiscontrarytodrillingonalathe.CuttingToolforDrillingOperationIndrillingoperations,acylindricalrotary-endcuttingtool,calledadrill,isemployed.Thedrillcanhaveeitheroneormorecuttingedgesandcorrespondingflutes,whichcanbestraightorhelical.Thefunctionoftheflutesistoprovideoutletpassagesforthechipsgeneratedduringthedrillingoperationandalsotoallowlubricantsandcoolantstoreachthecuttingedgesandthesurfacebeingmachined.Followingisasurveyofthecommonlyuseddrills.Twistdrill.Thetwistdrillisthemostcommontypeofdrill.Ithastwocuttingedgesandtwohelicalflutesthatcontinueoverthelengthofthedrillbody,.Thedrillalsoconsistsofaneckandashankthatcanbeeitherstraightortapered.Inthelattercase,theshankisfittedbythewedgeactionintothetaperedsocketofthespindleandhasatang,whichgoesintoaslotinthespindlesocket,thusactingasasolidmeansfortransmittingrotation.Ontheotherhand,straight-shankdrillsareheldinadrillchuckthatis,inturn,fittedintothespindlesocketinthesamewayastaperedshankdrills.Thetwocuttingedgesarereferredtoasthelips,andareconnectedtogetherbyawedge,whichisachisel-likeedge.Thetwistdrillalsohastwomargins,whichenableproperguidanceandlocatingofthedrillwhileitisinoperation.Thetoolpointangle(TPA)isformedbythetwolipsandischosenbasedonthepropertiesofthematerialtobecut.TheusualTPAforcommercialdrillsis118,whichisappropriatefordrillinglow-carbonsteelsandcastirons.Forharderandtoughermetals,suchashardenedsteel,brassandbronze,largerTPAs(130or140)givebetterperformance.Thehelixangleoftheflutesofthecommonlyusedtwistdrillsrangesbetween24and30.Whendrillingcopperorsoftplastics,highervaluesforthehelixanglearerecommended(between35and45).Twistdrillsareusuallymadeofhigh-speedsteel,althoughcarbide-tippeddrillsarealsoavailable.Thesizesoftwistdrillsusedinindustrialpracticerangefrom0.01upto3.25in.(i.e.,0.25upto80mm).Coredrills.Acoredrillconsistsofthechamfer,body,neck,andshank.Thistypeofdrillmayhaveeitherthreeorfourflutesandequalnumberofmargins,whichensuresuperiorguidance,thusresultinginhighmachiningaccuracy.thatacoredrillhasflatend.Thechamfercanhavethreeorfourcuttingedgesorlips,andthelipanglemayvarybetween90and120.Coredrillsareemployedforenlargingpreviouslymadeholesandnotfororiginatingholes.Thistypeofdrillischaracterizedbygreaterproductivity,highmachiningaccuracy,andsuperiorqualityofthedrilledsurfaces.Gundrills.Gundrillsareusedfordrillingdeepholes.Allgundrillsarestraight-fluted,andeachhasasinglecuttingedge.Aholeinthebodyactsasaconduittotransmitcoolantunderconsiderablepressuretothetipofthedrill.Therearetwokindsofgundrills,namely,thecenter-cutgundrillusedfordrillingblindholesandthetrepanningdrill.Thelatterhasacylindricalgrooveatitscenter,thusgeneratingasolidcore,whichguidesthetoolasitproceedsduringthedrillingoperation.Spadedrills.Spadedrillsareusedfordrillinglargeholesof3.5in.(90mm)ormore.Theirdesignresultsinamarkedsavingincostofthetoolaswellasatangiblereductioninitsweight,whichfacilitatesitshandling.Moreover,thistypeofdrilliseasytogrind.MillingandMillingCutterMillingisamachiningprocessthatiscarriedoutbymeansofamultiedgerotatingtoolknownasamillingcutter.Inthisprocess,metalremovalisachievedthroughcombiningtherotarymotionofthemillingcutterandlinearmotionsoftheworkpiecesimultaneously.Millingoperationsareemployedinproducingflat,contouredandhelicalsurfacesaswellasforthread-andgear-cuttingoperation.Eachofthecuttingedgesofamillingcutteractsasanindividualsingle-pointcutterwhenitengageswiththeworkpiecemetal.Therefore,eachofthosecuttingedgeshasappropriaterakeandreliefangles.Sinceonlyafewofthecuttingedgesareengagedwiththeworkpieceatatime,heavycutscanbetakenwithoutadverselyaffectingthetoollife.Infact,thepermissiblecuttingspeedsandfeedsformillingarethreetofourtimeshigherthanthoseforturningordrilling.Moreover,thequalityofthesurfacesmachinedbymillingisgenerallysuperiortothequalityofsurfacesmachinedbytrning,shaping,ordrilling.Awidevarietyofmillingcuttersisavailableinindustry.This,togetherwiththefactthatamillingmachineisaveryversatilemachinetool,makesthemillingmachinethebackboneofamachiningworkshop.Asfarasthedirectionofcutterrotationandworkpiecefeedareconcerned,millingisperformedbyeitherofthefollowingtwomethods.Upmilling(conventionalmilling).Inupmillingtheworkpieceisfedagainstthedirectionofcutterrotation.Aswecanseeinthatfigure,thedepthofcut(andconsequentlytheload)graduallyincreasesonthesuccessivelyengagedcuttingedges.Therefore,themachiningprocessinvolvesnoimpactloading,thusensuringsmootheroperationofthemachinetoolandlongertoollife.Thequalityofthemachinedsurfaceobtainedbyupmillingisnotveryhigh.Nevertheless,upmillingiscommonlyusedinindustry,especiallyforroughcuts.Downmilling(climbmilling).Indownmillingthecutterrotationcoincideswiththedirectionoffeedatthecontactpointbetweenthetoolandtheworkpiece.Itcanalsobeseenthatthemaximumdepthofcutisachieveddirectlyasthecutterengageswiththeworkpiece.Thisresultsinakindofimpact,orsuddenloading.Therefore,thismethodcannotbeusedunlessthemillingmachineisequippedwithabacklasheliminatoronthefeedscrew.Theadvantagesofthismethodincludehigherqualityofthemachinedsurfaceandeasierclampingofworkpieces,sincethecuttingforcesactdownward.TypesofMillingCuttersThereisawidevarietyofmillingcuttershapes.Eachofthemisdesignedtoperformeffectivelyaspecificmillingoperation.Generally,amillingcuttercanbedescribedasamultiedgecuttingtoolhavingtheshapeofasolidofrevolution,withthecuttingteetharrangedeitherontheperipheryoronanendfaceoronboth.Followingisaquicksurveyofthecommonlyusedtypesofmillingcutters.Plainmillingcutter.Aplainmillingcutterisadisk-shapedcuttingtoolthatmayhaveeitherstraightorhelicalteeth.Thistypeisalwaysmountedonhorizontalmillingmachinesandisusedformachiningflatsurfaces.Facemillingcutter.Afacemillingcutterisalsousedformachiningflatsurfaces.Itisboltedattheendofashortarbor,whichisinturnmountedonaverticalmillingmachine.Plainmetalslittingsawcutter.Indicatesaplainmetalslittingsawcutter.wecanseethatitactuallyinvolvesaverythinplainmillingcutter.Sidemillingcutter.Asidemillingcutterisusedforcuttingslots,grooves,andsplines.Itisquitesimilartotheplainmillingcutter,thedifferencebeingthatthistypehasteethonthesides.Asisthecasewiththeplaincutter,thecuttingteethcanbestraightorhelical.Anglemillingcutter.Ananglemillingcutterisemployedincuttingdovetailgrooves,ratchetwheels.T-slotcutter.AT-slotcutterinvolvesaplainmillingcutterwithanintegralshaftnormaltoit.Asthenamesuggests,thistypeisusedformillingT-slots.Endmillcutter.Endmillcuttersfindcommonapplicationsincuttingslots,grooves,flutes,splines,pocketingwork,andthelike.Indicatesanendmillcutter.Thelatterisalwaysmoun