A review on current research trends in electrical

InternationalJournalofMachineTools&Manufacture47(2007)1214–1228Areviewoncurrentresearchtrendsinelectricaldischargemachining(EDM)NorlianaMohdAbbas,DariusG.Solomon,Md.FuadBahariFacultyofMechanicalEngineering,UniversitiTeknologiMARA,40450ShahAlam,SelangorDarulEhsan,MalaysiaReceived15November2005;receivedinrevisedform20May2006;accepted17August2006Availableonline17November2006AbstractElectricaldischargemachining(EDM)isoneoftheearliestnon-traditionalmachiningprocesses.EDMprocessisbasedonthermoelectricenergybetweentheworkpieceandanelectrode.Apulsedischargeoccursinasmallgapbetweentheworkpieceandtheelectrodeandremovestheunwantedmaterialfromtheparentmetalthroughmeltingandvaporising.Theelectrodeandtheworkpiecemusthaveelectricalconductivityinordertogeneratethespark.TherearevarioustypesofproductswhichcanbeproducedusingEDMsuchasdiesandmoulds.Partsofaerospace,automotiveindustryandsurgicalcomponentscanbefinishedbyEDM.ThispaperreviewstheresearchtrendsinEDMonultrasonicvibration,dryEDMmachining,EDMwithpowderadditives,EDMinwaterandmodelingtechniqueinpredictingEDMperformances.r2006ElsevierLtd.Allrightsreserved.Keywords:EDM;Ultrasonicvibration;DryEDM;Powderadditives;Dielectric;Modeling1.IntroductionElectricaldischargemachining(EDM)isanon-tradi-tionalconceptofmachiningwhichhasbeenwidelyusedtoproducediesandmolds.Itisalsousedforfinishingpartsforaerospaceandautomotiveindustryandsurgicalcomponents[1].Thistechniquehasbeendevelopedinthelate1940s[2]wheretheprocessisbasedonremovingmaterialfromapartbymeansofaseriesofrepeatedelectricaldischargesbetweentoolcalledtheelectrodeandtheworkpieceinthepresenceofadielectricfluid[3].Theelectrodeismovedtowardtheworkpieceuntilthegapissmallenoughsothattheimpressedvoltageisgreatenoughtoionizethedielectric[4].Shortdurationdischargesaregeneratedinaliquiddielectricgap,whichseparatestoolandworkpiece.Thematerialisremovedwiththeerosiveeffectoftheelectricaldischargesfromtoolandworkpiece[5].EDMdoesnotmakedirectcontactbetweentheelectrodeandtheworkpiecewhereitcaneliminatemechanicalstresses,chatterandvibrationproblemsduringmachining[1].Materialsofanyhardnesscanbecutaslongasthematerialcanconductelectricity[6].EDMtechniqueshavedevelopedinmanyareas.Trendsonactivitiescarriedoutbyresearchersdependontheinterestoftheresearchersandtheavailabilityofthetechnology.Inabookpublishedin1994,Rajurkar[7]hasindicatedsomefuturetrendsactivitiesinEDM:machiningadvancedmaterials,mirrorsurfacefinishusingpowderadditives,ultrasonic-assistedEDMandcontrolandautomation.However,thereviewpresentedinthispaperisoncurrentEDMresearchtrendscarriedoutbyresearchersonmachiningtechniquesviz.ultrasonicvibration,dryEDMmachining,EDMwithpowderadditivesandEDMinwaterandmodelingtechniquesinpredictingEDMperformances.Theareasareselectedbecauseofthenoveltechniquesemployed(ultrasonicvibrationandpowderadditives),theenvironmentalaspect(drymachiningandEDMinwater)andefforttowardsvalidatingandpredictingEDMperformance(modelingtechnique).Eachtopicwillpresenttheactivitiescarriedoutbytheresearchersandthedevelopmentoftheareathatbringsittothecurrenttrends.WireEDMisalsodiscussedineachtopic.ARTICLEINPRESS:10.1016/j.ijmachtools.2006.08.026Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](N.MohdAbbas).2.UltrasonicvibrationIntroductionofultrasonicvibrationtotheelectrodeisoneofthemethodsusedtoexpandtheapplicationofEDMandtoimprovethemachiningperformanceondifficulttomachinematerials.ThestudyoftheeffectsonultrasonicvibrationoftheelectrodeonEDMhasbeenundertakensincemid1980s.Thehigherefficiencygainedbytheemploymentofultrasonicvibrationismainlyattributedtotheimprovementindielectriccirculationwhichfacilitatesthedebrisremovalandthecreationofalargepressurechangebetweentheelectrodeandtheworkpiece,asanenhancementofmoltenmetalejectionfromthesurfaceoftheworkpiece[8].Zhangetal.[9]proposedsparkerosionwithultrasonicfrequencyusingaDCpowersupplyinsteadoftheusualpulsepowersupply.Thepulsedischargeisproducedbytherelativemotionbetweenthetoolandworkpiecesimplifyingtheequipmentandreducingitscost.TheyhaveindicatedthatitiseasytoproduceacombinedtechnologywhichbenefitsfromthevirtuesofultrasonicmachiningandEDM.2.1.MachiningofmicroholesIn1995Zhixinetal.[10]hasdevelopedanultrasonicvibrationpulseelectro-dischargemachining(UVPEDM)techniquetoproduceholesinengineeringceramicsmaterial.Theyhaveconfirmedbyexperimentthatthisnewtechniqueiseffectiveinobtainingahighmaterialremovalrate(MRR).Ogawaetal.[11]provedthatthedepthofmicroholesbyEDMwithultrasonicvibrationbecomesasabouttwotimesasthatwithoutultrasonicvibrationandmachiningrateincreased.Thoeetal.[12]dealtwithcombinedultrasonicandelectricaldischargemachiningofceramiccoatednickelalloy.Theyfoundthefollowing:whendrilling1mmdiametersingleholeusingvarioustoolmaterials(tungsten,silversteel,mildsteelandcopper)withboroncarbideabrasiveslurryonceramiccoatednickelalloyworkpiece,mildsteelisfoundtobethemostresilientwhereastheothermaterialsfailasaresultoffati