英語(yǔ)翻譯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.”Topreventthosetinycoolantholesfrombecomingcloggedwithdebris,Davisalsorecommendsa5morfinercoolantfilter.Anotherrecommendationistomachineapilot,orguide,holetopreventthetoolfromwanderingontopoftheworkpieceandaidinproducingastraighthole.Whenapplyingapilotdrill,itsimportanttoselectonewithanincludedangleonitspointthatsequaltoorlargerthantheincludedangleonthethrough-coolantdrillthatfollows.Thepilotdrillsdiametershouldalsobeslightlylarger.Forexample,ifthepilotdrillhasa120includedangleandasmallerdiameterthanathrough-coolantdrillwitha140includedangle,“thenyourecatchingthecoolant-feddrillscornersandknockingthosecornersoff,”Davissaid,whichdamagesthedrill.LubriciousChillTofurtheraidchipevacuation,Davisrecommendsapplyinganoil-basedmetalworkingfluidinsteadofawaterbasedcoolantbecauseoilprovidesgreaterlubricity.Butifashopprefersusingcoolant,thefluidshouldincludeEP(extremepressure)additivestoincreaselubricityandminimizefoaming.“Ifyouvegotalotoffoam,”Davisnoted,“thechipsarentbeingpulledoutthewaytheyaresupposedtobe.”Headdedthatanotherwaytoenhanceatoolsslipperinesswhileextendingitslifeiswithacoating,suchastitaniumaluminumnitride.TiAlNhasahighhardnessandisaneffectivecoatingforreducingheatsimpactwhendrillingdifficult-to-machinematerials,likestainlesssteel.DavidBurton,generalmanagerofPerformanceMicroTool,Janesville,Wis.,disagreeswiththeideaofcoatingmicrotoolsonthesmallerendofthespectrum.“Coatingsontoolsbelow0.020typicallyhaveaeffectoneverymachiningaspect,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=tooldiameter0.26spindlespeed.)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.endmillmightbeabletoonlymakeaholeupto0.020deepwhereasadrillofthesamesizecangodeeperbecauseitsdesignedtoplacetheloadonitstipwhendrilling.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.Thetubesflushingholeenablescreatingaholewithahighdepth-to-diameterratioandhelpstoevacuatedebrisfromthebottomoftheholeduringmachining.OnesuchsinkerEDMforproducingholesassmallas0.00044(11m)isMakinosEdge2sinkerEDMwithfine-holeoption.InJapan,themachinetoolbuilderrecentlyproducedeightsuchholesin2minutesand40secondsthrough0.0010-thicktungstencarbideattheholelocations.Theelectrodewasasilver-tungstenrod0.00020smallerthantheholebeingproduced,toaccountforsparkactivityinthegap.Whenproducingholesofthatsize,therod,whilerotating,isdressedwithachargedEDMwire.Thefine-holeoptionincludesaW-axisattachment,whichholdsadiethatguidestheelectrode,aswellasamiddleguidethatpreventstheelectrodefrombendingorwobblingasitspins.Withtheoption,themachineisappropriatefordrillingholediameterslessthan0.005.AnothersinkerEDMformicro-holemakingistheMitsubishiVA10withafine-holejigattachmenttochuckandguidethefinewireappliedtoerodethematerial.“ItsastandardEDM,butwiththatattachmentfixedtothemachine,wecandomicroholedrilling,”saidDennisPowderly,sinkerEDMproductmanagerforMCMachinerySystemsInc.,WoodDale,Ill.HeaddedthattheEDMisalsoabletocreateholesdownto0.0004usingawirethatrotatesatupto2,000rpm.TurntoTungstenEDMingistypicallyaslowprocess,andthatholdstruewhenitisusedformicrodrilling.“Itsveryslow,andthefinerthedetails,thesloweritis,”said,presidentandownerofOptimationInc.TheMidvale,Utah,companybuildsProfile24PiezoEDMsformicromachiningandalsoperformsmicroEDMingonacontract-machiningbasis.Optimationproducestungstenelectrodesusingareverse-polarityprocessandmachinesandring-lapsthemtoassmallas10mindiameterwith0.000020roundness.Applyinga10m-dia.electrodeproducesaholeabout10.5mto11mindiameter,andblind-hole