微铣削使用二维振动切削 翻译原文Word下载.docx
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微铣削使用二维振动切削 翻译原文Word下载.docx
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accepted5July2005
Availableonline19August2005
Abstract
Thepurposeofthispaperistoinvestigatetheeffectsofassistedvibrationcutting(VC)onthemicro-millingqualityofaluminumalloyAl6061-T6.Thedesiredvibrationisproposedfromtheworkpiecesidebyatwo-dimensionalvibratingworktablewedeveloped.Theslotproducedbyendmillingisstudiedbyexaminingitsgeometricalshapeandmachiningaccuracy.Throughextensiveexperimentswithendmillsofdiameter1mm,wefoundthatslotoversize,displacementofslotcenterandslotsurfaceroughnesscouldbeimprovedbyimposingVC.TheemploymentofVCincreasesthenumberofslotsproducedwithinthetolerancewhenhighamplitudeandproperfrequencyareimposed.WiththehelpofTaguchimethodandanalysisofvariance(ANOVA),weanalyzedtheeffectofVCinendmillingbyinvestigatingtheslot-widthaccuracy.ItisfoundthattheuseofseconddirectionalVCtominimizeslot-widthoversizeinendmillingishelpful.
q2005ElsevierLtd.Allrightsreserved.
Keywords:
Vibrationcutting;
Micro-milling;
End-milling;
Vibratingworktable
1.Introduction
Precisionmachiningplaysanimportantroleinmanufacturing.Millingprocessisoneofthemostcommonlyusedmetalremovaloperationsinindustry.Itisbasedoninterruptedcuttingwhichisverysusceptibletovibrations.Problemsassociatedwithvibrationsinmachiningaremoreseriouswhensmall-diameterendmillsareemployed.Inthatcase,thetooldeformationisprominentanditdeterioratesthestabilityinamachiningprocess.Excessivedeflectionofamicroendmillmaycausetoleranceviolationsandpoorsurfaceroughness[1].Precisionmachiningishardto
achieveinthiscaseandhencethemachiningtechnologymustbeimproved.
Vibrationcutting(VC)isacuttingmethodinwhichperiodicalvibrationisimposedtothecuttingtoolortheworkpiece,besidestheoriginalrelativemotionbetweenthesetwo,toobtainbettercuttingperformance.ThefundamentalfeatureofVCisthatthetoolfaceisseparatedfromtheworkpiecerepeatedly.Thistechniquehadbeenfirstlyemployedintheprecisiondrillingofwood[2–3]andlowcarbonsteel[4].Ultraprecisionductilecuttingofglasscouldbeobtainedbyapplyingultrasonicvibrationinthecuttingdirection[5].Zhouetal.[6]pointedoutthatthecuttingforceinultrasonicVCwillbereducedduetotheeffectofdynamicfrictionandaerodynamiclubrication.ThemethodofultrasonicVChadalsobeenappliedtothe
turningofmachinableglassceramics[7],andthediamondturningofstainlesssteel[8].
BesidesultrasonicVC,lowfrequencyVChasbeenfoundtoprolongtoollifeandhelpreduceburrsizesindrilling[9,10].Adachietal.[9]developedanelectrohydraulicservosystemtocauseVCof100HzinthespindleofanNCverticalmillingmachine.Throughtheirexperimentalstudiesondrillingofaluminum,theyfoundthatburrsizecouldbereducedconsiderablywiththeassistanceofVC.ChernandLee[11]developedavibratingworktableindrillingtocreatethedesiredvibration(ofamaximumof10KHz)fromtheworkpieceside.Theyfoundthatholeoversize,displacementoftheholecenterandsurfaceroughnessofthedrilledwallcouldbeimprovedwiththeincreaseofvibratingfrequencyandamplitude.
TheresearchesmentionedaboveemployedonlyonedimensionalVC.ShamotoandMoriwaki[12,13]proposedan‘ellipticalvibrationcutting’.Synchronizedtwo-dimensionalvibrationisappliedtothecuttingedgeintheplanecontainingthecuttingdirectionandthechipflowdirectioninsuchawaythatthecuttingedgeformsanellipticallocusineachcycleofthevibration.Twopiezoelectricplateswithsomephaseshiftwereemployed,causinganabout20KHzvibration.Theirexperimentalresults,conductedonaturningmachine,showedthatthediamondcuttingonhardenedsteelcanbecarriedoutsuccessfullybyapplyingellipticalVC.TheeffectofultrasonicellipticalVConmachiningaccuracyinturninghasalsobeenanalyzed
theoretically[14].
IthasbeenfoundthattheheatgeneratedduringVCisreducedeffectively[15].Also,thefrictionofthetoolandworkmaterialcanbereducedaccordinglybytheformationmofoxidefilmsonthetoolrakeface.Thedecreasedcutting
forcemakesthechipthinner.Xiaoetal.[16]pointedthatVChasachatter-suppressingdynamicswhileconventionalcuttingisachatter-generatingone,meaningthatVChasahighercuttingstabilityascomparedwithconventionalcutting.Thus,overallmachiningqualityisimprovedwithVC.
Fromtheseresearches,itcanbeconcludedthatVCisaneffectivemethodtobeutilizedinamachiningoperation.However,VChasnotyetbeenemployedinthefieldofmicro-milling.Inthispaper,atwo-dimensionalvibratingworktablewasdesignedandmanufactured.VCisproducedfromtheworkpieceside,andnomodificationisneededonthemachiningcenterorthemillingmachinewhenutilizing
thevibratingworktable.Micro-amplitudevibrationisproducedintheworktableviapiezo-electricalmaterialsinordertoachievebettercuttingperformance.Withthehelp
ofTaguchimethodandanalysisofvariance,theeffectofVConslot-widthaccuracyisinvestigated.Theexperimentalresultsanddiscussionsarepresented.
2.Experimentalequipmentsandmethod
Piezoelectricactuatorsfeaturethecharacteristicsofgoodprecision,fastresponseandlargedrivingforce.Inthispaper,VCisrealizedbyemployingpiezoelectricactuatorsinconjunctionwiththerelativelysimpledesignedstructureforgeneratingthedesiredtwo-dimensionalvibration.Wefirstmadeatwo-dimensionalvibratingworktablecontainingtwopiezoelectricactuatorandtwolinearguideways,asshownschematicallyinFig.1.Thevibratingworktableservestwopurposes:
(1)toclamptheworkpiece;
and
(2)toproducethedesiredvibrationinthehorizontalXandYdirections.Itiscomposedof:
(A)workpiece-holdingblock,(B)linearguideway,(C)piezoelectricactuator,(D)adaptingplate,(E)spring,and(F)baseblock.
Theworkpiece-holdingblock(A)istoclamptheworkpieceduringmillingexperiments.TwoPhysikInstrumente(PI)-madepiezoelectricactuator(PImodelP-244.10)andtwolinearguidewaysareemployedintheworktable.P-244.10,havingamaximumoperatingfrequencyof16KHzandamaximumtravelingdistanceof10mm,iscooperatedwithatwo-channelhighpoweramplifier(PImodelP-270.02)andawaveformgenerator(HP-33120A)toproducethedesiredvibration.ThemaximumpushingforceofP-244.10is2000N.TheoutputvoltageofP-270.02isfrom0toK1000V.Itspeakcurrentis50mA.
Fig.1.Schematicillustrationofvibratingworktable.
Thelinearguidewaycanensureuni-axialmotionofP-244.10whenVCisapplied.Piezoelectricactuatorsarearrangedperpendicularly.Two-dimensionalvibrationofthe
workpiece-holdingblockisrealizedbythesetwopiezoelectricactuatorsthroughtheadaptingplate(D).Thespring(E)istoprovidethenecessarypreloadforP-244.10,sincethepiezoelectricactuatorisverybrittleandcanonlywithstandamaximumpullingforceof300N.PhotoofthevibratingworktableisshowninFig.2.
Otherexperimentalequipmentsaredescribedasfollows:
1.Machiningcenter(MC-1050P,Mitsubishi-520AMcontroller).therangeofthespindlespeedisfrom45to6000rpm.
2.Laserdisplacementmeter(KeyenceLC-2430).Thesamplingrateofthissensoris50KHz;
theresolutionis0.01mmandthelaserbeamspotis12mm.Vibrationamplitudeoftheworkpiecewasmeasuredbythishighaccuracyinstrument.
3.Toolmakers’microscope(Olympus,MM-11).toobservethemachinedsurfaces.Itpossessesamaximummagnificationof200times.
4.Surfaceroughnessmeasuringmachine(Talyround,series2).tomeasurethesurfaceroughnessoftheworkpieceafterendmilling.
5.Two-fluteendmill.standard,madeofhighspeedsteel(HSS),withadiameterof1mm,aflutelengthof5mm,ahelixangleof308.Shankdiameteris6mm.
6.Workmaterial.aluminumalloyAl6061-T6wastested.Togetreliabledata,theworkpieceswerecutandpolishedtoprecisepieces(42mm!
20mm!
8mm)beforetest.
7.Cuttingfluid.mineraloil.
Fig.2.Photoofvibratingworktable.
Fig.3.Micro-millingexperiments.
Themicro-millingexperimentswerecarriedout,producingaslotontheworkpieceaftereachcut,asshowninFig.3.Lengthofeachslotisfixedat10mm.Eachcombinationofmachiningparametersistestedfourtimes.Thereareseveralmethodstoevaluatethequalityofamachinedworkpieceafterendmilling.Themethodofanalysisisstatedasfollows.
2.1.Tool-wearexperiment
ThepurposeoftheexperimentistoinvestigatetheinfluenceofVContoollifeinendmilling.Numberofslotsproducedbyanendmillbeforeout-of-toleranceslotis
createdcanberegardedasameasurementoftoollife.Sincethediameteroftheendmillis1mm,thethresholdoftheslotwidthdeterminingtoollifeischosenas1mm.ThemachiningconditionissummarizedinTable1.Vibratingfrequencieschosenwere0,500Hz,1and10kHz.Vibratingamplitudesvariedfrom0,4,7,to10mm.Here,0Hzor0mmmeansthatnovibrationisimposed.Hundredslotswerecreatedforeachmachiningcondition.
2.2.UniaxialVCexperiment
ThepurposetheuniaxialVCexperimentistoinvestigatetheinfluenceofVConmachiningaccuracyinendmilling.Widthofmilledslotanddisplacementofslotcenterwereusedtorepresentthedimensionalaccuracyofendmilling.Slot-widthove
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