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ORIGINALARTICLEPerformanceimprovementofhardturningwithsolidlubricantsSinghDilbagP.V.RaoReceived10January2007/Accepted30April2007/Publishedonline7July2007SpringerVerlagLondonLimited2007AbstractProductqualityisoneofthemostimportantcriteriafortheassessmentofhardturningprocess.However,inviewofthehightemperaturesdevelopedinhardturningprocess,thesurfacequalitydeterioratesduetothetoolwear.Becauseofthestrictenvironmentalrestrictionsontheuseofcuttingfluids,newcuttingtechniquesarerequiredtobeinvestigatedtoreducethetoolwear.Inthepresentwork,theuseofsolidlubricantsduringhardturninghasbeenexploredwhilemachiningbearingsteelwithmixedceramicinsertsatdifferentcuttingconditionsandtoolgeometry.Resultsshowconsiderableimprovementinthesurfacefinishwiththeuseofsolidlubricants.Duetothepresenceofsolidlubricants,thereisadecreaseofsurfaceroughnessvaluesfrom8to15ascomparedtodryhardturning.KeywordsHardturning.Effectiverakeangle.Noseradius.Solidlubricants1IntroductionHardenedsteelsarewidelyusedinautomobile,bearing,toolanddieindustries.Thetraditionalmethodofmachininghardenedmaterialsincludesroughturning,heattreatment,andthengrindingprocess.However,hardturningeliminatessomeoftheunnecessarystepsinvolvedinthemachiningofhardmaterialsandhenceresultsintheincreaseofproductivityrate.Thevariousadvantagesofhardtuningarehigherproductivity,reducedsetuptimes,surfacefinishclosertogrindingandabilitytomachinethecomplexparts.Nowadays,hardturningisbeingemployedinindustriesasasubstituteforgrindingprocess.ThishasbecomepossibleduetothedevelopmentofnewcuttingtoolmaterialssuchasCBNandmixedceramics1.Variousresearchershavestudiedthemechanismofchipformation,residualstresses,surfacefinish,andtoolwearinthehardturningprocess.Lotofattentionisbeinggiventothequalityofthesurfacefinishproducedinthehardturningprocess.Therearealargenumberofparameterswhichaffectthecuttingforcesandsurfaceroughness.Theseincludecuttingtoolvariables,workpiecematerialvariables,andcuttingconditionsandthetypeoflubrication.Toolvariablesincludetoolmaterial,noseradius,rakeangle,cuttingedgegeometry,toolvibration,tooloverhang,toolpointangle.Workpiecevariablesincludematerial,hardnessandothermechanicalproperties.Cuttingconditionsincludespeed,feed,anddepthofcut.Typeoflubricationincludesdryhardturning,hardturningwithfloodedorwithminimumquantityoflubricantandsolidlubrication.Lowsurfaceroughness,minimalmicrostructuralalterationsandhighdimensionalaccuracycanonlybeattainedwithnewcuttingtools.So,theproperselectionofallthesevariablesfacilitatestheobjectivestobeachievedinhardturning.Duetothestrictregulationsandtheirenforcementregardingtheuseofthecuttingfluidsinindustries,theresearchershavestartedexploringthealterativemethodologies.Oneofthesolutionsistousethesolidlubricantsinordertoreducethetoolwearandtoimprovetheoverallperformanceofthemachiningprocess.Inthepresentstudy,theeffectoftoolgeometryandthecuttingconditionsonthesurfacefinishbyusingsolidlubricantsgraphiteandIntJAdvManufTechnol200838529–535DOI10.1007/s0017000710798S.DilbagP.V.RaoMechanicalEngineeringDepartment,IndianInstituteofTechnology,Delhi,NewDelhi110016,Indiaemailpvraomech.iitd.ernet.inmolybdenumdisulphideinthehardturningofthebearingsteelwiththemixedceramictoolswasstudiedandthecomparisonhasbeenmadewithdryhardturning.2LiteraturereviewHardturningprocessisassociatedwiththehightoolwearduetothehightemperaturedeveloped.Cuttingfluidsaregenerallyusedinmachiningprocessestoreducefrictionandwear,thusimprovingthetoollifeandsurfacefinish.Thesearealsousedtoreducetheforcesandenergyconsumption,tocool/lubricatethecuttingzone,washawaythechips,andtoprotectthemachinedsurfacesfromenvironmentalcorrosion.Tonshoffetal.2investigatedthetribologicalaspectsofhardturningwithceramictools.Accordingtothisstudy,coolingeffectreducesthethermalloadofthecuttingedge,andthusincreasestoollifeascomparedtodrycutting.Inaddition,surfacefinishoftheworkpiecescanbeimprovedeitherbychemicalinteractionbetweentheworkpiecesurfaceandextremepressureadditivesofthecoolantorbymineraloilapplication.But,rehardenedlayerswerefoundbothindryandwetcutting.ÁvilaandAbrao3investigatedtheeffectofcuttingfluidsonthemachiningofhardenedAISI4340steel.Inthiswork,theperformanceofthreetypesofcuttingfluidstwoemulsionsandonesyntheticfluidhasbeencomparedtodrymachiningusingmixedaluminainserts.Resultsshowthattheapplicationofacuttingfluidbasedonanemulsionwithoutmineraloilresultsinlongertoollifecomparedtodrycuttingandtheuseofcuttingfluidisresponsibleforreducingthescatterinthesurfacefinishvaluesathighcuttingspeeds.Dinizetal.4studiedtheinfluenceofrefrigeration/lubricationconditiononSAE52100hardenedsteelturningatseveralcuttingspeeds.DryandminimumvolumeofoilMVOshowedthesimilarvaluesofflankwear,whichisalwayssmallerthanthevaluesforwetmachining.AlsowetmachiningdidnotshowbettervaluesofsurfaceroughnesscomparedtoMVOanddrymachining.Varadarajanetal.5investigatedthehardturningwithminimalfluidapplicationHTMF,anditsapplicationwithdryandwetturning.Resultsshowthatoverallperformanceduringminimumcuttingfluidapplicationisfoundtobesuperiortothatduringdryturningandconventionalwetturningonthebasisofcuttingforces,toollife,surfacefinish,cuttingratio,cuttingtemperatureandtoolchipcontactlength.However,drymachiningisanewtrendbecauseofincreasedconcernaboutenvironmentalissuesandstrictregulationsregardingtheuseofcuttingfluids.Drycuttingisbeneficialbecauseofpollutionfreeenvironment.Alsothemachiningcostisreducedduetotheeliminationofthecuttingfluids.KlockeandEisenblätter6havereportedondrycutting.Accordingtothisstudy,cuttingfluidshelptoachieveaspecifiedresultintermsoftoollife,surfacefinishanddimensionalaccuracy,andfacilitatechipbreakingandtransport.However,thesealsoimposeproblemsrelatedtowastedisposalandenvironmentalproblems.So,withdrycutting,alltheproblemsrelatedwithwetmachiningcanbeeliminated.SreejithandNgoi7havereportedthedrymachiningasthemachiningofthefuture.Thispaperconcludesthatthedrymachiningcaneliminatecuttingfluidsandthisispossibleduetotheadvancementofthecuttingtoolmaterials.DinizandMicaroni8havestudiedthecuttingconditionsforfinishturningprocessindrycutting.Accordingtothisstudy,drymachiningrequireslesspowerandproducessmoothersurfacethanwetturning.Itisclearfromtheabovementionedliteraturethatdryturningimprovesthesurfacefinish,butthetoollifeandwearproblemsareassociatedwithit.Andhardturningwithcuttingfluidswhetherfloodedorminimumquantityisnotenvironmentalfriendlyandtheiruseisbeingrestricted.So,analternativemethodofincreasingthelifeofthecuttingtoolisessentialinhardturning.Thiscanbedonebyprovidingthenegativechamferangleonthecuttingtoolinsertsandbyreducingthefrictionbetweenthecuttingtoolandtheworkpiece.Recentlytheeffectsofthesolidlubricantsonthemachiningprocesseshavebeeninvestigated.Thecurrentliquidlubricantsappeartobeineffectiveforapplicationsinvolvinghightemperatures9.Lubricantsandadditivesofnewtypesareurgentlyneeded.Solidlubricantsaretheonlyoptionavailableforcontrollingwearandfrictioninalltypesoftribosystemsinvolvingseveretribologicalconditionse.g.,hightemperature,corrosivemedia,vacuumenvironment,highloadandspeed.Strongadhesionisessentialforlongserviceofsolidlubricantfilms.Ionbeamprocessesarecapableofimpartingstrongadhesionbetweensolidlubricantfilmsandceramicsubstrates.Ionbeammixingofceramicswithconventionalsolidlubricants,suchasMoS2,isfeasibleandappearspromisingfordemandingaerospaceapplications.Auniquesolidlubricant,boricacid,whichformsnaturallyonthesurfacesofceramicscontainingboricoxideandboron,hasbeenrecentlybeendiscovered.Ithasbeenestablishedthatthislubricantcanimpartremarkablylowfrictioncoefficientstoslidingceramicinterfacesinhumidenvironments,whereMoS2isknowntobeineffective.Erdemiretal.10havereportedthesolid/liquidlubricationofceramicsatelevatedtemperatures.Accordingtothisstudy,thesimultaneoususeofliquidandsolidfilmlubricantsatslidinginterfacesofceramic/ceramicandgraycastiron/ceramicpairscansignificantlyreducefrictionandwear.Thesolidlubricantwasthesilverfilmandtheliquidwaspolyolesterbasesyntheticoil.530IntJAdvManufTechnol200838529–535Someresearchershavereportedtheuseofsolidlubricantsinthemachiningprocess.ShajiandRadhakrishnan11haveinvestigatedtheeffectofsolidlubricantgraphiteonthesurfacegrindingprocess.Resultsshowtheimprovementofsurfacefinishincaseofhardermaterialswiththeapplicationofsolidlubricant.ShajiandRadhakrishnan12havealsoreportedtheapplicationofsolidlubricantsingrindingasanalternativefortheconventionalcoolants.Thesolidlubricantsusedinthisinvestigationweregraphite,calciumfluoride,bariumfluorideandmolybdenumtrioxide.Improvedprocessresultsrelatedtofrictionhavebeenreportedinthisstudy.Nakamuraetal.13havestudiedthelubricationbehaviorofsolidlubricantsintheupsettingprocess.Fourkindsofsolidlubricantsweretestedinordertoexaminethefrictionalcharacteristicsandtheyieldshearstressbythefrictiontestingapparatus.ThesolidlubricantsusedwerePTFE,UHMWPE,MoS2andgraphite.ItwasconfirmedintheFEMsimulationandalsobytheexperimentthatsolidlubricantscouldlubricatesuccessfullywithmetaltometalcontact.GopalandRao14haveinvestigatedtheuseofthesolidlubricantinthegrindingoftheSiChasbeeninvestigated.Ithasbeenestablishedbytheseauthorsthatthesurfacefinishimproveswiththegraphiteassistedmachining.ReddyandRao15havereportedtheperformanceoftheendmillingprocessbytheuseofthesolidlubricantsgraphiteandMoS2.Recently,Jianxinetal.16havereportedthetribologicalbehaviorsofhotpressedAl2O3/TiCceramiccompositeswiththeadditionsofCaF2solidlubricants.ThesestudieshaveconfirmedthatfrictioncoefficientofAl2O3/TiC/CaF2ceramiccompositesdecreasedwhenslidingagainstcementedcarbideandhardenedsteelwithanincreaseinCaF2content.ThereasonwasthattheCaF2releasedandsmearedonthewearsurfaceandactedasasolidlubricantbetweentheslidingcouple.AlsothewearrateofthesecompositedecreasedwiththeadditionofCaF2.Theabovementionedstudiesindicatethatthesurfacefinishcanbeimprovedbyreducingthetoolwear.Drymachiningandmachiningwiththeuseofcuttingfluidsfloodedorminimumquantityhavenotrespondedproperlyfortherequirementofimprovedtoollifeandsurfacefinish.Theuseofthesolidlubricantsinmachiningmaybetheviablealternativeofcuttingfluidsashasbeenreportedinsomeoftheabovementionedstudies.Soanattempthasbeenmadeinthisworktoinvestigatetheeffectoftoolgeometryandthecuttingconditionsonthesurfacefinishbyusingsolidlubricantsgraphiteandmolybdenumdisulphideinthehardturningofthebearingsteelwiththemixedceramictoolsandthecomparisonhasbeenmadebetweendryhardturningandthesolidlubricantsassistedhardturning.3ExperimentationTheperformanceofhardturningismeasuredintermsofcuttingforces,surfacefinish,andtoolwear.Therearealargenumberofvariablesaffectingtheperformance.Themainimportantparametersarethecuttingconditions,toolgeometryandthetypeoflubricant.Thatiswhy,thefourparametersnamelycuttingspeed,feed,effectiverakeangleandthenoseradiusofthecuttingtoolwereselectedfortheexperimentationinthisstudy.Fivelevelsofeachfactorwereselectedinordertoseetheeffectofeachparameter.Designofexperimentplaysaveryimportantroleinperformingtheexperimentswiththeavailableresources.Accordingtothedesignofexperiments,acentralcompositedesignwasselectedforexperimentationtoreducethenumberofexperiments.Thecuttingforcesandsurfacefinishwereselectedastheresponsevariables.Thecuttingspeed,feed,effectiverakeangle,andthenoseradiusaretheindependentvariablesinthisstudy.ThevariousprocessvariablesandtheirlevelsareshownintheTable1asunderAccordingtocentralcompositedesign,atotalof31experimentswerecarriedoutwithandwithoutthesolidlubricantsasperthedesignmatrixshownintheTable2.Alltheexperimentswerecarriedoutataconstantdepthofcutof0.2mm.AhighprecisionNH22HMTlathewasusedforexperimentation.Ithashighdegreeofaccuracyandrigidity,whicharerequiredforthehardturningprocess.Inthisinvestigation,theworkpiecematerialwastheAISI52100steelofdiameter70mm.Theworkpiecematerialwasheattreatedthroughhardenedtoget58±02HRC.Thismaterialisbeingusedforthemanufacturingoftheballandrollerbearingsandautomotivecomponents.ThechemicalcompositionofthematerialisshownintheTable3.Mixedceramicinsertsofdifferentgeometrywereused.ISOdesignationofceramicinsertsisSNGNwithdifferentnoseradiiandchamferangles.ISOfesignationofthetoolholderisCSBNR2525M12.Theapproachangleofthistoolholderwas75°.ThesurfaceroughnesswasmeasuredwithaTalysurf6at0.8mmcutoffvalue.Anaverageofthreemeasurementswasusedasaresponsevalue.ThetoolwearwascheckedwithaMitutoyoopticalTable1ProcessvariablesandtheirlevelsFactorsLevel–1Level–2Level–3Level–4Level–5vm/min5075100125150fmm/rev0.040.080.120.160.20α°1621263136rmm0.40.81.21.62.0IntJAdvManufTechnol200838529–535531microscope1μmresolutionat30magnificationtomeasurethewearafterexperimentation.Foreachexperimentalset,newcuttinginsertshavebeenused.Thesolidlubricantsselectedforthisstudyweregraphiteandmolybdenumdisulphide.Thefinepowderof2μmaverageparticlesizehasbeenused.Anexperimentalsetupforsupplyingthesolidlubricantontothecuttingzonehasbeendesignedanddevelopedforthisstudy.Theapparatushasbeensodesignedthatitcansupplythesolidlubricantfrom0.5gm/minto15gm/min.Aprovisionhasbeenprovidedontheapparatusforitsproperpositioningtosupplytheexactquantityofsolidlubricantsontothecuttingzone.Investigationwascarriedouttodeterminetheoptimumflowrateofsolidlubricantpowderusingthedesignedapparatus.Atthisstageitisalsorequiredtoseetheeffectofincreasingtheflowrateonthecuttingforceforthemachiningofhardenedbearingsteels.Figure1showsthevariationofcuttingforcewithflowrateatacuttingspeedof100m/min,feedof0.12mm/rev,26°effectiverakeangleand1.2mmnoseradiusingraphiteandmolybdenumdisulphideassistedmachining,respectively.Ithasbeenobservedfromgraphiteassistedmachiningthatthecuttingforcedecreaseastheflowrateincreasesfrom1gm/minto2gm/min.Afterthatthereisnosubstantialreductionofthecuttingforceeveniftheflowratehasbeenincreasedfrom2gm/minto10gm/min.Thesimilartrendhasbeenobservedfortheothercuttingconditions.Thesameisthecaseformolybdenumdisulphideassistedmachiningalso.Itcanbeconcludedthatflowrateof2gm/minissufficienttoprovidetherequiredlubrication.Hence,inthepresentinvestigation,flowrateofgraphiteandmolybdenumdisulphidepowdershasbeenkeptat2gm/minduringthemachiningofhardenedbearingsteelFig.1.4ResultsanddiscussionDuringhardturning,muchheatisgeneratedattheprimarydeformationzone,secondarydeformationzoneandmaximumtemperatureisdevelopedatthetool/chipinterfacewhichmayresultintheearlycuttingtoolfailureleadingtopoorqualityofthesurfaceproduced.So,thereisaneedtocontrolthecuttingzonetemperaturewithinthetolerablelimitsfortheoverallimprovementofhardturningprocess.Hence,inthepresentwork,graphiteandmolybdenumdisulphidewereusedassolidlubricantstoprovidetheproperlubricationandreducethefrictionbetweenthetoolandworkpieceandtherebyreducingheatgenerationatthetoolandworkpieceinterface.Surfaceroughnessgenerallyplaysanimportantroleasitinfluencesthefatiguestrength,wearrate,coefficientoffriction,andcorrosionresistanceofthemachinedcomponents.Surfacequalityisaffectedbymanyinterrelatedparametersduringthehardturningprocess.Thereductioninthetoolwearduringhardturningwillalsoaffectthesurfacequalitytoagreaterextent.Andagainthetoolwearisdependentuponthecuttingconditionsandtoolgeometry,andpropertiesoftheworkpieceandtoolmaterial.Henceinordertoseetheeffectofthesolidlubricants,graphiteandmolybdenumdisulphides,onthesurfacequality,experimentswereconductedtoseetheireffectatdifferentcuttingconditions.ThevariationofsurfaceroughnesswithrespecttocuttingspeedfordryhardturningandsolidlubricantsassistedhardturningisshownintheFigs.2and3.Itcanbeobservedfromthesefiguresthatsurfaceroughnesswasfoundtobedecreasingwiththeincreaseofthecuttingspeedupto125m/minandafterthatitagainstartedTable2CentralcompositedesignmatrixRunno.SpeedFeedRakeangleNoseradius1−1−1−1−12−1−1−113−1−11−14−1−5−11−1−16−−117−111−18−91−1−1−1101−1−11111−11−1121−1311−1−11411−1115111−116111117−2000182000190−202002002100−2022002023000−2240002250000260000270000280000290000300000310000Table3ChemicalcompositionofbearingsteelCMnSiCrSmaxPmax0.98–1.10.25–0.450.15–0.351.3–1.60.0250.025532IntJAdvManufTechnol200838529–535
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