Die-sinking Electrical Discharge Machining Research Articles

Influence of short-circuitng on machined surface quality in electrical discharge machining of carbon fiber reinforced plastics

This paper investigates the influence of a short circuit on machined surface quality in the electrical discharge machining (EDM) of carbon fiber reinforced plastics (CFRP) in order to obtain a machined surface with good quality. In the EDM of CFRP, short circuits caused by the attraction of frayed carbon fibers on the machining surface to the tool electrode frequently occur and has adverse effects on the quality of the machined surface. In this study, die-sinking EDM of CFRP using deionized water was carried out, and the influence of duration of stable state in which short circuit does not occur on quality of machined surface was investigated. The occurrence of short circuits was determined from the fluctuation of the z-axis position. The machined surface was investigated using an optical microscope and the quality of the machined surface was judged on the basis of the presence or absence of frayed carbon fibers. The experimental results show that each stable state continues for 50 seconds or less when elapsed time is from 0 to 20 minutes. On the other hand, when the elapsed time is from 20 to 40 minutes, the duration of each stable state becomes longer than 50 seconds. It was found that when the machining process was stopped during unstable state in which short circuits occur, the quality of the machined surface was poor. On the other hand, when the machining process was stopped after stable states for a certain amount of time, the quality of the machined surface was good.

The Methodologies Adopted To Improve the Machinability in Die-Sinking EDM

Electrical discharge machining (EDM) is one of the oldest nontraditional machining processes, commonly used in automotive, aerospace and ship building industries for machining metals that have high hardness, strength and to make complicated shapes that cannot be produced by traditional machining techniques. The process is based on the thermoelectric energy between the work piece and an electrode. EDM is slow compared to conventional machining, low material removal rate, high surface roughness, high tool wear and formation of recast layer are the main disadvantages of the process. Tool wear rate, material removal rate and surface quality are important performance measures in electric discharge machining process. Numbers of ways are explored by researchers for improving and optimizing the output responses of EDM process. The paper summarizes the research on die-sinking EDM relating to the improvements in the output response.

Single objective optimization of die- sinking electrical discharge machining with low frequency vibration assigned on workpiece by taguchi method

The integration of low frequency vibration with the workpiece can enhance the machining efficiency in die sinking electrical discharge machining. Since the adaptation of vibration increases the complexity in such process, the optimization of the process parameters is very important. In the present work, a research attempt has been made on Taguchi based single- objective optimization of vibration assisted die- sinking electrical discharge machining process while machining SKD61 die steel. The process parameters such as pulse current (I), pulse on- time (TON), pulse off- time (TOF), frequency of vibration (F) have been selected as input factors for investigation. Material removal rate has been chosen as quality indicator. From the experimental investigation, it has been found that material removal rate has been significantly improved by integrating vibration into the workpiece. The optimal combination of process parameters has been found with the accuracy of 6.90%.

MULTI-OBJECTIVE OPTIMIZATION OF EDM PROCESS PARAMETERS FOR MACHINING OF HYBRID ALUMINUM METAL MATRIX COMPOSITES (Al7075/TiC/B4C) USING GENETIC ALGORITHM

This study deals with the investigation on the effect of Electrical Discharge Machining (EDM) parameters during machining of hybrid composite (Al 7075/TiC/B4C). The optimum process parameters of die sinking EDM like pulse current, pulse duration and gap voltage on metal removal rate, tool wear rate and surface finish were investigated. Full factorial experimental design was selected for experiments. Analysis of variance was employed to study the influence of process parameters and their interactions on response variables. Among the process parameters considered, it was observed that the pulse current was found to be more influential in affecting MRR, TWR and SR. The other parameters have little effect on the response variable. Multi-objective optimization study was also performed using genetic algorithm to find the optimum parameter setting for controversial objective function combination such as high MRR and low SR and High MRR and low TWR. Scanning electron microscope study was performed to study the surface characteristics.

Electrical discharge machinable (Y, Nd) co-stabilized zirconia – Niobium carbide ceramics

Electrical discharge machining (EDM) of electrically conductive ceramics offers the possibility to manufacture customized ceramic components from sintered blanks. In this study two different yttria neodymia co-stabilized TZP materials containing 28 vol% niobium carbide were manufactured by hot pressing at 1275 °C–1400 °C and axial pressure of 60 MPa and compared to a 3Y-TZP based reference. The co-stabilized ceramics offer a strength up to 1250 MPa and a hardness of 14 GPa. The fracture resistance can be tailored between 7.4–9.7 MPa√m by variation of the yttria/neodymia ratio and the sintering temperature. These composites, however, require an exact setup of machining parameters. Die sinking EDM experiments revealed that the dominant material removal mechanism is melting. Machined surfaces can achieve low roughness Ra =0.3 μm combined with material removal rates of 1.5 mm³/min. The choice of excessively high energy parameters in EDM may lead to crack formation, spallation and phase accumulation during re-solidification.

Study on Effects of Low Frequency Vibration on Efficiency of Die Sinking Electrical Discharge Machining

The vibration integrated into die-sinking electrical discharge machining is a relatively new solution, so it has been creating the interest of researchers. In this paper, the authors studied the effect of low frequency vibration attached onto workpiece to efficiency of die- sinking electrical discharge machining. Copper electrode and SKD61 die steel were selected to investigate. Material removal rate, tool wear rate and surface roughness were quality indicators investigated in this study. Experimental results showed that the low frequency vibration has a positive effect on the efficiency of die-sinking electrical discharge machining. Comparing to die- sinking electrical discharge machining traditional, when the vibration unit is integrated onto work-piece in die-sinking electrical discharge machining, the largest increase of material removal rate was 34.94 %, the greatest reduction of tool wear rate was 16.0 % and the largest reduction of surface roughness was 26.36 % and profile of machined surface was better.

Experimental Investigation of Sunflower Oil as Dielectric Fluid in Die Sinking Electric Discharge Machining Process

Electric Discharge Machining (EDM) is used to machine complex geometries of difficult to cut materials in the area of making dies, mould and tools. Currently, hydrocarbon based dielectric fluids are used in EDM and which plays major role for material removal and it emits harmful emission. In this work, vegetable oil is attempted as dielectric fluid and their performance are studied during processing of AISI P20 steel. The effect of pulse on time (Pon) , pulse off time (Poff), and current (A) on Material Removal Rate (MRR), Tool wear rate (TWR) and surface roughness (SR) are analyzed. The result showed that vegetable oils are given good machining performance than conventional dielectric fluids. These proposed dielectric fluids are biodegradable eco friendly and enhance sustainability in EDM process.

INVESTIGATION OF EFFECTS OF DIELECTRIC TYPE AND POLARITY ON ELECTRIC DISCHARGE MACHINING OF AISI D2 STEEL USING RESPONSE SURFACE METHODOLOGY

This paper presents a study on optimisation of process parameters of die-sinking electric discharge machining. The influence of dielectric type, electrode polarity, discharge current and gap on the material removal rate (MRR) and surface roughness for machining of AISI D2 steel have been studied. Response surface methodology suggested in the existing literature was employed for conducting the experiments. Kerosene and transformer oils were found as the best dielectric for MRR and surface roughness, respectively. It was also found that electrode with positive polarity offers high MRR while negative polarity ensures best surface finish. ANOVA results indicated that discharge current was the most influencing factor affecting the performance measures, MRR and surface roughness. Although discharge gap showed low effect on MRR and surface roughness, it was effective for debris removal. Empirical models were developed to optimise the results of MRR and surface roughness.

Finishing performance of die-sinking EDM with ultrasonic vibration and powder addition through pulse train studies

Die-sinking electrical discharge machining (EDM) is widely used in die and mold-making industry. Finish EDM conditions are often selected to produce good quality surfaces. Attempts to enhance the finishing capabilities using ultrasonic vibration and powder-added dielectric medium have been reported in the literature. However, the changes in the gap phenomena with ultrasonic assistance and powder addition have not been analyzed. In this article, finish EDM of hardened D3 steel has been carried out based on full factorial design of experiment with three levels of setting voltage, setting current and pulse on time. The performance of ultrasonic assisted and graphite powder-added EDM are evaluated by analyzing the voltage and current pulse trains in finishing operation for the first time. Based on two new parameters, namely energy expended over a second (E) and ratio of energy due to sparks in relation to total discharge energy (PF), the results are discussed and also compared with those obtained with conventional EDM for selected conditions. Even though E of 102.9 J (PF = 0.862) with ultrasonic vibration is higher than E of 43.0 J (PF = 1.0) with powder mix, the molten metal is removed effectively from the gap by ultrasonic vibration which results in a relatively better surface. The micrographs of cross-section and surface of the workpieces obtained using optical and scanning electron microscopes, respectively, also reveal their relative performance.

Machining characteristics and optimization of process parameters in die-sinking EDM of Inconel 625

Inconel 625 superalloy is a versatile austenitic nickel-based superalloy with excellent strength and good ductility. It possesses excellent mechanical properties at both extremely low and extremely high temperatures with excellent resistance to pitting, crevice corrosion, cracking and crystalline corrosion. Inconel 625 superalloy is an important and frequently used material for an automobile, aerospace industries and marine application due to its excellent mechanical, chemical and physical properties. In the present research, empirical mathematical model for surface roughness and material removal rate (MRR) has been developed to study the influence of die-sinking electrical discharge machining (EDM) parameters, viz. peak current, pulse on time and pulse off time on Inconel 625. Central composite design is employed to plan experimental layout, and a quadratic model is adopted for empirical mathematical modeling. ANOVA is performed to test the adequacy of the model using F-test and p-test. Optimal setting of EDM parameters is obtained using composite desirability. ANOVA analysis reveals that peak current is the most dominating factor for MRR followed by pulse on time, while surface roughness is mostly influential by pulse on time followed by pulse off time. Surface roughness increases with the increase in pulse on time. MRR firstly increases with an increase in pulse on time and start decreasing after mid value (0), i.e., 15 µs whereas surface roughness continuously increases with an increase in pulse on time. Optimal setting of EDM parameters is obtained by composite desirability function. The goal is to minimize surface roughness and maximize MRR simultaneously. Results are validated by the confirmation experiment using the optimal set of EDM parameters. The confirmation experiments reveal that the experimental and predicted results are very close with error amounting of 2.19% and 2.58% for MRR and surface roughness respectively.

The Effect of Electropolishing Time Variation at Room Temperature and Low Voltage on the Surface Quality of Cardiovascular Stent

Electropolishing is an attractive method for surface smoothing of cardiovascular stent. This study investigated the effect of times of electropolishing on the surface characteristics both are upper surface and surface of the strut of cardiovascular stent after the by die sinking electrical discharge machining (EDM). The observed surface characteristics of the strut were recast layer, surface roughness and brightness. The weight analysis, and the reduction of the width strut were conducted. The recast layer was analyzed by optical microscope qualitatively, the surface roughness was measured by surface texture measuring instrument, the weight analysis and the reduction of width strut were calculated. The stent was made from steel AISI 316 L. The times which were used in the electropolishing were 3 minutes, 7 minutes, and 11 minutes. The experimental results show that the time for smoothing and brightening of stent at room temperature and low voltage 5 V is 7 minutes. The times affect the upper and EDM surface roughness, the weight of stent and the width of strut. The results show that increasing of times, than the value of surface roughness, the weight of stent and the width of strut will decrease, and vice versa. The average surface roughness of EDM surface after electropolishing is in the range of 3.49 – 1.62 µm. The average surface roughness of upper surface after electropolishing is in the range of 0.55-0.22 µm. The weight analysis show that the loss of weight is in the range of 0.12-1.12 %, and the reduction of width strut is in the range of 11.02 – 69.3 %.

Tool electrode wear compensation in block divided EDM process for improving accuracy of diffuser shaped film cooling holes

Diffuser shaped film cooling holes are increasingly being applied in the turbine blades of advanced aeroengines. It is a difficult problem to machine this kind of cooling holes due to their complicated shape and superalloy material. Currently, die-sinking electrical discharge machining (EDM) is regarded as an available process for machining the diffuser holes. However, the change of tool electrode shape caused by the electrode wear and difficult renew of dielectric fluid affect the processing precision. The worn tool electrode has to be replaced with a fresh one after machining one or several holes. The replacing procedure is time consuming to break the machining process. In the previous work, a novel block divided EDM process was proposed to efficiently machine the diffuser holes, but the machining accuracy needs to be further improved. In this research, the block divided EDM process firstly is analyzed and simulated in detail to know the key factor affecting the machined accuracy. Furthermore, a self-repair method and a profile error compensation method of the tool electrode wear are proposed for improving the processing accuracy. The self-repair method is to plan and control the rotation motion of the tool electrode for maintaining its shape. The profile error compensation method is to modify the Z coordinate of the tool electrode for decreasing the machining error. Machining experiments verified that the proposed methods can meet the accuracy requirements of the film cooling holes with diffusion angle error < 0.1° and average profile error < 10 μm.

Comparative evaluation of powder-mixed and ultrasonic-assisted rough die-sinking electrical discharge machining based on pulse characteristics

Electrical discharge machining is used in the machining of complicated shapes in hardened molds and dies. In rough die-sinking stage, attempts are made to enhance material removal rate with a consequential reduction in cycle time. Powder mix and ultrasonic assistance are employed in the electrical discharge machining process to create gap conditions favoring material removal. In the present work, experiments are carried out on hardened D3 die steel using full-factorial design based on three levels of voltage, current and pulse on time. The gap phenomena in graphite powder-mixed and ultrasonic-assisted rough electrical discharge machining are studied using a detailed analysis of pulse shapes and their characteristic trains. Two new parameters, namely, energy expended over a second ( E) and performance factor ( PF) denoting the ratio of energy associated with sparks to total discharge energy, bring out gap conditions effectively. In comparison with the conventional electrical discharge machining for the selected condition, it is seen that the graphite powder mixed in the dielectric enhances the material removal rate by 20.8% with E of 215 J and PF of 0.227, while these values are 179.8 J and 0.076 for ultrasonic-assisted electrical discharge machining with marginal reduction of 3.9%. Cross-sectional images of workpieces also reveal the influence of electrical discharge machining conditions on the machined surface. The proposed approach can be extended to different powder mix and ultrasonic conditions to identify condition favoring higher material removal.

Study on material removal rate, surface quality, and residual stress of AISI D2 tool steel in electrical discharge machining in presence of ultrasonic vibration effect

Electrical discharge turning is an emerging modification of die sinking electrical discharge machining process that enables to machine the difficult-to-cut round cylindrical bars. In the present study, the machinability of AISI D2 workpiece was studied while the tool electrode has high-frequency longitudinal vibration. Here, a series of experiments has been carried out taking into account the effect of ultrasonic power, spindle speed, discharge current, pulse on time, and pulse off time to study material removal rate (MRR), surface roughness (Ra), and residual stress (RS). The process has been studied through Taguchi orthogonal design through conducting of 27 experiments. Analysis of variances has also been carried out to find which factor has the greatest effect on process performance. Results indicated that among the factors, pulse current and workpiece rotation have the greatest effect on MRR and SR while the pulse on time is most influential on RS.

Investigating the effects of electric discharge machining parameters on material removal rate and surface roughness on AISI D2 steel using RSM-GRA integrated approach

The present research focuses on optimizing the process parameters of die-sinking electric discharge machining on tool steel. The basic objective of this research is to investigate the influence of two categorical factors including dielectric type and electrode polarity, and two numeric factors including discharge current, and Spark/Discharge Gap on material removal rate (MRR) and surface roughness (Ra) for machining of AISI D2 steel. Box-Bhenken design based on response surface methodology (RSM) was applied for experimental design. For estimation and evaluation, the effects of the process parameters on response variables, RSM has been integrated with grey relational analysis (GRA). Ranking of factors has been done with respect to the grey relational grade. (ANOVA) was further performed for determining the significance of grey relational grade. ANOVA results reveal that that polarity having 50% of percentage contribution was the most significant factor affecting the performance measures followed by the spark gap, discharge current, and dielectric type. The grey relational grades were further optimized through desirability function and the optimal condition for input parameters was obtained. The optimum levels were discharge current at 15 A, dielectric type of kerosene oil, spark gap at 6 mm, and polarity of positive has been determined. The confirmatory tests were run for verifying and validating the results and improvement in productivity (MRR) up to 17.23 mm3/min and quality (Ra) up to 3.86 μm at an optimum have been observed.

Die steel surface layer quality improvement in titanium μ-powder mixed die sinking electrical discharge machining

In practice, the improvement of surface roughness (SR) after die sinking electric discharge machining (EDM) is simple and inexpensive when compared with the microhardness of machined-surface layers (HV). In addition, when HV is low, the improvement of SR will be less effective and have no significance to the mold surface layer. Therefore, the HV of molds after die sinking EDM is improved and plays a more important role than the improvement of SR. Currently, powder-mixed die sinking EDM is a technological solution that can improve both the HV and SR simultaneously. However, SR is given a priority criterion popular choice for many studies into powder-mixed die sinking EDM. In this current study, the researchers improve the quality of the steel surface layer of the mold using titanium (Ti) powder-mixed die sinking EDM. In the research, HV is selected as a criterion to optimize input parameters, and SKD61, SKD11, and SKT4 mold steels as well as Cu and Gr electrode materials are used. The effects of the workpiece material (A), electrode material (B), electrode polarity (C), pulse-on time (D), pulse-off time (F), current (E), Ti powder concentration (G), and some interactive A × B, A × G, and B × G to HV surface layers are analyzed and evaluated. Finally, the Taguchi method is used to optimize the parameters. Results indicated that parameters such as the electrode material, the pulse-on time, the concentration powders, A × G, and B × G significantly affect the HV. The Ti powder concentration has the largest effect on HV. When the powder concentration increased, HV was increased; its largest increase was 41.81%, and the optimal value of HVopt = 864.363 ± 61.68 HV at a Ti powder concentration of 10 g/l. The machined surface analysis of SEM and SR after powder-mixed die sinking EDM using Ti powder at optimal conditions showed that the quality of the surface layer was significantly improved. The qualities of surface layers, such us mechanical properties, topography, and the microstructure after EDM with titanium powder mixed into dielectric fluid, was significantly improved under optimal conditions for various mold steels.

Metaheuristic Approach of Multi-Objective Optimization during EDM Process

In modern-day manufacturing Electric Discharge Machining (EDM) process has successfully placed itself in the domain of precision machining and generating complex geometries where secondary machining processes are eliminated. In this research paper, a die sinking EDM is applied to machine mild steel in order to measure the different multi-objective results like Material Removal Rate (MRR) and Over Cut (OC). This contradictory objective is accomplished by using the control parameters like a pulse on time, duty factor, gap current and spark gap employing copper tool with lateral flushing. Here the individual objective function of the responses is created through regression analysis. Primarily the contradictory objectives are optimized by employing Taguchi Methodology, then Regression analysis is done on the test results. Additionally, the experimental results are optimized using Response Surface Methodology (RSM). It is followed by a multi-objective optimization through Overlaid contour plots and Desirability functions to ascertain the best parametric combination amongst the set of feasible alternatives.

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.

ANALYSIS OF SURFACE LAYERS OF HOT – FORGING DIES OF SKD61 STEEL FABRICATED BY DIE – SINKING ELECTRICAL DISCHARGE MACHINING USING COPPER AND TITANIUM ELECTRODES

Electrical discharge machining (EDM) is a popular unconventional method for manufacturing tools, molds, and dies. Currently, the surface layer of the hot die after EDM needed to be polished to remove the layer of » 50 mm. This is accepted according to practical experience and the lack of scientific basis because of limited research on the surface layer quality of the products after EDM and the study is focused on the evaluation of the product quality in the final processing. This study is aimed at the investigation of performance and structure of the surface layer in hot-forging die following die-sinking EDM. The machining conditions included the use of copper (Cu) and titanium (Ti) as electrode materials. A cross-sectional micrographic and hardness analysis was performed, as well as surface roughness measurements, in order to study the thermally affected zones of the hot-forging die surface layer of the SKD61 steel after EDM using oil as the dielectric fluid. The results showed that the performance of the die was reduced due to changes in the hardness and the chemical composition of the workpiece surface. The surface quality of hot-forging die after EDM with Ti or Cu electrode are similar. In this case, EDM using Ti electrode to improve the quality of hot die surface layer was unreasonable.

Experimental Investigation of EDM Parameters on Al-LM6/SiC/B4C Hybrid Composites

In this work, a Material removal rate (MRR), Tool wear rate (TWR), Radial and overcut (ROC), a study on the die-sinking Electrical discharge machining (EDM) of Al-LM6/SiC/B4C hybrid composites has been carried out. The selection of above-mentioned hybrid composite was made considering its widespread application in aerospace, automotive, defense, biomedical and marine industries, due to its light weight and higher mechanical properties. This experiment was made only for the finish stage and has been carried out on the influence of four design factors: composition, discharge current (Ip), Pulse-on-time (Ton), Radial overcut (ROC) and Duty factors (Tau), over the previously mentioned, responded variables. This has been done by means of the method of design of experiment (DOE) which allows us to carry out the above-mentioned analysis performing a relatively small number of experiments. The study indicates that when discharge current (Ip) increases, Material removal rate increased. In the case of Tool wear rate the most influencing factor is discharge current, then pulse on time. In radial over cut most influence factor is discharge current then pulse on time, duty factor and composition has least.