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,September2001.41CharacteristicsofMicroMachiningUsingTwoDimensionalToolVibrationJungHwanAhn1,HanSeokLim2andSeongMinSon31Schoolofmechanicalengineering,PuSanNationalUniversity,BuSan,SouthKorea2DepartmentofMechanicalengineering,NationalUniversityofSingapore,Singapore,Singapore3DepartmentofMechanicalandIntelligentSystemsEng.,PuSanNationalUniversity,BuSan,SouthKoreaABSTRACTThispaperdiscussesthefeasibilityofimprovingmicromachiningaccuracybyusingtwodimensional2Dvibrationcutting.Vibrationcuttingisgeneratedbytwopiezoactuatorsarrangedorthogonallyoneisactuatedbyasinecurvevoltageinput,andtheotherisactuatedbyaphaseshiftedsinecurvevoltage.Atoolattachedtothevibratoroscillatesina2Dellipticalmotion,dependingonthefrequencies,amplitudes,andthephaseshiftsoftwoinputsignalsandtheworkpiecefeedrate.Alongtheellipticaltoollocus,cuttingisdoneinthelowerpart,andnoncuttingisdoneintheupperpart.Bythiswayauniquefeatureof2Dvibrationcutting,thatis,airlubricationbetweenatoolandchips,iscaused.Anotheruniquefeatureof2Dvibrationcuttingwasexperimentallyverified,thatis,somenegativethrustforceoccursasthedirectionofchipmovementonatoolrakefaceisreversed.Thosefeaturesnotonlyhelpchipsflowsmoothlyandcontinuouslybutalsoreducecuttingforce,whichresultsinahigherqualitymachinedsurface.Throughtoolpathsimulationsandexperimentsunderseveralmicromachiningconditions,the2Dvibrationcutting,comparedtoconventionalcutting,wasfoundtoresultinagreatdecreaseinthecuttingforce,amuchsmoothersurface,andmuchlessburr.KeywordsTwodimensional2Dvibrationcutting,Piezoactuator,Ellipticallocus,Micromachining1.IntroductionHighprecisionmicromachiningtechnologyformanufacturingopticssuchasnonsphericalmirrorsandflatlenseshasbeeninprogress.Becauseaudio/videoproductsneedtobecompactandcomfortable,coreopticalparts,suchasfresnellensesanddiffractiongratings,continuetobecomemoreminiaturizedandmultifunctionedwhiletheirprofilesbecomemorecomplicated.Thisiswhyhighprecisionmicromachiningisbecomingmoreimportantthanever.Ingeneral,thesizeeffectinevitableinmicromachining,whichmakesthespecificcuttingforcelarge,causessuchundesirableproblemsasformdeformation,chatter,andburr,allofwhichdeterioratethequalityofopticalpartsintermsofbothformaccuracyandsurfaceroughness1.Manystudieshaveattemptedtodevelopenewmethodstoovercometheabovementionedproblems.Thestudiesareonstiffstructureswithlowthermalerrorofmachinetools,microfeedingmechanism,andthemicromachiningprocessitself.Vibrationcuttingisanattempttodecreasethesizeeffectbytheuseofintermittentairlubricationbetweenavibratorytoolandchips2,3,4.Thisstudyaimsatinvestigatingtheeffectsoftwodimensional2Dvibrationcuttingoncuttingforce,surfaceroughness,burrandsoon.Atoolvibratorcomposedoftwopiezoactuatorsisdeveloped,andacontrolprogramtogenerateanappropriatetoolmotionisdeveloped.2.ModeloftwodimensionalvibrationcuttingOnedimensionalvibrationmechanism,inwhichaJungHwanAhn,HanSeokLimandSeongMinSonInternationalJournaloftheKSPE,Vol.2,No.3.42hornisusedtoachieveavibrationofhighfrequencyandquitelargeamplitude,wasprovedveryeffectiveindecreasingthecuttingforce2.Incomparison,2Dtoolvibrationhastheadditionaladvantageofbeingabletogenerateavarietyoftoolpathsbycombiningtwoaxisvibratorytoolmovements.Fig.1showstheprincipleoftwodimensionalvibrationcutting.AssumingamplitudeA,frequencyf,phaseshiftΦ,andworkpiecefeedratevinthe2Dvibrationcutting,thetoollocusisexpressedbyequations1.ThetoolisengagedindowncuttingduringperiodI,whileitcutstheworkpieceupwardduringperiodII.Therefore,cuttingforcesareexpectedtoincreaseduringperiodIanddecreaseinperiodII.Then,intherestofacyclictoollocus,thetoolisnotincontactwiththeworkpiece.Inthiswaythewholecyclerepeats.sinsinftAYvtftAXφ1ThetheoreticalmaximumsurfaceroughnessRmaxcanbecalculated,dependingonthetoolvibrationparameters.AssumingthatΦisconstant,Rmaxisexpressedasequation2.2,1,1max⎟⎟⎠⎞⎜⎜⎝⎛∝vfAFRPhaseshiftΦ,whichaffectsthetoollocuspattern,shouldbeselectedinordertoobtainanappropriatetoollocusoncethedepthofcutandthefeedratearegiven.Theoretically,thelargertheamplitude,thehigherthefrequency,andtheslowerthefeedrate,themachinedsurfacebecomessmoother.Inreality,however,becausetooslowafeedratelowersthecuttingefficiencyandavibrationmechanismhasitsownlimiteddynamiccharacteristics,suchparametersasamplitude,frequency,andfeedratemustbedecidedappropriatelyconsideringthosefactors.3.Piezodriven2DvibratingtoolsupportFig.2showsthestructureofapiezodriven2Dvibratingtoolsupportanditsactuationsignalgeneratingsystem.TwoPZTactuatorsarelocatedperpendicularlytoeachotherinametalplate,whichisshapedforthetoolholdertobeelasticallydeformedintheXandYdirectionsbythePZTactuatingforces.Inordertoremovethecrossinterferenceofeachaxisdisplacement,crossshapedvoidsaredevisedinthetoolholder.Ifasinewavegeneratedfromafunctiongeneratorisinputtedtoatwophasesignalgenerator,twosinewaveswithaphaseshiftΦ,correspondingtoarequiredtoolpatternareoutputted.Usingatwochannelsignalamplifier,thetwophasesignalsareamplifiedenoughtoactuatetheFig.1Principleof2DVibrationCuttingFig.2PiezoDriven2DVibratingToolSupportaStructurebActuatingsignalgeneratorJungHwanAhn,HanSeokLimandSeongMinSonInternationalJournaloftheKSPE,Vol.2,No.3.43PZTactuators.AcurrentboosterisneededtomakethePZTactuatorsrespondquicklyandwelltoarapidinput.Fig.3showsanexampleoftheellipticaltoollocimeasuredbygapsensorswhenthefrequencyis1kHz,thephaseshiftis45°,andtheamplitudesofthetwoaxesareabout5µm.Theslopeofthetoollociisabout50°.Table1showstheexperimentalmeasurementsofstatic/dynamicstiffnessofbothtoolsupportsusedforconventionalandvibrationcutting.Thestaticstiffnessofbothprincipaldirectionandthrustdirectionislargerforconventionalcuttingthanforvibrationcutting.Incontrast,forthedynamicstiffness,theprincipalcomponentbecomesmuchbiggerforvibrationcuttingthanforconventionalcutting.Thatiswhyvibrationcuttingisexpectedtobemoreusefulthanconventionalcuttinginachievingbetteraccuracy,especiallyinmicromachining.Table1StiffinessofToolSupportsunitN/µmConventionalcuttingVibrationcuttingPrincipalThrustPrincipalThrustStaticStiffness11.93116.749.065.77DynamicStiffness1.434.4421.103.934.MachiningExperiments4.1ExperimentalapparatusFig.4showsaschematicdiagramoftheexperimentalapparatussetupforthe2Dvibrationcutting.AdesktopmachinetooliscomposedofanXYtablewitharesolutionof1µm,andaZaxiscolumnwitharesolutionof0.17µm.The2Dvibratingtoolsupportisfixedatthetoolmountonthecolumnslider,whereasfortheconventionalcutting,atoolisfixeddirectlyatthetoolmount.Cuttingforceandtooldisplacementsweremeasuredwithatooldynamometerandgapsensors.4.2CuttingconditionsThecuttingparameters,i.e.,thedepthofcutandthefeedrate,werevaried,whereasthevibrationparameterswerefixedtoappropriatevaluesinaccordancewiththephysicalcharacteristicsofthetoolvibrator.Table2summarizestheexperimentalconditionsusedinthisstudy.Table2Conditionfor2DVibrationCuttingToolArtificialDiamondWorkpiece7030BrassDepthofCut1,1.25,2,3,4,5µmCuttingConditionFeedrate0.5,1,2,3,4mm/secPhase45°Frequency1kHzVibrationConditionAmplitude5µm5.Experimentalresults5.1CuttingforceWithadiamondtoolofarc180°,feedrateof1㎜/sec,anddepthofcutof1∼5㎛,thebehaviorofthecuttingforcewasinvestigatedduringcutting.Figures5aand5brespectivelyshowtheprincipalandthethrustcuttingforcesforconventionalandvibrationFig.3MeasuredToolLociofthe2DVibratingToolFig.4SchematicdiagramofexperimentalJungHwanAhn,HanSeokLimandSeongMinSonInternationalJournaloftheKSPE,Vol.2,No.3.44cutting.Whilethelevelsofthecuttingforcesforconventionalcuttingwerealmostconstantwithsomenoises,thoseforvibrationcuttingperiodicallychangedinsinusoidalfashion.ThisfactjustifiesthemodeldescribedinFig.1,inwhichthetoolcutsdowngraduallytothedeepestpointinperiodI,whereasthedepthofcutdecreasestozeroinperiodII.Thefactalsoprovesthatthereisevenaregioninacycleoftheellipticaltoolmotionwherethethrustforcebecomesnegative.Fig.6showscomparisonsoftheaveragecuttingforcefrom1to5㎛depthofcut.Theprincipalforceforthevibrationcuttingrangedfrom0.7Nto2.2N,dependingonthedepthofcut,whichisabouthalfasmuchasthatforconventionalcutting.Thethrustforcefortheconventionalcuttingrangedfrom0.3Nto0.7N,whileitwasnearlyzeroforthevibrationcutting.Itisthoughtthatthemuchsmallercuttingforceforthevibrationcuttingismainlyduetotheairlubrication–intermittentlyprovidedbythetoolvibrationbetweenthetoolandchips.5.2SurfaceroughnessTheeffectsofvibrationcuttingonsurfaceroughnesswasinvestigatedbyvaryingthedepthofcutorcuttingspeedwithadiamondtoolofarc180°.Fig.7showsthecomparativeeffectsofthedepthofcutforvibrationcuttingandconventionalcutting.Thesurfaceroughnessforconventionalcuttingfluctuatedalittlebelowadepthofcutof2㎛.Thismaybebecauseofunstablecuttingsuchasploughingduetotooshallowdepthofcut,comparedtothetooledgeradius.Forvibrationcutting,however,thesurfaceroughnesswasstable,evenintheregionoflessthan2㎛,andbetterthanthatofaConventionalCuttingb2DVibrationCuttingFig.5MeasuredCuttingForcesPrincipal,ThrustFig.6ComparisonofCuttingForcesbetweenConventionalandVibrationCutting