Grinding-SomeobservationsFortheproductionoffinishedcomponentsofdesiredshape,sizeandaccuracy,machiningisthecommonlyusedmanufacturingprocess.Machiningprocessinvolvestheusageofsingleormultiplepointcuttingtoolstoremovetheunwantedmaterialsformthestockintheformofchips(Komandurai,1993).Amongthevariousmetalcuttingprocessavailable,Grindingisoneoftheimportantmetalcuttingprocessusedextensivelyinthefinishingoperationofdiscretecomponents.Itisaversatileandalsofinishmachiningprocessintheproductionofcomponentsrequiringclosedimensionaltolerances,geometricalaccuraciesandrequiredsurfacefinish(Rajmohanetal.,1994).Mostoftheproductionprocessesareincompletewithoutgrindingprocess.AccordingtoSubramanian(1999),itisamajormanufacturingprocess,whichaccountsforabout25%ofthetotalexpenditureonmachiningoperationsinindustrializedcountries.Almostalltheengineeringcomponentsareprocessedingrindingmachiningmachinesatsomestagesofitsproduction.Grindingisaslowprocessintermsofunitremovalofthestock.Hence,othermethodsareusedfirsttobingtheworkclosetoitsrequireddimensionsandthenitisgroundtoachievethedesiredfinish.Insomeapplications,grindingisalsoemployedforhighermetalremovalrate.Insuchheavydutygrindingoperationsmoreabrasiveisconsumed.Inthesecases,themainobjectiveistoremovemoreamountofmaterialthattooasquicklyandeffectivelyaspossible.Thus,thegrindingprocesscanbeappliedsuccessfullytoalmostanycomponentrequiringprecisionorhardmachininganditisalsooneofthewidelyusedmethodsofremovingmaterialfromtheworkpieceafterhardening.Inordertodecreasethecostandincreasetheproductionrate,thegrindingmachinemustbesettooperatewithintheshortestpossiblegrindingcycletime.Hence,itisoftenimportanttosetthecorrectgrindingmachineparameterssoastoproducepartsofrequiredquality.Theselectionofgrindingparametersifitisdoneonhitandmisstechniquenotonlywastestimebutalsoleadstoaninefficientprocess.Toovercomethisdifficulty,Guptaetal.(2001)intheirworkoptimizedthegrindingprocessparametersusingtheenumerationmethod.Theparametersshouldbeselectedsoastoresultinanoptimalsolution.Selectionofgrindingprocessparametersismadeeasyemployingthe“Expertsystem”.ShajiandRadhakrishnan(2002)analyzedtheprocessparameterssuchasspeed,feed,unfeedandmodeofdressingasinfluentialfactorsontheforcecomponentsandsurfacefinishdevelopedbasedonTaguchi’sExperimentaldesignmethods.FengguoCaoetal.(2003)developedtheconceptofintegratingneuralnetwork,greyrelationalanalysisandgeneticalgorithmfortheoptimizationofprocessparametersinincreased.ExplosiveElectricalDischargeGrindingProcessliesintheproperselectionandintroductionofsuitabledesignofexperimentattheearlieststageoftheprocessandproductdevelopmentcyclessoasobtainqualityandproductivityimprovement.Amongtheexistingtypesofgrindingprocesses,cylindricalgrindingprocessistheone,whichisverywidelyusedinthefinishmachiningofnumberofautomobilecomponentswithsurfacesofrevolution.Incylindricalgrindingprocess,thefrictionalresistanceencounteredbetweentheworkmaterialandthetool,chiptoolinterfaceandtheresistancetodeformationduringshearingofthechipscontributestoriseintemperatureatthecontactzone(Triggeretal.1951).Thetemperaturegeneratedisnotonlyveryhighbutthetemperaturegradientsarealsosevere.Suchtemperaturesofsufficientmagnitudecancauseadversechangesinworkpiecemetallurgicalstructure,lossindimensionalaccuracyandacceleratedwear[or]dullingofthetool(DesRuisseauxandZerkle,1970;TakashiUedaetal.,1985).Inadditiontocausingsurfacedamage,grindingheatmaycausethermalexpansion/distortioninthecomponentgroundandthusadverselyaffecttheattainableaccuracy.MasudaandShiozaki(1974)demonstratedhowgrindingheatinplungesurfacegrindingresultsinout-of-flatnessofthefinishedpart.Betterflatnesswasobtainedwithsmallerdepthsofcutandhigherworkpiecevelocities.Bothofthemcauselessergrindingheatandwithincreasedcoolantflowratethecoolingoftheworkpieceisenhancedandthethermaldistortionisminimized.Chandrsekaretal.(1996)studiedthethermalaspectsofsurfacefinishingprocess.Ingrinding,thelocalizedabrasiveworkpiececontactpressuresandhighslidingspeedproducehightemperaturesattheinterfacebetweenanabrasiveparticleandtheworksurface,aswellasintheworksub-surfacesduetofrictionalheating.Hightemperaturesaretheimportantsourceofdamageonthemachinedsurface.First,thetransienttemperatureandthetemperaturegradientaretheprinciplesourcesforresidualstressesandmicrocrackingongroundsurfaces.Secondly,thelocalizedtemperaturescancausewarpingofthecomponentsbeingmachined,especially,whenitisofsmallsizeandhasarelativelylargesurfaceareatovolumeratio.Thisisaseriousprobleminthefinishingofsmallelectronicdevicessuchasrecordingheads.Thirdly,thishightemperaturecanalsoleadtophasetransformationsinthematerialsbeingmachined.ThenatureofgrindingdamagewassurveyedbyTarasov(1950),whoidentifiedthreemainkindsofgrindingdamage,namelycracking,rehardeningburnandtemperingburn.Duringgrindingofhardenedsteel,ifthesurfacetemperatureoftheworkpieceissufficientlyhigh,thesurfacereaustenizesandisrapidlyquenched.Consequently,thereisaformationofbrittle,untemperedmartensiteatthesurface.Thistypeofthermaldamageisalsocommonlyreferredtoasworkpieceburnandishighlyundesirable(Tarasov,1950;Torrance,1978).Amartensitictypeofphasetransformationalsooccursduringthegrindingoftoughenedzirconia.Here,thetransientmechanicalandthermalstressesgeneratedduringgrindingdrivesthetransformation.Theseformsofthermaldamagechangethemechanical,magneticandelectricalpropertiesoftheworkmaterials.Thelocaltemperaturesplayanimportantroleinthedegradationoftheabrasiveparticlesandthebondingpropertyofthematerial.Theheatgeneratedduringgrindingischaracterizedby,i)Instantaneousconcentratedsource,ii)Highrateofliberation,andiii)Verysmallcontactperiod.Heatassociatedwiththeenergyexpendedbygrindingistransportedawayfromthegrindingzonebytheworkpiece,grindingfluid,grindingchipsandgrindingwheel.Ofparticularinterestisthefractionofthetotalgrindingenergytransportedtotheworkpieceatthegrindingzone,whichcausestheriseinworkpiecetemperatureandpossiblethermaldamage.ForregulargrindingwithconventionalAluminumoxidewheels,theenergypartitiontotheworkpiecetypicallyrangesfrom60-80%dependingontheactualgrindingsituation(MalkinandAnderson,1974;Roweetal.,1995and1997).Onlyafewisolatedattemptshavebeenreportedsofaronexperimentalanalysisofthetemperaturedevelopedatthewheelworkcontactzone,energypartitionratio,graincontacttimeandthermaldamages.Atthispoint,itappearsthatpracticaloptimizationstrategyandreliablemathematicalmodelsarestillrequiredtoanalyzethethermaldamageingrinding.FieldandKahles(1971)investigatedthedissipationofheatingrindingandtheresultinginfluenceonthesurfaceintegrityoftheworkpiece.GuoandMalkin(1992)describedthatdependingonthegrindingconditiontheheatfluxtakespartmainlyviatheworkpieceandleadstoalargethermalloadinginthesurface.Thisthermalloadissuperimposedbymechanicalloadcausingahightemperatureinthesurface.Thisthermo-mechanicalloadcausessomeundesiredalterationsinthesurfacelayer,likecracks,temperedzoneorwhiteetchingareas(WEA).ShawandVyas(1994)gaveanimpressivetheoreticaldescriptionofmetallurgicalchangesingroundsurfaces.Underabusivegrindingconditions,theformationofheat-affectedzonewasobserved.DesRuisseauxandZerkle(1970)analyzedthattheheat-affectedzoneunderabusivegrindingconditionsdamagesthegroundsurfaceofthehardenedsteelveryfrequently.Athermallydamagedcomponentmaythereforeincurasignificantcosttothemanufacturerinfailingqualitystandard.Thus,thethermalphenomenaplayakeyroleintheeconomicsandmechanicsofabrasivemachiningprocesses.Anestimationoftheamountofenergygenerated,worksurfacetemperatureandanunderstandingoftheirroleinmetallurgicalchangesongroundsurfacesarestillchallengingtotheproductionengineers(SoyesandMaris1978).MalkinandFedoseev(1991)analyzedthemethodtopredicttheundesiredalterationstoavoidthermaldamagesingrindinggardenedsteel.Inanycase,thegeneratedheatquantitiesingrindingareconsideredasarestrictingfactor.Theinventionofadvancedgrindingprocesses,whichenabledthesurfacehardeningofsteelparts,wasdescribedforthefirsttimein1994.Insuchoperations,namedgrindhardening,thedissipatedheatingrindingisutilizedtoinducedmartensiticphasetransformationinthesurfacelayerofcomponents(BrinksmeierandBrockhoff,1997).Bettersurfacefinishwithincreasedhardnessatthesurfacebyutilizingtheheatgeneratedduringgrindingispossibleunderoptimumoperatingconditions.Thus,oneoftheareafortheresearcherstoconcernabouttheuniqueoptimalsettingsofgrindingprocessparameters-Depthofcut,Numberofpasses,WheelspeedandworkspeedformaximizingthesurfacehardnessandminimizingthesurfaceroughnesswhilegrindingAISIsteelmaterialswithAl2O3grindingwheels.“Ishikawacauseeffectdiagram”ofmachiningisstudiedtoidentifytheinfluentialprocessparametersthatmayaffectthesurfaceintegrityofgroundedpartsbyRamamoorthyetal.,2001and;Harisinghetal.,2004.Taguchi’sparameterdesignapproachhasbeenusedtoaccomplishtheobjective.Aspecialmathematicaltoolknownasgreyrelationalanalysiscanbeusedwithresponsegraphapproachandsignaltonoiseratioapproachfortheoptimization.Itiswellknownthatphysicalsurfacepropertiescandeterminethelifetimeandthefunctionofhighlyloadedworkpieceandcomponents.Forthisreason,manufacturingindustriesrequireinformationaboutthetechniquestoinfluencethesurfacestateofworkpieceandachieveconsistentproperties(Kegg,1982).Thisinteresthasitsimportanceduetothefactthatmagnitudeoftheresidualstressinterferesonthefatiguestrengthofthematerials(Novasakietal.,1996).Residualsrtessisthemostrepresentativeparametertodescribethequalityofthesurface(Brinksmeieretal.,1982)amongvarioussurfacealterationslikephasetransformations,hardnessvariations,microcracks,grindingburnetc.BanerjeeandChattopadhyay(1987)investigatedthecontrolofresidualstressingrindingbycryogeniccoolingwhichresultsinmuchlesstensileresidualstresses.Kruszynskietal.(1991)madeanattempttopredictresidualstressesingrindingofmetalswiththeaidofanewgrindingparameter.Hucker(1994)showedthattherewasaquantitativerelationbetweentheeffectivework-surfacetemperatureandtheresidualstressproducedongroundsurfacesofhardenedsteels.X-raydiffractiontechniqueswereusedtomeasuretheresidualstresses.ItwasreportedthatCBNgrindingisfoundtoproducecompressivestressatthesurfaceincontrasttoAl2O3grinding.However,manyoftheresearchesprovedthatundertheconditionsofmartensiticformation(roughgrinding)compressiveresidualstressesareformedwhengroundwithAl2O3wheel.BrockhoffandBrinksmeier(1997)intheircomprehensiveviewongrindhardeningfundoutthatcompressiveresidualstressesareexistingintheWhiteEtchingAreas,whichcontinueintotheareaofetchablemartensiteandwhicharecompensatedbylowtensileresidualstressesinagreaterdistancefromthesurface.LitmannandWulff(1955)foundthatforhardenedsteels,whichhavebeenburnedduringgrinding,theworkpiecesub-surfaceconsistsofarehardenedzonenearthesurfaceandasoftenedtemperedzonebeneathit.Thiswouldsuggestthattheonsetofburningischaracterizedbytheformationofausteniteoversomeportionoftheworkpiecesub-surface.Rehardeningatthesurfaceoccursbyacicularmartensite(thatappearsintheformofparallelneedleswithinformeraustenitegrains)formationasthecoolermaterialinthebulkoftheworkpiecequenchesthesurface.Thisreferstophasetransformationingrinding.Aftergrindingunderidealconditions,thegroundsurfacewillbecrackfreeandwillexhibitcompressiveresidualstressesfavorableforcorrosionresistanceandlonglifeundercyclicloadingconditions.Incontrast,manygrindingconditionsaresuchthatthesurfaceproducedsufferstensilestresses,sub-surfacecrackingandoxidationleadingtofailureinsurface.Inordertostrikeabalancebetweenqualityandstrengthingroundedpartsitisdesirabletohaveacontrolovertheresidualstress.Thisnecessitatesadetailedstudyofthefreework-surfacetemperature,amountofheatgeneratedandthemagnitudeofresidualstressformed.對磨削的一些觀察為了使在零部件的生產中達到預期的形狀、尺寸和精度，機械加工被廣泛運用于生產加工工藝中。機械加工過程中會運用到一個或多個切削工具，來去除工件上不需要的部分，使之成為切屑。在眾多已應用的金屬切削工藝中，磨削加工是金屬加工工藝常用于零件最終加工的重要加工工藝之一。它用途廣泛，也經常用于尺寸公差、幾何精度和表面精度要求高的零件的機械加工工藝中。絕大多數產品的生產工藝中都少不了磨削加工。根據Subramanian的統計數據，在工業國家的生產支出中，磨削加工占了25%，處于主要地位。幾乎所有的工程零件在其生產的某些階段會在磨削機床上加工。在工件的單元切削中，磨削加工是一個緩慢的過程。因此，在工件開始加工時，一般采用其他的加工方式使工件達到與要求相近的精度，然后采用磨削完成加工。在某些應用中，磨削也具備更高的金屬切削效率。在如重載磨削中，更多的磨料會被消耗，在這些情況下，盡可能快而有效去除更多的金屬材料是主要的目標。因而，磨削加工能成功地用于任何高精度或難加工零件的加工過程中，并且它也是可廣泛應用于硬化表面材料去除的加工工藝之一。Shaw曾報告稱，磨削加工是存在很多相關變量的復雜工藝，而這些相互作用的變量是同磨削方式所決定的。在平面磨削中所產生的幾何形狀會受到如下因素的影響：砂輪因素：砂輪直徑、磨粒類型和尺寸、砂輪等級、砂輪構造、粘結劑、敷料工藝、砂輪的平衡等級等。工件因素：加工表面硬度、構造、化學特征等。機床因素：主軸和工作臺剛度、阻尼、動力特性等。加工參數：砂輪轉速、進給量、背吃刀量、磨削液等。為了減少消耗，提高生產效率，磨削機床必須設定加工時間處于最短的可能磨削周期內。因此，設置正確磨削機床參數對獲得需要的精度往往非常重要。如果磨削參數選擇不符合技術要求，就會導致時間浪費效率低下。為了解決這個問題，Gupta在他們的研究中，采用列表的方法來使磨削參數最優化。參數的選取應使工作方案最優化，當采用“專家系統”時，磨削工藝參數的選取就變得容易了。Shaji和Radhakrishnan在Tagudhi的實驗設計方法基礎上分析了砂輪轉速、進給量、背吃刀量、敷料的方式對磨削力的構成、表面加工的影響。FengguoCao提出了一體化神經網絡、灰色相關分性分析、遺傳算法的概念，來對工藝參數進行優化提高。爆炸式電火花磨削工藝正是立足于對最早工藝階段和產品開發周期的合理實驗設計的選擇推廣上，來獲得品質和效率的提升。在已有的磨削工藝形式中，外加磨削廣泛應用于汽車回轉零件的表面加工中。在外圓，產生于工件材料與刀具之間的摩擦阻力，刀具表面的剪切變形抗力會使得接觸區域的溫度上升。產生的溫度很高并且分布很不均勻，這樣劇烈的高溫會使工件的金相結構發生不利的改變，使其尺寸精度喪失，并且加速刀具鈍化。除了導致表面損壞，磨削熱也會使工件在磨削過程產生熱膨脹或熱變形，從而對工件精度產生不利的影響。Masuda和Shiozaki闡述了磨削熱如何尋到工件表面變得不平整。當采用較小的切深和更高的切削速度時，會獲得更高的平面度。同時，也能減少磨削熱的產生。再加快冷卻液的流動速率，使工件冷卻效果加強，能使熱變形減小。Chandrsekar研究了表面加工過程的熱效應。在磨削過程中，局部的接觸應力和高的滑動速度會在工件和磨削刃接觸面產生高溫，同時在次層面產生摩擦熱。高溫是造成已加工表面損壞的重要因素。首先，分布不均勻的瞬態高溫是工件殘余應力和表面微裂紋的主要來源。第二，局部高溫會使已加工的部分發生形變。尤其是對尺寸較小卻具有較大體積比率的工件，變形尤為嚴重，這對于某些小型電子設備如電磁記錄頭的加工，是一個很嚴峻的問題。第三，高溫會導致已加工材料的物相發生改變。Tarasov對磨削操作的性質做了調查研究，確定了三種主要的損傷類型，分別是開裂，二次淬火燒傷和高溫燒傷。在磨削硬質的鋼材時，如果表面溫度過高，就會發生表面再次奧氏體化，并急速冷卻，從而在工件表面會形成具有的回火馬氏體。這種形式的熱損傷也是覺的工件燒傷形式，需要避免。在更質氧化鋯的磨削過程中，也會發生類似馬氏體類型的物相變化。這種變化是同磨削過程中產生的瞬態機械應力和熱應