外文翻译--二维振动切削的微加工特征 英文版.pdf

InternationalJournaloftheKoreanSocietyofPrecisionEngineering,Vol.2,No.3,September2001.41CharacteristicsofMicro-MachiningUsingTwo-DimensionalToolVibrationJung-HwanAhn1,Han-SeokLim2andSeong-MinSon31Schoolofmechanicalengineering,PuSanNationalUniversity,BuSan,SouthKorea2DepartmentofMechanicalengineering,NationalUniversityofSingapore,Singapore,Singapore3DepartmentofMechanicalandIntelligentSystemsEng.,PuSanNationalUniversity,BuSan,SouthKoreaABSTRACTThispaperdiscussesthefeasibilityofimprovingmicro-machiningaccuracybyusingtwo-dimensional(2-D)vibrationcutting.Vibrationcuttingisgeneratedbytwopiezoactuatorsarrangedorthogonally:oneisactuatedbyasinecurvevoltageinput,andtheotherisactuatedbyaphase-shiftedsinecurvevoltage.Atoolattachedtothevibratoroscillatesina2-Dellipticalmotion,dependingonthefrequencies,amplitudes,andthephaseshiftsoftwoinputsignalsandtheworkpiecefeedrate.Alongtheellipticaltoollocus,cuttingisdoneinthelowerpart,andnon-cuttingisdoneintheupperpart.Bythiswayauniquefeatureof2-Dvibrationcutting,thatis,airlubricationbetweenatoolandchips,iscaused.Anotheruniquefeatureof2-Dvibrationcuttingwasexperimentallyverified,thatis,somenegativethrustforceoccursasthedirectionofchipmovementonatoolrakefaceisreversed.Thosefeaturesnotonlyhelpchipsflowsmoothlyandcontinuouslybutalsoreducecuttingforce,whichresultsinahigherqualitymachinedsurface.Throughtoolpathsimulationsandexperimentsunderseveralmicro-machiningconditions,the2-Dvibrationcutting,comparedtoconventionalcutting,wasfoundtoresultinagreatdecreaseinthecuttingforce,amuchsmoothersurface,andmuchlessburr.Keywords:Two-dimensional(2-D)vibrationcutting,Piezoactuator,Ellipticallocus,Micro-machining1.IntroductionHigh-precisionmicro-machiningtechnologyformanufacturingopticssuchasnon-sphericalmirrorsandflatlenseshasbeeninprogress.Becauseaudio/videoproductsneedtobecompactandcomfortable,coreopticalparts,suchasfresnellensesanddiffractiongratings,continuetobecomemoreminiaturizedandmulti-functionedwhiletheirprofilesbecomemorecomplicated.Thisiswhyhigh-precisionmicro-machiningisbecomingmoreimportantthanever.Ingeneral,thesizeeffectinevitableinmicro-machining,whichmakesthespecificcuttingforcelarge,causessuchundesirableproblemsasformdeformation,chatter,andburr,allofwhichdeterioratethequalityofopticalpartsintermsofbothformaccuracyandsurfaceroughness1.Manystudieshaveattemptedtodevelopenewmethodstoovercometheabovementionedproblems.Thestudiesareonstiffstructureswithlowthermalerrorofmachinetools,micro-feedingmechanism,andthemicro-machiningprocessitself.Vibrationcuttingisanattempttodecreasethesizeeffectbytheuseofintermittentairlubricationbetweenavibratorytoolandchips2,3,4.Thisstudyaimsatinvestigatingtheeffectsoftwo-dimensional(2-D)vibrationcuttingoncuttingforce,surfaceroughness,burrandsoon.Atoolvibratorcomposedoftwopiezoactuatorsisdeveloped,andacontrolprogramtogenerateanappropriatetoolmotionisdeveloped.2.Modeloftwo-dimensionalvibrationcuttingOne-dimensionalvibrationmechanism,inwhichaJung-HwanAhn,Han-SeokLimandSeong-MinSon:InternationalJournaloftheKSPE,Vol.2,No.3.42hornisusedtoachieveavibrationofhighfrequencyandquitelargeamplitude,wasprovedveryeffectiveindecreasingthecuttingforce2.Incomparison,2-Dtoolvibrationhastheadditionaladvantageofbeingabletogenerateavarietyoftoolpathsbycombiningtwo-axisvibratorytoolmovements.Fig.1showstheprincipleoftwo-dimensionalvibrationcutting.AssumingamplitudeA,frequencyf,phaseshift,andworkpiecefeedratevinthe2-Dvibrationcutting,thetoollocusisexpressedbyequations(1).Thetoolisengagedindown-cuttingduringperiodI,whileitcutstheworkpieceupwardduringperiodII.Therefore,cuttingforcesareexpectedtoincreaseduringperiodIanddecreaseinperiodII.Then,intherestofacyclictoollocus,thetoolisnotincontactwiththeworkpiece.Inthiswaythewholecyclerepeats.)sin()sin(ftAYvtftAX=+=(1)Thetheoreticalmaximumsurfaceroughness(Rmax)canbecalculated,dependingonthetoolvibrationparameters.Assumingthatisconstant,Rmaxisexpressedasequation(2).)2(,1,1maxvfAFRPhaseshift,whichaffectsthetoollocuspattern,shouldbeselectedinordertoobtainanappropriatetoollocusoncethedepthofcutandthefeedratearegiven.Theoretically,thelargertheamplitude,thehigherthefrequency,andtheslowerthefeedrate,themachinedsurfacebecomessmoother.Inreality,however,becausetooslowafeedratelowersthecuttingefficiencyandavibrationmechanismhasitsownlimiteddynamiccharacteristics,suchparametersasamplitude,frequency,andfeedratemustbedecidedappropriatelyconsideringthosefactors.3.Piezo-driven2-DvibratingtoolsupportFig.2showsthestructureofapiezo-driven2-Dvibratingtoolsupportanditsactuationsignalgeneratingsystem.TwoPZTactuatorsarelocatedperpendicularlytoeachotherinametalplate,whichisshapedforthetoolholdertobeelasticallydeformedintheXandYdirectionsbythePZTactuatingforces.Inordertoremovethecross-interferenceofeachaxisdisplacement,cross-shapedvoidsaredevisedinthetoolholder.Ifasinewavegeneratedfromafunctiongeneratorisinputtedtoatwo-phasesignalgenerator,twosinewaveswithaphaseshift,correspondingtoarequiredtoolpatternareoutputted.Usingatwo-channelsignalamplifier,thetwo-phasesignalsareamplifiedenoughtoactuatetheFig.1Principleof2-DVibrationCuttingFig.2PiezoDriven2-DVibratingToolSupport(a)Structure(b)ActuatingsignalgeneratorJung-HwanAhn,Han-SeokLimandSeong-MinSon:InternationalJournaloftheKSPE,Vol.2,No.3.43PZTactuators.AcurrentboosterisneededtomakethePZTactuatorsrespondquicklyandwelltoarapidinput.Fig.3showsanexampleoftheellipticaltoollocimeasuredbygapsensorswhenthefrequencyis1kHz,thephaseshiftis45°,andtheamplitudesofthetwoaxesareabout5µm.Theslopeofthetoollociisabout50°.Table1showstheexperimentalmeasurementsofstatic/dynamicstiffnessofbothtoolsupportsusedforconventionalandvibrationcutting.Thestaticstiffnessofbothprincipaldirectionandthrustdirectionislargerforconventionalcuttingthanforvibrationcutting.Incontrast,forthedynamicstiffness,theprincipalcomponentbecomesmuchbiggerforvibrationcuttingthanforconventionalcutting.Thatiswhyvibrationcuttingisexpectedtobemoreusefulthanconventionalcuttinginachievingbetteraccuracy,especiallyinmicro-machining.Table1StiffinessofToolSupports:unit(N/µm)ConventionalcuttingVibrationcuttingPrincipalThrustPrincipalThrustStaticStiffness11.93116.749.065.77DynamicStiffness1.434.4421.103.934.MachiningExperiments4.1ExperimentalapparatusFig.4showsaschematicdiagramoftheexperimentalapparatussetupforthe2-Dvibrationcutting.Adesk-topmachinetooliscomposedofanXYtablewitharesolutionof1µm,andaZ-axiscolumnwitharesolutionof0.17µm.The2-Dvibratingtoolsupportisfixedatthetoolmountonthecolumnslider,whereasfortheconventionalcutting,atoolisfixeddirectlyatthetoolmount.Cuttingforceandtooldisplacementsweremeasuredwithatooldynamometerandgapsensors.4.2CuttingconditionsThecuttingparameters,i.e.,thedepthofcutandthefeedrate,werevaried,whereasthevibrationparameterswerefixedtoappropriatevaluesinaccordancewiththephysicalcharacteristicsofthetoolvibrator.Table2summarizestheexperimentalconditionsusedinthisstudy.Table2Conditionfor2-DVibrationCuttingToolArtificialDiamondWorkpiece70-30BrassDepthofCut1,1.25,2,3,4,5µmCuttingConditionFeedrate0.5,1,2,3,4mm/secPhase45°Frequency1kHzVibrationConditionAmplitude5µm5.Experimentalresults5.1CuttingforceWithadiamondtoolofarc180°,feedrateof1/sec,anddepthofcutof15,thebehaviorofthecuttingforcewasinvestigatedduringcutting.Figures5(a)and5(b)respectivelyshowtheprincipalandthethrustcuttingforcesforconventionalandvibrationFig.3MeasuredToolLociofthe2-DVibratingToolFig.4SchematicdiagramofexperimentalJung-HwanAhn,Han-SeokLimandSeong-MinSon:InternationalJournaloftheKSPE,Vol.2,No.3.44cutting.Whilethelevelsofthecuttingforcesforconventionalcuttingwerealmostconstantwithsomenoises,thoseforvibrationcuttingperiodicallychangedinsinusoidalfashion.ThisfactjustifiesthemodeldescribedinFig.1,inwhichthetoolcutsdowngraduallytothedeepestpointinperiodI,whereasthedepthofcutdecreasestozeroinperiodII.Thefactalsoprovesthatthereisevenaregioninacycleoftheellipticaltoolmotionwherethethrustforcebecomesnegative.Fig.6showscomparisonsoftheaveragecuttingforcefrom1to5depthofcut.Theprincipalforceforthevibrationcuttingrangedfrom0.7Nto2.2N,dependingonthedepthofcut,whichisabouthalfasmuchasthatforconventionalcutting.Thethrustforcefortheconventionalcuttingrangedfrom0.3Nto0.7N,whileitwasnearlyzeroforthevibrationcutting.Itisthoughtthatthemuchsmallercuttingforceforthevibrationcuttingismainlyduetotheairlubricationintermittentlyprovidedbythetoolvibration-betweenthetoolandchips.5.2SurfaceroughnessTheeffectsofvibrationcuttingonsurfaceroughnesswasinvestigatedbyvaryingthedepthofcutorcuttingspeedwithadiamondtoolofarc180°.Fig.7showsthecomparativeeffectsofthedepthofcutforvibrationcuttingandconventionalcutting.Thesurfaceroughnessforconventionalcuttingfluctuatedalittlebelowadepthofcutof2.Thismaybebecauseofunstablecuttingsuchasploughingduetotooshallowdepthofcut,comparedtothetooledgeradius.Forvibrationcutting,however,thesurfaceroughnesswasstable,evenintheregionoflessthan2,andbetterthanthatof(a)ConventionalCutting(b)2-DVibrationCuttingFig.5MeasuredCuttingForces:Principal,ThrustFig.6ComparisonofCuttingForcesbetweenConventionalandVibrationCutting