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Residual stress in grinding.pdf

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Residual stress in grinding.pdf

ResidualstressingrindingBogdanW.Kruszyn´ski,RyszardWo´jcikTechnicalUniversityofŁo´dz´,Skorupki6/8,90924Ło´dz´,PolandAbstractResultsofinvestigationsonresidualstressinsurfacegrindingarepresentedinthepaper.AcoefficientBcombiningpowerdensityandwheel/workpiececontacttimewasdeveloped.Experimentalsetupandsoftwaretoestimatethecoefficientduringgrindingaredescribedinthepaper.Experimentswerecarriedoutforsurfaceplungegrindingforseveralworkmaterialsinawiderangeofgrindingconditions.TheinfluenceofprocessparametersonthecoefficientBaswellastherelationbetweenBandmaximumresidualstresswereexperimentallyevaluated.Theusefulnessofthecoefficienttopredictresidualstressinsurfacegrindingwasproved.2001ElsevierScienceB.V.Allrightsreserved.KeywordsResidualstressGrindingWheel/workpiece1.IntroductionGrindingisoneofthemostpopularmethodsofmachininghardmaterials.Becauseitisusuallyoneofthefinaloperationsofthetechnologicalprocess,propertiesofsurfacelayercreatedingrindinginfluencedirectlythefunctionalpropertiesoftheworkpiecesuchasfatiguestrength,abrasiveandcorrosionresistance,etc.Creatingfavourablesurfaceintegrity,especiallyingrindingwithaluminiumoxidegrindingwheelsisdifficultduetotwooppositetendencies.Ononehand,highprocessparametersarepreferredinordertoincreaseproductivity.Unfortunately,suchparametersusuallyleadtotheincreaseofgrindingpowerengagedincreationofthenewsurfaceoftheworkpiece.Ontheotherhand,theincreaseofgrindingpowermakesgrindingtemperaturesgrow,whichmaycauseaseriousdamagetothesurfacelayercreatedingrinding.Findingacompromisebetweenhighproductivityandadvantageoussurfacelayerpropertiesisextremelydifficultduetothelackofrelativelysimpleanduniversalroutines,amongothers.Becauseoftheimportanceofgrindingoperationtheinvestigationsofthisprocessareperformedinmanyresearchcentres.Somegeneralapproachesareobservedintheseinvestigations.Thefirstone,strictlyanalytical4,5,isbasedonthemathematicaldescriptionofphysicalprocessesinvolvedinsurfacelayercreation.Ingrindingthermaleffectsareusuallydescribed.Onthebasisofthecalculationsoftemperaturedistributionintheworkpiece,suchchangesinsurfacelayerlikemicrohardness,residualstresses,microstructure,etc.areestimated5.Suchanapproachisverypromisingbutatthepresentstageitislimitedtotheoreticalinvestigationsbecauseofcomplexcalculationsandstilllimitedknowledgeaboutmaterialbehaviourinextremegrindingconditions.Theexperimentalapproach1,7aimsatfindingacorrelationbetweengrindingconditionsandsurfacelayerparameters.Thisisarelativelysimplemethodwithsomedisadvantages.Experimentalworksareusuallytimeandcapitalconsumingwhichlimitstheirapplication.Moreover,thereisalimitedpossibilitytoextrapolatetheexperimentalresultsondifferentgrindingmethodsandgrindingconditions.Thereisalsoathirdapproachtotheproblemofcontrolofsurfacelayercreation,whichinvolvesasearchforsuchgrindingcoefficients,whicharestronglycorrelatedwithsurfacelayerproperties2,4.Therearemanysuchcoefficientsexisting.ThemostpopularareequivalentchipthicknessheqandpowerdensityP0.Theformerisprovedtobeusefulingrindingceramics,thelatterisoftenappliedwhengrindingwithaluminiumoxidegrindingwheelsisinvestigated2.Themaindisadvantageofbothcoefficientsisthattocalculatethemitisnecessarytoestimatetheeffectivegrindingdepthoreffectivewheel/workpiececontactlength.Bothvaluesareverydifficulttoestimateonlinegrindingaccurately.Thus,aneasytoestimategrindingcoefficient,whichwouldbestronglycorrelatedwithsurfaceintegrityparameters,isstilllacking.TheinvestigationonthecorrelationbetweenthecoefficientcombiningpowerdensityandtheJournalofMaterialsProcessingTechnology1092001254–257Correspondingauthor.09240136/01/–seefrontmatter2001ElsevierScienceB.V.Allrightsreserved.PIIS0924013600008074wheel/workpiececontacttimeandresidualstressinsurfacegrindingisdescribedbelow.2.GrindingcoefficientcombiningpowerdensityandcontacttimeItwasproved3thatresidualstressesinsurfacelayeraftergrindingarecloselycorrelatedwithmaximumgrindingtemperature.Theanalysisofequationsusedfortemperaturecalculationingrinding6indicatesthatitisnotonlythepowerdensitythatinfluencesthegrindingtemperaturebutthereisalsoasecondimportantfactorwheel/workmaterialcontacttime.Insurfacegrindingthecontacttimeoftheparticularworkpiecepointwithheatsourcegrindingwheelcanbeeasilycalculatedastclevw1whereleisaneffectivewheel/workpiececontactlengthandvwistheworkspeed.TheproposedgrindingcoefficientBisaproductofpowerdensityP0andcontacttimetcBP0tcPbdlelevwPbdvw2wherePisthetotalgrindingpowerandbdthegrindingwidth.Thefirstadvantageofthiscoefficientisthatallquantitiesinthisequationgrindingpower,grindingwidthandworkspeedareeasytomeasureonlineinagrindingprocess.3.ExperimentalsetupExperimentswerecarriedoutforthefollowinggrindingconditions.workmaterialscarbonsteel0.45C,28HRCmarkedS,alloysteel40H0.38C,0.9Cr,0.28Ni48HRCH,bearingsteelŁH15equivalentto100Cr662HRCLgrindingwheels38A60J8VJ,99A80M7VMwheelspeed26m/sconstantgrindingdepthfrom0.005to0.06mmworkspeedfrom0.08to0.5m/sgrindingfluidemulsionornone.Grindingparametersintheseinvestigationswerelimitedbythepowerofthemainwheeldrive,tablespeedregulationrangeandbytheappearanceofunacceptablechangesinthesurfacelayer,microcracksandburns.ToestimatecoefficientBitwasnecessarytomeasuregrindingpower,workspeedandgrindingwidth.GrindingpowerwasmeasuredintwodifferentwaysbythemeasurementofpowerconsumedbywheelmaindrivePmandsimultaneousmeasurementoftangentialgrindingforceFtandwheelspeedvs.ThegrindingpowercanthenbecalculatedasPcFtvs.ThecomparisonoftheresultsobtainedfrombothmethodsisshowninFig.1.Averygoodcorrelationcanbeseenfromthisfigure,whichprovesthatmeasurementofpowerconsumptionofwheelmaindriveisaccurateenoughtoestimatecoefficientBinthecasewhenonlygrindingwheelisdrivenbythisdrive.Thewheelspeedwasmeasuredbymeansofdisplacementtransducerandgrindingwidthwastakenasawidthofthesamplebeingground.4.ExperimentalresultsOnthebasisofmeasuredvaluesofP,vwandbdinsurfacegrinding,thecoefficientBwascalculatedineachgrindingtest.Measurementscarriedoutduringgrindingallowed,firstofall,toevaluatetheinfluenceofgrindingconditionsonthecoefficientB,cf.Figs.2–7.ThelineardependencebetweeneffectivegrindingdepthandBcanbeseenfromFigs.2,4and6.Slopesoftheselinesdependmainlyongrindingwheel,workspeedFigs.2and6andongrindingfluidFig.4.ThecorrectnessoflinearapproximationwasprovedinastatisticalwayvaluesofR2werehigherthan0.9inallcases.Fig.1.Comparisonofmeasuredandcalculatedgrindingpower.Fig.2.TheinfluenceofgrindingdepthandgrindingwheelgradeoncoefficientBforcarbonsteelS.B.W.Kruszyn´ski,R.Wo´jcik/JournalofMaterialsProcessingTechnology1092001254–257255TheinfluenceofworkspeedoncoefficientB,Figs.3,5and7,isnotasuniformasthoseobtainedforgrindingdepth.MuchhigherinfluenceofvwonBisobservedforalowerrangeofworkspeeds.ItindicatesthatthereisalimitedpossibilitytoinfluencecoefficientBbychangesoftheworkspeed.VerysimilardependencieswereobtainedforthethirdworkmaterialinvestigatedalloysteelH.Forallexperiments,inwhichmicrocracksand/orburnswerenotpresent,residualstressdistributionwasmeasuredbymeansofthewellknownmaterialremovalmethod.Fromresidualstressvs.depthbelowsurfacediagramsobtainedforeachgrindingtest,maximalresidualstressesinthesurfacelayerweredetermined.Usually,residualstressesreachtheirmaximumtensilevaluesclosetothesurfaceondepthsof10–20mm.RelationsbetweencoefficientBandmaximumresidualstressforinvestigatedworkmaterialsareshowninFigs.8–10.Inthesediagramstheresultsaresummarisedforeachworkmaterialregardlessofothergrindingconditionsgrindingwheelproperties,grindingfluid,grindingparameters.IneachcasethelineardependencewasassumedwhichwasprovedinastatisticalwayR2from0.8529to0.9074.ItresultsfromthesefiguresthattheslopesofresidualstresscoefficientBlinesarecharacteristicforthegivenworkmaterialandseemtobeindependentofothergrindingconditions.ThehighestslopewasobtainedforbearingsteelL,Fig.10,andthelowestoneforalloysteelH,Fig.9.Fig.3.TheinfluenceofworkspeedandgrindingwheelgradeoncoefficientBforcarbonsteelS.Fig.4.TheinfluenceofgrindingdepthandgrindingfluidoncoefficientBforcarbonsteelS.Fig.5.TheinfluenceofworkspeedandgrindingfluidoncoefficientBforcarbonsteelS.Fig.6.TheinfluenceofgrindingdepthandgrindingwheelgradeoncoefficientBforbearingsteelL.Fig.7.TheinfluenceofworkspeedandgrindingwheelgradeoncoefficientBforbearingsteelL.256B.W.Kruszyn´ski,R.Wo´jcik/JournalofMaterialsProcessingTechnology1092001254–257SomeadditionalobservationsrecordedduringinvestigationsindicatethatthereisapossibilitytousethecoefficientBtopredictand/orcontrolsuchchangesinsurfacelayerlikemicrocracks,burnsormicrostructurechanges.Additionalinvestigationsarenecessarytoconfirmtheusefulnessofthiscoefficientinothergrindingmethods.5.Conclusions1.ThegrindingcoefficientBcombiningpowerdensityandwheel/workpiececontacttimewasdevelopedtopredictresidualstressinsurfacegrinding.2.AlinearcorrelationbetweencoefficientBandmaximumresidualstresswasfoundexperimentally.Itwasconfirmedforseveralworkmaterials.3.TherelationbetweencoefficientBandmaximumresidualstressseemstobeindependentofgrindingconditions.4.CoefficientBincreaseslinearlywiththeincreaseofgrindingdepthanddecreaseswiththeincreaseofworkspeed.Thisdecreaseshowslessintensityintherangeofhigherworkspeeds.5.ThecoefficientBiseasytoestimate,evenonline,inindustrialpractice.6.ThecoefficientBmaybeusefulinpredictingsuchsurfacelayerpropertiesingrindinglikemicrocracks,burnsormicrostructurechanges.References1P.G.Althaus,Residualstressininternalgrinding,Ind.DiamondRev.31985124–127.2E.Brinksmeier,H.K.To¨nshoff,Basicparametersingrinding,Ann.CIRP4211993795–799.3E.Brinksmeier,S.T.Comet,W.Ko¨nig,P.Leskovar,J.Peters,H.K.To¨nshoff,Residualstressmeasurementandcauses,Ann.CIRP3121982491–510.4B.W.Kruszyn´ski,C.A.Luttervelt,Anattempttopredictresidualstressesingrindingofmetalswiththeaidofthenewgrindingparameter,Ann.CIRP4011991335–337.5H.K.To¨nshoff,J.Peters,I.Inasaki,T.Paul,Modellingandsimulationofgrindingprocess,Ann.CIRP4121992677–688.6E.Vansevenant,Asubsurfaceintegritymodelingrinding,Ph.D.Thesis,KULueven,1987.7Y.Zheyun,H.Zhonghui,SurfaceintegrityofgrindingofbearingsteelGCr15withCBNwheels,Ann.CIRP3811989677–688.Fig.8.Maximumresidualstressvs.coefficientBforcarbonsteelS.Fig.9.Maximumresidualstressvs.coefficientBforalloysteelH.Fig.10.Maximumresidualstressvs.coefficientBforbearingsteelL.B.W.Kruszyn´ski,R.Wo´jcik/JournalofMaterialsProcessingTechnology1092001254–257257

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