微铣削使用二维振动切削 翻译原文.docx

微铣削使用二维振动切削 翻译原文.docx

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微铣削使用二维振动切削翻译原文

Usingtwo-dimensionalvibrationcuttingformicro-milling

Gwo-LianqChern*,Yuan-ChinChang

DepartmentofMechanicalEngineering,NationalYunlinUniversityofScienceandTechnology,123UniversityRoad,Sec.3,Touliu,Yunlin640,Taiwan,ROC

Received10March2005;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