DOI10.1007/s00170-004-2087-6ORIGINALARTICLEIntJAdvManufTechnol(2005)26:965969Gwo-LianqChernStudyonanewturningmethodtosimulateorthogonalcuttingandtoverifyanedgebreakoutmodelReceived:01September2003/Accepted:13January2004/Publishedonline:12January2005Springer-VerlagLondonLimited2005AbstractInordertoverifyanedgebreakoutpredictingmodelinorthogonalcutting,whichwasproposedbytheauthorspreviouswork,orthogonalmachiningexperimentsmustbeconducted.ACNClathewasutilizedtocarryoutsimulatedorthogonalcut-tings.Theworkpiece,madeofaluminumalloyAl6061-T6,isacylindricalbarwithsquarethreadsandaxial/radialgrooves.Threadingandgroovinginsertswithaflatcuttingedgewerechosenasthecuttingtools.Theexperimentaldatawereusedtoverifythepreviouslydevelopededgebreakoutmodel.Thetestsshowedexcellentagreementwiththemodelpredictions.KeywordsEdgebreakoutOrthogonalcuttingThreadingTurning1IntroductionItiswellknownthatthecuttingprocesscauseslocalizedshearinadiscretezonethatextendsfromthecuttingedgetothework-materialfreesurface1,2.Researchonthemicro-morphologyofmachinedchipsusingthescanningelectronmicroscope(SEM)hadrevealedthatthechipformationoccursbyrepeatedshearacrossthin“shearfront”ornarrowbands,whichproducealamellarstructureinthechips3.Mostofthesemachiningresultswereobtainedundertheconditionsoforthogonalcutting.SinceMerchant4developedthemetalcuttingmodelin1940s,manyfollowershadtriedtoestablishamoreaccuratefor-mulatopredicttheshearangleinorthogonalcutting2,57.Thusorthogonalcuttingbecomesthefundamentalprocessandthemostbasictopicinmetalcutting.ChernandDornfeld8hadfoundthateitherburroredgebreakoutwasformedwhenthecuttingtoollefttheworkpieceinorthogonalcutting.Achamfercouldbeobservedontheworkpieceifedgebreakoutoccurred.G.-L.ChernDept.ofMechanicalEngineering,NationalYunlinUniversityofScienceandTechnology,Yunlin,Taiwan640,R.O.C.E-mail:CHERNGL.twTel.:+886-5-534260/ext.4145Theydevelopedacriterionfortheformationofburroredgebreakoutandproposedaburr/breakoutpredictingmodel.Inorthogonalcutting,theperfectlysharpcuttingedgeisastraightlineextendingperpendiculartothecuttingvelocityandgeneratesaplanesurfaceafterthecut.Inrealmanufacturingpro-cesses,however,trueorthogonalcuttingisrarelyseen.Slotting(horizontalmilling)andshapingaretwotypesoforthogonalma-chiningprocesses.Buttherangeofcuttingvelocityofashaperisquitelimitedandthedepthofcut(whichistheundeformedchipthickness)isnotuniformduringslotting.Thus,bothshapingandslottinghavesomelimitationstoperformthedesiredcut-tingoperationandviolatesomerequirementsoftheorthogonalcutting.Awidelyusedarrangementtoachieveorthogonalcuttingis“turningendoftube.”Theendofatubeiscutinalathebyatoolwithzeroinclinationangle.Sincethediameterofthetubeismuchgreaterthanthethicknessofthewall,thecuttingvel-ocitycanbetreatedasconstantalongthetubethicknessduringthecutting.Thisarrangementofsetupisgoodforexperimentsinvestigatingthecuttingbehavior,butisnotsuitabletoobservetheformationofedgebreakoutattheexitstageofcutting.Inordertosimulateorthogonalcutting,ChernandDorn-feld8usedauniversalimpactmachinetoservethispurpose.Theconfigurationofthis“impactmachining”testisshowninFig.1.Thetoolisfixedtothependulumbythespeciallyde-signedtoolholder.Apre-cutisnecessaryinordertoobtainaconstantundeformedchipthickness.ThisexperimentalsetupFig.1.Schematicillustrationofimpactmachiningtest8966wasusedtogetsomeburrorbreakoutattheworkpieceedgeandtoverifytheirburr/breakoutpredictingmodel.Butthecut-tingspeedcannotbeadjustedinthetestssincetheinitialpositionofthependulumisfixed.Also,theundeformedchipthicknessishardtocontrol.Thispaperproposesanewexperimentalarrangementtosim-ulateorthogonalcuttingtoovercometheselimitationsanddis-advantages.Itintroducesthegeometryofthespeciallydesignedworkpieceandthecuttingtool.Theexperimentaldatawereusedtoverifytheedgebreakoutmodel,whichwaspreviouslyde-velopedbytheauthor8,9,attheexitstageoforthogonalcut-ting.Theexperimentalresultsshowedexcellentagreementwiththemodelpredictions.2EdgebreakoutpredictingmodelAttheexitoftheorthogonalcutting,eitherburroredgebreakout(negativeburr)isformed.Theauthorhadstudiedthemechan-ismsattheexitstageoforthogonalcuttingonburrformationandedgebreakoutusinganSEMsubstage8,9.Anegativedefor-mationplanebeginstoformwhenthesteadystatechipformationstopsasthetoolapproachestheendofthecut.Plasticbendingandshearingofthenegativedeformationplanearethedominantmechanismsofburrformationwhereascrackpropagationalongtheplanecausestheedgebreakout.Achamferiscreatedontheworkpiecewhenedgebreakoutoccurs.Basedontheseobservation,aburr/breakoutmodelwaspro-posedasshowninFig.2.InFig.2a,thetoolwitharakeangleadvancestoAwhereburrformationinitiates.istheshearangleandtoistheundeformedchipthickness,whichisalsothedepthofcutinthiscase.Initiationofburrformationischaracterizedbytheinitialnegativedeformationangle,denotedaso,andtheinitialtooldistanceoftooltipAfromtheendofworkpiece,.Developmentandfinalburrformationinvolvesomerotation,ascanbeseeninFigs.2band2c.Fig.2ad.Burr/breakoutformationmodel8ainitiationbdevelopmentcfinalburrformationdworkpiecewithexitangleDetailsofthemathematicalderivationofthisburr/edgebreakoutmodelcanbefoundinReferences8and9.Inthispaper,onlytheequationsnecessaryforthepredictionoftheedgebreakout,Eqs.14,arequotedasfollows.Thelengthoftheedgebreakoutsurface,isdefinedasthedistanceAJinFig.2dandcanbecalculatedas=to(cot+0.5coto)sin1tanocot.(1)Theexitangle,isdefinedastheanglebetweenthecuttingvelocityandtheedgeoftheworkpiece,asshowninFig.2d.Theshearangle,inchipformationwithaconstantcuttingvelocitycanbepredictedassuggestedbyWright2:=12sin1bracketleftbigg2yusinparenleftBig45+2parenrightBigcosparenleftBig452parenrightBigsinbracketrightbigg+2,(2)whereyistheyieldstressanduistheultimatetensilestrength.TheadvantageofusingEq.2isthatitisfullypredictiveifthework-materialpropertiesareknown.Theangleofthenegativedeformationplane,o,isobtainedbyChernandDornfeld8fromtheminimumwork-rateassumptionandmustsatisfyddo(cottano+0.5)2+3coto3cot(+o)=0.(3)TheequivalentstrainatAinFig.2d,A,iscalculatedbyusingthevonMisestheory10asA=13cotocot(+o).(4)WhenAreachesthevalueoff,whichisthefracturestrainofthematerial,fractureoccursalongthenegativedeformationplaneandedgebreakoutisformed.Otherwiseaburrisformed,whichisnotconsideredanddiscussedinthispaper.3ExperimentalsetupAsetofexperimentswasdesignedtosimulateorthogonalmachining,utilizingacylindricalbarwith“threads.”Squaregroovesarecreatedalongtheaxialdirectionofthebartoprovideexitedges.Moreover,thegeometryofeachgrooveisspeciallydesignedtohaveacertainexitangleforthisstudy.Thedimen-sionandthecross-sectionoftheworkpieceareshowninFig.3.Theexitanglesforeachgrooveare30,60,90,and120degrees,respectively,ineachrevolution.Theratiooftheradiusoftheworkpiece,44.45mm(1.75in),tothemaximumdepthofcut,0.25mm(0.01in),is175:1.Thustheeffectduetothecurvatureoftheworkpiececanbeneglected.TheexperimentswereconductedonaCNClathe.ThetoolusedforthesetestsisaKennametalthreadingandgroovingin-sert(#NB3R-K420)withaflatcuttingedge.Thetoolholder(#NSR-2525M3)wasmodified,byremovingitsclearanceangleof967Fig.3.Dimensionandcross-sectionofthedesignedworkpieceTable1.CuttingconditionsandtoolgeometryCuttingspeed1.52,3.05,4.57,6.1m/s(5,10,15,20ft/s)Depthofcut,to0.15,0.25mm(0.006,0.01in)Exitangle,30,60,90,120(onworkpiece)Rakeangle,0Noseradius0.03mm(0.0012in)CuttingfluidAirthreedegrees,toprovideauniformdepthofcutinthemachiningtests.WorkpiecesbeingmachinedweremadeofaluminumalloyAl6061-T6.Theyieldstressandtheultimatetensilestrengthare275MPaand310MPa,respectively.Table1showsthecuttingconditionsofthese“threadcut-ting”tests.Thewidthofthecuttingedgeis4.95mm.Inordertoobtainauniformwidthofcutof3.175mm(0.125in),thefeedrateintheaxialdirectionisfixedasthepitchofthethreads,6.35mm/rev(0.25ipr).Depthofcut(undeformedchipthick-ness)inthesetestsistheadvancemovementofthetoolintheradialdirectionoftheworkpiece,beingchosenas0.15mm(0.006in)and0.25mm(0.01in).Therangeofthecuttingspeedisfrom1.52m/sto6.1m/s(5ft/sto20ft/s).Sincetheratioofthemaximumdepthofcuttothewidthofcutislessthan1/10,aplanestrainconditionissustained.4ResultsandmodelverificationToutilizethepreviouslydevelopedmodel,theshearangle,wasfirstcalculatedfromEq.2tobe31degrees.Onceisknown,thenegativedeformationangle,o,canbedeterminedbyEq.3foragivenexitangle,.Thentheequivalentstrain,A,iscalculatedfromEq.4.ThecalculatedvaluesofoandATable2.CalculatedvaluesofnegativedeformationangleandequivalentstrainExitangleNegativedeformationangleEquivalentstrain3012.02.106020.71.079029.20.7012040.80.48foreachexitangleareshowninTable2.Comparingthecalcu-latedAwiththefracturestrainoftheworkpiece,whichis0.5,wecanpredictwhetheredgebreakoutwilloccur.Itisfoundthatedgebreakoutoccursexceptfortheedgeswitha120-degreeexitangle.Lengthoftheedgebreakoutsurface,orbreakoutlength,canbepredictedbyEq.1.Figure4showsthesilhouetteofthemachinedworkpiecewithabreakout.Thebreakoutlengthsweremeasuredbyanopticalmicroscope.Figures5and6showthemeasuredandpredictedbreakoutlengthswithrespecttodifferentexitanglesandcuttingspeeds.Fromthesefigureswecanseethata90-degreeexitangletendstocausesmallerbreakoutlengths.Thepredictionfromthepro-posedmodelalsoshowssuchatendency.Thereasonforthisphenomenonisthatthenegativedeformationanglefora90-degreeexitangleislargerthanforboth30-degreeand60-degreeexitangles.ThismakesthelocationofpointAinFig.2dclosertopointJ,whereAJdeterminesthebreakoutlength.Foragivenexitangle,breakoutlengthincreaseswiththedepthofcut,ascanbeseenbycomparingFig.5withFig.6fordifferentdepthofcut.Thecuttingspeedcausessomevariationsonthebreakoutlengths.However,itsinfluence,comparedwiththedepthofcutandtheexitangle,isnotdominantunderthecho-sencuttingconditions.ThiscanbeunderstoodfromEq.2,whichexpectsthatshearangledoesnotchangewiththecuttingspeed.Followingthecalculatingprocedureasdepicted,thepredictedbreakoutlengthisfoundtobethesameforagivenshearangle.Thisisthelimitationfollowingfromthechosenshear-anglepre-dictingformula.Theangleofedgebreakoutonthemachinedworkpiece,whichisthesameasthenegativedeformationangleoforacertainexitangle,wasnotmeasuredinthisexperiment,duetotheconstraintsoftheexperimentalsetup.However,wecanFig.4.Photographshowingamachinedworkpiecewithabreakout968Fig.5.Measuredandpredictedbreakoutlengthsfordepthofcutof0.15mmstillqualitativelystudythisanglebyexaminingthebreakoutchamferformedafterthecutting.Itwasobservedthattheedge-breakoutangleincreaseswiththeexitangle