外文翻譯微孔的加工方法.doc

大連交通大學2010屆本科生畢業(yè)設計（論文）外文翻譯1外文原文Optionsformicro-holemakingAsinthemacroscale-machiningworld,holemakingisoneofthemostifnotthemostfrequentlyperformedoperationsformicromachining.Manyoptionsexistforhowthoseholesarecreated.Eachhasitsadvantagesandlimitations,dependingontherequiredholediameteranddepth,workpiecematerialandequipmentrequirements.Thisarticlecoversholemakingwiththrough-coolantdrillsandthosewithoutcoolantholes,plungemilling,microdrillingusingsinkerEDMsandlaserdrilling.HelpfulHolesGettingcoolanttothedrilltipwhilethetooliscuttinghelpsreducetheamountofheatatthetool/workpieceinterfaceandevacuatechipsregardlessofholediameter.Butthrough-coolantcapabilityisespeciallyhelpfulwhendeep-holemicrodrillingbecausethetoolsaredelicateandpronetofailurewhenexperiencingrecuttingofchips,chippackingandtoomuchexposuretocarbidesworstenemyheat.Whenapplyingfloodcoolant,thedrillitselfblocksaccesstothecuttingaction.“Somewhereabout3to5diametersdeep,thecoolanthastroublegettingdowntothetip,”saidJeffDavis,vicepresidentofengineeringforHarveyToolCo.,Rowley,Mass.“Itbecomeswisetouseacoolant-feddrillatthatpoint.”Inaddition,floodcoolantcancausemoreharmthangoodwhenmicroholemaking.“Thepressurefromthefloodcoolantcansometimessnapfragiledrillsastheyenterthepart,”Davissaid.Thetoolmakeroffersalineofthrough-coolantdrillswithdiametersfrom0.039to0.125thatareabletoproduceholesupto12diametersdeep,aswellasmicrodrillswithoutcoolantholesfrom0.002to0.020.Havingthrough-coolantcapacityisntenough,though.Coolantneedstoflowataratethatenablesittoclearthechipsoutofthehole.Davisrecommends,ataminimum,600to800psiofcoolantpressure.“Itworksmuchbetterifyouhavehigherpressurethanthat,”headded.Topreventthosetinycoolantholesfrombecomingcloggedwithdebris,Davisalsorecommendsa5morfinercoolantfilter.Anotherrecommendationistomachineapilot,orguide,holetopreventthetoolfromwanderingontopoftheworkpieceandaidinproducingastraighthole.Whenapplyingapilotdrill,itsimportanttoselectonewithanincludedangleonitspointthatsequaltoorlargerthantheincludedangleonthethrough-coolantdrillthatfollows.Thepilotdrills大連交通大學2010屆本科生畢業(yè)設計（論文）外文翻譯2diametershouldalsobeslightlylarger.Forexample,ifthepilotdrillhasa120includedangleandasmallerdiameterthanathrough-coolantdrillwitha140includedangle,“thenyourecatchingthecoolant-feddrillscornersandknockingthosecornersoff,”Davissaid,whichdamagesthedrill.Althoughnotmandatory,peckingisagoodpracticewhenmicrodrillingdeepholes.Davissuggestsapeckingcyclethatis30to50percentofthediameterperpeckdepth,dependingontheworkpiecematerial.Thisclearsthechips,preventingthemfrompackingintheflutevalleys.LubriciousChillTofurtheraidchipevacuation,Davisrecommendsapplyinganoil-basedmetalworkingfluidinsteadofawaterbasedcoolantbecauseoilprovidesgreaterlubricity.Butifashopprefersusingcoolant,thefluidshouldincludeEP(extremepressure)additivestoincreaselubricityandminimizefoaming.“Ifyouvegotalotoffoam,”Davisnoted,“thechipsarentbeingpulledoutthewaytheyaresupposedtobe.”Headdedthatanotherwaytoenhanceatoolsslipperinesswhileextendingitslifeiswithacoating,suchastitaniumaluminumnitride.TiAlNhasahighhardnessandisaneffectivecoatingforreducingheatsimpactwhendrillingdifficult-to-machinematerials,likestainlesssteel.DavidBurton,generalmanagerofPerformanceMicroTool,Janesville,Wis.,disagreeswiththeideaofcoatingmicrotoolsonthesmallerendofthespectrum.“Coatingsontoolsbelow0.020typicallyhaveanegativeeffectoneverymachiningaspect,fromthequalityoftheinitialcuttotoollife,”hesaid.Thatsbecausecoatingsarenotthinenoughandnegativelyaltertherakeandreliefangleswhenappliedtotinytools.However,workcontinuesonthedevelopmentofthinnercoatings,andBurtonindicatedthatPerformanceMicroTool,whichproducesmicroendmillsandmicroroutersandresellsmicrodrills,isworkingonaprojectwithotherstocreateasubmicron-thicknesscoating.“Wereprobably6monthsto1yearfromtestingitinthemarket,”Burtonsaid.ThemicrodrillsPerformanceoffersarebasicallycircuit-boarddrills,whicharealsoeffectiveforcuttingmetal.Allthetoolsarewithoutthrough-coolantcapability.“Ihadacustomerdrilla0.004-dia.holeinstainlesssteel,andhewasamazedhecoulddoitwithacircuit-boarddrill,”Burtonnoted,addingthatpeckingandrunningatahighspindlespeedincreasethedrillseffectiveness.TherequirementsforhowfastmicrotoolsshouldrotatedependonthetypeofCNCmachinesashopusesandthetooldiameter,withhigherspeedsneededasthediameterdecreases.(Note:Theequationforcuttingspeedissfm=tooldiameter0.26spindle大連交通大學2010屆本科生畢業(yè)設計（論文）外文翻譯3speed.)Althoughrelativelylow,5,000rpmhasbeenusedsuccessfullybyBurtonscustomers.“Werecommendthatourcustomersfindthehighestrpmatthelowestpossiblevibrationthesweetspot,”hesaid.Inadditiontominimizingvibration,aconstantandadequatechiploadisrequiredtopenetratetheworkpiecewhileexertinglowcuttingforcesandtoallowtheraketoremovetheappropriateamountofmaterial.Ifthedrilltakestoolightofachipload,therakefacewearsquickly,becomingnegative,andtoollifesuffers.Thisapproachisoftentemptingwhendrillingwithdelicatetools.“Ifthecustomerdecideshewantstobabythetool,hetakesalighterchipload,”Burtonsaid,“and,typically,thecuttingedgewearsmuchquickerandcreatesaradiuswherethelandofthatradiusiswiderthanthechipbeingcut.Heendsupusingitasagrindingtool,tryingtobumpmaterialaway.”Fortoolslargerthan0.001,Burtonconsidersachiploadunder0.0001tobe“babying.”Ifthedrilldoesntsnap,prematurewearcanresultinabysmaltoollife.Toomuchrunoutcanalsobedestructive,buthowmuchisdebatable.BurtonpointedoutthatPerformancepurposelydesignedamachinetohave0.0003TIRtoconductin-house,worst-casemillingscenarios,addingthatthecompanyisstillabletomilla0.004-wideslot“dayinanddayout.”Headded:“Youwouldthinkwith0.0003runoutandachiploadathirdthat,say,0.0001to0.00015,thetoolwouldbreakimmediatelybecauseoneflutewouldbetakingtheentireloadandthenthebackendoftheflutewouldberubbing.Whendrilling,heindicatedthatupto0.0003TIRshouldbeacceptablebecauseoncethedrillisinsidethehole,thecuttingedgesontheendofthedrillcontinuecuttingwhilethenoncuttinglandsontheODguidethetoolinthesamedirection.Minimizingrunoutbecomesmorecriticalasthedepth-to-diameterratioincreases.Thisisbecausetheflutesarenotabletoabsorbasmuchdeflectionastheybecomemoreengagedintheworkpiece.Ultimately,toomuchrunoutcausesthetoolshanktoorbitaroundthetoolscenterwhilethetooltipisheldsteady,creatingastresspointwherethetoolwilleventuallybreak.TakingaPlungeAlthoughstandardmicrodrillsarentgenerallyavailablebelow0.002,microendmillsthatcanbeusedto“plunge”aholeare.“Whenpeoplewanttodrillsmallerthanthat,theyuseourendmillsandareprettysuccessful,”Burtonsaid.However,theholescantbeverydeepbecausethetoolsdonthavelongaspect,ordepth-to-diameter,ratios.Therefore,a0.001-dia.endmillmightbeabletoonlymakeaholeupto0.020deepwhereasadrillofthesamesize大連交通大學2010屆本科生畢業(yè)設計（論文）外文翻譯4cangodeeperbecauseitsdesignedtoplacetheloadonitstipwhendrilling.Thistransfersthepressureintotheshank,whichabsorbsit.Performanceoffersendmillsassmallas5microns(0.0002)butisntkeenonincreasingthatlinessales.“Whenpeopletrytobuythem,Iveryseriouslytrytotalkthemoutofitbecausewedontlikemakingthem,”Burtonsaid.Partoftheproblemwithtoolsthatsmallisthecarbidegrainsnotonlyneedtobesubmicroninsizebutthesizealsoneedstobeconsistent,inpartbecausesuchatooliscomprisedoffewergrains.“The5-micronendmillprobablyhas10grainsholdingthecoretogether,”Burtonnoted.Headdedthathehasseencarbidepowdercontaining0.2-microngrains,whichisabouthalfthesizeofwhatscommerciallyavailable,butitalsocontainedgrainsmeasuring0.5and0.6microns.“Itjustdoesnthelptohavesmallgrainsiftheyrenotuniform.”MicrovaporizationElectricaldischargemachiningusingasinkerEDMisanothermicro-holemakingoption.Unlike,whichcreatesmallholesforthreadingwirethroughtheworkpiecewhenwireEDMing,EDMsforproducingmicroholesareconsiderablymoresophisticated,accurateand,ofcourse,expensive.Forproducingdeepmicroholes,atubeisappliedastheelectrode.ForEDMingsmallerbutshallowerholes,asolidelectrodewire,orrod,isneeded.“Wetrytousetubesasmuchaspossible,”saidJeffKiszonas,EDMproductmanagerforMakinoInc.,AuburnHills,Mich.“Butatsomepoint,nobodycanmakeatubebelowacertaindiameter.”Headdedthatsomesuppliersoffertubesdownto0.003indiameterformakingholesassmallas0.0038.Thetubesflushingholeenablescreat