机械类毕业设计外文翻译微孔的加工方法.docx

机械类毕业设计外文翻译微孔的加工方法.docx

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机械类毕业设计外文翻译微孔的加工方法

外文原文

Optionsformicro-holemaking

Asinthemacroscale-machiningworld,holemakingisoneofthemost—ifnotthemost—frequentlyperformedoperationsformicromachining.Manyoptionsexistforhowthoseholesarecreated.Eachhasitsadvantagesandlimitations,dependingontherequiredholediameteranddepth,workpiecematerialandequipmentrequirements.Thisarticlecoversholemakingwiththrough-coolantdrillsandthosewithoutcoolantholes,plungemilling,microdrillingusingsinkerEDMsandlaserdrilling.

HelpfulHoles

Gettingcoolanttothedrilltipwhilethetooliscuttinghelpsreducetheamountofheatatthetool/workpieceinterfaceandevacuatechipsregardlessofholediameter.Butthrough-coolantcapabilityisespeciallyhelpfulwhendeep-holemicrodrillingbecausethetoolsaredelicateandpronetofailurewhenexperiencingrecuttingofchips,chippackingandtoomuchexposuretocarbide’sworstenemy—heat.

Whenapplyingfloodcoolant,thedrillitselfblocksaccesstothecuttingaction.“Somewhereabout3to5diametersdeep,thecoolanthastroublegettingdowntothetip,”saidJeffDavis,vicepresidentofengineeringforHarveyToolCo.,Rowley,Mass.“Itbecomeswisetouseacoolant-feddrillatthatpoint.”

Inaddition,floodcoolantcancausemoreharmthangoodwhenmicroholemaking.“Thepressurefromthefloodcoolantcansometimessnapfragiledrillsastheyenterthepart,”Davissaid.

Thetoolmakeroffersalineofthrough-coolantdrillswithdiametersfrom0.039"to0.125"thatareabletoproduceholesupto12diametersdeep,aswellasmicrodrillswithoutcoolantholesfrom0.002"to0.020".

Havingthrough-coolantcapacityisn’tenough,though.Coolantneedstoflowataratethatenablesittoclearthechipsoutofthehole.Davisrecommends,ataminimum,600to800psiofcoolantpressure.“Itworksmuchbetterifyouhavehigherpressurethanthat,”headded.

Topreventthosetinycoolantholesfrombecomingcloggedwithdebris,Davisalsorecommendsa5μmorfinercoolantfilter.

Anotherrecommendationistomachineapilot,orguide,holetopreventthetoolfromwanderingontopoftheworkpieceandaidinproducingastraighthole.Whenapplyingapilotdrill,it’simportanttoselectonewithanincludedangleonitspointthat’sequaltoorlargerthantheincludedangleonthethrough-coolantdrillthatfollows.Thepilotdrill’sdiametershouldalsobeslightlylarger.Forexample,ifthepilotdrillhasa120°includedangleandasmallerdiameterthanathrough-coolantdrillwitha140°includedangle,“thenyou’recatchingthecoolant-feddrill’scornersandknockingthosecornersoff,”Davissaid,whichdamagesthedrill.

Althoughnotmandatory,peckingisagoodpracticewhenmicrodrillingdeepholes.Davissuggestsapeckingcyclethatis30to50percentofthediameterperpeckdepth,dependingontheworkpiecematerial.Thisclearsthechips,preventingthemfrompackingintheflutevalleys.

LubriciousChill

Tofurtheraidchipevacuation,Davisrecommendsapplyinganoil-basedmetalworkingfluidinsteadofawaterbasedcoolantbecauseoilprovidesgreaterlubricity.Butifashopprefersusingcoolant,thefluidshouldincludeEP（extremepressure）additivestoincreaselubricityandminimizefoaming.“Ifyou’vegotalotoffoam,”Davisnoted,“thechipsaren’tbeingpulledoutthewaytheyaresupposedtobe.”

Headdedthatanotherwaytoenhanceatool’sslipperinesswhileextendingitslifeiswithacoating,suchastitaniumaluminumnitride.TiAlNhasahighhardnessandisaneffectivecoatingforreducingheat’simpactwhendrillingdifficult-to-machinematerials,likestainlesssteel.

DavidBurton,generalmanagerofPerformanceMicroTool,Janesville,Wis.,disagreeswiththeideaofcoatingmicrotoolsonthesmallerendofthespectrum.“Coatingsontoolsbelow0.020"typicallyhaveanegativeeffectoneverymachiningaspect,fromthequalityoftheinitialcuttotoollife,”hesaid.That’sbecausecoatingsarenotthinenoughandnegativelyaltertherakeandreliefangleswhenappliedtotinytools.

However,workcontinuesonthedevelopmentofthinnercoatings,andBurtonindicatedthatPerformanceMicroTool,whichproducesmicroendmillsandmicroroutersandresellsmicrodrills,isworkingonaprojectwithotherstocreateasubmicron-thicknesscoating.“We’reprobably6monthsto1yearfromtestingitinthemarket,”Burtonsaid.

ThemicrodrillsPerformanceoffersarebasicallycircuit-boarddrills,whicharealsoeffectiveforcuttingmetal.Allthetoolsarewithoutthrough-coolantcapability.“Ihadacustomerdrilla0.004"-dia.holeinstainlesssteel,andhewasamazedhecoulddoitwithacircuit-boarddrill,”Burtonnoted,addingthatpeckingandrunningatahighspindlespeedincreasethedrill’seffectiveness.

TherequirementsforhowfastmicrotoolsshouldrotatedependonthetypeofCNCmachinesashopusesandthetooldiameter,withhigherspeedsneededasthediameterdecreases.（Note:

Theequationforcuttingspeedissfm=tooldiameter×0.26×spindlespeed.）

Althoughrelativelylow,5,000rpmhasbeenusedsuccessfullybyBurton’scustomers.“Werecommendthatourcustomersfindthehighestrpmatthelowestpossiblevibration—thesweetspot,”hesaid.

Inadditiontominimizingvibration,aconstantandadequatechiploadisrequiredtopenetratetheworkpiecewhileexertinglowcuttingforcesandtoallowtheraketoremovetheappropriateamountofmaterial.Ifthedrilltakestoolightofachipload,therakefacewearsquickly,becomingnegative,andtoollifesuffers.Thisapproachisoftentemptingwhendrillingwithdelicatetools.

“Ifthecustomerdecideshewantstobabythetool,hetakesalighterchipload,”Burtonsaid,“and,typically,thecuttingedgewearsmuchquickerandcreatesaradiuswherethelandofthatradiusiswiderthanthechipbeingcut.Heendsupusingitasagrindingtool,tryingtobumpmaterialaway.”Fortoolslargerthan0.001",Burtonconsidersachiploadunder0.0001"tobe“babying.”Ifthedrilldoesn’tsnap,prematurewearcanresultinabysmaltoollife.

Toomuchrunoutcanalsobedestructive,buthowmuchisdebatable.BurtonpointedoutthatPerformancepurposelydesignedamachinetohave0.0003"TIRtoconductin-house,worst-casemillingscenarios,addingthatthecompanyisstillabletomilla0.004"-wideslot“dayinanddayout.”

Headded:

“Youwouldthinkwith0.0003"runoutandachiploadathirdthat,say,0.0001"to0.00015",thetoolwouldbreakimmediatelybecauseoneflutewouldbetakingtheentireloadandthenthebackendoftheflutewouldberubbing.

Whendrilling,heindicatedthatupto0.0003"TIRshouldbeacceptablebecauseoncethedrillisinsidethehole,thecuttingedgesontheendofthedrillcontinuecuttingwhilethenoncuttinglandsontheODguidethetoolinthesamedirection.Minimizingrunoutbecomesmorecriticalasthedepth-to-diameterratioincreases.Thisisbecausetheflutesarenotabletoabsorbasmuchdeflectionastheybecomemoreengagedintheworkpiece.Ultimately,toomuchrunoutcausesthetoolshanktoorbitaroundthetool’scenterwhilethetooltipisheldsteady,creatingastresspointwherethetoolwilleventuallybreak.

TakingaPlunge

Althoughstandardmicrodrillsaren’tgenerallyavailablebelow0.002",microendmillsthatcanbeusedto“plunge”aholeare.“Whenpeoplewanttodrillsmallerthanthat,theyuseourendmillsandareprettysuccessful,”Burtonsaid.However,theholescan’tbeverydeepbecausethetoolsdon’thavelongaspect,ordepth-to-diameter,ratios.Therefore,a0.001"-dia.endmillmightbeabletoonlymakeaholeupto0.020"deepwhereasadrillofthesamesizecangodeeperbecauseit’sdesignedtoplacetheloadonitstipwhendrilling.Thistransfersthepressureintotheshank,whichabsorbsit.

Performanceoffersendmillsassmallas5microns（0.0002"）butisn’tkeenonincreasingthatline’ssales.“Whenpeopletrytobuythem,Iveryseriouslytrytotalkthemoutofitbecausewedon’tlikemakingthem,”Burtonsaid.Partoftheproblemwithtoolsthatsmallisthecarbidegrainsnotonlyneedtobesubmicroninsizebutthesizealsoneedstobeconsistent,inpartbecausesuchatooliscomprisedoffewergrains.“The5-micronendmillprobablyhas10grainsholdingthecoretogether,”Burtonnoted.

Headdedthathehasseencarbidepowdercontaining0.2-microngrains,whichisabouthalfthesizeofwhat’scommerciallyavailable,butitalsocontainedgrainsmeasuring0.5and0.6microns.“Itjustdoesn’thelptohavesmallgrainsifthey’renotuniform.”

Microvaporization

ElectricaldischargemachiningusingasinkerEDMisanothermicro-holemakingoption.Unlike,whichcreatesmallholesforthreadingwirethroughtheworkpiecewhenwireEDMing,EDMsforproducingmicroholesareconsiderablymoresophisticated,accurateand,ofcourse,expensive.

Forproducingdeepmicroholes,atubeisappliedastheelectrode.ForEDMingsmallerbutshallowerholes,asolidelectrodewire,orrod,isneeded.“Wetrytousetubesasmuchaspossible,”saidJeffKiszonas,EDMproductmanagerforMakinoInc.,AuburnHills,Mich.“Butatsomepoint,nobodycanmakeatubebelowacertaindiameter.”Headdedthatsomesuppliersoffertubesdownto0.003"indiameterformakingholesassmallas0.0038".Thetube’sflushingholeenablescreatingaholewithahighdepth-to-diameterratioandhelpstoevacuatedebrisfromthebottomoftheholeduringmachining.

OnesuchsinkerEDMforproducingholesassmallas0.00044"（11μm）isMakino’sEdge2sinkerEDMwithfine-holeoption.InJapan,themachinetoolbuilderrecentlyproducedeightsuchholesin2minutesand40secondsthrough0.0