1、InternationalJournaloftheKoreanSocietyofPrecisionEngineering/Vol/2/No/3/September2001/41CharacteristicsofMicro-MachiningUsingTwo-DimensionalToolVibrationJung-HwanAhn1/Han-SeokLim2andSeong-MinSon31Schoolofmechanicalengineering/PuSanNationalUniversity/BuSan/SouthKorea2DepartmentofMechanicalengineering
2、/NationalUniversityofSingapore/Singapore/Singapore3DepartmentofMechanicalandIntelligentSystemsEng//PuSanNationalUniversity/BuSan/SouthKoreaABSTRACTThispaperdiscussesthefeasibilityofimprovingmicro-machiningaccuracybyusingtwo-dimensional(2-D)vibrationcutting/Vibrationcuttingisgeneratedbytwopiezoactuat
3、orsarrangedorthogonally/oneisactuatedbyasinecurvevoltageinput/andtheotherisactuatedbyaphase-shiftedsinecurvevoltage/Atoolattachedtothevibratoroscillatesina2-Dellipticalmotion/dependingonthefrequencies/amplitudes/andthephaseshiftsoftwoinputsignalsandtheworkpiecefeedrate/Alongtheellipticaltoollocus/cu
4、ttingisdoneinthelowerpart/andnon-cuttingisdoneintheupperpart/Bythiswayauniquefeatureof2-Dvibrationcutting/thatis/airlubricationbetweenatoolandchips/iscaused/Anotheruniquefeatureof2-Dvibrationcuttingwasexperimentallyverified/thatis/somenegativethrustforceoccursasthedirectionofchipmovementonatoolrakef
5、aceisreversed/Thosefeaturesnotonlyhelpchipsflowsmoothlyandcontinuouslybutalsoreducecuttingforce/whichresultsinahigherqualitymachinedsurface/Throughtoolpathsimulationsandexperimentsunderseveralmicro-machiningconditions/the2-Dvibrationcutting/comparedtoconventionalcutting/wasfoundtoresultinagreatdecre
6、aseinthecuttingforce/amuchsmoothersurface/andmuchlessburr/Keywords/Two-dimensional(2-D)vibrationcutting/Piezoactuator/Ellipticallocus/Micro-machining1/IntroductionHigh-precisionmicro-machiningtechnologyformanufacturingopticssuchasnon-sphericalmirrorsandflatlenseshasbeeninprogress/Becauseaudio/videop
7、roductsneedtobecompactandcomfortable/coreopticalparts/suchasfresnellensesanddiffractiongratings/continuetobecomemoreminiaturizedandmulti-functionedwhiletheirprofilesbecomemorecomplicated/Thisiswhyhigh-precisionmicro-machiningisbecomingmoreimportantthanever/Ingeneral/thesizeeffectinevitableinmicro-ma
8、chining/whichmakesthespecificcuttingforcelarge/causessuchundesirableproblemsasformdeformation/chatter/andburr/allofwhichdeterioratethequalityofopticalpartsintermsofbothformaccuracyandsurfaceroughness1/Manystudieshaveattemptedtodevelopenewmethodstoovercometheabovementionedproblems/Thestudiesareonstif
9、fstructureswithlowthermalerrorofmachinetools/micro-feedingmechanism/andthemicro-machiningprocessitself/Vibrationcuttingisanattempttodecreasethesizeeffectbytheuseofintermittentairlubricationbetweenavibratorytoolandchips2/3/4/Thisstudyaimsatinvestigatingtheeffectsoftwo-dimensional(2-D)vibrationcutting
10、oncuttingforce/surfaceroughness/burrandsoon/Atoolvibratorcomposedoftwopiezoactuatorsisdeveloped/andacontrolprogramtogenerateanappropriatetoolmotionisdeveloped/2/Modeloftwo-dimensionalvibrationcuttingOne-dimensionalvibrationmechanism/inwhichaJung-HwanAhn/Han-SeokLimandSeong-MinSon/InternationalJourna
11、loftheKSPE/Vol/2/No/3/42hornisusedtoachieveavibrationofhighfrequencyandquitelargeamplitude/wasprovedveryeffectiveindecreasingthecuttingforce2/Incomparison/2-Dtoolvibrationhastheadditionaladvantageofbeingabletogenerateavarietyoftoolpathsbycombiningtwo-axisvibratorytoolmovements/Fig/1showstheprinciple
12、oftwo-dimensionalvibrationcutting/AssumingamplitudeA/frequencyf/phaseshift/andworkpiecefeedratevinthe2-Dvibrationcutting/thetoollocusisexpressedbyequations(1)/Thetoolisengagedindown-cuttingduringperiodI/whileitcutstheworkpieceupwardduringperiodII/Therefore/cuttingforcesareexpectedtoincreaseduringper
13、iodIanddecreaseinperiodII/Then/intherestofacyclictoollocus/thetoolisnotincontactwiththeworkpiece/Inthiswaythewholecyclerepeats/)sin()sin(ftAYvtftAX=+=(1)Thetheoreticalmaximumsurfaceroughness(Rmax)canbecalculated/dependingonthetoolvibrationparameters/Assumingthatisconstant/Rmaxisexpressedasequation(2
14、)/)2(/1/1maxvfAFRPhaseshift/whichaffectsthetoollocuspattern/shouldbeselectedinordertoobtainanappropriatetoollocusoncethedepthofcutandthefeedratearegiven/Theoretically/thelargertheamplitude/thehigherthefrequency/andtheslowerthefeedrate/themachinedsurfacebecomessmoother/Inreality/however/becausetooslo
15、wafeedratelowersthecuttingefficiencyandavibrationmechanismhasitsownlimiteddynamiccharacteristics/suchparametersasamplitude/frequency/andfeedratemustbedecidedappropriatelyconsideringthosefactors/3/Piezo-driven2-DvibratingtoolsupportFig/2showsthestructureofapiezo-driven2-Dvibratingtoolsupportanditsact
16、uationsignalgeneratingsystem/TwoPZTactuatorsarelocatedperpendicularlytoeachotherinametalplate/whichisshapedforthetoolholdertobeelasticallydeformedintheXandYdirectionsbythePZTactuatingforces/Inordertoremovethecross-interferenceofeachaxisdisplacement/cross-shapedvoidsaredevisedinthetoolholder/Ifasinew
17、avegeneratedfromafunctiongeneratorisinputtedtoatwo-phasesignalgenerator/twosinewaveswithaphaseshift/correspondingtoarequiredtoolpatternareoutputted/Usingatwo-channelsignalamplifier/thetwo-phasesignalsareamplifiedenoughtoactuatetheFig/1Principleof2-DVibrationCuttingFig/2PiezoDriven2-DVibratingToolSup
18、port(a)Structure(b)ActuatingsignalgeneratorJung-HwanAhn/Han-SeokLimandSeong-MinSon/InternationalJournaloftheKSPE/Vol/2/No/3/43PZTactuators/AcurrentboosterisneededtomakethePZTactuatorsrespondquicklyandwelltoarapidinput/Fig/3showsanexampleoftheellipticaltoollocimeasuredbygapsensorswhenthefrequencyis1k
19、Hz/thephaseshiftis45/andtheamplitudesofthetwoaxesareabout5m/Theslopeofthetoollociisabout50/Table1showstheexperimentalmeasurementsofstatic/dynamicstiffnessofbothtoolsupportsusedforconventionalandvibrationcutting/Thestaticstiffnessofbothprincipaldirectionandthrustdirectionislargerforconventionalcuttin
20、gthanforvibrationcutting/Incontrast/forthedynamicstiffness/theprincipalcomponentbecomesmuchbiggerforvibrationcuttingthanforconventionalcutting/Thatiswhyvibrationcuttingisexpectedtobemoreusefulthanconventionalcuttinginachievingbetteraccuracy/especiallyinmicro-machining/Table1StiffinessofToolSupports/
21、unit(N/m)ConventionalcuttingVibrationcuttingPrincipalThrustPrincipalThrustStaticStiffness11/93116/749/065/77DynamicStiffness1/434/4421/103/934/MachiningExperiments4/1ExperimentalapparatusFig/4showsaschematicdiagramoftheexperimentalapparatussetupforthe2-Dvibrationcutting/Adesk-topmachinetooliscompose
22、dofanXYtablewitharesolutionof1m/andaZ-axiscolumnwitharesolutionof0/17m/The2-Dvibratingtoolsupportisfixedatthetoolmountonthecolumnslider/whereasfortheconventionalcutting/atoolisfixeddirectlyatthetoolmount/Cuttingforceandtooldisplacementsweremeasuredwithatooldynamometerandgapsensors/4/2Cuttingconditio
23、nsThecuttingparameters/i/e//thedepthofcutandthefeedrate/werevaried/whereasthevibrationparameterswerefixedtoappropriatevaluesinaccordancewiththephysicalcharacteristicsofthetoolvibrator/Table2summarizestheexperimentalconditionsusedinthisstudy/Table2Conditionfor2-DVibrationCuttingToolArtificialDiamondW
24、orkpiece70-30BrassDepthofCut1/1/25/2/3/4/5mCuttingConditionFeedrate0/5/1/2/3/4mm/secPhase45Frequency1kHzVibrationConditionAmplitude5m5/Experimentalresults5/1CuttingforceWithadiamondtoolofarc180/feedrateof1/sec/anddepthofcutof15/thebehaviorofthecuttingforcewasinvestigatedduringcutting/Figures5(a)and5
25、(b)respectivelyshowtheprincipalandthethrustcuttingforcesforconventionalandvibrationFig/3MeasuredToolLociofthe2-DVibratingToolFig/4SchematicdiagramofexperimentalJung-HwanAhn/Han-SeokLimandSeong-MinSon/InternationalJournaloftheKSPE/Vol/2/No/3/44cutting/Whilethelevelsofthecuttingforcesforconventionalcu
26、ttingwerealmostconstantwithsomenoises/thoseforvibrationcuttingperiodicallychangedinsinusoidalfashion/ThisfactjustifiesthemodeldescribedinFig/1/inwhichthetoolcutsdowngraduallytothedeepestpointinperiodI/whereasthedepthofcutdecreasestozeroinperiodII/Thefactalsoprovesthatthereisevenaregioninacycleofthee
27、llipticaltoolmotionwherethethrustforcebecomesnegative/Fig/6showscomparisonsoftheaveragecuttingforcefrom1to5depthofcut/Theprincipalforceforthevibrationcuttingrangedfrom0/7Nto2/2N/dependingonthedepthofcut/whichisabouthalfasmuchasthatforconventionalcutting/Thethrustforcefortheconventionalcuttingrangedf
28、rom0/3Nto0/7N/whileitwasnearlyzeroforthevibrationcutting/Itisthoughtthatthemuchsmallercuttingforceforthevibrationcuttingismainlyduetotheairlubricationintermittentlyprovidedbythetoolvibration-betweenthetoolandchips/5/2SurfaceroughnessTheeffectsofvibrationcuttingonsurfaceroughnesswasinvestigatedbyvary
29、ingthedepthofcutorcuttingspeedwithadiamondtoolofarc180/Fig/7showsthecomparativeeffectsofthedepthofcutforvibrationcuttingandconventionalcutting/Thesurfaceroughnessforconventionalcuttingfluctuatedalittlebelowadepthofcutof2/Thismaybebecauseofunstablecuttingsuchasploughingduetotooshallowdepthofcut/comparedtothetooledgeradius/Forvibrationcutting/however/thesurfaceroughnesswasstable/evenintheregionoflessthan2/andbetterthanthatof(a)ConventionalCutting(b)2-DVibrationCuttingFig/5MeasuredCuttingForces/Principal/ThrustFig/6ComparisonofCuttingForcesbetweenConventionalandVibrationCutting
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