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AdvancesinProductionEngineering&Management ISSN1854‐6250

Volume14|Number3|September2019|pp323–332 Journalhome:apem‐journal.org

https://doi.org/10.14743/apem2019.3.330 Originalscientificpaper

 

Effect of aluminium and chromium powder mixed dielectric fluid on electrical discharge machining effectiveness  

Modi, M.a,*, Agarwal, G.b 

 aDepartment of Mechanical Engineering, Acropolis Institute of Technology and Research, Indore, Madhya Pradesh, India 

 bDepartment of Mechanical Engineering, Malaviya National Institute of Technology, Jaipur, Rajasthan, India   

A B S T R A C T   A R T I C L E   I N F O

Thisarticlestudiedtheimpactsofusingdifferentpowdersontheproductivityof electro discharge machining (EDM) of Nimonic 8OA alloy. The powdersused for experiments are chromium (Cr) and aluminium (Al), though thesepowders are in contrasts in their thermo‐physical characteristics.With themixingofthesepowders indielectric fluid,effectonsurfaceroughness(SR),materialremovalrate(MRR),andmechanismofthemachiningprocesshavebeen studied in this researchwork.On going through the results of experi‐ments, itwasobserved that evenvolumetricproportionofpowders, size ofmolecules, its density, electric resistance, andheat conductivityof additiveswerevitalparameters thataltogether influenced theproductivityofpowdermixed‐electrodischargemachining(PMEDM)process.Withadditionofprop‐erratioofpowdersindielectricfluid,itenhancedthematerialremovalrate,and consequently, reduced the surface roughness.Under a similarmoleculevolumetricproportiontests,theminutessuspendedmoleculesizeofpowderprompted the largest material removal rate and consequently, the surfaceroughness increased.Conclusion is thataddingchromiumpowder improvesto the highest material removal rate, but poor surface finish while addingaluminiumpowderhasthereverseeffects.

©2019CPE,UniversityofMaribor.Allrightsreserved.

Keywords:Powdermixed‐electrodischargemachining(PMEDM);Aluminiumpowder;Chromiumpowder;Dielectricfluid;Productivity;Materialremovalrate(MRR);Surfaceroughness;Nimonic80Aalloy

*Correspondingauthor:manojmnitjaipur1@gmail.com(Modi,M.)

Articlehistory:Received12April2019Revised13September2019Accepted15September2019

1. Introduction 

Electricaldischargemachining(EDM)hasbeenanessentialprocedureforthedieandtoolmak‐ingenterprisesforalongtime.Thismachiningprocedureisfindinggrowingutilizationinindus‐tries due to the feasibility of machining geometrically intricate shapes irrespective of thehardnessofmaterialsthatareverytoughbyutilizingthetraditionalmachiningprocedures[1].In EDM,managed distinct electrical sparks between the electrode and thework‐piece wouldproducearcing,i.e.concentrationofsparkwhenanexcessiveamountofscatteredtinymaterialremainsintheinter‐electrodegapinlightoftheinabilitytoclearscatteredtinymaterial.Arcingoccurswhenasuccessionofsparksstrikesmorethanonceonasimilarspot.

This,intheend,causesharmtothecathodeoftheapparatusandthework‐pieceifthecon‐trollerofthemachinedoesnotstopitquickly.TheEDMprocedureinthismannerendsupun‐steadyandineffective.ToenhancetheeffectivenessofEDmachining,itisnecessarytoupgradeprocesssteadiness.Thispresentlyremainsamajortoughtask.Kiyaketal.[2]conductedexper‐imentalworkonEDMwithAISIP20toolsteel.Theyexaminedtheimpactofprocessfactorsonsurface roughness (SR) in EDM and observed that littler values of ampere‐current, pulse‐on‐duration and proportionately greater value of pulse‐off‐duration produced a descent surface

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finish (SF).Hasçalıketal. [3] did experimentalwork onEDMwithTi6Al4V anddifferent toolmaterials.TheyinvestigatedthattheMRR,SR,electrodewear,andaveragewhitelayerthickness(AWLT)ascendwith increment inampere‐currentandpulse‐on‐duration.Theyalsoexaminedthesurface‐integrityofworkwithEDMprocessfactors.Fondaetal.[4]conductedexperimentalworkonEDMwithTi6AL4Vwork‐pieceandreportedtheimpactofpropertiesofthematerialonEDMefficiency.Chowetal.[5]didexperimentsonmicro‐slitelectricaldischargemachining(MSEDM)with Ti6Al4Vworkpiece. They examined the impact of silicon carbide powder blendedwithdielectricfluid(DF)onMRR,SR,andgapsize(GS).Chowetal.[6]conductedexperimentsonEDMwithTi6Al4V.Theyobserved that thesilicon‐carbideandaluminiumpowderblendedwithkeroseneisliableforincreasingthegap‐sizeamongtheelectrodes.ThedevelopedGSesca‐latesthedebrisremovalrate(DRR),andmaterialremovaldepth(MRD).TheyalsoexaminedtheimpactofaddingthepowdersmoleculeindielectricfluidonMRDandontheSR.Zhaoetal.[7]didexperimentalworkonEDMwithsteelasaworkpieceandredcopperasatoolmaterial.TheydescribedthemechanismofEDM,andpowdermixedelectricaldischargemachining(PMEDM)process and found thatPMEDMprocessupgrades themachiningefficiencyandSF in contrastwithEDMprocessbypickingthesuitablefactorsset.Pecasetal.[8]performedtheexperimentsonPMEDMwithandwithoutsiliconpowderblendedDF.Theyreportedthatthemixingofpow‐der‐molecule inDFaltersfewprocessparametersandmakesthecircumstancestoaccomplishthepeaksurfacequalityinvastregions.Pecasetal.[9]conductedexperimentsonPMEDMwithAISI H13. They explained that silicon powder blended DF enhances the process polishing‐effectiveness and reduces thewhite layer thickness (WLT), depth, anddiameter of the cavity.Theyreportedthatexact‐controloftheflushing‐rateandvolumetricproportionofpowderistherequirement for achieving theadvancement in the shiningabilityofprocess.Kozaketal. [10]conductedexperimentsonEDMwithtoolsteel.Experimentswereconductedwithkeroseneandwithpowderblendeddemonizedwater.Theynarratedabout the impactofprocess factorsonMRRandSRwithvariousvolumetricproportionsofpowders indielectric liquids.Kansaletal.[11]narratedthatDFwithpowderinPMEDMprocessreducesthedielectricinsulating‐strengthandenhances the gap among the tool andwork.They also found that theadditionofpowderenhancestheprocess‐outcomes.Kansaletal.[12]didexperimentalworkonPMEDMofAISID2die‐steelwith silicon powder blendedDF. They found that the chosen process factors have aremarkableimpactonMR.Pecasetal.[13]carriedouttheexperimentsonEDMwithAISIH13workandcopperasanelectrodewithandwithoutsiliconpowderblendedDF.Theoutcomesoftheexperimentsaccomplishedconfirmastraightconnectionamongtheelectrodeareaandthesurface quality measures and also a noteworthy execution enhancement when the powderblendedDFisutilized.Modietal.[14]describedthedetailofEDMandPMEDMprocessandde‐veloped the mathematical models of process responses through dimensional analysis (DA)method.Modietal.[15]didtheexperimentsonEDDSGwithTi6AL4V.TheyreportedthatGrey‐TMmethodologyenhancesmachiningeffectiveness.

Marashi etal. [16] reported the intensive review of the impact of powder addition on themechanism of EDM process, the most influential powder parameters, future patterns in thistechnology,andarelativesurveyofpowdermaterialsisadditionallyexhibitedinthisarticletofacilitateadeeperinsightintopowderselectionparametersforfutureinvestigations.Theyalsoportrayed thatmain factorswhichmust be considered in PMEDMare powder size, type, andconcentration. At last in this paper, PMEDM research patterns, gaps, findings, and industrialtroublesarediscussedextensively.Kalamanetal.[17]presentedthestudyabouttheintroduc‐tionandsurveyoftheresearchworkinPMEDM.Theinvestigationsconcerningmachiningeffi‐ciency, surface integrity, andgenerationof functional surfacesarepresentedanddiscussed inthe lightofcurrentresearchpatterns.Attemptsmade to improvebiocompatiblesurfaceswiththe utilization of the process additionally included clarifying the future patterns in PMEDM.Daneshmandetal.[18]conductedtheexperimentsonEDMwithCK45steeltoexaminetheim‐pacts of current, voltage, andpulse frequencyonSR. In this testwork, kerosene is utilized asdielectric fluid and copper as an electrode. Design of experimentswith non‐linear regressionmodelwasutilized to estimate theprocess response.Rajuetal. [19] carriedout an extensiveliteraturestudytoprovideatotaldescriptiononμ‐EDMprocess, itsnecessities,executionand

Effect of aluminium and chromium powder mixed dielectric fluid on electrical discharge machining effectiveness

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applications.The experiment frame‐ups and its subsystems, trial studies andoptimizing tech‐niques,createdmicrofeatureanddifferentapplicationsareadditionallydescribedinthispaper.

Inspiteofthefavorableoutcomes,theEDMprocedurewithaddedsubstancesisnotyetuti‐lized broadly in industry. One of the essential reasons is that numerous key factors of thePMEDMprocedure,incorporatingthemechanismofmachiningwithdifferentaddedsubstances,which are not surely known. The complicated nature of this procedure, particularly from theimpacts of the thermo‐physical characteristic of added powders, subsequently, justifies theextrainvestigation.TheobjectiveofthearticleistomakeapreciseinvestigationoftheimpactsofpowderpropertiesinDFontheeffectivenessofEDMachiningwiththeendgoaltoimprovethe applicability of the procedure in the industry. The release‐transivity, particularly, deter‐minesthefrequencyofsparkingthatcontrolsthewholeMRR,thoughthepowder‐particlesstrik‐ingimpacthasaninsignificantcuttingimpactprovidingprimarilytotheenhancementoftheSF.

2. Materials, methods and experimental set‐up

ThispaperusesnomenclaturegiveninAppendixA.Nimonic 80A nickel‐chromium alloy is widely utilized in several industries due to its re‐

sistance against to corrosion and high strength applications because of excellent mechanicalproperties at eminent temperature. PMEDM is an efficient process formachining hard‐to‐cutmateriallikeNimonic80A.ThecompositionofNimonic80Ais19.82%Cr,2.59%Ti,1.57%Al,2.63%Fe,andbalance%Ni.ThePMEDMframe‐upcontainstheservoarrangementofZNCEDMmachine(ZNC50×30,diesinkingtype,EMTltd.,India)isutilizedtokeepupthepredeterminedseparationamongthetoolandwork,whosewidthrelyonthegapvoltage.Totaltestswerecon‐ducted on this frame‐upwithNimonic 80A as awork‐piece andbronze as an anode. For thisreason,an independent fittinghasbeenplannedandcreatedwithin theEDMtank;adifferentacrylictankhavingthecapacityof36litersofDFwassettledontheEDMtablewithbolts.Thedifferent stirrer and pump arrangement are settled in the acrylic tank. The stirrer and pumparrangementisutilizedforpropermixingandcirculationofpowderblendeddielectricliquidintheinter‐electrodegap.Theschematicdiagramofthisframe‐upisdisplayedinFig.1.

Table 1 displays the EDM process factors. The thermal characteristics of aluminim, andchromiumpowdermoleculesaredepicted inTable2.Fig.2(a)displays themechanismofma‐chininginPMEDMprocessandtheoccurrenceofseriesdischargeinPMEDMprocessisdepictedinFig.2(b).

Fig.1TheschematicdiagramofPMEDMframe‐up

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(a) (b)

Fig.2(a)MechanismofmachininginPMEDMprocesses,(b)Occurrenceofseriesdischarge

Table1EDMprocessfactorsElectrode(+) Bronze(ϕ =10mm)Workpiece(‐) Nimonic80A(ϕ =20mm)Timeofmachining HalfhourDielectricfluid KeroseneFlowrateofdielectricfluid 4l/minPowder Aluminium,ChromiumPowdersizes 0.080‐0.090μmand15‐20μmVolumetricproportionofpowdermolecules(cm3/l) 0.30,0.60,1.20CurrentI(A) 2.0,5.0Ton(μs) 5,30,80Dutycycle 0.67

Table2Powdersproperties

PowderDensityρ,(kg/cm3)

Thermalconductivityλ,W/(cm·K)

Electricalresistivityρ,(Ω·cm)

Melting‐point‐temperatureTm,

(K)

SpecificheatC,

Cal/(kg·K)Chromium 7.1610‐3 0.67 2.60 2148 0.110103Aluminium 2.7010‐3 2.38 2.45 933 0.215103

Intheseexperiments,thelevelsofinputparametershavebeenselectedaftertheconductionofpilot experiments. TheMRR,GS, and SR have beenmeasured as the responses in this experi‐mental work.We conducted the various experiments on PMEDM setup andmade the graphsbetween the input variables and the output responses. From these graph, conclusions weredrawn.

3. Results and discussion

3.1 Impacts of powder properties on gap size 

Fig.3displaystheeffectofmixingofAlandCrpowderparticlesintheDFontheGS.Itwasob‐servedthatthegapamongtheanodeandcathodewithAlpowderismarginallymorewhencon‐trastedwiththeCrpowderblendeddielectricliquidwasfoundattributabletoitslittlerelectri‐cal‐resistivity.ThislittlestGSwouldbeaccountableforextremegasblastpressurewithCrpow‐der.Furthermore,theCrpowderdensityisgreaterthantheAlpowderdensity,resultinginarc‐ing rather sparking. Consequently, SR is higher with Cr when contrasted with Al powder. AlpowderdeliveredthebetterSFtrailedbyCrpowder.

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Fig.3TheimpactofmixingofAl,andCrpowdersparticleonthegapsize(I=5A,DC=0.67,Volumetricproportion=0.60cm3/l)

3.2 Impacts of powder particle size on material removal rate 

Fig.4demonstratestheimpactoftwoAlpowder‐moleculesizesatdifferentvolumetricpropor‐tionsonMRR.Itwasseenthattheappropriatemixingofpowder‐particlesimprovesthemachin‐ingproductivitybyadditionalsettlingoftheelectric‐release.Theenhancementinprocessdura‐bilityoccurredduetothefairlylargerGSininter‐electrodegap.Theoutcomesadditionallydis‐closedthattheriseinthesizeofthepowderparticleresultedinadecreaseintheenhancementoftheMRR.Thiscanbeascribedtobothlesserelectricalpowerdensityandamoreprobabilityofanomalousrelease.

Moreover,whenthesizeofthemoleculewasmorethanthespark‐gap(about06‐55μm),theefficiency of machining evidently decayed. The MRR outcomes for the minimal size of themolecule (80‐90nm)atdifferentvolumetricproportionsofpowderparticleswereevenmorethanthosewith(15‐20μm)moleculesizeofpowderparticles.Thisishappenedduetotheexist‐enceoflesssparkgapamongtheelectrodes.Forthecurrentat5A,andvolumetricproportionofmoleculemorethan0.60cm3/l,demonstratedanotablefallingtrendinMRR.Thiswasbecauseofthejoinedimpactsoflowerelectrical‐density,thelesserstrikingofpowderparticles,unevenlydistributionofparticles,andverylowgrowthintherelease‐transitivity.

Fig.4TheimpactofparticlesizeandvolumetricproportionofaluminiumpowdersonMRR(Ton=30μs,DC=0.67)

Fig.5TheimpactofTonandvolumetricproportionof80‐90nmaluminiumpowdersmoleculeonMRR(DC=0.67)

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Fig.6TheimpactofTonandvolumetricproportionof15‐20μmaluminiumpowdersmoleculeonMRR(DC=0.67)

3.3 Impacts of molecule concentration on material removal rate  

Fig.4additionallydemonstratesthatMRRwasaffectedbythevolumetricproportionofalumini‐umpowders.ThereasonabledistinctioninMRRisobservedforthecurrentatahigherlevelbe‐causeof thegenerationofmoresparkenergyasdisplayed inFigs.4,5, and6. Itwasalsoob‐servedfromFig.4thatthehighestMRRisobtainedat5Acurrent,0.6cm3/lofAlpowders,Ton=30μs,andmoleculessizesunder95nm.Thisdemonstratesthatanidealsparkgapwasacquiredat this setting of the volumetric proportion of powder andTon, which delivered the optimumfactorssettingofpowerdensity,strikingofmoleculeandrelease‐transitivityintheEDMproce‐dure.

Figs.5and6demonstratethattheimpactsofthevolumetricproportionofmoleculeof80‐90nmand15‐20μmaluminiumpowdersparticlefluctuatedalongwiththeTon.AtthelesserTonof5μs,0.6cm3/lprovidethegoodMRR,trailedby1.2cm3/l,andwith0.30cm3/lbeingtheinferior.Though,itmaybefoundinFig.6thatatthe5.0Acurrent,whentheTonwasraisedto30μs,theimpactsbeguntoalterwith15‐20μmaluminiumpowdersparticle.Thevolumetricconcentra‐tionof0.6cm3/lstilldeliveredthegoodMRR,however,0.30cm3/lwassuperiorascomparedto1.2cm3/l.Thispatternproceededwith therise in theTon.Whenthe timewasraised to80μs,0.30 cm3/l exceed 1.2 cm3/l inMRR outcomes for both 80‐90 nm, and 15‐20 μm aluminiumpowders particle. Thiswas because of extrawarming impacts due to the rising theTon.Moreevacuatedmoltenmaterialswereconsequentlyproducedthatinthelongrundecreasedtheper‐formanceofthevolumetricproportionof1.2cm3/linimprovingtheproceduresteadiness.

Thepurposebehindtheprimaryoutcomeswith15‐20μmaluminiumpowdersparticlewasbelievedtobebecauseofthebiggermoleculesizeanditsimpacts.Itdemonstratedthatthebig‐germoleculesizeofaddedsubstancesamongthesparkgapwasincreasinglydelicatetoevacu‐atethetinyworkmaterialsproduction.

3.4 Impacts of molecule characteristics on material removal rate 

Fig.7demonstratestheimpactsoftwovolumetricproportionsofAl,andCrpowdersparticleontheMRR.ThetestoutcomesdemonstratedthatchromiumgeneratedthebestMRR,andalumini‐umthe leastwhen thevolumetricproportionofpowderwas<1.2cm3/land I=5.0A.At thepoint,whentheampere‐currentwasat2.0A,thedistinctioninMRR turnedouttobelittlebe‐causeofthelessinputofenergy.Fig.3demonstratesthatthesparkgapforchromiumislesserthanthat foraluminiumasclarifiedalready. Inprinciple, therewasasomewhathigherpowerdensityandgasexplosionpressureforchromium.

Moreover, chromium powder density is double than the aluminium powder, ensuing in apowerfulpowder‐particlecollision.Additionally, theheatconductivityofaluminiumpowderisabout3timesbiggerascomparedtochromiumpowder,whichshowedthatmoreenergyistak‐enoutbythealuminiumpowderblendeddielectricliquid.Subsequently,CrcreatedthebiggestMRR.

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Fig.7Theimpactofampere‐currentandvolumetricproportionof15‐20μmaluminiumandchromiumpowdersmoleculeonMRR(DC=0.67,Ton=30μs)

3.5 Effects of particle size on surface roughness 

Fig.8demonstrates the impactsof twoaluminiumandchromiumpowdermoleculesizeswithdifferentvolumetricproportionsonSR.ThebestsortsofpowdersforupgradingthesmoothnessofthesurfaceareAl,Cretc.Aluminiumpowder‐particlecreatesagoodsurfaceforallthemole‐culeproportions.Itispredominantlybecauseofthejoinedimpactsofsmallelectrical‐resistivity,adequatethermal‐conductivity,andless‐densityofaluminium.Lesselectrical‐resistivitymakesahighsparkgap,goodthermal‐conductivityremovesmoreheat,andless‐densityavoidthearcingamongtheelectrodes.Theseimpactsjointlyleadtolessdensityofelectricalsparkbringingthelow gas blast, in thisway just shallowholes are created on themachined surface. Al powderproducedthebestsurfacefinishfollowedbytheCrpowder.Thebestsurfacefinishisobtainedatthevolumetricproportionof1.2cm3/lofaluminiumpowderwith15‐20μmparticlesize.

Fig.8Theimpactofparticle‐sizeandvolumetricproportionofAlpowdersmoleculeonSR(DC=0.67,Ton=30μs)

3.6 Effects of particle concentration on surface roughness 

AsappearedinFig.9,itwasseenthatatthe5Acurrent,thealuminiumpowdervolumetricpro‐portionofmoleculehasbuiltamajoreffectinSRduetothebiggerMR. Itwasnoticedthatthebiggestmoleculevolumetricproportionof1.20cm3/lprovidetheworstSFatTon=80μsdueto

Fig.9TheimpactofTonandvolumetricproportionof80‐90nmaluminiumpowdersmoleculeonSR(DC=0.67,I=5A)

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itshighestreleasetransitivity.ItisalsonotedfromFig.9thatthevolumetricproportionofpow‐dermoleculewasnotthemainparametercontrollingtheSRintheEDMprocedure.Alternately,Tonseemedbyallaccount,tobethemostvitalparameter.

3.7 Impacts of molecule characteristics on surface roughness 

Fig.10demonstratestheimpactofsevenmoleculevolumetricproportionlevelsofaluminium,andchromiumpowder‐particlesontheSR.ItwasseenthataluminiumpowderproducedthegoodSFthanthechromiumpowderparticleforboththe2Aaswellasat5Acurrent.ThishappensbecausetheevacuationofmoremoltenmaterialfromworksurfaceinpresenceofCrpowderascomparedtothepresenceofAlpowderinDF.Subsequently,CrgeneratedthebiggestSR.

Moreover, chromium powder density is double than the aluminium powder, ensuing in apowerful powder‐particle collision and result in arcing. Additionally, the heat conductivity ofaluminiumpowder is about3 timesbigger as compared to chromiumpowder,which showedthatmoreenergyistakenoutbythealuminiumpowderblendeddielectricliquid.

Fig.10Theimpactofampere‐currentandvolumetricproportionof15‐20μmaluminium,andchromiumpowdersmoleculeonSR(DC=0.67,andTon=30μs)

4. Conclusions

Inviewofthetestoutcomes,thefollowingconclusionsaredrawn:

Themoleculesize,volumetricproportionofpowders,itsdensity,electrical‐resistivity,andthermal‐conductivityarethesignificantattributesofpowdersinfluencingperformanceofEDMachiningprocess.

DuetotheinclusionofpowderparticleinDF,thegapforsparkwasincreased. Sparkgapvarieswiththemixingofpowdersofvarioussizesinthedielectricfluid.Spark

gap increaseswith increasingsizeofpowdermolecules.Theminimumrise in thegap isproducedwithasizeof80‐90nmpowdersandwith15‐20μmgeneratingthehighestgap.

HighestMRRwasobservedwithpowdersofsize80‐90nmandwith15‐20μmgeneratingthesmallest.FortheSF,theoppositepatternisnoticed.

Highersparkgapwasobservedbyaddingaluminiumpowderparticlesfollowedbyusingchromiumpowder.

BestMRRwas observedwith adding chromium followedby aluminiumpowder. ForSF,theoppositepatternwasnoticed.

Thevolumetricproportiononmixing thepowderwith thedielectric fluid in theratioof0.6cm3/lgivesbestMRRoutcomes.

With2A,and5Acurrent,resultsarequitehigherthantheimpactofmoleculesize,volu‐metricproportionofpowder,andotherfactors.

TheMRR and SR varywith different combination ofmolecule sizes, volumetric propor‐tionsofAl,andCrpowdersindielectricfluidinPMEDMprocess.

Experimentscanbeconductedbyusingdifferentcombinationofmaterials,dielectricflu‐ids,andalsovariouspowderstogetdifferentfindingsinthePMEDMprocess.

Effect of aluminium and chromium powder mixed dielectric fluid on electrical discharge machining effectiveness

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Appendix A The following nomenclature is used in the paper:

AWLT Average white layer thickness DC Duty cycle DF Dielectric fluid DRR Debris removal rate EDDSG Electro discharge diamond surface grinding EDM Electrical discharge machining GRA Grey relational analysis GS Gap size I Current (A) MR Machining rate MRD Material removal depth MRR Material removal rate (mm3/min) MS EDM Micro-slit EDM PMEDM Powder mixed electrical discharge machining Ra Average roughness of surface (µm) SF Surface finish SR Surface roughness TM Taguchi method Ton Pulse on-time (µs) WEDM Wire electrical discharge machining WLT White layer thickness

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