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外文翻译--三轴和五轴表面仿形铣削加工 英文版.pdf

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外文翻译--三轴和五轴表面仿形铣削加工 英文版.pdf

ThreeandfiveaxesmillingofsculpturedsurfacesR.Baptistaa,,1,J.F.AntuneSimo˜esb,2aInstitutoSuperiorTe´cnico,TechnicalUniversityofLisboa,Libson,PortugalbEscolaSuperiordeTecnologia/Inst.Polite´cnicodeSetu´bal,SchoolofTechnology/PolytechnicInstituteofSetu´bal,Setu´bal,PortugalAccepted17December1999AbstractTheaimofthisworkistheanalysisoftheinfluenceofthemillingparametersonthesurfacefinish.Thisworkisofinteresttobothscienceandindustry.Ononehand,ittriestoreducethemanualpolishingtime,whichrepresentsahighpercentageoftheproductiontimeofmoulds.Ontheotherhand,whiletheliteraturemainlyreferstosteelmoulds,thisworkwascarriedoutonaluminiumbecauseofitsadvantagesformachininganditssuitabilityformoulds.Insmallbatchproductionthemanufacturersareinterestedintheproductionofaluminiummoulds.A5axisCNCmillingmachinewasusedforthesurfacefinishingofseveralparts,previously3axismachined,withinequalcuttingconditions.Differentmachiningconditionson3and5axesfinishingoperationsweretested.Thecomparisonoftheresultsallowstoconcludethatabettersurfacefinishisachievedwith5axismillingusinganendmillinclinedinthefeedinsteadofthetraditional3axismillingwithaballnosecutter.TheapplicationoftheDesignofExperimentstechniquetogetherwithmultiplelinearregressionenablestheestablishmentofamathematicalmodeloftheprocessthatgivestheprocessparametervaluesthatleadtotheminimummachiningtimeinordertoachieveacertainroughness.KeywordsThreeandfiveaxesmillingTooltypeandorientationSurfacefinishandmachiningtime1.IntroductionThedevelopmentoftheaeronauticandautomobileindustriesbroughtnewtechnologicalchallenges,relatedtothegrowingcomplexityoftheproductsandthenewgeometriesmodelledinCADsystems.Thesemorecomplexgeometriesimposenewchallengingmanufacturingsituationsforthemillingofmouldsandstampingtools.Thisisanimportantreasonforthedevelopmentofnewmillingtechnology,namely5axismilling.Thestudyofthesenewmillingtechniqueisveryimportantinordertoidentifyinwhatconditionseachoneofthesetechniquescangivethebestresult.Manualpolishingofsculpturedsurfacesisalmostnecessarytoobtainthedesiredsurfaceroughness.Thiskindofoperationisaconsequenceoftheinabilityofthemillingprocesstoachieveeconomicallytherequiredsurfacequalityandinourdaysismoreandmoreaffectedbythedecreasingnumberofqualifiedworkers.The5axismillingis,now,oneofthetechniquesthatcangiveenormousadvantagesinmachiningoperations,potentialforsignificantreductionoftherequiredmanualfinish.Inthispaper,theroughnessRaofthemachiningsurfaceisrelatedtotheoperatingparameters,appealingtoamathematicalstatisticmodel.Thepartgeometrywasselectedinordertorepresent,inablockofsmalldimensions,allthedifferentgeometriesthatcanbefoundinmouldsandstampingtools.Theequationsrelatingtheroughnessleveltothemachiningconditionsfeedpertoothandstepover,onparticularpartarea,weredetermined.Asexpected,thedevelopedmathematicalmodelexpressesadequatelytheexperimentalresultsandenablestheutilisationofanoptimisationcriterion,machiningtimeinthiscase.Thisfactemphasisestheimportanceofthemathematicalmodelstoestablishthemachiningparametersaimingtheoptimaluseoftheresources.TheexperimentalworkplanningandtheanalysisoftheresultsweredoneaccordingtotheDesignofExperimentsmethod.2.ExperimentalworkThisworktargetsaspecificindustrialproblemthefinishingofsculpturedsurfacebymillingoperation.TheJournalofMaterialsProcessingTechnology1032000398–403Correspondingauthor.1M.S.O.,AssistantProfessoroftheIST.2C.P.,AssistantoftheEST.workcarriedoutconsistedonthecomparisonoftheperformanceof5axismillingcomparativetothe3axismillingofsculpturedsurfaces.Alloftheprocessvariableshavebeenidentifiedandthemostrelevantoneswereselectedforstudy.Thefinalobjectiveistoquantifytheirvaluesinordertoobtaintheminimummachiningtimeforafixedroughness.2.1.IdentificationandselectionofprocessvariablesTheprocessparametersselectedfortheexperimentalworkwerethestepover,thefeedpertooth,thefeeddirectionandthe3andthe5axesmillingtechnology.Asthemillingmachinehadalowrotationlimitof4.200rpm,andthetoolcouldworkinhigherspeed,itwasdecidedtokeepthecuttingspeedconstant.Also,thetooldiameterwaskeptconstantandasmalldiameterof10and12mm,suchasoccurswithindustrialpractice,werechoseninordertoavoidgeometricalinterferencebetweenthetoolandthepart.Thecuttingdepthwasalsomaintainedconstantnotonlytoreducethenumberofvariablesbutalsobecauseinfinishingoperationsthedepthisalwayssmall.2.2.EquipmentThemillingoperationswereperformedona5axisCNCmillingmachineHermleUWF1202HequippedwithanHeidenhainTNC425CNCcontroller.MasterCamversion5.54wasusedtocreatetheCNCpartprograms.Multisurfmodulefor3axisandFlowlinemodulefor5axis,wereused.3.ExperimentalsetupTheexperimentalworkwasdividedintotwophases.Thefirstphasewasthe3axismillinganalysis,withaballnosemill.Thesecondphasewasthe5axismilling,withtwokindsoftools,aballnoseandanendmill.Thecontrolparametersconsideredwerethesurfaceroughness,dimensionalaccuracyandshapeofthepartgeometry,andmachiningtime.Thepartsgeometryhasfourdifferentshapesaconvexshape,aconcaveshape,anhorizontalplaneshapeandaninclinedplaneshapeFig.1.Althoughthisstudyisabout5axismilling,theparthadacurvatureonlyinonedirectionthedoublecurvaturewillbringonlymorecomplexity,andthismodelcanalsobeappliedinthatcase.So,itwasdecidedtoinvolveonlyonerotationaxisAaxisrotationoverthelinearXaxis.Thepartsmaterialwasanaluminiumalloyofthe7.000series,usedinthemanufacturingofplasticsinjectionmouldsforsmallandmediumseriesproduction.3.1.ThreeaxismillingInitially,theimportanceofthestepoverandthefeedpertoothparametersonfinishingoperationswereinvestigatedbythreeaxismilling.Afterthisinitialstudy,thefeeddirectionimportancewasanalysed.Thisparameterwasstudiedconsideringthreedifferentdirectionsathedirectionof08bthedirectionof458cthedirectionof908contouringFig.2.Asthenextpictureprintsout,oneofthecharacteristicsin3axismillingoperationsisthatthelead/lagangleisnotconstant.Thisangleisdefinedbetweenthetoolaxisandthesurfacenormal.On3axismillingoperationsitispossibletoidentifythreedifferentcuttingtypesthedownwardcutting,theplanecutting,andtheupwardcutting,Fig.31.Thecuttingspeedisnotconstantalongthemachiningpath.Fig.3alsoshowsthatthecuttingspeeddistributioninthetooledgeisdifferentforeachoneofthethreecuttingtypes.3.2.FiveaxismillingOnthefinishingoperationsby5axismillingtheleadbf0/lagbf0Thetoolshasthesamediameterandstepover.Fig.6.aInclinationoftheballnosemillbf158binclinationoftheendmillbf48.400R.Baptista,J.F.AntuneSimo˜es/JournalofMaterialsProcessingTechnology1032000398–403therearedifferentvaluesofstepoverandfeedpertoothleadingtothesameroughnessvalue,butwithdifferentmachiningtimeforthestepoverandfeedpertoothparameters,thereisalowerlimitwhereadramaticaggravationonthemachiningtimebegins.Processmodel.Withthelastresultsfortheinclinedplaneshapeaprocessmodelwasdeveloped.RoughnessRa078104676logStepover12436logFeedpertooth1Eq.1relatestheroughnesswiththestepoverandthefeedpertooth.Thisequationwasobtainedbyamultiplelinearregressionthelogarithmicapproachdisplayedthebestresults.Machiningtime92194Stepover7498Feedpertooth31082Eq.2relatesthemachiningtimetothestepoverandfeedpertooth.Itisanapplicationoftheuniformmovementequation.Afterthedefinitionoftherequiredroughnessvalue,inthiscasea1mmroughnesswaschosen,theprocessvariablesfortheminimummachiningtimewereoptimisedEq.3,Fig.9.Table1Averageroughness,RammStepovermmFeedpertoothmm/tooth0.0300.0400.0500.0600.0800.1320.1390.1700.0630.290.550.1000.461.150.1550.471.360.2000.630.700.751.630.2500.850.850.901.420.2750.981.430.3001.081.110.3251.480.3501.270.3751.640.4401.551.631.710.5001.940.6002.270.7003.10Table2MachiningtimesStepovermmFeedpertoothmm/tooth0.0300.0400.0500.0600.0800.1320.1390.1700.0631.5606250.1007402390.1556751470.200482305250930.250390254208960.275223880.3003251720.325750.3502800.375650.440225134860.5001040.600870.70074Fig.7.Stepovermm.Fig.8.Feedpertoothmm/tooth.Fig.9.Minimummachiningtime.R.Baptista,J.F.AntuneSimo˜es/JournalofMaterialsProcessingTechnology1032000398–403401

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