机械英语文章

StudyonEffectofGrindingFluidSupplyParametersonSurfaceIntegrityinQuick-pointGrindingforGreenManufacturing

Abstract.Inhighandsuper-highspeedgrindingprocess,thereisanairflowlayerwithhighspeedaroundthecircleedgeofthegrindingwheelthathindersthegrindingfluidintocontactlayer,namely,theairbarriereffect.Thespeedofairflowlayerisdirectlyproportionaltothesquareofthewheelspeed.Quick-pointgrindingisanewtypeofhighandsuper-highspeedgrindingprocesswithapointcontactzoneandlessgrindingpower.TheedgeeffectoftheairbarrierisweakenedbecausethethinCBNwheelisappliedintheprocess.Bytheanalysisofdynamicpressureandvelocitydistributionsintheairflowlayeraroundthewheeledge,themathematicmodelsoftheflowandjetpressureofgrindingfluidforeffectivesupplyintheprocesswereestablishedandtheprocessofoptimizationcalculationofthejetnozzlediameterforgreenmanufacturingwasalsoanalyzedbasedonthethermodynamicsandthetechnicalcharacterofquick-pointgrindingprocess.Thequick-pointgrindingexperimentforsurfaceintegrityinfluencedbygrindingfluidsupplyparameterswasperformed.

Introduction

Grindingisthemachiningprocessthathasheavyeffectonbothenvironmentandresource.Theheavyeffectresultsfromthegrindingpowderandgrindingfluidthatisusedingrindingprocesslargelyforcooling,washingandlubricatingfunctionsmainly.Especiallyforhighandsuper-highgrindingspeedprocess,thereistheairflowlayerwithhighrotaryspeedaroundthecircleedgeofthegrindingwheelthathindersthegrindingfluidintothecontactlayer[1],namelytheairflowbarriereffect.Soithastoincreasethegrindingfluidsupplyparameterstokeepthefluideffectduringgrindingprocess.Inrecentyears,ithasbeenthefocusofresearchinengineeringtoimprovethegrindinggreennessanddevelopthegreengrindingprocess.Quick-pointgrindingisanewtypeofhighandsuper-highspeedgrindingprocesswithsomeexcellentperformances,suchaslowgrindingforceandtemperature,goodcoolingconditions,longwheellifeandsoon.Itispossibletoachievethedrygrindingbydesigningthegrindingfluidsystemandthegrindingfluidsupplyparametersreasonably,andoptimizinggrindingprocessparametersforgreenmanufacturing.

AnalysisofPressureandVelocityofAirflowLayeraroundWheel

Grindingheatisgeneratedfromthedeformationandfrictionofmaterialsduringthegrindingprocessandmakesthegrindingtemperaturerise,whichcanresultinthethermalsurfacedamageofworkpiece.Therefore,areliablegrindingfluidsystemisnecessaryforthemostgrindingprocesstokeepcooling,washingandlubricatingfunctions.Forhighandsuper-highspeedgrindingprocess,thegrindingfluidsupplyparametersandjetwaymustbedesignedreasonablytoovercometheairflowbarriereffectonfluidsupply,increasetheratiooftheeffectivefluidandreducethesplashandwasteofthefluid.Inquick-pointgrindingprocess,itisthepointcontactbetweenwheelandworkpieceduetothepointgrindinganglesandthethinCBNwheel(Fig.1),sotheairflowlayerisverynarrowandtheairflowbarriereffectweakens,thefluideffectisimprovedgreatly,asaresult,thegrindingfluidsupplyparameterscanbelessened.

Fig.1Principleofquick-pointgrinding

Thethicknessandpressureoftheairflowlayerwithhighrotaryspeedaroundthecircleedgeofgrindingwheelisthemainfactorstoinfluencethefluideffectinhighspeedgrinding,thehigherthewheelspeed,thethickertheairflowlayerisandthehigherthepressureoftheairflowlayeris.AccordingtoBernoulliEquation[2],thedynamicpressureoftheairflowlayerisgivenby

wherevaistheairflowspeed[m/s],ρaistheairdensity[kg/m3].Ifthedynamicpressurepaoftheairflowlayerismeasuredonthedifferentwheelposition,theairflowspeedatsamepositioncanbecalculated.Table1givestheexperimentvaluesofdynamicpressureandspeedofairlayer.Ifthediameterofwheelis600mmandthewheelspeedis30m/sand60m/srespectively,themeasuredvaluesofthedynamicpressureandtheairflowspeedareshowninTable1.Itisvisiblethatthedynamicpressureoftheairflowlayerisincreasedwithincreaseofthewheelspeed.

Table1Measuredvaluesofdynamicpressureandspeedofairflowlayer

Fig.2showsthedistributionofthespeedofairflowlayerwiththedistancetbetweentheairflowlayerandthewheeledge[3].Theairflowspeedisdecreasedwiththeincreaseofthedistancebetweentheairflowlayerandthewheel,andincreasedwiththeincreaseofwheelspeed.Themaximumspeedofairflowisgeneratedonthecircleofthewheeledgeandapproachesthemaximumperipheralwheelspeed.Buttherearethesharpergradsoftheairflowspeedalongtheradialdirectionofthewheel.Therefore,therotaryairflowlayerwithhighpressurekeepsthegrindingzoneoffgrindingfluidandlowerstheworkpieceintegrityandthewheellifeduetothefailinthefluideffect.Inquick-pointgrindingprocess,itisthepointcontactbetweenwheelandworkpieceintheorybecausetheaxesofthewheelandtheworkpieceareunparalleleachother(Fig.1)whichisdifferentfromtheconventionalcylindricalgrinding,sothecoolingconditionisbetter.BecausethethinCBNwheelisusedintheprocess,inaddition,theairflowlayerbarriereffectongrindingfluidisweakened.

CalculationofGrindingFluidFlow

Ingeneral,theworkof85%~90%tobeabsorbedfordeformationandfrictionofmaterialsconvertsintoheatenergyatnormaltemperature[4,5],namelythethermaleffect.Forgrindingprocess,thedeformationandfrictionofmaterialsasthemainworkisgeneratedthroughthewholeprocess.Therefore,itcanbeconcludedthatthemostnon-elasticityworkconvertintoheatingrindingprocess.Basedontheheat-workbalanceequation,theflowofgrindingfluidisgivenby

whereρisthefluiddensity[kg/m3],Nisthegrindingpower[kW],cisthespecificheat[J/kg·K],Gisthecoolingcoefficientthatrestswiththecontactareabetweenwheelandworkpieceandtheratiooftheeffectivefluidtoentergrindingzone,generally,Gisselectedinrangeof1.0~2.0,Δtistheincrementoftemperatureandselectedinrangeof5~15℃.Forthegrindingfluidsupplysystem(Fig.3)inquick-pointgrinding,thelargerGcanbeselectedduetothebettercoolingconditionsandthelesscontactarea.

AnalysisofFluidJetPressure

Toovercometheairflowbarriereffectandmakethefluidentercontactzone,thegrindingfluidjetpressuremustfitforthefollowinginequation

wherev0isthefluidjetspeed[m/s].Giventhediameterofthefluidjetnozzle,thefluidflowQisincreasedwiththeincreaseofthefluidjetpressure.Ontheotherhand,thehigherthejetpressureoffluid,theheavierthesplashandsprayofthefluidare,andthemoretheconsumedpoweris.Therefore,thejetpressureisusually0.3~3MPainhighandsuper-highspeedgrindingprocess.Inquick-pointgrindingprocess,itisthepointcontactbetweenthewheelandtheworkpieceintheorybecausetheaxesofthewheelandtheworkpieceareunparalleleachother(Fig.1)whichisdifferentfromtheconventionalcylindricalgrinding,sothelesscontactarealowersthegrindingheatandforcegreatly,andimprovesthecoolingperformanceandthegrindingfluideffect.Inaddition,thethinCBNwheelmakestheairflowbarriereffectweaken.Therefore,giventhefluidjetpressure,theflowcanbelessenedbyreducingthediameterofthejetnozzletoweakentheinfluenceofgrindingfluidonenvironmentandimprovethegreennessofthegrindingprocess.

CalculationofJetNozzleDiameter

Thefluidfluxthroughthejetnozzleiscalculatedby

whered0isthejetnozzlediameter[mm].CombinedEq.3withEq.4,themaximumdiameterofjetnozzleisgivenby

Forimprovingthefluideffect,doublenozzlesareappliedinquick-pointgrindingprocess(Fig.3).Giventhefluidflux,themaximumdiameteroftheprimaryandsecondaryjetnozzleiscalculatedby

Inquick-pointgrindingprocess,providedthatthelocalareanearthecontactpointwasconsideredonlyandthecurvatureeffectofthecontactarcontheworkpiecewasomitted,therealcontactlengthmaybelessthan0.5mm[6],thereforethelargerGcanbeselectedduetothebettercoolingconditions.

ExperimentforEffectofGrindingFluidonSurfaceIntegrity

ExperimentConditions.TheexperimentconditionsareshowninTable2.

ThegrindingwheelandfluidsystemareshowninFig.4andgroundworkpieceisshowninFig.5。ThehardnessismeasuredwithTH550RockwellHardnessTesteratthedepth0.1mmfromthesurface.

AnalysisofExperimentResults.Giventhefluidjetpressure2MPa,thegroundsurfaceroughnesspresentsadeclinetrendappreciablywithincreaseoffluidflowattherangeof0~20L/min,butthedeclineextentisveryless.Sothegrindingfluidfluxisnotamainfactortoinfluencethesurfaceroughnessundercertainfluidjetpressure.Giventhefluidjetpressure2MPa,thegroundsurfacehardnesspresentsadeclinetrendappreciablywithdecreaseofthefluidfluxattherangeof0~20L/min.Especiallyindrygrinding,thesurfacehardnessdropsobservably,whichshowsthatthethermaldamageisgeneratedatacertainextent.Consequently,althoughthedrygrindingcanbeappliedinquick-pointgrindingprocesssometimeforhighgreenness,itisnecessarytodesignthepropergrindingfluidsupplyparametersagainstthethermaldamagesingrindingsomequenchedsteels.

Conclusions

(1)Inhighandsuper-highgrindingspeedprocess,thereistheairflowlayerwithhighrotaryspeedaroundthecircleedgeofgrindingwheelthathindersthegrindingfluidintocontactlayer.Thepressureoftheairflowlayerincreaseswithraiseoftherotaryspeedofgrindingwheel.Therearethesharperspeedgradsintheairflowlayeralongtheradialdirectionofthewheel.

(2)Thelesscontactareainquick-pointgrindingmakesthegrindingheatandforcelowerobservably,andthecoolingperformanceandthegrindingfluideffectincrease.DuetothethinCBNwheelused,theairflowbarriereffectisweakened.Therefore,itispossibletolowerthefluidsupplyparametersinquick-pointgrindingprocessforweakeningtheinfluenceofgrindingfluidonenvironmentandimprovingthegreennessofthegrindingprocess.

(3)Thegrindingfluidflowisnotmainfactortoaffectthesurfaceroughnessundercertainfluidjetpressure.Althoughthedrygrindingcanbeappliedinquick-pointgrindingprocessforhighgreenness,itisnecessarytodesignthepropergrindingfluidparametersagainstthethermaldamagesingrindingsomequenchedsteels.

Acknowledgments

ThisresearchwasfinanciallysupportedbytheScienceandTechnologyFoundationofLiaoningProvinceofChinaundergrantedNo.20072030andtheNationalNaturalScienceFoundationofChinaundergrantedNo.50775032.

References

[1]E.Brinksmeier,M.Heinzel.AnnalsoftheCIRP,1999,Vol.2:48(1999),p.581-598

[2]M.T.Tan:MicrocosmicInvestigationonMetalCutting(ShanghaiScienceandTechnologyPress,China1988)

[3]G.L.Song:BasicStudyonSuper-highSpeedGrindingTechnology.(Ph.D.NortheasternUniversity,Shenyang,1997)

[4]S.C.Chen,Q.R.Ye:PrincipleofPlasticityProcessforMetal.(TsinghuaUniversityPress,Beijing,1991)

[5]J.X.Ren,andD.A.Hua:GrindingPrinciple.(NorthwestTechnicalUniversityPress,Xian,1988),p.234-238

[6]S.C.Xiu,G.Q.CaiandY.D.Gong.DiamondandAbrasivesEngineering,No.4(2005),p.33-35

GrindingatVeryLowSpeed

Abstract.

Grindingisaverycomplexmachiningprocess.Singlegraingrindingmethodsareusefultostudycomplexgrindingaction.Verylowspeedsingle-graingrindingtestswerecarriedoutfor45steeland20Cralloywith14#ZAgrain.Thegrindinggroovewidthanddepth,thegrindingforceratio,specificgrindingforces,andgrainwearandfracturearestudied.Theplowingdecreaseswiththegrindingsectionareaorgrindingdepthincrease.Theaveragetangentialforceatgrainfractureintheexperimentsis54.4N;theaveragenormalforceatgrainfractureis949.6N.Theratiooftangential-to-normalforcevariessuddenlywhengrainfracture.

Introduction

Grindingisamachiningprocesswhichutilizesagrindingwheelconsistingofabrasivegrains.Itisaverycomplexprocesswithmanyvariations.Inscientificresearch,complexphenomenaareusuallyabstractedtosimplemodels.Thesinglegraingrindingisanimportantmethodtostudycomplexgrindingaction[1-6].Singlegraingrindingexperimentsareusefulbecausewiththeapplicationofalargeload,theextentofdamagecanbeamplifiedforinterpretationwhileunaffectedbyinteractions

withthedamageinsurroundinglocationsundergoingsimilarprocesses.Themethodprovidesthemostdetailedpictureofthecross-sectionalshapeofagrindingpoint.Manyscholars,studiedthegrainwearandcrash,thechipformationandthegrindingforceswithanidealshapeofgrain,andobtainedsomeusefulconclusions.Inthispaper,singlegraingrindingtestsfor45carbonsteeland20Cralloywith14#ZAgrain(aluminumoxide,10~15%ZrO2)havebeenconducted.Grindingforceratio,grainwearandfracturearediscussed.

ExperimentalConditionandProcedure

TheexperimentshavebeendoneonamachinetoolinNortheasternUniversity.Asinglegrainisadheredtoabolt.Theboltisinstalledonthedynamometerdevice.ThedeviceisshowninFig.1.ThetangentialandnormalgrindingforcesaremeasuredbyY82-7piezoelectricitycrystalloidforce-sensor(sensitivedegree:4.08pc/N,intrinsicfrequency:30KHZ)andFDH-2Telectricityamplifier.ThesignalisoutputtoCS2092dynamictestinginstrumenttonoteanddealwiththedataafteramplified.Inordertoreducenoiseandimproveaccuracy,thesensorsareprestressed.Thedynamometercanbeinbetterconditionbecauseoftheforceprestressed.Thecalibrationisdoneafterthedynamometerdeviceisfixed.

Thegrainusedintheexperimentsis14#ZAAluminumOxide(10~15%ZrO2).Thematerialsofworkis45steel(HVhardness,222kg/mm2)and20Cralloy(HVhardness,162kg/mm2).TheexperimentalconditionsofsinglegraingrindingisshowninTable1.Theexperimentswerecarriedoutinatmosphericconditionofroomtemperature20℃;relativehumidity,40-60%.

Fig.1Configurationofsinglegraingrindingtest

Table1Conditionsoftest

ResultsandDiscussion

GrindingGrooveMorphology.ThegroovecrosssectionisshowninFig.2.wisgroovewidth,anddgroovedepth.TherelationshipsbetweengroovewidthanddepthunderdifferentconditionsareshowninFig.3.Thoserelationsreflectconditionsofgrainscuttingbladeandelasticcomebackofgroove.

Fig.2Crosssectionofgrindinggroove

ForceRatioε.Forceratiocanbedefinedasε=Ft/Fn,whereFtistangentialforce,Fnnormalforce.Forceratioεisveryusefultostudythefrictionbetweengrainandwork,toevaluategraincuttingconditions.Forsharpgrains,tangentialforceFtismainlyusedtoformchips,Forceratioεislargerthanthatforbluntgrain.TherelationshipbetweenforceratioεandgroovecrosssectionareaisshowninFig.4.AsshowninFig.4,forceratioεincreasewithgroovecrosssectionarea.Thisdemonstratesthattheplowingdecreaseswithgrindingsectionareaincrease.Itindicatesthattheslidingdecreaseswiththegrindingsectionareaorgrindingdepthincrease.

Fig.3Schemeofthegrindwidthversusthegrinddepthofgrooves

Fig.4Relationbetweenratiooftangential-to-normalforceandgroovesectionarea

SpecificGrindingForce.Specificgrindingforcedefiniteasσ’=Fgt/A.Specificgrindingforceσ’mayreflectcharacteristicofworkmaterialandgraintartnessdegree.Specificgrindingforcehasthesimilarphysicsmeaningandthesamedimensionwithspecificenergy.Thespecificmeltingenergyofsteelsis10.35J/mm3.Thespecificforceforsinglegraingrinding45carbonsteeland20Cralloyisabout12×103N/mm2atv=2.8cm/swiththecrosssectionareaofundeformedchipincrease.Thatvalueishigherthanthespecificmeltingenergyofsteels.

FractureofGrain.Theactualcuttingpointsonabrasivegrainsatwheelsurfacearemicro-cuttingtoolswhichinteractwiththeworkmaterial.Thegrainfracturecanproducenewabradeonthegrain.Thatisthefoundationofthecharacteristicofwheelself-sharpen.Theratiooftangential-to-normalforceεvariesalongthegroovei