Examination of machining parameters on surface roughness in EDM of tool steel

(BQ) This paper is devoted to a study of the influences of EDM parameters on surface roughness for machining of 40CrMnNiMo864 tool steel (AISI P20) which is widely used in the production of plastic mold and die. The selected EDM parameters were pulsed current (8, 16 and 24 A), pulse time (2, 3, 4, 6, 12, 24, 48 and 100 s) and pulse pause time (2 and 3s). It was observed that surface roughness of workpiece and electrode were influenced by pulsed current and pulse time, higher values of these parameters increased surface roughness. Lower current, lower pulse time and relatively higher pulse pause time produced a better surface finish.
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Examination of machining parameters on surface roughness in EDM of tool steelJournal of Materials Processing Technology 191 (2007) 141–144Examination of machining parameters on surfaceroughness in EDM of tool steelM. Kiyak a,∗ , O. Cakır b¸aDepartment of Mechanical Engineering, Yildiz Technical University, 34349 Istanbul, Turkeyb Department of Mechanical Engineering, Dicle University, 21280 Diyarbakir, TurkeyAbstractElectrical discharge machining (EDM) is one of the important non-traditional machining processes and it is widely accepted as a standardmachining process in the manufacture of forming tools to produce molds and dies. Since its introduction to manufacturing industry in late 1940s,EDM became a well-known machining method. The method is based on removing material from a workpiece by means of a series of repeatedelectrical discharges, produced by electric pulse generators at short intervals, between an electrode (tool) and a part being machined in dielectricfluid medium. This paper is devoted to a study of the influences of EDM parameters on surface roughness for machining of 40CrMnNiMo864 toolsteel (AISI P20) which is widely used in the production of plastic mold and die. The selected EDM parameters were pulsed current (8, 16 and24 A), pulse time (2, 3, 4, 6, 12, 24, 48 and 100 ␮s) and pulse pause time (2 and 3 ␮s). It was observed that surface roughness of workpiece andelectrode were influenced by pulsed current and pulse time, higher values of these parameters increased surface roughness. Lower current, lowerpulse time and relatively higher pulse pause time produced a better surface finish.© 2007 Elsevier B.V. All rights reserved.Keywords: EDM; Tool steel; Current; Surface roughness1. IntroductionElectric discharge machining (EDM) is one of the most popular non-traditional material removal processes and has becamea basic machining method for the manufacturing industries ofaerospace, automotive, nuclear, medical and die-mold production. The theory of the process was established by two Sovietscientists B.R. and N.I. Lazarenko in the middle of 1940s. Theyinvented the relaxation circuit and a simple servo controller toolthat helped to maintain the gap width between the tool and theworkpiece. This reduced arcing and made EDM machining moreprofitable and produced first EDM machine in 1950s. Majordevelopment of EDM was observed when computer numericalcontrol systems were applied for the machine tool industry. Thus,the EDM process became automatic and unattended machiningmethod [1].The process uses thermal energy to generate heat that meltsand vaporizes the workpiece by ionization within the dielectric∗Corresponding author.E-mail addresses: kiyak@yildiz.edu.tr (M. Kiyak), ocakir@dicle.edu.tr(O. Cakır).¸0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2007.03.008medium. The electrical discharges generate impulsive pressureby dielectric explosion to remove the melted material. Thus, theamount of removed material can be effectively controlled to produce complex and precise machine components. However, themelted material is flushed away incompletely and the remaining material resolidifies to form discharge craters. As a result,machined surface has microcracks and pores caused by hightemperature gradient which reduces surface finish quality.There have been many published studies considering surfacefinish of machined materials by EDM. It was noticed that various machining parameters influenced surface roughness andsetting possible combination of these parameters was difficultto produce optimum surface quality. The influences of somemachining parameters such as pulsed current [2–9], pulse time[2–6,8,9], pulse pause time [2,5,9], voltage [4,6], dielectric liquid pressure [4,6,8,10] and electrode material [11] have beenexamined. One study examined P20 tool steel and provided useful information the effects of some machining parameters onsurface roughness, but the selected of pulsed current values wasvery low 1–8 A [12].The present study examines the effects of pulsed current,pulse time and pulse pause time on surface roughness in the40CrMnNiMo864 tool steel (AISI P20) tool steel.142M. Kiyak, O. Cakır / Journal of Materials Processing Technology 191 (2007) 141–144¸Table 1Properties of workpiece materialChemical composition (%)CCrMnMoNiSSi0.3721.40.21Max. 0.010.3HardnessElasticity module (E)Thermal conductivity290–341 HB205 GPa29 W/m KFig. 1. Effects of pulse time and pulsed current on surface roughness of workpiece (2 ␮s pulse pause time).2. Experimental proceduresThe experimental study was carried out on AJAN EDM 982 machine. Thedielectric liquid was a brand of Cuttex Fel Ultra. The viscosity of dielectric fluid was 2.2–2.7 at 40 ◦ C and the lightning point was 105 ◦ C/min. Theselected workpiece material was 40CrMnNiMo864 (AI ...