A review on influence of electrical process parameters in EDM process

archives of civil and mechanical engineering 15 (2015) 87–94<br /> <br /> Available online at www.sciencedirect.com<br /> <br /> ScienceDirect<br /> journal homepage: http://www.elsevier.com/locate/acme<br /> <br /> Review<br /> <br /> A review on influence of electrical process<br /> parameters in EDM process<br /> T. Muthuramalingam a,*, B. Mohan b<br /> a<br /> b<br /> <br /> Department of Mechatronics Engineering, SRM University, Kattankulathur, India<br /> Department of Mechanical Engineering, CEG Campus, Anna University, Chennai, India<br /> <br /> article info<br /> <br /> abstract<br /> <br /> Article history:<br /> <br /> Since the thermal energy produced in electrical discharge machining process is due to the<br /> <br /> Received 12 July 2013<br /> <br /> applied electrical energy, it is very important to enhance the electrical process parameters to<br /> <br /> Accepted 16 February 2014<br /> <br /> improve the process efficiency. The present study discusses about having an overview of the<br /> <br /> Available online 14 April 2014<br /> <br /> EDM process, modeling of process parameters, and influence of process parameters such as<br /> input electrical variables, pulse shape, and discharge energy on performance measures such<br /> <br /> Keywords:<br /> <br /> as material removal rate, surface roughness and electrode wear rate. This study also<br /> <br /> EDM<br /> <br /> discusses about controlling the electrical process parameters, and empirical relationships<br /> <br /> EWR<br /> <br /> between process parameters and optimization of process parameters in EDM process. From<br /> <br /> Discharge<br /> <br /> the review results, it has been observed that the efficacy of the machining process can be<br /> <br /> MRR<br /> <br /> improved by electrical process parameters, and only less attention has been given for<br /> <br /> Surface<br /> <br /> enhancing such parameters.<br /> # 2014 Politechnika Wrocławska. Published by Elsevier Urban & Partner Sp. z o.o. All<br /> rights reserved.<br /> <br /> 1.<br /> <br /> Introduction<br /> <br /> Electrical discharge machining (EDM), otherwise known as<br /> thermal erosion process, is one of the non-conventional<br /> machining processes, where tool and workpiece do not come<br /> into contact with each other during the machining process. The<br /> progression of events constituting the process of material<br /> erosion from the work surfaces by an electrical discharge<br /> machining can be explained in the following way. If an<br /> appropriate voltage is developed across the tool electrode<br /> (normally cathode) and the workpiece (normally anode), the<br /> breakdown of dielectric medium between them happens due to<br /> <br /> the growth of a strong electrostatic field. Owing to the electric<br /> field, electrons are emitted from the cathode toward the anode<br /> on the electrode surfaces having the shortest distance between<br /> them. These electrons impinge on the dielectric molecules of<br /> the insulating medium, breaking these dielectric fluid molecules into positive ions and electrons. These secondary<br /> electrons travel along on the same ionization path. This event<br /> causes an increase in the electric field strength across the work<br /> surfaces and liberates a large number of electrons. It creates an<br /> ionized column in the shortest spark gap between the tool<br /> electrode and the workpiece, thereby decreasing the resistance<br /> of the fluid column and causing an electrical discharge in the<br /> shortest distance point between the tool and the workpiece. The<br /> <br /> * Corresponding author. Tel.: +91 9994872013; fax: +91 4422232403.<br /> E-mail addresses: muthu1060@gmail.com, muthu_456@yahoo.com (T. Muthuramalingam), mohan@mitindia.edu (B. Mohan).<br /> http://dx.doi.org/10.1016/j.acme.2014.02.009<br /> 1644-9665/# 2014 Politechnika Wrocławska. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.<br /> <br /> 88<br /> <br /> archives of civil and mechanical engineering 15 (2015) 87–94<br /> <br /> 3.<br /> Enhancing the performance of pulse<br /> generator<br /> <br /> Fig. 1 – Basic mechanism involved in EDM.<br /> <br /> enormous thermal energy melts and vaporizes the material<br /> from the workpiece, which creates a small crater over the work<br /> surface. There happened a collapse of the ionized column with<br /> the termination of the electrical energy by means of the<br /> switching circuit and then surrounding dielectric fluid occupies<br /> its place. The melted debris is removed by the flushing process.<br /> The conduction of dielectric medium can be determined by the<br /> current, duration and pulse energy [1]. Fig. 1 explains the<br /> formation of ionized column in the shortest distance of work<br /> surfaces using the EDM process [1].<br /> <br /> 2.<br /> <br /> State of art in EDM process<br /> <br /> Since the electrical discharge machining process is of with<br /> non-linear nature, it requires a lot of improvements on it.<br /> Many authors have discussed about the research works for<br /> improving process efficiency of the EDM process. The fundamentals of EDM process mechanism and research works<br /> carried out from the inception to the development of the diesinking EDM process within the past decade have been<br /> discussed by Ho and Newman [2]. It has been reported and<br /> discussed about the EDM researches relating to improve the<br /> process performance measures, optimizing the process variables, and monitoring and control of the sparking process.<br /> Abbas et al. presented the recent research trends to improve<br /> the performance characteristics involved in all the aspects of<br /> electrical discharge machining process. They discussed about<br /> the need for controlling the process parameters to enhance the<br /> machining process efficiency of the EDM process [3]. The<br /> development of new technologies for improving the surface<br /> quality of workpiece is a significant research area in EDM<br /> process. Kumar et al. presented a review on the phenomenon<br /> of surface modification by EDM and future trends of its<br /> applications [4]. It has been observed that most of the research<br /> works concentrated on surface modification using the powder<br /> mixed dielectric medium in EDM process. The study of the<br /> impact of the electrical process parameters on surface<br /> modification of the workpiece has been taken up by very<br /> few researchers.<br /> <br /> Since the electrical energy is supplied to the EDM process<br /> informing the DC pulses, the pulse generator needs to be<br /> upgraded to improve the performance measures in the<br /> machining process. The lower energy pulses enhance the<br /> surface finish of the workpiece whereas the higher energy<br /> pulses improve the material removal rate.<br /> Jahan et al. conducted a detailed experimental investigation to find out the influence of major operating parameters on<br /> surface quality of tungsten carbide with both transistor and<br /> RC-type generators in EDM process [5]. It has been proved that<br /> RC pulse generator has produced a smoother surface finish<br /> than the transistor pulse generator due to its lower discharge<br /> energy distribution over the surface of tungsten carbide. Han<br /> et al. designed and developed a modified transistor pulse<br /> generator with pulse frequency of 1 MHz to produce higher<br /> material removal rate than the RC pulse generator in the<br /> electrical discharge machining process [6]. They found that the<br /> transistor pulse generator has provided two or three times<br /> higher machining speed than the conventional RC pulse<br /> generator while machining tungsten workpiece with brass<br /> electrode.<br /> A pulse generator based on fixed pulse width modulation<br /> has been developed by Yan and Liu to generate the high<br /> frequency 4.4 MHz and short duration pulse control signals to<br /> reduce surface roughness of the workpiece tungsten carbide in<br /> the EDM process [7]. From the experimental results, it has been<br /> observed that the very low discharge energy pulse applied<br /> between tool and electrode has improved the surface quality of<br /> workpiece during the machining process. Yan and Chiang<br /> discussed about the development and application of a new<br /> power supply in wire electrical discharge machining process<br /> [8].<br /> A transistor-controlled power supply composed of a low<br /> energy discharge circuit has been designed to provide the<br /> functions of high frequency and lower energy pulse control.<br /> The experimental results have shown that the low peak<br /> current has been resulted in better surface finish in EDM<br /> process. Muthuramalingam and Mohan discussed about effect<br /> of uniform distribution for improving the surface quality using<br /> iso current pulse generator in EDM process [9]. Fig. 2 shows the<br /> surface quality of workpiece made by three different pulse<br /> generators. It has been observed that the iso current pulse<br /> generator could produce better surface finish than the<br /> conventional pulse generators such as RC pulse generator<br /> and transistor pulse generator.<br /> Han et al. designed and developed a new transistor type<br /> pulse generator with high frequency response to produce<br /> higher erosion rate of the workpiece in the electrical discharge<br /> machining process [10]. From the experimental results, it has<br /> been observed that the modified transistor pulse generator has<br /> produced 24 times higher material removal rate than the RC<br /> pulse generator in the EDM process. Yan and Lai presented the<br /> development of a fine-finish power supply with high frequency in EDM process [11]. This power supply has been composed<br /> with full bridge circuit, two snubber circuits and a pulse control<br /> circuit. It has been found that the proposed power supply has<br /> <br /> archives of civil and mechanical engineering 15 (2015) 87–94<br /> <br /> 89<br /> <br /> Fig. 2 – Surface topography of machined surface using different pulse generators.<br /> <br /> produced lower discharge energy and thus contributed to<br /> lower surface roughness. Muthuramalingam and Mohan<br /> developed a semiconductor based pulse switching circuit to<br /> produce lower energy discharge pulses during finishing level<br /> of the process for enhancing the EDM performance characteristics [12]. Casanueva et al. attempted to establish a new EDM<br /> impulse generator based on high frequency switched DC-toDC series-parallel resonant converter [13]. It has been claimed<br /> that the capacitance effect has affected the overall impedance<br /> of the EDM arrangement and thus altered the machining<br /> characteristics of EDM process.<br /> <br /> 4.<br /> Influence of pulse shape on performance<br /> measures<br /> Studying the variation of the EDM process response characteristics due to change in shape of the generated pulse is one<br /> of the research aspects in the EDM process. The discharge<br /> pulse shape affects the average spark energy which is<br /> delivered on the surface. Since the machining characteristics<br /> in EDM process depend on the electrical energy, the pulse<br /> shape which has an effect on the machining characteristics<br /> such as material removal rate, surface quality and electrode<br /> wear rate as shown in Fig. 3.<br /> The effects of the voltage excitation of the pre-ignition<br /> spark pulse on the performance measures such as material<br /> removal rate, electrode wear rate and average surface<br /> roughness have been discussed by Ghoreishi and Tabari<br /> [14]. Based on the results, it is clear that applying voltage<br /> excitation of the pulse has produced an effective pulse which<br /> in turn increased material erosion and surface quality. The<br /> influence of the current impulse on machining tungsten<br /> <br /> carbide and SKD die steel with electrolytic copper tool<br /> electrode in the EDM process has been investigated by Tsai<br /> and Lu [15]. From the experimental results, it has been found<br /> that the material removal rate and tool wear rate have been<br /> affected by the energy density. Muthuramalingam and Mohan<br /> discussed about influence of discharge current impulse on the<br /> performance measures in EDM process [16].<br /> Son et al. investigated the influences of electrical pulse<br /> condition on the machining characteristics in the EDM process<br /> [17]. It has been found that the duration of pulse considerably<br /> affects the machining characteristics such as material removal<br /> rate, tool wear rate and surface accuracy. It has also been<br /> realized that the shorter EDM pulse could be efficient to make a<br /> precision part. Liu et al. described the influence of the EDM<br /> discharge pulse shape on the machining characteristics such<br /> as material removal mechanism of Si3N4–TiN [18]. The surface<br /> texture of machined workpiece has been investigated with<br /> different form of discharge pulse such as relaxation and iso<br /> current pulse. It has been proved that uniform discharge<br /> energy has produced good surface topography. Janardhan and<br /> Samuel analyzed the effect of machining parameters on<br /> material removal rate and average surface roughness using<br /> the pulse train data acquired at the spark gap with the help of<br /> MATLAB software package [19]. It has been observed that the<br /> material erosion rate has been increased with decrease in the<br /> pulse off time in EDM process. Yeo et al. proposed a new pulse<br /> discriminating technique for monitoring electrical discharge<br /> machining process [20]. This system has employed the current<br /> pulse as the main detecting parameter as it has been<br /> considered to be a better representation of the spark energy<br /> inside the plasma channel as compared to the voltage. There<br /> should be less arcing effect to enhance the surface finish for an<br /> ideal EDM process. Muthuramalingam and Mohan discussed<br /> and proved that the uniform duration pulse shape for the<br /> discharging phenomenon in EDM process has improved the<br /> surface quality of the workpiece with less arcing effect [21].<br /> <br /> 5.<br /> Influence of electrical process parameters<br /> on performance measures<br /> Fig. 3 – Relation between pulse shape and machining<br /> characteristics in EDM process.<br /> <br /> There are many research works that have been conducted to<br /> find the influence of process parameters especially electrical<br /> <br /> 90<br /> <br /> archives of civil and mechanical engineering 15 (2015) 87–94<br /> <br /> Fig. 4 – SEM images of surface using EDM process.<br /> <br /> process parameters on EDM process. Most of the research<br /> works reveal that the discharge current and machining time<br /> have the most influencing nature on the EDM performance<br /> measures. Fig. 4 shows the SEM images of EDM surface while<br /> machining AISI 202 stainless steel with tungsten carbide tool<br /> electrode.<br /> Gostimirovic et al. investigated the effects of electrical<br /> process parameters on the performances of die-sinking<br /> electrical discharge machining process with RC pulse generator<br /> while machining manganese-vanadium tool steel workpiece<br /> using graphite tool electrode. They found that the discharge<br /> current and pulse duration have highly influenced the material<br /> removal rate of the EDM process [22]. Mohan et al. analyzed the<br /> effect of EDM process parameters such as electrode material,<br /> polarity, pulse duration, current and rotation of the electrode on<br /> the material removal rate, tool wear rate and surface roughness<br /> [23]. It has been found that the material removal rate and tool<br /> wear rate have been increased with the discharge current during<br /> machining process. Nowicki et al. analyzed the effects<br /> individual electrical discharge on the crater volume of the<br /> workpiece in EDM process [24]. They found that the crater<br /> surface exhibits strong interaction with the electrical discharge<br /> spark. Mohan et al. investigated the surface roughness of the<br /> SiC/6025Al composite surface using electrical discharge machining process with brass as the tool electrode [25]. From the<br /> experimental results, it has been observed that increasing peak<br /> current has resulted in higher surface roughness during the<br /> machining process.<br /> Seo et al. discussed about the drilling process of a<br /> functionally graded 15–35 vol.% of silicon carbide particulate<br /> reinforced Al359 metal matrix composite by electrical discharge<br /> machining process to assess the machinability and workpiece<br /> quality [26]. It has been observed that the peak current and pulse<br /> on time have increased the material removal rate. It has also<br /> been reported that increase in percentage SiC particles has<br /> increased the material removal rate and electrode wear rate.<br /> Puertas et al. carried out a study on the influence of the factors of<br /> current intensity, pulse time and duty cycle over the material<br /> removal rate, surface quality and electrode wear rate [27]. They<br /> modeled the relationship between the input parameters and<br /> <br /> response parameters in the die-sinking EDM process using<br /> response surface methodology. It has been concluded that the<br /> lower values of the current intensity and the machining time<br /> have to be used in order to obtain a good surface finish. The use<br /> of the dimensional analysis for investigating the effects of the<br /> electrical and the physical parameters on the material removal<br /> rate of a die-sinking EDM process has been described by Yahya<br /> and Manning [28]. From the experimental results, it has been<br /> found that the material removal rate has been increased with<br /> discharge current, gap voltage and pulse on time.<br /> Huang et al. made an attempt to unveil the influence of the<br /> process parameters on the machining performances in the EDM<br /> process [29]. It has been found that the pulse on time and spark<br /> gap have the most significant nature to affect the performance<br /> measures such as surface roughness and white layer depth<br /> using numerical analysis. Kuppan et al. reported about the<br /> experimental investigation of small deep hole drilling of Inconel<br /> 718 with electrolytic copper tool electrode using the electrical<br /> discharge machining process [30]. The experimental results<br /> have shown that the material removal rate has been increased<br /> with the increase in the peak current and duty factor. Patel et al.<br /> investigated the feasibility of fabricating micro holes in SiCp–Al<br /> composites using electrical discharge machining with a rotary<br /> tube electrode [31]. They have investigated the material removal<br /> rate, electrode wear rate and hole tapper as the responses for the<br /> study. The experimental results have revealed that pulse on<br /> duration has significantly affected the response characteristics<br /> involved in EDM process. Pelicer et al. focused on investigating<br /> the influence of EDM process parameters and electrode<br /> geometry on feature micro accuracy on tool steel for mold<br /> fabrication purposes [32]. A set of designed experiments with<br /> varying process parameters such as pulse current, open voltage<br /> and pulse duration have been carried out in H13 steel using<br /> different shaped copper electrodes. It has been concluded that<br /> the triangular shaped electrode would produce highly inefficient output, since the fast wearing nature of the electrode<br /> edges. Wang et al. carried out a series of experiments to<br /> investigate the impacts of machining polarity, electrode<br /> rotation speed and nominal capacitance on the material<br /> removal rate and tool wear rate with poly crystalline diamond<br /> [33]. It has been demonstrated that favorable machining<br /> performance of EDM process on the workpiece could be<br /> achieved in tool with negative polarity as compared to the<br /> positive polarity.<br /> Tosun et al. presented an investigation on the effect and<br /> optimization of machining parameters on kerf and material<br /> removal rate in wire EDM process with Taguchi method [34]. The<br /> experimental studies have been conducted under varying pulse<br /> duration, gap voltage, wire speed and flushing pressure with<br /> AISI 4140 steel as workpiece material. Based on the ANOVA<br /> method, the high effective parameter on both kerf and material<br /> removal rate has been found as pulse duration. Ji et al. presented<br /> a new process of machining SiC ceramics using electrical<br /> discharge milling process [35]. The effects of tool polarity, pulse<br /> duration, voltage and peak current on the process performances<br /> such as material removal rate, electrode wear rate and surface<br /> roughness have been investigated. It has been found that the<br /> negative polarity tool electrode with longer pulse duration has<br /> produced high material removal rate and surface roughness.<br /> Rebelo et al. presented an experimental study on the effect of<br /> <br /> archives of civil and mechanical engineering 15 (2015) 87–94<br /> <br /> electric discharge machining parameters on material removal<br /> rate and surface quality with high strength copper–beryllium<br /> alloys [36]. They found that the plasma diameter has been<br /> decreased with pulse duration and discharge current during the<br /> machining process.<br /> Yu et al. examined the use of electrical discharge machining on machining poly-crystalline silicon [37]. The effects of<br /> different WEDM process parameters on machining characteristics have been explored. From the experimental results, it<br /> has been indicated that the pulse on time has the great<br /> influence on the cutting speed in Wire EDM process. Batish<br /> et al. investigated the effect of process parameters and<br /> mechanism of material deposition in electric discharge<br /> machining on surface properties of EN31, H11 and high carbon<br /> high chromium die steel materials [38]. It has been discussed<br /> about material transfer mechanism involved in EDM process.<br /> It has been found that die steels have been machined<br /> effectively with copper tool electrode using EDM process.<br /> Patel et al. presented a detailed experimental investigation of<br /> machining characteristics such as surface integrity and<br /> material removal mechanisms of advanced ceramic composite Al2O3–SiCw–TiC with EDM process [39]. It has been<br /> concluded that the surface roughness and material removal<br /> rate have been increased with pulse duration in EDM process.<br /> <br /> 6.<br /> Influence of discharge energy on<br /> performance measures<br /> In view of the fact that when the discharge energy is converted<br /> into the thermal energy to melt and vaporize the material in<br /> EDM process, it is unavoidable to discuss the influence of the<br /> pulse energy on the machining characteristics in such a<br /> process.<br /> Jahan et al. conducted an experimental investigation with<br /> the view of obtaining fine surface finish in die-sinking EDM<br /> process of tungsten carbide using different tool electrodes<br /> such as tungsten, copper tungsten and silver tungsten [40]. It<br /> has been found that the surface finish has been influenced by<br /> the discharge energy during machining process. It has been<br /> realized that the lower discharge energy has produced good<br /> surface finish. Yeo et al. discussed about the machining of<br /> zirconium based bulk metallic glass by EDM process with<br /> different tool electrodes such as copper, brass and tungsten<br /> rod electrode [41]. The experimental results have shown<br /> that the usage of lower input energy has produced the<br /> lower surface roughness and electrode tool wear. Khanra<br /> et al. investigated the influence of energy input on the<br /> workpiece surface during the machining in the EDM process.<br /> In this experimental investigation, a well-polished mild steel<br /> (C – 0.18%) plate has been used for machining by EDM [42]. It has<br /> been observed that the energy input has influenced the debris<br /> particle size in the EDM process.<br /> Popa et al. showed the importance of optimizing the<br /> process parameters that could influence the quality of the EDM<br /> process [43]. They formulated the equation of crater depth in<br /> terms of discharge energy in EDM process. From the relation, it<br /> has been observed that the crater depth has been increased<br /> with the discharge current flowing through the workpiece and<br /> tool electrode. Kojima et al. described about the spectroscopic<br /> <br /> 91<br /> <br /> measurement of arc plasma diameter in EDM [44]. They found<br /> that the arc plasma has been increased with increasing<br /> discharge current. It has been verified that crater diameter and<br /> depth decrease with increasing gap width due to the increased<br /> plasma diameter. The arc plasma diameter has been increased<br /> with increasing spark gap and thus clarified the reason for<br /> lower material removal rate and smoother surface finish with<br /> longer spark gap. Wong et al. developed a single spark pulse<br /> generator using resistance–capacitance arrangement to study<br /> the erosion characteristics in the EDM process from the crater<br /> size [45].<br /> The volume and size of the craters have been found to be<br /> more consistent at lower energy discharge sparks than the<br /> higher energy discharge sparks. The higher energy pulse leads<br /> to the micro surface crack on the work surface. Guu et al.<br /> aimed to investigate the machining characteristics of manganese–zinc ferrite magnetic materials using electrical discharge<br /> machining process [46]. The experimental results have<br /> indicated that the morphology of debris revealed the mechanism of material removal. It has been observed that the better<br /> machined surface has been obtained by setting process<br /> parameters at low pulse energy. Nowicki et al. made an<br /> attempt to machine superficial layer of the workpiece using<br /> brush EDM process by modifying the spark energy [47]. The<br /> theoretical modeling of the EDM process based upon the heat<br /> transfer equations has been established by Singh [48]. In the<br /> study, the input energy equation has been developed as a<br /> function of pulse duration, current, polarity of electrode and<br /> properties of the workpiece and tool electrodes. This model<br /> has been helpful to calculate the optimal process parameters<br /> for obtaining optimum discharge energy.<br /> <br /> 7.<br /> <br /> Monitoring and control of the EDM process<br /> <br /> The EDM process parameters have to be monitored during the<br /> machining process so that the controlling of those parameters<br /> can be done to obtain the required response parameters. The<br /> main action of monitoring and controlling the process is to<br /> observe and measure process parameters to reduce the<br /> deviation of performance measures from the expected level.<br /> An adaptive control system for process monitoring,<br /> identification and control in the wire electrical discharge<br /> machining process has been developed by Yan [49]. It has been<br /> realized that the wire breaking has been controlled by<br /> adjustment of pulse interval of each pulse cycle of supply.<br /> Caydas et al. developed an adaptive neuro-fuzzy inference<br /> system model for the prediction of the surface roughness of<br /> machined surface using wire EDM process as a function of<br /> process parameters such as open circuit voltage, pulse<br /> duration and wire feed rate [50]. From the experimental<br /> results, it has been found that the proposed control system has<br /> improved the surface quality in EDM process.<br /> Yilmaz et al. introduced a used friendly intelligent system<br /> based on the knowledge of the skilled operators for the<br /> selection of the EDM process parameters for machining AISI<br /> 4340 stainless steel [51]. The system has been provided with a<br /> compact selection tool based on expert rules and enabled an<br /> unskilled user to select necessary parameters which lead to<br /> lower electrode wear rate and better surface quality. Zhou and<br /> <br />