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外文翻译--关于模仿正交切削和核实边缘断裂模型的一个新的车削方法的研究 英文版.pdf

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外文翻译--关于模仿正交切削和核实边缘断裂模型的一个新的车削方法的研究 英文版.pdf

DOI10.1007/s0017000420876ORIGINALARTICLEIntJAdvManufTechnol200526965–969GwoLianqChernStudyonanewturningmethodtosimulateorthogonalcuttingandtoverifyanedgebreakoutmodelReceived01September2003/Accepted13January2004/Publishedonline12January2005©SpringerVerlagLondonLimited2005AbstractInordertoverifyanedgebreakoutpredictingmodelinorthogonalcutting,whichwasproposedbytheauthorspreviouswork,orthogonalmachiningexperimentsmustbeconducted.ACNClathewasutilizedtocarryoutsimulatedorthogonalcuttings.Theworkpiece,madeofaluminumalloyAl6061T6,isacylindricalbarwithsquarethreadsandaxial/radialgrooves.Threadingandgroovinginsertswithaflatcuttingedgewerechosenasthecuttingtools.Theexperimentaldatawereusedtoverifythepreviouslydevelopededgebreakoutmodel.Thetestsshowedexcellentagreementwiththemodelpredictions.KeywordsEdgebreakoutOrthogonalcuttingThreadingTurning1IntroductionItiswellknownthatthecuttingprocesscauseslocalizedshearinadiscretezonethatextendsfromthecuttingedgetotheworkmaterialfreesurface1,2.ResearchonthemicromorphologyofmachinedchipsusingthescanningelectronmicroscopeSEMhadrevealedthatthechipformationoccursbyrepeatedshearacrossthinshearfrontornarrowbands,whichproducealamellarstructureinthechips3.Mostofthesemachiningresultswereobtainedundertheconditionsoforthogonalcutting.SinceMerchant4developedthemetalcuttingmodelin1940s,manyfollowershadtriedtoestablishamoreaccurateformulatopredicttheshearangleinorthogonalcutting2,5–7.Thusorthogonalcuttingbecomesthefundamentalprocessandthemostbasictopicinmetalcutting.ChernandDornfeld8hadfoundthateitherburroredgebreakoutwasformedwhenthecuttingtoollefttheworkpieceinorthogonalcutting.Achamfercouldbeobservedontheworkpieceifedgebreakoutoccurred.G.L.ChernDept.ofMechanicalEngineering,NationalYunlinUniversityofScienceandTechnology,Yunlin,Taiwan640,R.O.C.EmailCHERNGLpine.yuntech.edu.twTel.8865534260/ext.4145Theydevelopedacriterionfortheformationofburroredgebreakoutandproposedaburr/breakoutpredictingmodel.Inorthogonalcutting,theperfectlysharpcuttingedgeisastraightlineextendingperpendiculartothecuttingvelocityandgeneratesaplanesurfaceafterthecut.Inrealmanufacturingprocesses,however,trueorthogonalcuttingisrarelyseen.Slottinghorizontalmillingandshapingaretwotypesoforthogonalmachiningprocesses.Buttherangeofcuttingvelocityofashaperisquitelimitedandthedepthofcutwhichistheundeformedchipthicknessisnotuniformduringslotting.Thus,bothshapingandslottinghavesomelimitationstoperformthedesiredcuttingoperationandviolatesomerequirementsoftheorthogonalcutting.Awidelyusedarrangementtoachieveorthogonalcuttingisturningendoftube.Theendofatubeiscutinalathebyatoolwithzeroinclinationangle.Sincethediameterofthetubeismuchgreaterthanthethicknessofthewall,thecuttingvelocitycanbetreatedasconstantalongthetubethicknessduringthecutting.Thisarrangementofsetupisgoodforexperimentsinvestigatingthecuttingbehavior,butisnotsuitabletoobservetheformationofedgebreakoutattheexitstageofcutting.Inordertosimulateorthogonalcutting,ChernandDornfeld8usedauniversalimpactmachinetoservethispurpose.TheconfigurationofthisimpactmachiningtestisshowninFig.1.Thetoolisfixedtothependulumbythespeciallydesignedtoolholder.Aprecutisnecessaryinordertoobtainaconstantundeformedchipthickness.ThisexperimentalsetupFig.1.Schematicillustrationofimpactmachiningtest8966wasusedtogetsomeburrorbreakoutattheworkpieceedgeandtoverifytheirburr/breakoutpredictingmodel.Butthecuttingspeedcannotbeadjustedinthetestssincetheinitialpositionofthependulumisfixed.Also,theundeformedchipthicknessishardtocontrol.Thispaperproposesanewexperimentalarrangementtosimulateorthogonalcuttingtoovercometheselimitationsanddisadvantages.Itintroducesthegeometryofthespeciallydesignedworkpieceandthecuttingtool.Theexperimentaldatawereusedtoverifytheedgebreakoutmodel,whichwaspreviouslydevelopedbytheauthor8,9,attheexitstageoforthogonalcutting.Theexperimentalresultsshowedexcellentagreementwiththemodelpredictions.2EdgebreakoutpredictingmodelAttheexitoftheorthogonalcutting,eitherburroredgebreakoutnegativeburrisformed.TheauthorhadstudiedthemechanismsattheexitstageoforthogonalcuttingonburrformationandedgebreakoutusinganSEMsubstage8,9.Anegativedeformationplanebeginstoformwhenthesteadystatechipformationstopsasthetoolapproachestheendofthecut.Plasticbendingandshearingofthenegativedeformationplanearethedominantmechanismsofburrformationwhereascrackpropagationalongtheplanecausestheedgebreakout.Achamferiscreatedontheworkpiecewhenedgebreakoutoccurs.Basedontheseobservation,aburr/breakoutmodelwasproposedasshowninFig.2.InFig.2a,thetoolwitharakeangleαadvancestoAwhereburrformationinitiates.φistheshearangleandtoistheundeformedchipthickness,whichisalsothedepthofcutinthiscase.Initiationofburrformationischaracterizedbytheinitialnegativedeformationangle,denotedasβo,andtheinitialtooldistanceoftooltipAfromtheendofworkpiece,ω.Developmentandfinalburrformationinvolvesomerotation,ascanbeseeninFigs.2band2c.Fig.2a–d.Burr/breakoutformationmodel8ainitiationbdevelopmentcfinalburrformationdworkpiecewithexitangleDetailsofthemathematicalderivationofthisburr/edgebreakoutmodelcanbefoundinReferences8and9.Inthispaper,onlytheequationsnecessaryforthepredictionoftheedgebreakout,Eqs.1–4,arequotedasfollows.Thelengthoftheedgebreakoutsurface,η,isdefinedasthedistanceAJinFig.2dandcanbecalculatedasηtocotφ0.5cotβosinϕ1−tanβocotϕ.1Theexitangle,ϕ,isdefinedastheanglebetweenthecuttingvelocityandtheedgeoftheworkpiece,asshowninFig.2d.Theshearangle,φ,inchipformationwithaconstantcuttingvelocitycanbepredictedassuggestedbyWright2φ12sin−1bracketleftbigg2σyσusinparenleftBig45α2parenrightBigcosparenleftBig45−α2parenrightBig−sinαbracketrightbiggα2,2whereσyistheyieldstressandσuistheultimatetensilestrength.TheadvantageofusingEq.2isthatitisfullypredictiveiftheworkmaterialpropertiesareknown.Theangleofthenegativedeformationplane,βo,isobtainedbyChernandDornfeld8fromtheminimumworkrateassumptionandmustsatisfyddβo{cotφtanβo0.523cotβo−3cotφβo}0.3TheequivalentstrainatAinFig.2d,εA,iscalculatedbyusingthevonMisestheory10asεA1√3cotβo−cotφβo.4WhenεAreachesthevalueofεf,whichisthefracturestrainofthematerial,fractureoccursalongthenegativedeformationplaneandedgebreakoutisformed.Otherwiseaburrisformed,whichisnotconsideredanddiscussedinthispaper.3ExperimentalsetupAsetofexperimentswasdesignedtosimulateorthogonalmachining,utilizingacylindricalbarwiththreads.Squaregroovesarecreatedalongtheaxialdirectionofthebartoprovideexitedges.Moreover,thegeometryofeachgrooveisspeciallydesignedtohaveacertainexitangleforthisstudy.ThedimensionandthecrosssectionoftheworkpieceareshowninFig.3.Theexitanglesforeachgrooveare30,60,90,and120degrees,respectively,ineachrevolution.Theratiooftheradiusoftheworkpiece,44.45mm1.75in,tothemaximumdepthofcut,0.25mm0.01in,is1751.Thustheeffectduetothecurvatureoftheworkpiececanbeneglected.TheexperimentswereconductedonaCNClathe.ThetoolusedforthesetestsisaKennametalthreadingandgroovinginsertNB3RK420withaflatcuttingedge.ThetoolholderNSR2525M3wasmodified,byremovingitsclearanceangleof967Fig.3.DimensionandcrosssectionofthedesignedworkpieceTable1.CuttingconditionsandtoolgeometryCuttingspeed1.52,3.05,4.57,6.1m/s5,10,15,20ft/sDepthofcut,to0.15,0.25mm0.006,0.01inExitangle,ϕ30◦,60◦,90◦,120◦onworkpieceRakeangle,α0◦Noseradius0.03mm0.0012inCuttingfluidAirthreedegrees,toprovideauniformdepthofcutinthemachiningtests.WorkpiecesbeingmachinedweremadeofaluminumalloyAl6061T6.Theyieldstressandtheultimatetensilestrengthare275MPaand310MPa,respectively.Table1showsthecuttingconditionsofthesethreadcuttingtests.Thewidthofthecuttingedgeis4.95mm.Inordertoobtainauniformwidthofcutof3.175mm0.125in,thefeedrateintheaxialdirectionisfixedasthepitchofthethreads,6.35mm/rev0.25ipr.Depthofcutundeformedchipthicknessinthesetestsistheadvancemovementofthetoolintheradialdirectionoftheworkpiece,beingchosenas0.15mm0.006inand0.25mm0.01in.Therangeofthecuttingspeedisfrom1.52m/sto6.1m/s5ft/sto20ft/s.Sincetheratioofthemaximumdepthofcuttothewidthofcutislessthan1/10,aplanestrainconditionissustained.4ResultsandmodelverificationToutilizethepreviouslydevelopedmodel,theshearangle,φ,wasfirstcalculatedfromEq.2tobe31degrees.Onceφisknown,thenegativedeformationangle,βo,canbedeterminedbyEq.3foragivenexitangle,ϕ.Thentheequivalentstrain,εA,iscalculatedfromEq.4.ThecalculatedvaluesofβoandεATable2.CalculatedvaluesofnegativedeformationangleandequivalentstrainExitangleNegativedeformationangleEquivalentstrain3012.02.106020.71.079029.20.7012040.80.48foreachexitangleareshowninTable2.ComparingthecalculatedεAwiththefracturestrainoftheworkpiece,whichis0.5,wecanpredictwhetheredgebreakoutwilloccur.Itisfoundthatedgebreakoutoccursexceptfortheedgeswitha120degreeexitangle.Lengthoftheedgebreakoutsurface,orbreakoutlength,canbepredictedbyEq.1.Figure4showsthesilhouetteofthemachinedworkpiecewithabreakout.Thebreakoutlengthsweremeasuredbyanopticalmicroscope.Figures5and6showthemeasuredandpredictedbreakoutlengthswithrespecttodifferentexitanglesandcuttingspeeds.Fromthesefigureswecanseethata90degreeexitangletendstocausesmallerbreakoutlengths.Thepredictionfromtheproposedmodelalsoshowssuchatendency.Thereasonforthisphenomenonisthatthenegativedeformationanglefora90degreeexitangleislargerthanforboth30degreeand60degreeexitangles.ThismakesthelocationofpointAinFig.2dclosertopointJ,whereAJdeterminesthebreakoutlength.Foragivenexitangle,breakoutlengthincreaseswiththedepthofcut,ascanbeseenbycomparingFig.5withFig.6fordifferentdepthofcut.Thecuttingspeedcausessomevariationsonthebreakoutlengths.However,itsinfluence,comparedwiththedepthofcutandtheexitangle,isnotdominantunderthechosencuttingconditions.ThiscanbeunderstoodfromEq.2,whichexpectsthatshearangledoesnotchangewiththecuttingspeed.Followingthecalculatingprocedureasdepicted,thepredictedbreakoutlengthisfoundtobethesameforagivenshearangle.Thisisthelimitationfollowingfromthechosenshearanglepredictingformula.Theangleofedgebreakoutonthemachinedworkpiece,whichisthesameasthenegativedeformationangleβoforacertainexitangle,wasnotmeasuredinthisexperiment,duetotheconstraintsoftheexperimentalsetup.However,wecanFig.4.Photographshowingamachinedworkpiecewithabreakout968Fig.5.Measuredandpredictedbreakoutlengthsfordepthofcutof0.15mmstillqualitativelystudythisanglebyexaminingthebreakoutchamferformedafterthecutting.Itwasobservedthattheedgebreakoutangleincreaseswiththeexitangle.ThiscanbeverifiedbyEq.3,whichdeterminesthenegativedeformationangleforagivenshearangleandanexitangle,ascanbeseeninTable2.Thesepredictedresultsfullycoincidewiththeexperimentalobservations.5ConclusionsFromtheproposedmachiningtests,someconclusionscanbedrawn1.Thedevelopedmodelgivesexcellentpredictionsofthebreakoutphenomenonasevaluatedintheproposedsimulatedorthogonalmachiningtests.2.Thebreakoutlengthincreaseswiththedepthofcut,whichisequaltotheundeformedchipthicknessinorthogonalcutting.Fig.6.Measuredandpredictedbreakoutlengthsfordepthofcutof0.25mm3.Thenegativedeformationangleisverysensitivetotheexitangleandthusinfluencestheequivalentstrainwhenburr/breakoutformationisinitiated.Thefracturestrainoftheworkpiecedeterminesatwhatexitanglebreakoutwilloccurinsteadofburrformation.4.Theedgebreakoutangleincreaseswiththeexitangle.Thecuttingspeeddoesnotdemonstrateassignificantaninfluenceonthebreakoutformationasdothedepthofcutandtheexitangle.References1.vonTurkovichBF1970Shearstressinmetalcutting.JEngInd921151–1572.WrightPK1982Predictingtheshearplaneangleinmachiningfromworkmaterialstrainhardeningcharacteristics.JEngInd1043285–292

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