Experimental Investigations into the Effect of Process Parameters on Performance Measures of Sink EDM Process: A Review Year 2011 to 2015 and Future Work

Experimental Investigations into the Effect of Process Parameters on Performance Measures of Sink EDM Process: A Review Year 2011 to 2015 and Future Work

Prabhu Basanna Choudri

Associate professor

Ph D Research Scholar, VTU-RRC, Visvesvaraya Technological University, Belgaum-590 018 Department of Mechanical Engineering

KLE Societys KLE College of Engineering and Technology, Chikodi-591 201, Belgaum, Karnataka, India

Dr. S. V. Gorabal

Principal

SK and SVMA College of Engineering and Technology, Laxmeshwar-582 116,

District- Gadag, Karnataka, India

AbstractSink Electrical Discharge Machining (Sink EDM) is a one of the important NTM process wherein electrically conductive work pieces are melted, vaporized (thermal erosion) by immersing in a dielectric fluid; tool electrode and work piece between the DC supply two poles either positive or negative and electric discharges takes place produces very high temperature in few micro seconds. It is widely used in defense, aerospace, automotive, micro systems, mould and die making industries. Recently researchers have discovered many ways to improve process parameters for achieving higher MRR, lower TWR and better surface quality. The paper reviews the works carried out from 2011 to till 2015. It reports on the research related to improve performance measures. The primary objective of analysis is to optimize the process parameters with the help of taguchi robust design methodology, design of experiment (DOE), analysis of variance(ANOVA), signal to noise ratio(S/N ratio, analysis of means (ANOM), face centered or rotational central composite design (CCD), scanning electron microscopy (SEM), X ray diffraction (XRD), response surface methodology (RSM), gray relational analysis (GRA), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), multiple regression analysis (MRA), mass spectrometry, optical microscopy techniques, fractional factorial design(FFD) with CCD and finite element analysis (FEM), etc. In end of the paper suggestions useful for future work has been indicated.

Keywords: Sink EDM, MRR, TWR, EWR, WR, SR, SF, OC, ROC, TOC, WLT, HAZ, HV

1. INTRODUCTION

   Todays industries are facing much challenges problems for machining advanced materials viz. W, Mo, Cb, hard and difficult to cut types. EDM is used to achieve higher MRR with lower TWR, greater SF and surface quality at lesser time with lower machining cost.

2. COMPONENTS, WORKING, PROCESS PARAMETERS AND PERFORMANCE MEASURES

   1. IMPORTANT COMPONENTS

      EDM consists of: DC Power supply unit; Dielectric fluid reservoir with pump, filter and control valve; Workpiece, work holder, work table; Tool electrode, electrode holder, table; Servo control tool feed mechanism.

   2. WORKING PRINCIPLE

      The tool and work directly connected between the DC supply two poles either positive or negative; both submerged in the dielectric fluid media. For maintaining the constant spark gap between anode and cathode, a servo feed mechanism is used. Figure 1 shows the principle of the process. When supply is given to the circuit, the voltage reaches at about 250 volts and electric discharges takes place between tool and work called spark gap, produces very high temperature in few micro seconds; the material melts, vaporizes and flushed away by the circulation of dielectric fluid.

      Figure 1: Principle of Die Sink EDM Process

   3. PROCESS PARAMETERS

      Two categories:-1) Electrical Pulse-on/off times, open circuit voltage, gap voltage, discharge current, peak current, average current, duty factor, discharge energy, electrode polarity, spark gap, pulse frequency, intensity factor, threshold, capacitance, etc.2) Non electrical- Work material, electrode material, electrode shape, electrode size, electrode properties, rotation of tool electrode, dielectric fluid, dielectric type and concentration of powder, flushing system and pressure, servo-head, dielectric level, feed rate, electrode diffusivity coefficient, electrode thermal conductivity and electrode melting point, etc.

   4. PERFORMANCE MEASURES

   Material removal rate (MRR, mm3/min); electrode wear rate (EWR) or tool wear rate (TWR); wear ratio (WR) or relative wear ratio or volumetric wear ratio; surface roughness (SR) or surface finish (SF); overcut (OC) or radial overcut (ROC) or tool overcut (TOC) or half taper angle or variation of the side overcut; white layer thickness (WLT) or recast layer (RCL); depth of heat-affected zone (HAZ) and micro crack density or micro hardness (HV).

3. LITERATURE REVIEW

   In this review paper, few selected research papers considered and primarily concerned with the different work materials, electrode-materials shape configurations, different machining input parameters and how these affect the performance measures.

   S. Prabhu et al. (2011) carried out study [1] to optimize input parameters viz. voltage, duration, current with Cu tool having dielectric fluid as multi wall carbon nano tube for machining INCONEL-825 by using taguchi technique, ANOVA, AFM analysis and found that there was an improvement in the SR and surface quality. S.P. Sivapirakasam et al. (2011) conducted [2] investigations on the effect of process parameters viz. duration, peak current, level of dielectric above the spark location, flushing pressure with Cu tool on high C high Cr tool steel by using taguchi

   method, plasma with gas chromatography, mass spectrometry and SEM-XRD techniques. They found that peak current, duration are very important parameters on concentration of breathing zone of aerosol. D. V. Ghewade et al. (2011) carried out study [3] on cutting of INCONEL 718 with a Cu tool using taguchis method and analyzed the effect of each parameter viz. pulse on time, gap voltage, peak current, duty cycle on the machining characteristics and predicted the optimal choice. They found that MRR mainly affected by current and voltage; EWR influenced by duty cycle, pulse on time; duty cycle, peak current have highest effect on ROC; half taper angle mainly influenced by, duty cycle, pulse on time. Promod K. et al. (2011) conducted study [4] on modification of surface using specially prepared PM compact tools by depositing a hard layer over the work surface of C-

   40 plain carbon steel considering process parameters viz. pulse on time, peak current, duty factor, compaction pressure, sintering temperature, composition for determining thickness of the deposited layer, rate of mass transfer, TWR, SR and MH by using L-16 OA taguchi DOE technique, ANOVA, SEM-XRD, optical microscopy techniques. They found that deposited layer of 3 to 785 m enriched with W and Cu tools with the WC formation and having at the hardest zone micro hardness of 9.81-12.75 GPa was deposited over the work surface. Shabgard M. et al. (2011) were carried out study [5] investigating the effect of input parameters viz. current, pulse on time for machining AISI H13 workpiece with round Cu tool by using taguchi, ANOVA, SEM techniques. The study found that higher pulse on time leads to an higher MRR, SR, WLT, depth of HAZ; higher pulse current leads to a sharp higher in the MRR, SR. The TWR lowered by the increase of pulse on time; increases by the higher in pulse current but a slight lower in WLT observed by an increase in current; by constant discharge energy level, higher current with low pulse on time leads to lower WLT, HAZ on work surface. Hao Ning Chiang el at.(2011) conducted study [6] to investigate the side overcut variation, bottom overcut variation, electrode dimensions, spark hole dimensions and machine positioing accuracy considering input parameters Viz. pulse on/off times, voltage, current with square cu tool on AISI D2 and AISI S2 tool steels by ANOVA analysis. They found that coupling effect was an primary factor to estimate the side overcut variation. Horacio T. S. et al. (2011) constructed [7] an model of inversion for establishing input parameters viz. pulse on/off times, peak current for predicting output performance characteristics viz. MRR, EWR, SR for machining AISI 1045 steel with prismatic Cu tool by using ANOVA and regression models. Bhola Jha et al. (2011) conducted [8] a study on overview of technology and research in electrode design and manufacturing in sinking EDM. He suggested number of ways to improve electrode design and devised various ways of manufacturing for optimizing performance measures and reducing manufacturing time with cost. They also concluded that EDM technology plays important role in design and manufacturing of electrode.

   Harpreet Singh et al. (2012) conducted a study [9] for investigating the influence of pulse on/off times on machining AISI D3 die steel using Cu, brass tools with

   dielectric as kerosene oil. They found that higher the MRR with higher in pulse off time; lower MRR with higher in pulse on time in case of brass electrode and decrease in Cu electrode. Lei Li et al. (2012) conducted study [10] to investigate the influence of methods of flushing and input process parameters with hexagonal shaped Cu bunched electrode for machining S45C carbon steel on performance measures by using experiments and simulations. They found that multi hole inner flushing bunched electrode suffers much greater peak current and results in higher MRR and high. Manish Vishwakarma et al. (2012) were carried out [11] investigation study to determine the process optimal factors viz. pulse on time, input current, duty cycle gap voltage, flushing pressure for machining AISI 4140 grade steel alloy rectangular plates on output responses through RSM using the technique of DOE, ANOVA based on the CCD. They found that higher peak current, duty factor results higher MRR; higher voltage higher MRR, similarly higher capacitance higher MRR; higher spark gap lowers MRR. Renjie Ji et al. (2012) conducted [12] investigations on effect of input parameters like electrode polarity, pulse on/off times, peak current, peak voltage and dielectric fluid on output performance measures viz. MRR, SR for ED milling of SiC ceramic with tool as steel-toothed wheel using three kinds of emulsions as the dielectric. Furthermore, the machined surface micro-structure was examined with SEM, XRD and EDS techniques. Ignacio Puertas et al. (2012) carried out [13] investigations on optimization of EDM conditions such as pulse duration, intensity, open-circuit voltage duty cycle, and flushing pressure in the processing of hot-pressed B4C and cobalt-bonded WC conductive ceramics with Cu tool on the quality of the manufactured products such as SR, volumetric EW and MRR by using FFD with CCD. S. P. Nipanikar et al. (2012) carried out study for optimizing [14] process parameters such as pulse on time, duty cycle, current, gap voltage on output responses on AISI D3 with Cu tool by using taguchis methodology, ANOVA. They found that higher the peak current higher MRR; MRR not much influenced by duty cycle. Higher the peak current higher EWR; very least influenced by gap voltage, the peak current has maximum effect on ROC and least affected by gap voltage.

   Nilesh M. Vohra (2013) was conducted study [15] investigating the optimum cutting parameters viz. pulse on/off times, current, gap voltage on performance measures viz. MRR, TWR, SR for machining SS 304 work piece using Cu, Al and brass tools by using taguchi method in combination on fuzzy logic control. He found that the gap voltage has highest effect on MRR. Jun Li et al. (2013) were carried out study [16] investigating modeling and analysis of micro-hole in die-sinking EDM process on Ti-6Al-4V, controlling input parameters like pulse on/off times and discharge current through RSM, DOE, ANOVA, CCD and found that TWR, WLT were much affected by discharge current; some difference unlike the others reported that WLT also affected by pulse off time; WLT can be minimized at lower pulse on time, discharge current and higher pulse off time. P. B. Wagh et al. (2013) were carried out [17] study investigating the influence of process parameters viz. pulse

   on/off times, discharge current, gap voltage on EN31 material with Cu tool through RSM, DOE, ANOVA based on the face CCD matrix. They found that SR much influenced by pulse duration and discharge current; choice of the electrical parameters depends largely on the material combination of the tool and work piece. Raghuraman S. et al. (2013) conducted study [18] investigating set of optimal input controllable variables viz. pulse on/off times and current on performance measures viz. MRR, TWR, SR for machining mild steel IS2026 work piece with Cu electrode by using L9 OA taguchi method, S/N ratio and GRA. They found that the taguchi GRA is being effective technique to optimize the machining parameters. D. C. Chen et al. (2013) conducted study [19] to find set of optimal input controllable variables viz. pulse on/off times, current and duty cycle for machining A6061-T6 aluminium alloy work material using Cu tool by using taguchi robust design methodology, analysis of means, ANOVA. They found that current and duty cycle factors important to determine the magnitude of SR. A CuZn40 brass alloy specimen is machined using the optimal process parameters and were found to have a lower mean SR than the A6061-T6 aluminium alloy workpiece. A. M. Nikalje et al. (2013) conducted study [20] to investigate the effect of input controllable variables viz. discharge current, pulse off time and pulse on time for optimizing performance measures viz. MRR, TWR, relative WR, SR for machining MDN 300 steel with Cu tool by using taguchi method, SEM technique. They found that high pulse on time, high current gave SR with more craters, debris globules and micro cracks than that of lower current and lower pulse on time. Shailendra Kumar Singh et al. (2013) were conducted [21] study to optimize input controllable variables viz. current, pulse off time, pulse on time for machining Ti- 6AL- 4V alloy with Cu tool using taguchi robust design methodology, S/N ratio and ANOVA and it shown that SR much affected by followed by pulse off time and least affected by pulse on time; duty cycle influence to increase in TOC initially but late decreased. They found that duty cycle was most important factor influences TOC followed by discharge current, pulse on time; least affected by gap voltage. Shivendra Tiwari (2013) was conducted [22] study investigating set of optimal input controllable variables viz. pulse on/off times, peak current by conducting three sets of trial runs with constant servo-head and positive polarity for Cu tool with commercial grade EDM oil on MS work material for determining MRR and TWR. The discharge current was applied in different steps in positive mode. Singaram Lakshmanan et al. (2013) were [23] performed experimental investigation for correlating the process parameters such as current, pulse on/off times, voltage for machining EN 31 tool steel workpiece using Cu tool through RSM using rotatable CCD, ANOVA. They estimated the optimum machining conditions for better MRR. Rao P.S et al. (2013) conducted study [24] investigating the influence of process parameters viz. current, voltage, duty cycle, servo for machining AISI 304 stainless steel with rectangular Cu tool by applying mixed factorial DOEs and MRA. They found that MRR influenced by servo, duty cycle, current and voltage; TWR influenced by current, servo and duty cycle; SR influenced by current; MH is influenced by servo in the decreasing order of importance of parameters. Harpreet singh

   et al. (2013) conducted a study [25] on cryogenic and non cryogenic electrode with pulse on/off times as parameter on machining of steel. Cryogenic treatment is used for increasing MRR and loering TWR and found that TWR is decreased in both cryogenic treated and non cryogenic cu electrodes with increase in pulse on time; increase in pulse off time increases TWR and TWR is very less in cryogenic treated electrode as compared to non cryogenic treated tool. Mohammed S. Rasheed, (2013) carried out study [26] investigating comparison study based on micro-holes produced by micro-EDM with LBM for MRR, surface quality of micro-holes with tungsten and brass electrodes by using taguchi method, ANOVA, SEM and optical microscopy techniques. He found that the performance measures of the processes mainly depends upon the machining parameters; When surface quality is not a criterion, LBM can be used for higher MRR; finally for higher MRR with good SF, the positive features of processes can be used to make hybrid process.

   Abhishek Gaikwad et al. (2014) conducted [27] research work investigating the influence of process parameters viz. pulse on/off times, current, fluid pressure for machining SS 316 workpiece using Cu electrode with taguchi technique, DOE, ANOVA. They found that increasing pulse off time followed by current increases MRR and is least affected by fluid pressure. EWR decreases with increasing current followed by pulse off time and is least affected by fluid pressure. Vikasa et al. (2014) conducted study [28] investigating the influence and optimization of process parameters viz. pulse on/off times, current, voltage for machining EN19 and EN41 work materials with Cu tool using taguchi method. They found that the discharge current was having larger impact on the MRR. T. Roy et al. (2014) were carried out study [29] investigating the influence of input controllable variables viz. pulse duration, current, duty cycle and voltage based on TOC on SS 304 grade work material through L9 OA taguchis robust design technique, S/N ratio and ANOVA. They found that TOC decreases initially and then increases by gradual increase of the pulse on time; the duty cycle factor causes an increase in TOC initially but decreases afterwards. They found that TOC affected much by duty cycle followed by current, pulse on time; TOC least influenced by gap voltage. Brajesh Kumar et al. (2014) described [30] optimization of process parameters viz. pulse on time, current, voltage on SR of CFRP composite material with copper tool by using parametric design of Taguchi methodology, S/N ratio, and ANOVA. They found that the discharge current was the most influential factors on the SR. N. Radhika et al. (2014) conducted study [31] investigating on optimization input controllable variables viz. pulse on time, current, pressure for machining aluminium hybrid composites on performance measures by using Taguchi method, S/N ratio and ANOVA. They found that SR much affected by peak current followed by pulse on time, flushing pressure; flushing pressure followed by peak current and pulse on time gave higher MRR and pulse on time followed by peak current, flushing pressure affects much on TWR. N. Annamalai et.al (2014) conducted study [32] on investigation and modeling of input

   controllable variables viz. current, pulse on/ off times for machining AISI 4340 steel with electrolytic Cu electrode tool by using Box Behnken design of RSM, ANOVA technique. They found that higher peak current much higher the MRR and SR; higher pulse on time higher the MRR and SR; whereas there was no much impact when pulse off time is increased. Viral B. Prajapati et al. (2014) were carried out study [33] of review on optimization of input controllable variables viz. pulse on/off times and current for machining AISI SS 410 work material with Cu electrode and EDM oil as dielectric for improving performance such as MRR, SR using taguchi DOE procedure with full factorial design and ANOVA method. Shashikant et al. (2014) were carried out

   [34] investigation on optimization of input controllable variables viz. pulse on/off times, current, voltage for machining EN19 workpiece with electrolytic Cu tool by using RSM, ANOVA. They found that pulse off time, current, voltage and the interaction terms were very important where as the pulse on time least effect on MRR. Vishal J Nadpara et al.(2014) were carried out [35] work on optimization of input controllable variables viz. pulse on time, current, duty cycle, voltage and dielectric flow rate; their interactions on performance measures for machining AISI D3 tool steel with graphite tool electrode using Taguchis experimental design method. They found that the MRR mainly influenced by peak current and very less influenced by duty cycle; peak current influences much on EWR and very least affected by gap voltage. Chandramouli S et al. (2014) conducted [36] investigating the influence and optimization of input controllable variables viz. pulse on/off times, current 0n performance measures viz. MRR, TWR, SR for machining RENE80 nickel super alloy workpiece with aluminum tool electrode by using Taguchi method, ANOVA and revealed that proper selection of input parameters is very important. Shishir M Shrivastava et al. (2014) has studied
   [37] the influence of input controllable variables viz. pulse on/off times, current, tool shape configurations viz. circular, square, triangular, rectangular, and diamond cross sections of Cu, brass and graphite electrodes on the machining characteristics. This review was based on various studies carried by various researchers. They found that tool electrode with negative polarity gave better machining performance and also observed that pulse on/off times, peak current factors mainly responsible for higher MRR; whereas peak current, pulse on time mainly influence TWR; peak current influences SR; higher MRR with lower TWR achieved by circular tool shape followed by above said other cross sections. Dhirendra nath mishra et al. (2014) were carried out study [38] on EDM containing general introduction, principle of EDM, principles of operation, types of EDM, important parameters of die-sinking EDM, wire cut EDM, major components in wire cut machine, principle of WEDM, important parameters of WEDM, modelling of material removal and product quality, specification on EDM, dielectric fluid- functions, properties, requirements, types, selection, tool materials- characteristics, types, selection, comparison of die-sinker and wire-cut machines, flushing methods, applications of EDM and WEDM, advantages of EDM and WEDM, disadvantages of EDM and WEDM. They concluded that EDM were used effectively for machining of

   complex geometries, process is independent of material properties, can result in high accuracy. Varinder Khurana et al. (2014) were carried out study [39] investigating effect and interaction between input controllable variables viz. pulse on/off times, current, voltage using tubular copper electrode with internal flushing on the response variables viz. MRR, SR of AISI-D2 high-carbon, high-chromium steel through L9 OA Taguchi technique, S/N ratio and ANOVA. They found that individual parameters like discharge current and voltage are more influencing than other factors viz. pulse on/off times. Arumugam Kadirvel ET AL. (2014) were carried out study [40] investigating optimization of the die sinking micro-EDM process parameters viz. voltage, threshold, capacitance, feed rate for multiple performance characteristics such as higher MRR, lower TWR and minimum SR by using L16 OA Taguchi method, S/N ratio, ANOVA and GRA. They found that capacitance and the gap voltage were the most significant controlled factors influencing the performance of the machining process. Sushil Kumar Choudhary et al. (2014) were carried out study [41] on recent advancements in various aspects of EDM that reflect the states of the art in these processes are presented in this review paper. Researcher worked on enhancement of MRR, reduction of TWR; improve Surface Quality by experimental investigation. Various EDM approaches employed for increase of efficiency, use of gas instead of oil electrolyte, powder mixed EDM. The process also plays a important role in automotive, aeronautic industry, optical, medica, Jewelry and making a various mechanical components in manufacturing industries. Abhijeetsinh V Makwana et al. (2014) were carried out [42] detailed literature review and analysis of various process parameters of EDM process by using different electrode shapes on the performance. In this research they used taguchis method for DOEs with three input parameters and their three levels of experiments with kerosene diluted with water as dielectric. They observed the main influences of input factors on MRR, TWR, SR and cavities. Present paper proposed to select carefully parameters for machining cavities with multiple and intricate shaped electrodes. They found that higher MRR is achieved with the copper. Bharat Raj Bundel et al. (2014) were carried out study [43] investigating TWR in the form of weight and length of electrode was controlling different input controllable variables such as pulse on/off times, current in die-sinking EDM on D-3 die steel (HRC-58) with electrolytic cylindrical Cu tool. They found that the increase in current supply as well as pulse on time and pulse off time increases TWR; decrease in current supply but at particular lower current and pulse on/off times decreases TWR where SF was also good. They found that round copper tool can be used for longer period without redressing.

   S. Barman et al. (2015) were carried out [44] investigation on surface quality, shape, size and elemental characterization of blind micro-holes in micro EDM by adopting a destructive method having high aspect ratio. They also studied deformation of electrodes and tool profiles. Avdesh Chandra Dixit et al. (2015) carried out study [45] investigating the influence of input controllable variables viz. pulse on/off times, current, pressure while machining of AISI

   D3 material fitted with a Cu electrode by using Taguchi method and was found that the peak current influenced much on MRR, other factors have very less effect; peak current and pulse on time infulenced much on TWR and, fluid pressure has no effect it. J Jeevamalar et al. (2015) were carried out

   [46] review study on die sinking EDM parameters and concluded that machining done on steel materials, EN series, Ti-6AL-4V, S45C, SiC, B4C, WC-Co, Al2O3+Ti and Inconel 718. Copper often used as a tool in various shapes and also found that pulse on/off times, voltage and current were the primary electrical parameters; dielectric fluid, flushing pressure, electrode rotation are the non electrical parameters which were considered in EDM. Acc. to them most of the much work carried out to improve the performance measures viz. MRR, TWR, WR and SF and many research works have been carried out by using optimization techniques like, RSM, ANNOVA, Taguchi, SEM, CCD, GRA and MRA. Bai Shao et al. (2015) were carried out [47] investigation on electro- thermal modelling of the crater formation incorporating realistic machining conditions in micro-EDM. They applied input controllable variables viz. pulse on time, pulse energy distribution fraction and pulse energy with model and solved by using the FEM. They found that pulse energy distributed to the anode, and to the cathode, average error of the crater radius and of the cater volume. Sharma et al. (2015) were carried out [48] study to investigate the WR of SKD11 steel material in titanium abrasives mixed EDM process considering input factors viz. pulse on time, peak current, gap voltage, polarity, concentration of abrasive with Cu electrode tool plus dielectric fluid as EDM oil by using L18 OA Taguchi method, ANOVA technique. They found that WR is less at positive polarity in comparison of negative polarity, pulse on time decreases the WR and increases the MRR and also enhances the productivity of SKD11 steel material and the addition of abrasives particles in EDM oil has also put the effect on wear ratio of material. M. A. Md Ali et al. (2015) were carried out [49] study to investigate the performance of copper, copper tungsten, graphite and brass electrodes on performance measures for machining aluminium alloy LM6 (Al-Sil2) considering process parameters viz. voltage, pulse on/off times, peak current by using L9 OA Taguchi technique and ANOVA. They found that graphite electrode produces the highest MRR with low SR as compare to others electrodes. Meanwhile, copper generates high SR and low EWR with copper tungsten. Brass tool shown low ability to withstand of spark energy that produced highest EWR. Thus, it showed that output quality of material characteristics of workpiece mainly influenced by thermal conductivity and melting point of electrode materials. Dr. Sanjeev Saini et. al. (2015) were conducted [50] investigating optimization of input controllable variables viz. pulse on/off times, discharge current on EN31, DS P20 and HCHC D2 workpieces with U- shaped copper cathode tools of dia. 8mm and 10mm having side flushing by using Taguchi strategy, S/N ratio and ANOVA to identify the optimum cutting parameters and found that different combinations of input controllable variables were needed to have greater MRR and better SF. Amoljit S. Gill et al. (2015) were carried out [51] study to investigate the phenomenon of H11 hot die steel surface

   alloying by considering six input parameters using copper- tungsten tool by using L18 OA Taguchi method, DOE, ANOVA, SEM-XRD and EDS to achieve the high SF and MH. They found the on the machined surface by XRD technique, there was a formation of cementite and tungsten carbide. Surinder et al (2015) were carried study [52] investigating WR of EN-8 steel with copper too in abrasive mixed sinking EDM process by choosing the process factors such as pulse on time, current, polarity, voltage and concentration of titanium abrasives in EDM oil using Taguchi method, S/N ratio, ANOVA and found that WR at positive polarity is less than the WR at negative polarity, high peak current decreases the WR, gap voltage increases WR decreases and pulse on time, abrasives concentration produce very little effect on WR. F. Kolahan et al. (2015) were carried out [53] investigations to optimize input controllable variables viz. pulse on/off times, current, duty factor, voltage for machining AISI 2312 hot work steel alloy by using L36 OA Taguchi method, S/N ratio, ANOVA and GRA. The three performance characteristics are combined into a single objective using GRA to minimize TWR and SR and maximize MRR. Ahmed Raza Khan et al. (2015) were carried out [54] work investigating influence of different types of electrode materials on quality of blind holes machined in AISI P20 work material in term of SR, diameter error and axial error considering three current conditions, i.e., 5 amp, 8 amp and 10 amp via die sinker EDM process and found that graphite as an electrode provides the most suitable values overall for most of the stated performance measures among all the electrodes. Copper provides the best SF for closely followed by graphite; graphite was the best electrode material for dimensional accuracy and provides the least values of the errors. M. Priyadarshini et al. (2015) conducted study [55] investigating the parametric optimization of EDM for machining Ti-6Al-4V alloy with copper electrode for desired responses using L25 OA Taguchi method, ANOVA and GRA. They found that for achieving higher MRR and greater SF, various combinations of optimal input controllable variables were needed. Sumit Raj et al. (2015) were carried out [56] investigations on optimization and prediction of MRR in die sinking EDM of EN45 steel tool work material considering input controllable variables viz. pulse on/off time, current and voltage using L27 OA Taguchi method, ANOVA. They found that more significant factor for MRR were peak current and pulse off time. Goran Mijuskovic et al. (2015) carried out [57] study investigating the effect of input controllable variables viz. width of cut, depth of cut and feed on deflection of tool in micro milling of graphite electrodes using measuring technique laser-based one. The results showed that RSM of deflection of tool used to determine the process behavior across a useful cuting conditions range. S. Bharathi Raja et al. (2015) carried out [58] study investigating the optimization of input controllable variables viz. pulse on time, current on performance measures viz.SR, machining time for machining hardened die steel by using taguchi method, firefly algorithm with development of mathematical model. They predicted the values of actual machining time and SR. F. Zhang et al. (2015) were carried out [59] study investigating the time integration effect of the expanding

   spark for anode erosion with water as dielectric by developing FEM based thermal model for predicting craters and MRR. They found the very nearer agreement with experimental results. G. K. Bosea et al. (2015) were carried out [60] study investigating effect of input controllable variables viz. pulse on/off times, current, spark gap on MRR, SR, OC using Cu tool of square shaped for machining of AISI H13 tool steel with lateral flushing by using Taguchi methodology, ANOVA, S/N ratio, GRA. They focused with multi criteria decision making and found that gap current influenced much on MRR; pulse on time pulse on time influenced much on SR. Kulkarni et al. (2015) were carried out project [61] to investigate the effect of input controllable variables viz. pulse on/off times, current for machining of Al- SiC MMC work material with copper-tungsten tool by using RSM approach, CCD and ANOVA. They found that MRR mainly influenced by pulse on time and current; TWR mainly influenced by pulse off time and current. M.H. Joudiv et al. (2015) were carried out [62] study investigating effect of thermal diffusivity coefficient of tool material on TWR in the EDM process using copper alloy, copper-iron alloy, aluminum alloy and graphite as tools and AISI H13 as work piece by using LevenbergMarquardt technique. They found that increase of thermal diffusivity of tool material decreases TWR; tool electrodes with low thermal diffusivity coefficient, increase of current, increase of pulse on-time significantly increased TWR. L. Selvarajan et al. (2015) were carried out [63] study on optimization of input controllable variables viz. pulse on/off times, current, spark gap, pressure on MRR, EWR, circularity, cylindricity, and perpendicularity for machining inter-metallic base MoSi2-SiC composites with copper tool by using L18 OA Taguchi methodology, ANOVA and GRA. They found that accuracy and precision mainly influenced by pulse on time, current, dielectric pressure. Banh Tien Long et al. (2015) were carried out [64] investigating the effect of varying concentrations of titanium powder by keeping constant input controllable variables viz. pulse time, current, voltage on MRR, SR and topography surface while machining H13 steel in powder mixed EDM with graphite electrode in rough machining by using Taguchi method, ANOVA, SEM, EDS and XRD techniques. The results revealed that the concentration of Ti powder has a high influence on MRR, SR and topography surface. Mona

   A. Younis et al. (2015) were carried out [65] study investigating the effect of electrode materials viz. Dura graphite 11 and Poco graphite EDMC-3 to avoid resulting residual stresses, SR and cracks resulted during EDM on DIN 1.2080 and DIN 1.2379 tool steels by choosing different machining methods such as rough, medium, and soft using Taguchi methodology, ANOVA, SEM, EDS, XRD techniques. They found that the Dura graphite 11 upon DIN 1.2379 exhibits more surface cracks, POCO Graphite EDMC-3 electrode results higher residual stresses. Harshit K. Dave et al. (2015) were carried out [66] study on influence of input controllable variables viz. pulse on/off times, current, gap voltage, tool electrode scanning speed, aspect ratio while cutting of micro-slots by using Taguchis method, DOE, ANOVA. They found that over-cut mainly influenced by current; TWR mainly influenced by scanning speed of tool electrode. Jyoti Bhaghi, et al. (2015) were

   carried out [67] review studies on influence of input controllable variables on various performance measures. They found that there are a number of process parameters which must be selected correctly for obtaining sound products. S. Chakraborty et al. (2015) were carried out [68] a literature review on use of dielectric fluids, their effects. They found that utilizing the removal phenomenon with dielectric; working dielectric fluid played a very major role affecting MRR and properties of the machined surface by choosing the right dielectric fluid is critical for successful operations. T. Muthuramalingam et al. (2015) were carried out [69] the study and discussed about having an overview of the EDM process, modeling, effect of input controllable variables viz. electrical parameters, pulse shape, discharge energy on MRR, SR, TWR. They also discussed about controlling the electrical process parameters and empirical relationships between and optimization of process parameters. From the review results, they found that the electrical parameters can improve process effectiveness. Dignesh Thesiya et al. (2015) were carried out [70] study investigating the influence of input controllable variables viz. pulse on/ off times, peak current, servo voltage on performance measures viz. HAZ, RLT while machining of titanium alloy Ti-6Al-4V using copper, graphite electrodes with positive polarity through L18 OA Taguchi technique of DOE, SEM. They found that gap voltage and peak current are also responsible for RCL formation to some extent. In Titanium alloy (Ti-6Al-4V), higher SR and less RCL were found during low voltage and peak current while machining using Cu tool; this condition is vice-versa for graphite tool. Makwana A.V. et al. (2015) carried out [71] study investigating the influence of input controllable variables viz. pulse on/off times, current with various tool electrode shape configurations on machining AISI 316 stainless steel workpiece with pure Cu electrode by using L9 OA based on the Taguchi method, DOE, ANOVA, SEM. They found that greater MRR greater MRR possible only by pulse on time, current, optimum tool shapes; lower EWR and better SR is circular followed by rectangular, triangular sections. Harmanpreet et al. (2015) were carried out [72] study for the optimization and improvement of various input controllable variables viz. pulse on time, pulse off time, current, spark gap, duty cycle by using Taguchi method. They worked for minimizing TWR, SR; maximizing MRR. Review revealed that metal cutting by EDM and WEDM is generally assessed on the basis of MRR, TWR, SR; some of the important factors that influence the machining characteristics were pulse on time, pulse off time, duty cycle, dielectric flushing pressure, peak current, voltage.

4. CONCLUSION AND SUGGESTIONS

   CONCLUSION

   The review of research trends has been taken for last 5 years till the year 2015. From the above reviews conclude that,

   • Most of the EDM work that has been carried on Steel materials(C-40, MS IS2026, MDN 300 steel,SKD11, DSP20, H13, AISI -D2,D3, S2,1045 steel, 4140, SS 304, SS316 ,SS410, 4340, 2312),EN series (EN19, 31, 41, 45),

     Ti-6AL-4V, S45C, SiC, B4C, WC-Co, Al2O3+Ti, Al-

     Sil2, A6061-T6 aluminium alloy, CuZn40, Inconel-718, 825, CFRP composite material, RENE80 nickel super alloy, hybrid Al-SiC MMC, MoSi2-SiC composites.

   • Graphite, brass, copper (prismatic, round, square hexagonal, tubular, U shaped), copper alloy, copper-iron alloy, aluminium, aluminum alloy, tungsten, gun metal, copper-tungsten, silver- tungsten, cryogenic and non cryogenic treated, Al-Cu-Si-TiC powder metallurgy Composite used as a tool materials, copper is often used in various shapes and found cylindrical as good one.

   • Pulse on/off times, pulse/peak currents, voltage are the primary electrical parameters and dielectric fluid (kerosene, commercial grade EDM oil, emulsions, carbon nano tube), pressure, tool rotation are the non electrical parameters which are considered and very few have considered parameters like electrode polarity, electrode shape configuration(square, triangular, rectangular, and diamond crss sections) intensity factor, ,duty cycle, servo-head, dielectric level, composition, compaction pressure, sintering temperature, spark gap, threshold, capacitance, feed rate, electrode diffusivity coefficient, thermal conductivity and melting point of electrode.

   • Most of the researches carried out to improve performances measure viz. MRR, TWR, EWR, Volumetric EW, relative WR, SR, SF and very few for OC (overcut), TOC (tool overcut), ROC, dimensional precision, surface quality, RCL or WLT, depth of HAZ, micro cracks or HV, half taper angle, mass transfer rate and variation of the side overcut.

   • Many research works have been taken by the optimization techniques like Taguchi, DOE, S/N ratio, RSM, ANNOVA, CCD, SEM, XRD, CCD, GRA, Micro Crack by AFM technique, XRD,EDS, regression models, Multiple Regression analysis (MRA), mass spectrometry, optical microscopy techniques, analysis of means , fractional factorial design (FFD) and FEM.

     SUGGESTIONS USEFUL FOR FUTURE WORK

     There is an urgent need to work on effect of process parameters on performance measures by keeping into consideration the following problems:

   • The experimental investigation of optimal machining parameters for hot die steels viz. H11, H13 is very essential, it is one advanced material used in applications of extreme loads and response characteristics.

   • Urgent need to recognize important cutting conditions viz. pulse on/off times, duty factor, current, voltage, electrode polarity, spark gap, and other machining parameters like electrode material/shape/size/properties, dielectric fluid, dielectric type, flushing system and pressure, etc must be selected for optimizing performance measures viz maximizing MRR, SF and minimizing TWR, WR, Over Cut, WLT, HAZ, MV. Now here is a need to carry out systematically research work

   by the techniques like one factor at a time (OFAT) approach, Taguchis methodology, SEM-EDS, XRD, Micro Crack by AFM, RSM with CCD, GRA, Single response process parameters optimization using RSM and desirability function, Multi-objective process parameters optimization using desirability function in conjunction with RSM and using Taguchis technique with utility concept. The efforts should be made to investigate experimentally the influence of input controllable variables on performance measures especially with a cryogenic cutting environment and the weightages to be assigned to various characteristics in models of multi- response optimization should be based upon requirements of industries.

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