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外文翻译--高精度自动组合机床设计 英文版.pdf

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外文翻译--高精度自动组合机床设计 英文版.pdf

Designofultraprecisionmodular,Freeform®machinetoolR.KoningandM.WalterPrecitechInc,Keene,NH03431Keywordsultraprecisionmachining,freeformoptics,diamondmilling,modularAbstractTheFreeform®3000ultraprecisionmachinetoolhasbeendevelopedtosatisfyaneedforaunifiedaffordablemultiaxismachinewiththecapabilityofmilling,grindingandturningultraprecisionsurfaces.Demandforauniversalultraprecisionmachineemergesfromdevelopmentsingrindingandmillingconformaloptics,lensarrays,groovedpatternsanddiamondturning.ThispaperdiscussesthedesignchallengesoftheFreeform®3000machineandtheculminationofenablingtechnologies.Thefinalmachineconfigurationwasdeterminedbyevaluatingprecision,stiffnessandmodularity.Ultraprecisionmachineelementshavebeenreinventedtoaccommodatethenewconfiguration.Finiteelementmodelswereusedtoevaluatestaticanddynamicperformanceofmachinecomponents.Asteadystatethermalanalysisofthemachinehasbeencompiledwhichpinpointedareasforthermalerrorreduction.Athermalenvironmenthasbeencreatedtoholdthemachinetemperaturestabletolessthan±.05C°.1F°.Cuttingtestsdisplaythatthemachineisappropriateformillingthreedimensionalforms,diamondturningaxissymmetriccomponentsandgrindinginafloodcooledenvironment.ConfigurationSeveralmachineconfigurationshavebeenevaluatedforthefollowingcriteriaFloodcoolantcompatible,commonalityofparts,easeofbuild,abilitytosinglepointdiamondturn,abilitytodiamondmill,andmodularity.Itiscommontothinkofmachineconfigurationsinaconventionalmanner,howeverthiscanleadtheultraprecisiondesignerdownthewrongpath.Fundamentaltoultraprecisionmachinedesignisthatrelativemotionbetweenmovingelementsbefacilitatedbyafluidfilmandbefreeofcontact.Thefluidfilmprovidesanaveragingeffect,whichinturnproducesstraightnessandtruthofmotioninexcessoftheindividualelements.Contactbetweenmovingelementsthroughasealorserviceloopproducesundesirableforcesanderrormotion.Sealingslidesfrommachiningdebrismustbefacilitatedthroughtheuseofnoncontactinglabyrinths.Serviceloopsmustbesuppleandthenumberofcablesminimizedwheneverpossible.Finally,cablesmustbebundledinamannertoprovideaneutralaxisthatremainsparallelthroughouttheslidetravel.Figure1Freeform®3000machineGuardsandcoversremovedToproducethreeaxesofmotion,atleastoneaxismustbemountedontoanother.However,ifthemovingslidewaycausesatransferofmass,thenacompromiseinslidestraightnesswillresult.TheFreeform®3000wasdesignedwitha150mmverticalslidemountedontoa350mmhorizontalslideandathird250mmhorizontalslidemountsorthogonaltotheothertwoslidestoproducethefinalaxisofmotion.DuringtheconceptualphaseoftheFreeform®3000,itwasdeterminedthatanoncontactingbulkheaddesignwouldseparatethecuttingprocessfromthecombinationslideways,toprovideisolationforfloodcoolant1.TheFreeform®3000isbasedonamodulardesign.Themachinebase,oilhydrostaticboxslides,frame,electricalandpneumaticcabinetsweredesignedtobecommonforafamilyofthreeseparatemachinetools,Nanoform®350,Nanoform®700andtheFreeform®3000.Thecommonmodulardesignfacilitateseconomiesofscaleforthecomponentsandanabilitytobuildupthemachinesubassembliestoalevelandthenquicklyreacttocustomerdemands.MachineElementsAllthreelinearslidewaysutilizeoilhydrostaticpads,atasupplypressureof250psi,andlinearmotorstoproduceultraprecisioncontouringandpositioning.Hydrostaticboxtypeslidewayswerechosenineachaxisfortheirstiffnessandabilitytoprovidestraightslidetravel.Asmallhighstiffnessverticalslidewasdevelopedtomountontoahorizontalaxisviaananglebracket.Emphasisfortheverticalslidedesignwasplacedonreducingthemovingmass,whichwouldenabletheservobandwidthtoremainhigh.Severalcounterbalancedesignconceptswereevaluatedfortheirabilitytoproduceaneutralizingforce,benoninfluencing,convenientandinexpensive.Acounterbalanceairpistonwaschosenbecauseitwouldnotcontributeasignificantamountofinertia.Otherfrictionlessdesignssuchasacablemasscounterbalancedoublethemovingmassandcreateasecondorderharmonic.Finally,theairpistoncounterbalancewouldbeconvenientandinexpensivetoimplement.Astandardcommerciallyavailablecylinderwasinitiallyusedwhichwasratedforafrictionalforceequalto12ofappliedload.Duringimplementationofthecylindersontheverticalslide,itwasfoundthatthefrictionproducedanundesirableslideerror.Severaleffortstoreducethefrictionresultedinadesignofanoncontactingaerostaticpistonthatwasnoninfluencing2Figure2.Toavoidreversalerrorandhysteresis,adesignwasemployedwhichprovidesconstantpressuretotheairpiston.Thesystemincludesaprecisionregulator,whichmaintainsconstantpressuretoableedvalve.Thebleedvalveallowsanexcessof10timesthevolumedisplacedbythemaximumtraverserate,tobeexhaustedtotheenvironmentFigure3.The1AlexanderH.Slocum,PrecisionMachineDesign,PrenticeHall,1992,P.372JuliusC.Boonshaft,U.S.PatentNo.3,319,534,1967Figure2FrictionlessairpistoncounterbalanceFigure3Counterbalanceairpistonschematicconstantnonreversingflowthroughthesystemreducesvariationsinforceasafunctionofslidetraveldirection.Thenewgenerationoflensandreflectorelementsisthefreeformsurfaceshape,thathasnoaxisofrevolutionbutceshapethatcouldbedefinedbyamapofpoints,anequation,oracomputerepresentedinsolidfFreeformcomponentsrequirepartcutsofuptoseveraldaysandcompletethermalstabilization.TheFreeform®3000requiredathermalenclosureandtemperaturecontrollerwhichproducedanenvironmentwithin±.05C°.1F°Figure4.KeymachineelementssuchasthespindleriserandflycutterwheelweremanufacturedwithInvar36,alowcoefficientofexpansionnickelbasedalloy.WithadiamondtoolholdermountedontothemillingspindleriserFigure5andaspindlemountedontothehorizonFreeform®3000canbeconfiguredasalathe.Atoolholderdesignwasevelementanalysisforstiffnessandmodesofvibration.Baselinedesignparknowndiamondturninglathehaveastiffnessgreaterthan150,000lbs/inandfirstmodeofvibrationgreaterthan700Hz.Severaliterationswererequiredtoproduceatoolholder,whichmetthesecriteriaandstillmaintainedasmallmovingmass.Figure6.3P.D.Brehm,TheSinglePointDiamondMachiningofOpticalMicrostructuresandFreefConferenceProceedings,Vol.2,199920.52121.52222.52323.521000021400022200023000023400002000100001400022000300003400044000200000004000TIMETEMPERATURECROOMTEMPPRECITEMPDUCTABOVESPINDLEAIRSUPPLYFigu10HrmachinetemperatureFigure5Freeform®3000shownasadiamondturninglatheFigure6Toolholderfordiamondturning20000000isinsteadasurfarmodelorm3.talslide,thealuatedusingfiniteametersderivedfromaormSurfaces,Euspen55677re4stabilitychart714HzMachiningResultsDiamondmilledsurfaceshavebeengeneratedtoaformaccuracyof0.204µmper1500mm2inan8hrcyclewithasurfacefinishof15nmRMS.Diamondturnedsurfaceshavebeencreatedtoaformaccuracyof.057µmPVwithasurfacefinishof3nmonaØ75mm250mmconvexradiussphericalaluminumpart.Peripheralgroundpartshavebeengeneratedtoaformaccuracyof.214µmandasurfacefinishof4.4nmRMS.Arepeatabilitytestdisplayedthatfreeformpartscanbecreatedconsistentlyina2.5hrcuttingtest.Totalvariationforfivepartcuts,was0.038umPV.Surfacefinishforfreeformmachiningisdefinedbythecuspheightoftheinterruptedcut.Thermalstabilityofthemachineisrequiredforlongpartcuts.SurfacefinishcanbepredictedusingthefollowingequationsConclusionTheFreeform®3000establishesanultraprecisiondiamondmachiningplatformwhichisversatileinconfiguration,thermallystable,andeasytooperate.Themachinehasbeendevelopedtomeettheneedforconformalfreeformoptics,lensarraysandgratingpatterns,whilemaintainingutilityasaturning/grindingplatform.Precisionengineeringdisciplineshavebeenappliedtoproduceacosteffectiverobustdesign.Machiningresultshaveproducedcomponentsthatexceedinitialexpectations.Figure9CuspheightdefinitionFigure8FreeformCuttingresults

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