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A review on influence of electrical process parameters in EDM process

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(BQ) The present study discusses about having an overview of the EDM process, modeling of process parameters, and influence of process parameters such as input electrical variables, pulse shape, and discharge energy on performance measures such as material removal rate, surface roughness and electrode wear rate.

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Nội dung Text: 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 />
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