Conventional Electrical Discharge Machining Research Articles

Improving EDM performance by adapting gap servo-voltage to machining state

Electrical discharge machining (EDM) has become popular after its development over 70 years, but its potentialities have still not yet been fully exploited. That is because EDM process is so complicated that it seemed impossible to form a closed-loop control of EDM process because of lack of an efficient quantitative description of the process. In this case, EDM performance which is composed of machining ability and machining rate has been stagnant for decades. In this paper, a close-loop control system for EDM was built to adapt an EDM crucial parameter, gap servo-voltage, to the timely varied machining states in machining for the purpose of improving EDM performance. To this end, the discharging pulses in the gap between electrode and work-piece were firstly discriminated from sampled signals of gap voltages and currents, and then arcing ratio was calculated to be a control index representing machining state. Gap servo-voltage was taken to be a control variable corresponding to the index since it is the sole parameter among process parameters that can immediately change machining situation by physically changing gap distance which is proportion to gap servo-voltage, and is thus the most efficient parameter to modify machining state. Through adjusting gap distance by adaptively regulating gap servo-voltage, arcing ratios were forced to follow an arcing ratio expectation closely with restricted variations around the expectation. Thus, both an efficient and stabilized machining can be achieved simultaneously. Comparable experiments demonstrated that the potentiality of the conventional EDM Tool assisted by the established adaptive gap servo-voltage control system has been exploited and EDM performance was enhanced greatly that machined depth had been improved nearly 3 times from the conventional EDM, and more than 2 times than the EDM assisted by another adaptive electrode-discharge-time control system; and the machining rate was also much faster than those of the other two.

Surface Roughness and Surface Topography of Inconel 718 in Powder Mixed Dielectric Electrical Discharge Machining (PMEDM)

In high speed EDM, maximum material removal rate (MRR) is a desirable to increase productivity rate and reducing production cost to the need of industry. However, the surface finish of the machined surface also cannot be neglected since it related to product quality and safety factor especially when to cut difficult to machine material such Inconel 718, which is widely used in aerospace industry. Surface roughness as one of the surface integrity criteria was choose as a response in this research. High discharge current from 20A to 40A, longer pulse on-time (pulse duration) from 200µs to 400µs and the different concentration of the nano Alumina powder were selected as the main parameters, respectively. The effect of powder mixed dielectric in EDM performance in terms of surface roughness was evaluated. The dielectric circulating system known as High Performance Electrical Discharge Machine (HPEDM) was attached to the conventional EDM machine to run the experiments involving powder mixed dielectric. The experiment results shows that, the highest peak current deteriorated the surface roughness. The surface roughness, Ra was increased with the increasing of the peak current. The result also shows that an increasing of the pulse duration the surface roughness was slightly improved. It is observed that, the value of Ra was closely related to the surface topography characteristic of the machined surfaces and directly depends on the applied discharge energy. There is no improvement in surface roughness when powder additive was mixed in a dielectric fluid.

Effect of deep cryotreated tungsten carbide electrode and SiC powder on EDM performance of AISI 304

Powder mixed electric discharge machining (PMEDM) is a further advancement of conventional EDM process in which electrically conductive powder is suspended in the dielectric fluid to enhance the material removal rate (MRR) along with the surface quality. Cryotreatment is introduced in this process for improving the cutting tool properties as well as tool life. In this investigation, EDM is performed for the machining of AISI 304 stainless steel using cryotreated double tempered tungsten carbide electrode when SiC powder is suspended in the kerosene dielectric. The influence of process parameters viz. pulse on time, peak current, duty cycle, gap voltage and powder concentration on tool wear rate (TWR), surface roughness (Ra), and MRR has been studied. Metallographic analysis was carried out for the machined surfaces. By the addition of powder concentration and cryotreated double tempered electrode, significant improvement in the machining efficiency has been found out. When cryotreated electrode used MRR, TWR and Ra decreased by 12%, 24% and 13.3%, respectively and when SiC powder used MRR increased by 23.2%, TWR and Ra decreased by about 25% and 14.2%, respectively.

Electrical Discharge Drilling of Metal Matrix Composites with a Hollow Hexagonal Electrode

Aimed at the problems of the conventional electrical discharge machining of particle-reinforced aluminum matrix composites (PR-AMCs), a novel hollow hexagonal electrode has been employed and the influence of the electrode structure on the MRR has been investigated. In this study, 3-D model of the working medium fluid flow field has been established to study the structure effect of the hexagonal electrode. And a lot of single factor comparison experiments are carried out between the hexagonal hollow electrode and round hollow electrode. The effects of peak current, duty cycle, machining rotation speed and pulse width on the MRR of work-piece has been studied respectively. The Response Surface Method (RSM) is adopted to imitate the law of machining surface of the hexagonal hollow electrode. The theoretical and experimental results both show that the MRR of the work-piece can be improved remarkably by using a hexagonal hollow electrode. Moreover, according to the RSM, the maximum MRR of machining AMCs of the hexagonal hollow electrode is 225mm3/min, while the optimum combination of parameters that the peak current (12A), the duty cycle (0.75), machining rotation speed (900 r/min) and flushing pressure (1.5MPa) is exerted.

On the design and application of hybrid electrical discharge and arc machining process for enhancing drilling performance in Inconel 718

In recent years, Inconel 718 is widely used in industries like aerospace, oil and gas, and automobile due to their unique combination of hardness, strength, temperature, and corrosion resistance properties. However, these materials pose challenges during conventional machining due to their high work hardening tendency, poor thermal conductivity, and chemical affinity towards the tool material. Consequently, rapid tool wear during the machining of Inconel 718 results in poor productivity. To overcome these issues, a non-contact hybrid electrical discharge and arc machining (HEDAM) process has been developed to machine such difficult-to-cut materials. Firstly, the design and development of the HEDAM circuit has been discussed. Subsequently, the working principle of the newly developed process has been studied followed by its performance comparison with the conventional EDM process. In addition, the material removal mechanism has also been discussed in detail. Finally, experimental results were reported, where holes were drilled using the developed HEDAM process. The HEDAM process has exhibited significant improvements in terms of material removal rate (MRR) which is around 12 times higher and electrode wear ratio (EWR) that is half when compared to conventional EDM. This high performance HEDAM process resulted in successful and efficient drilling of Inconel 718.

Multi-channel aerosol dielectric electrical discharge machining ablation based on discrete electrode

The electrical discharge machining (EDM) ablation processing energy comes from the chemical energy released by metal combustion, which is much higher than in conventional EDM. In singular pulse voltage, only one discharge channel induces and activates metal substrate. Thus, the processing energy is concentrated, which impedes the improvement of material removal efficiency and workpiece surface quality. Multi-channel EDM ablation in aerosol dielectric is proposed in this study. Multi-channel discharge induces multi-spot ablation, which not only expands the scope of the ablation region and improves the machining efficiency of EDM ablation, but also disperses the discharge energy and enhances the surface quality of EDM ablation. The discrete electrode in which the method is based contained multiple copper tube electrodes. Each electrode was electrically insulated and connected to the pulse generator through a resistance. It generated multi-channel discharge in singular pulse voltage. In this study, the mechanism of multi-channel discharge was elucidated, and the machining characteristics of multi-channel aerosol dielectric EDM ablation were evaluated. On the basis of the results of the experiment by using Cr12 die steel as the workpiece, it was concluded that relative to that in aerosol dielectric EDM ablation, the material removal rate in multi-channel aerosol dielectric EDM ablation was improved by 92%. This rate was 3.12 times higher than that obtained in multi-channel inner jetted EDM and nearly 10 times higher than that in inner jetted EDM. The surface quality was improved as well.

Comparison of Gas Assisted Hybrid EDM, Rotary EDM and Conventional EDM Processing of High Carbon High Chromium Die Steel

The high carbon high chromium die steel is most widely used in various industrial applications. However, effective machining of high carbon-chromium die steel is extremely difficult due to its high hardness and stiffness. In the present work, comparative analysis of Gas Assisted Hybrid EDM (GAHEDM), Rotary EDM (REDM), and Conventional EDM processes have been done with respect to process responses like electrode wear ratio (EWR), material removal rate (MRR), and surface roughness (SR). Experimentation has been done to the study influence of process factors like discharge current, pulse on time, duty cycle, tool rotation and discharge gas pressure on MRR, EWR and SR. Further, from a comparative study, it has been observed that high MRR, low EWR and low SR are obtained in GAHEDM process in comparison of REDM and EDM processes. Analysis of surface morphology reveals that the formation of recast layer and cracks on the surface are fewer in number on work piece machined by GAHEDM process with respect to specimen machined with REDM and EDM processes. The results show that the use of compressed helium gas in GHEDM process has a positive impact on the machining performance. This process may be used for industrial machining operation.

Analysis and optimization of process energy consumption and environmental impact in electrical discharge machining of titanium superalloys

Abstract Process energy consumption and environmental impact have been considered as important performance indicators for the sustainable electrical discharge machining (EDM) process. This paper presents a sustainable manufacturing technique known as magnetic field-assisted EDM (MF-EDM) to enhance the machine characteristics for the purpose of reducing the energy consumption and environmental hazards of the conventional EDM machining Ti6Al4V. Firstly, the principles of energy consumption, machining noise impact, and MF-EDM are respectively described. Thereafter, a set of experiments is carried out to investigate the effects of the main process parameters on the electrode wear rate ( E W R ), energy consumption ( S E C ), and environmental impacts (including carbon emission and machining noise) extensively, using the Taguchi method. The results indicate that the pulse on time (ranging from 100 to 200 μs) and magnetic field intensity (ranging from 0.05 to 0.10 T) are the two most significant factors affecting the MF-EDM sustainable manufacturing performance. Furthermore, the optimal process parameters were obtained by optimizing the MF-EDM process economically and environmentally using the modified non-dominated neighbor immune algorithm (M-NNIA) method. Compared to the minimum outputs of the experimental results, the optimal solutions of the E W R , S E C , and machining noise were significantly decreased, by 18.30%, 61.43%, and 20.95%, respectively. Therefore, it can be concluded from the above research that the proposed hybrid MF-EDM technique offers significant advantages and potential for applications in the sustainable manufacturing field.

Effect of using SiC powder-added dielectric media during electro-discharge machining of Inconel 718 superalloys

Inconel 718 is a nickel-based superalloy widely applied in aerospace, automotive and defense applications. Low thermal conductivity, extreme high temperature strength, high work-hardening characteristics make them ‘difficult-to-machine.’ In order to improve EDM performance on Inconel 718, powder-mixed electro-discharge machining is reported herein. PMEDM is carried out by mixing SiC powder in the dielectric media in consideration with varied peak discharge current. As compared to conventional EDM, the morphology and topographical features of the machined surface including surface roughness, crack density, white layer thickness, metallurgical aspects (phase transformation, crystallite size, micro-strain and dislocation density), material migration, residual stress as well as micro-indentation hardness, etc., are studied. Additionally, effects of peak discharge on PMEDM performance features, namely material removal rate, tool wear rate, surface roughness, surface crack density, white layer thickness, are discussed and compared with conventional EDM.

Magnetic Field Influence on Surface Modifications in Powder Mixed EDM

The present study deals with the optimization of parameters to check the effectiveness of thermoelectric machining of aluminum based SiC reinforced composites. Here, hybrid ED machining of Al-SiC metal matrix composites (MMCs) is investigated in magnetic field incorporated conventional Electrical Discharge Machining (EDM). The input processing parameters, such as pulse-on/off duration, current were assessed to analyze their outcome on the response parameters in terms of material erosion rate (MER), microhardness (MH), surface roughness (SR) and recast layer formation. The experimental results witnessed decrease in microhardness values and reduced thickness of recast layer, accompanied by a significant effect on MER and surface finish while machining in the magnetic field coupled higher spark energy. The experimental results conferred the process stability and an excellent correspondence with experimental verifications.

On sustainable manufacturing titanium alloy by high-speed EDM milling with moving electric arcs while using water-based dielectric

Abstract In order to solve the environmental pollution and low machining efficiency of conventional EDM process, a sustainable manufacturing method of high-speed EDM milling while using water-based dielectric is proposed. Firstly, the machining principle of moving electric arcs was investigated. Then, models were established and utilized to explain the characteristics of high-speed EDM milling with moving electric arcs. Experiments on machining titanium alloy with this method were carried out to analyze the machining characteristics. The experimental results showed that the material removal rate (MRR) was significantly improved. The maximum MRR was almost five times greater than that of conventional EDM. Moreover, the lower tool-electrode wear in high-speed EDM milling was obtained, which can be attributed to the high-speed rotation of tool-electrode and protective layer formation on the tool-electrode surface caused by sputtering and deposition of Ti-6Al-4V.

A study on the effect of tool electrode thickness on MRR, and TWR in electrical discharge turning process

Turning by electrical discharge machining (EDM) is an emerging area of research. Generally, wire-EDM is used in EDM turning because it is not concerned with electrode tooling cost. In EDM turning wire electrode leaves cusps on the machined surface because of its small diameters and wire breakage which greatly affect the surface finish of the machined part. Moreover, one of the limitations of the process is low machining speed as compared to constituent processes. In this study, conventional EDM was employed for turning purpose in order to generate free-form cylindrical geometries on difficult-to-cut materials. Therefore, a specially designed turning spindle was mounted on a conventional die-sinking EDM machine to rotate the work piece. A conductive preshaped strip of copper as a forming tool is fed (reciprocate) continuously against the rotating work piece; thus, a mirror image of the tool is formed on the circumference of the work piece. In this way, an axisymmetric work piece can be made with small tools. The developed process is termed as the electrical discharge turning (EDT). In the experiments, the effect of machining parameters, such as pulse-on time, peak current, gap voltage and tool thickness on the MRR, and TWR were investigated and practical machining was carried out by turning of SS-304 stainless steel work piece.

The influence of Span-20 surfactant and micro-/nano-Chromium (Cr) Powder Mixed Electrical Discharge Machining (PMEDM) on the surface characteristics of AISI D2 hardened steel

The application of powder mixed dielectric to improve the efficiency of electrical discharge machining (EDM) has been extensively studied. Therefore, PMEDM have attracted the attention of many researchers since last few decades. Improvement in EDM process has resulted in the use of span-20 surfactant and Cr powder mixed in dielectric fluid, which results in increasing machiniability, better surface quality and faster machining time. However, the study of powder suspension size of surface charateristics in EDM field is still limited. This paper presents the improvement of micro-/nano- Cr powder size on the surface characteristics of the AISI D2 hardened steels in PMEDM. It has found that the reacst layer in PMEDM improved by as high as 41-53 % compared to conventional EDM. Also notably, the combination of added Cr powder and span-20 surfactant reduced the recast layer thickness significantly especially in nano-Cr size. This improvement was great potential adding nano-size Cr powder to dielectric for machining performance.

Machining characteristics and removal mechanisms of moving electric arcs in high-speed EDM milling

Low machining efficiency is the major challenges of conventional electrical discharge machining (EDM). To resolve this problem, a novel machining method of high-speed EDM milling with moving electric arcs was developed, which can remove material continuously without discharge intervals of pulse power supply and achieve extremely low tool-electrode wear for the direct-current power supply employed. An EDM milling equipment was devised to explore machining characteristics and removal mechanisms of moving electric arcs in high-speed EDM milling process. Firstly of all, the motion characteristics of moving electric arcs were investigated. The theoretical analysis shows that the arcs maintain an independent movement relative to the tool-electrode and workpiece. Then, the plasma channels were captured by high-speed video camera, which contributed to develop the model of removal mechanisms of moving electric arcs. Finally, the machining experiments were carried out based on titanium alloy, which verified that a much higher material removal rate could be easily achieved by moving electric arc. Moreover, the tool-electrode wear in high-speed EDM milling is much lower than conventional EDM due to the protective layer formation.

Effect of magnetic polarity on surface roughness during magnetic field assisted EDM of tool steel

Electrical discharge machining (EDM) is one of the non-traditional machining techniques where the process offers wide range of parameters manipulation and machining applications. However, surface roughness, material removal rate, electrode wear and operation costs were among the topmost issue within this technique. Alteration of magnetic device around machining area offers exciting output to be investigated and the effects of magnetic polarity on EDM remain unacquainted. The aim of this research is to investigate the effect of magnetic polarity on surface roughness during magnetic field assisted electrical discharge machining (MFAEDM) on tool steel material (AISI 420 mod.) using graphite electrode. A Magnet with a force of 18 Tesla was applied to the EDM process at selected parameters. The sparks under magnetic field assisted EDM produced better surface finish than the normal conventional EDM process. At the presence of high magnetic field, the spark produced was squeezed and discharge craters generated on the machined surface was tiny and shallow. Correct magnetic polarity combination of MFAEDM process is highly useful to attain a high efficiency machining and improved quality of surface finish to meet the demand of modern industrial applications.

Effect of electrical discharge machining on corrosion and corrosion fatigue behavior of aluminum alloys

Electrical discharge machining (EDM) is often used in the manufacturing of fatigue test coupons because it allows for the production of complex shapes and sharp starting notches. However, the effect that the machining process has on the corrosion susceptibility due to the surface alterations is unknown. This work focuses on the effect the machining method has on the corrosion and corrosion fatigue behavior of aluminum alloys. The study is aimed at understanding the influence of EDM processes on environmentally assisted cracking evaluations, namely crack growth rate. Conventional milling and electrical discharge machining were the machining process examined in this study; the machining parameters used were best practices for laboratory fatigue sample production. The following aluminum alloys (AA) 2024-T351, 5083-H116, 6061-T6 and 7075-T651 were evaluated in this study. EDM was performed using a 0.152 mm (0.006 in.) hard brass wire. Surface quality evaluations, microstructural analysis, electrochemical tests and corrosion fatigue testing in sodium chloride (NaCl) solution were completed. The study found corrosion rates are affected by the EDM machining in all aluminum alloys. In final testing, crack growth rate tests were completed in sodium chloride solution with starter notches that were traditionally cut and EDM machined for 7xxx and 2xxx series alloys. The testing showed accelerated fatigue crack growth rates for the samples with EDM notches as compared to cut notches.

Technology of ablation milling by fast-moving electrode

To improve the efficiency of conventional electrical discharge machining (EDM) milling, this study proposes a highly efficient machining method that employs continuous oxygen feeding and fast-moving electrode. High-efficiency machining is achieved by the method of feeding with small thickness, allowing the electrode suspended above the workpiece to reduce short circuit and using a high discharge probability to ignite the workpiece in order to realizing high efficiency machining with great chemical energy released from metal combustion. Comparative tests for conventional EDM milling, EDM ablation milling, and ablation milling by fast-moving electrode were performed in the milling process. In this study, we analyzed the mechanism, machining efficiency, electrode relative wear ratio, and machining quality. The machining efficiency of EDM ablation milling was 6.8 times higher than that of conventional EDM milling, and the relative tool wear ratio was 20% of conventional EDM milling; the machining efficiency of ablation milling by fast-moving electrode can reach 11.2 times higher than that of conventional EDM milling, and the electrode relative wear ratio decreased by 86%.

Comparative Study of Powder Mixed EDM and Conventional EDM Using Response Surface Methodology

Powder mixed electrical discharge machining (PMEDM) is an advanced machining process. It is used for cutting hard material and for creating intricate shapes. In present work Inconel 825 is used as workpiece due to some of its unique properties like oxidation and corrosive resistance in high pressure and temperature environment as well as it retains its strength at higher temperature. The difficulty in machining it due to its fast work hardening is one of the reasons to use Electrical Discharge Machining (EDM) process is used in which there no direct contact of tool and workpiece so less chances of residual stress. To obtain the efficient output response parameter aluminium oxide (Al2O3) micro powder is mixed with dielectric was used. The input process parameters are gap voltage, pulse on time, powder concentration and peak current. The output process parameters are surface roughness (SR), material removal rate (MRR) and surface integrity. To analyse the surface morphology FESEM image is used. On the basis of application Inconel is used as studs in space shuttle, thrust chamber of rocket engine and engine combustion chamber etc. It has been observed that MRR and SR are directly influenced by the peak current (Ip),pulse on time(Ton) and gap voltage (GV).By using powder in dielectric surface roughness is improved as compare to conventional EDM process.

Electrical Discharge Drilling of D3 Die Steel using Air Assisted Rotary Tubular Electrode

This articles focus on developing a hybrid EDM process using liquid cum gaseous dielectrics to study its influence on tool wear rate (TWR), material removal rate (MRR) and over cut (OC) of workpiece. The compressed air flow through a rotary tubular electrode removed and flushed out the debris from the working gap and hence it improves the flushing efficiency and stability of the process. This study describe the experimental investigation of formation of holes in D3 die steel workpiece with conventional EDM and air assisted electrical discharge drilling (AAEDD). An attachment was designed and developed to carry out AAEDD process on the existing EDM machines. The entire arrangement is in the form of an independent unit which could be attached to the existing EDM machine. The influence of various machining parameters such as discharge current, pulse on time, duty cycle and tool speed on output response viz., MRR, TWR and OC have been studied. Under the same machining condition, high MRR and low TWR as well as OC obtained when AAEDD machining was performed as compared to conventional EDM machining. Experimental findings suggested that supply of compressed air through rotary tubular electrode in die sinking electrical discharge drilling have a positive influence on MRR, OC and TWR. However, rotation of tool has a negative effect on OC. The SEM images of selected specimens were also in line with the experimental findings.

Study of Machining of Inconel 825 Super Alloy Using Powder Mixed EDM Process

Powder mixed electrical Discharge Machining (PMEDM) plays vital role in machining process of some very difficult to machine materials. Inconel 825 are highly demanding materials for today’s industries due to their unique properties. Properties like high creep resistance under high stress condition, high resistant to corrosion, good machinability, ductility, weldibility, low value of thermal expansion makes it durable for high speed aeroplanes and supersonic jets. In present work Inconel 825 (nickel alloy) which is widely used in aerospace industries, power plants, nuclear power plants, petro chemical, chemical rockets has been used as work piece and machined with using powder mixed electrical discharge machining process (PMEDM). Peak current (IP), gap voltage (GV), powder concentration (PC) and pulse on time (TON) are opted as input experimental parameters. Whereas, surface roughness (SR) and material removal rate (MRR) are considered as output response parameters. Tool used during experiment is tungsten carbide. Tungsten carbide is hard materials in which wear is minimum. It could be concluded from the experiment that there is significant improvement in MRR as well as SR. Tool wear is negligible. Further, surface machined by PMEDM is compared with conventional EDM and analysed using field emission electron microscopy (FESEM) and RSM (response surface methodology). Images obtained by FESEM also confirm improvement in surface integrity. Moreover, less micro-crack, micro-holes and shallower craters were observed on the surface generated by PMEDM as compare to conventional EDM