Electrical Discharge Machining Surface Research Articles

Wire electrochemical finishing of wire electrical discharge machined surfaces on the same machine

Compared to surfaces machined by electrical discharge machining (EDM), surfaces machined by electrochemical machining (ECM) tend to show smoother surface finish. Heat-affected zone is generated on the EDMed surface, but not on the ECMed surfaces. Hence, the previous study aimed to finish wire-EDMed surfaces with wire-ECM, using the same machine. A bipolar pulse current with positive pulse duration of 100 µs and negative pulse duration of 150 µs resulted in mirror like surface finish for stainless steel (SUS304). However, previous research showed low surface quality for cold tool steel SKD11 with wire-ECM finishing. This is because the precipitate of chromium carbide was preferentially corroded. Hence, in this study, surface quality of SKD11 finished with various positive pulse duty factor was investigated. As a result, it was found that the surface can be machined uniformly when the duty factor is 30%. Whereas the chromium carbide was less machined and protruded when the duty factor was lower, and it was machined faster than the other metallic structure and resulted in pit corrosion when the duty factor was higher than 30%.

Electrical discharge machining of boron carbide-graphene nanoplatelets composites

Boron carbide (B4C) composites containing 0–10 wt.% graphene nanoplatelets (GNPs) were consolidated using hot pressing at 1950 °C for 60 min under 30 MPa in an argon atmosphere. Their electrical discharge machining (EDM) characteristics were evaluated for the first time. Additionally, the effects of GNPs on the microstructure, electrical conductivity, material removal rate (MRR), and surface roughness (Ra) of B4C composites were investigated. The results show that the B4C composite containing 10 wt.% GNPs exhibited the highest electrical conductivity of 4997 S·m−1 because of the formation of GNPs conductive networks. Under a fine machining condition, the MRR of the B4C composite was enhanced by 43.5 % (from 6.55 to 9.40 mm3 min−1) compared with that of monolithic B4C. Furthermore, the Ra decreased to 1.12 μm, which was significantly lower than that of pure B4C (2.44 μm). Scanning electron microscope and energy disperse spectroscopy analysis of the EDM surfaces were used to determine that the main material removal mechanisms for B4C composites with less than 2 wt.% GNPs were spalling and melting. As the GNPs content increased, B4C grain fallout, melting, and evaporation became more dominant. The other mechanisms, including thermal shock and oxidation, are also discussed in detail.

Sliding abrasive wear when combining WEDM conditions and polishing treatment on H13 disks over 1045 carbon steel pins

Forging dies are crucial in forging to manufacture accurate workpieces. These dies are generally made of AISI H steel series and hardened and tempered medium carbon alloy steel. Dies are processed by using high-speed milling + polishing or electrical discharge machining + polishing. The surface quality of the workpiece depends on the surface properties of these dies, where surface roughness, material hardness, and wear evolution of their surfaces are critical aspects to consider. This research analyzes different wire electrical discharge machining surface conditions combined with polishing treatment to describe their influence on friction and wear. Wire electrical discharge machining defines the disks’ surface properties in finishing and roughing conditions, and polishing treatment varies in time and paper sand depending on the roughness. Abbott-Firestone curves and Rsk-Rku roughness parameters characterize the surface roughness of each studied configuration. Room temperature pin-on-disk tests were performed to analyze friction coefficients and wear rate for AISI 1045 pins and AISI H13 disks. On average, the highest (0.284) and the lowest (0.201) friction coefficients were found for the combination of finishing wire electrical discharge machining + polishing and roughing wire electrical discharge machining conditions, respectively. Scanning electron microscope images were taken to describe the wear tracks and pin degradation for different sliding abrasive configurations. The diagram correlating the surface morphology and the friction coefficient predicts the wear damage on initial surface conditions, which is crucial in the forging industry to determine tool maintenance or replacement.

Effect of pulse current in manufacturing of cardiovascular stent using EDM die-sinking

This paper proves that die-sinking electrical discharge machining (EDM) is an alternative and attractive manufacturing method of producing cardiovascular stent. This study investigates the effect of pulse currents on the material removal rate (MRR), the surface of EDM, and the upper surface of the strut stent. The observed surface characteristics of the strut were surface roughness, recast layer, and the diameter of the crater. The recast layer and crater were analyzed by an optical microscope, and the surface roughness was measured by a surface profilometer. The pulse currents which were used in the manufacturing of stent by die-sinking EDM were 1.5 A/45 μs, 3.0 A/90 μs, 4.5 A/120 μs, and 6 A/150 μs. The experiment shows that the stent is successfully manufactured from minitube AISI 316L by die-sinking EDM. The diameter, length, and thickness of the stent are 4 mm, 20 mm, and 0.3 mm, respectively. The results show that increasing of pulse current will cause the increase of MRR, the thickness of recast layer, the surface roughness, and the crater diameter. The MRR, thickness of the recast layer, surface roughness, and crater diameter are also influenced by the pulse on time. The EDM surface roughness, the average thickness of recast layer, and the diameter of crater are in the range of 3.49–9.53 μm, 17.6–97 μm, and 75.84–276.5 μm, respectively, and the upper surface roughness of the strut is 0.5534 μm. The best quality of the strut is generated from the pulse current 1.5 A/45 μs.

Surface roughness evaluation and morphology reconstruction of electrical discharge machining by frequency spectral analysis

In this paper, it is proposed a method that using mathematical equation to describe the surface morphology of electrical discharge machining (EDM). In particular, response surfaces and the effect of current and pulse width are established by measuring diameter and depth of the pits. A matrix of surface heights is collected by scanning EDM surface with appropriate magnification. Combined with the fractal theory, the suitable fitting frequency range is obtained by analyzing power spectral density of one of the row profiles. Wavelet decomposition is used to separate the profile into signal layers in different frequency ranges. Through picking five suitable signal layers, the characteristic frequencies and corresponding amplitudes of each layer are obtained based on the sizes of the single-pulse pit. These five groups of characteristic parameters are used to reconstruct row profile and surface topography. The mathematical equation of the EDM surface is obtained, and it is verified effective.

Measurement and inspection of electrical discharge machined steel surfaces using deep neural networks

We propose an industrial measurement and inspection system for steel workpieces eroded by electrical discharge machining, which uses deep neural networks for surface roughness estimation and defect detection. Specifically, a convolutional neural network (CNN) is used as a regressor in order to obtain steel surface roughness and a CNN based on spatial pooling pyramid is applied for defect classification. In addition, a new method for the region of interest selection based on morphological reconstruction and mean shift filtering is proposed for defect detection and localization. The regressor and classifier based on deep neural networks proposed here outperform state-of-the-art methods using handcrafted feature extraction. We achieve a mean absolute percentage error of 7.32% on roughness estimation; on defect detection, our approach yields an accuracy of 97.26% and an area under the ROC curve metric of 99.09%.

Research on discharge characteristics of working mediums of electric discharge machining

Successful surface modification can be obtained by Electrical Discharge Machining (EDM). In this work the discharge characteristics in misted deionized water and near-dry powder-mixed medium was studied systematically, as well as the microstructure and properties of electrical discharge strengthened layers on TC4 alloy. It indicates that the breakdown voltage of EDM in misted deionized water medium has been reduced to about 1/3 than in air medium. In near-dry powder-mixed medium, it is reduced to about 1/9, because the discharge gap is much larger than that of other mediums. In other words, a stable discharge can be obtained by larger discharge gaps and lower pulse energy than traditional EDM surface strengthening method, which leads to more stable discharge process. Experimental researches show that dense and sound combination with matrix like, multiphase hybrid intensification and chrysanthemum petal-like microstructure of strengthened layers can be observed in the near-dry powder-mixed medium. Meanwhile, it is found that the microhardness of the strengthened layer is up to about 1200 HV, which is four times higher than the base material.

Metal Removal Rate & Surface Morphological Analysis of Electrical Discharge Machined Co-Cr Alloy

Electrical discharge machining (EDM) confirmed its importance in the machining of hard and complex geometrical material which are difficult to machine or modified by traditional machining technique. The EDM process parameters – namely, pulse-on time, pulse-off time, current, voltage and dielectric medium – significantly influence the machining performance, such as surface traits, roughness and surface films. Therefore, in this study, the influence of EDM performance parameters on the metal removal rate (MRR) and surface roughness (SR) was examined. Experimentation was conducted according to the Taguchi L18 orthogonal array. Further, the analysis of variance (ANOVA) was employed for analyzing the S/N ratio results of the MRR and SR of various samples. The results revealed that cobalt (Co)–chromium (Cr) alloy substrates machined with a tungsten (W)–copper (Cu) electrode at the higher current setting (16 A, P on = 150 μs, P off = 150 μs) in EDM oil exhibited appropriate MRR and surface roughness value. Moreover, the EDM surfaces also exhibited suitable biocompatibility and excellent osseointegration.

Simulation Study on Surface Drag Reduction Performance of Beryllium Copper Alloy by EDM

Electrical discharge machining (EDM) is a method that removing material by pulse discharge between the workpiece and the electrode. The surface after EDM would leave discharge craters, the size of the crater and the surface morphology are close related to the processing parameters. Beryllium copper alloy material is used, we focus on the surface after EDM treatment. The height of the surface is measured, and the datum are used to analyze the characteristic amplitude data. Then relationship between the surface topography and the EDM parameters are established. calculating the fitting frequencies and amplitudes of the surface, and the surface reconstruction is realized. Establishing the feature model of the surface, then simulate analyzing the velocity distribution of the fluid on the EDM surface by Fluent software under different machining parameters to investigate the drag reduction performance. The results are verified by real test experiment. This simulation study expands the EDM technology in engineering production for the drag reduction application.

Surface Integrity of Micro EDM Surface Using Electrodes of Various Diameters

The surface integrity of a micro electrical discharge machining (micro EDM) surface represents the surface quality of workpiece. The surface quality of micro EDM can be further improved by clarifying the machining mechanism and optimizing processing technology. In this paper, experiments were carried out to investigate the influence of the tool electrode diameter on the machined surface integrity of micro EDM. The evolutions of the tool diameter on the micro topography, element migration, and surface roughness of workpiece surface machined in pure water and EDM oil were illustrated. The results show that the surface roughness Ra decreases as the tool electrode diameter increased, regardless of the open circuit voltage and dielectric type, owing to the skin effect. The good fluidity and cooling property of pure water and the effect of electrochemical corrosion cause the surface roughness Ra of surface machined in pure water is much larger than that machined in EDM oil. Tool material migrates to the workpiece surface during the micro EDM process, whether pure water or EDM oil is adopted as the working medium. The influence of electrode size on the Cu content of the workpiece surface shows no significant trend. Pure water is more suitable for high efficiency, low-precision micro EDM, while EDM oil is better for high-precision micro EDM.

Major Developments in EDM Surface Alloying using Composite Material Tool Electrode

Electric Discharge alloying/Coating (EDC) is an emerging field for the surface modification of advanced engineering materials like tool steel, high heat resistance alloy, titanium alloy etc. The advanced engineering materials have good mechanical properties and are used for the engineering applications like dies, aerospace, and automotives. To treat these difficult-to-machine advanced engineering materials with new challenges, numerous advancements in electrical discharge machining (EDM) processes have been carried out. Electrode materials for EDM are usually made up of copper, and its alloys. Proper selection with composition of electrode materials are required to avoid cracks, residual stresses etc during or after Electrical Discharge Machining and at the same time to have better surface finish and material removal rate and lower tool wear rate of the electrode. Further electrodes can be prepared by different methods like powder metallurgy, stir casting technique etc. This paper presents the brief details of effect of different electrodes on the surface and machining characteristics.

Investigation on spark electrical discharge machining of Si3N4 based advanced conductive ceramic composites

Ceramics are increasingly being used in aerospace, and have been used in the engineering industry for many years. Because ceramic is generally lighter than metal alloys, EDM has long been used for conductive ceramic materials for their forming complex shaped holes and design of all kinds of industrial applications. Furthermore, a considerable number of engineering challenges can be expected regarding the processing of ceramic materials on a percentage of composition level. In order to examine the investigation of the material removal mechanism and surface topography at a different processing temperature in the limit of high-temperature 1200–1600 °C of silicon nitride (Si3N4) based advanced ceramic composites (ACC) and analyzing various process parameters of spark EDM. Establish the relationship between the geometrical tolerances, crack behavior, Thermal spalling, pores and craters were investigated. Furthermore, the advantage, disadvantage, application, and productivity introduced conductive ceramic composites has been explored. In this work we reviewed the EDM characteristics of Si3N4-TiN and Nickel-Titanium alloys and also comparative analyses of the microstructure; hardness and composition of Electrical discharge machined surfaces were discussed.

Surface roughness evaluation of electrical discharge machined surfaces using wavelet transform of speckle line images

The surfaces produced by electrical discharge machine (EDM) were illuminated using a redline laser source and the speckle line images of the specimens were captured using a CMOS camera. Signal vectors were generated from the speckle line images which are 1 × 2592 matrices, represented the grey scale intensity of the speckle line images. The image signal vectors were then decomposed using a wavelet transform by key local intensity variation method. The fourth and the fifth levels of the six-level decomposition of bi-orthogonal wavelet were expected to bear the details about the surface roughness. The root mean square (RMS) and variance of the 4th and the 5th level decomposition were obtained and were compared with the surface roughness parameters roughness average (Ra), arithmetic mean slope (Rda), and root mean square slope (Rdq). RMS and variance of the 4th level decomposed signals were found to correlate well with surface roughness parameters.

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 %.

Ti6Al4V Surface Modification by Hydroxyapatite Powder Mixed Electrical Discharge Machining for Medical Applications

Titanium surface modification by the Hydroxyapatite (HA) mixed Electrical Discharge Machining (EDM) is an alternative and promising technique to enhance the biocompatibility and to promote the biological performance in bone, which is dependent on surface properties, such as surface roughness, chemistry, and wettability. HA powder is used for the first time with electrical discharge machining to improve osteoblastic cell activity on the developed surfaces for Ti6Al4V. Different HA concentrations in deionized water were tested as an experimental variable during EDM. Abrasive polishing and electrical discharge machined control surfaces without powder addition also analyzed to compare the results. The surface characteristics of analyzed samples were evaluated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffractometry (XRD), white light interferometry, and contact angle measurements. The wettability tests suggest that the hydroxyapatite powder mixed EDM’ed surfaces shows highly hydrophilic characteristics compared the other surfaces, abrasive polished and EDM’ed without powder addition in the dielectric. The results from the MTT assay revealed that those surfaces modified using HA powder addition in distilled water dielectric liquid promoted the most significant cell attachment/growth. The results indicate that HA powder mixed EDM offers a promising method for the surface modification of biomaterials such as titanium alloys

Fabrication of superhydrophobic metallic surface on the electrical discharge machining basement

Fabrication of superhydrophobic surface (SHS) on metal can effectively enhance its utility value. Herein, electrochemical etching for the electrical discharge machining (EDM) surface of beryllium copper (Be-Cu) alloy is carried out in the hydrochloric acid electrolyte, to obtain a hierarchical micro-nanostructure. After modification by stearic acid, the contact angle is up to 167.1 ± 2.6° and the sliding angle to 2.4 ± 0.7°. The microstructure constructed by EDM improves the quality of the SHS availably. The corrosion and abrasion resistance tests show that the performance is significantly higher than that without EDM. EDM can be used as a pretreatment process for the fabrication of SHS. It can also be applied to the EDM functional unit of parts to achieve specific functions. In addition, EDM for hole, the inner wall of the superhydrophobic hole was obtained, confirmed the excellent self-cleaning performance. This method has a good application prospect in the fabrication of SHS of metallic engineering materials.

Experiment investigation of using wire electrochemical machining in deionized water to reduce the wire electrical discharge machining surface roughness

When the workpiece is sliced by using wire electrical discharge machining (WEDM), the materials are removed by melting and evaporation. Owing to the material removal mechanism, the surface of the workpiece after WEDM is composed of recast layer and numerous discharge craters, leading to the low surface roughness. In this study, wire electrochemical machining (WECM) is introduced to eliminate the recast layer and improve the surface quality of the workpiece cut by using WEDM. Two methods, which are based on electrochemical dissolution reactions, are proposed to dissolve the recast layer and craters on the WEDM surface. The processes are conducted on the same machine tool with the same electrolyte (deionized water) and the same machining parameters. Two factors, which have a great influence on the surface roughness, namely the feed rate of the wire electrode and the movement distance of the workpiece, are analyzed. Experiment results show that the recast layer and craters on the WEDM surface can be dissolved owing to the anodic dissolution of WECM, and the surface quality can be improved. In order to obtain the good surface roughness, the wire electrode should be fed as slow as possible during the electrolysis, and the movement distance of the workpiece should be appropriate.

Corrosion Behavior of Wire Electrical Discharge Machined Surfaces of P91 Steel

The extensive usage of P91 steel in certain reactor components requires its precision fabrication by wire electrical discharge machining (WEDM). The WEDM cut surfaces consist of primarily re-melted and solidified layer (recast layer) of 2-8 µm. The recast layer is a result of fast removal of heat by unaffected metallic substrate and dielectric medium leading to rapid cooling. The WEDM surface is expected to affect the component performance in terms of its corrosion properties. The microstructural changes taking place due to EDM cutting of P91 steel bring about a drastic change in the electrochemical response of surface as compared to that for bulk P91 steel. The surface microstructure is shown to alter the passivation behavior and resistance to localized corrosion. Electrochemical polarization studies were done to evaluate passivation, pitting and intergranular corrosion (IGC) behavior and field emission gun—scanning electron microscopy was used for microstructural characterization of P91 steel surfaces. The passivation behavior for P91 steel WEDM cut surfaces was better than that for diamond polished surface. But pitting corrosion resistance decreased for the P91 steel WEDM surface which is a result of inhomogeneities in the microstructure of recast layer. The IGC resistance though increased due to the decreased grain size in the surface layer.

Application of TOPSIS to Taguchi method for multi-characteristic optimization of electrical discharge machining with titanium powder mixed into dielectric fluid

Mixing powder into dielectric fluid in electrical discharge machining (PMEDM) is a very interesting technological solution in current research. This method has the highest efficiency in simultaneously improving the productivity and quality of a machined surface. In this study, material removal rate (MRR), surface roughness (SR), and the micro-hardness of a machined surface (HV) in electrical discharge machining of die steels in dielectric fluid with mixed powder were optimized simultaneously using the Taguchi–TOPSIS method. The process parameters used in the study included workpiece materials (SKD61, SKD11, SKT4), electrode materials (copper, graphite), electrode polarity, pulse-on time, pulse-off time, current, and titanium powder concentration. Some interaction pairs among the process parameters were also used to evaluate the effect on the optimal results. The results showed that MRR and HV increased and SR decreased when Ti powder was mixed into the dielectric fluid in EDM. Factors such as powder concentration, electrode material, electrode polarity, and pulse-off time were found to be significant in the optimal indicator (C*) and the S/N ratio of C*. Powder concentration was also found to be the most significant factor; its contribution to C* was 50.90%, and S/N ratio of C* was 51.46%. The interactions of the powder concentration and certain process parameters for C* were found to be largest. The optimum quality characteristics were MRR = 38.79 mm3/min, SR = 2.71 μm, and HV = 771 HV. The optimal parameters were verified by experiment, and its accuracy was good (max error ≈13.38%). The finished machined surface under optimum conditions was also analyzed. The machined surface quality under optimum conditions was good. In addition, the results of the study showed the TOPSIS limitations of TOPSIS in a multi-criteria optimization problem.

Mathematical Modeling and Analysis of Spark Erosion Machining Parameters of Hastelloy C-276 Using Multiple Regression Analysis

Electrical discharge machining has the capability of machining complicated shapes in electrically conductive materials independent of hardness of the work materials. This present article details the development of multiple regression models for envisaging the material removal rate and roughness of machined surface in electrical discharge machining of Hastelloy C276. The experimental runs are devised as per Taguchi’s principles and empirical relations are established using multiple regression analysis. Taguchi’s methodology can be applied as a single aspects optimization technique for attaining the best set of possible process parameter for material removal rate and roughness of the machined surface. A statistical tool called analysis of variance is employed for determining the significance of input process variables that influences the desired performance measures such as material removal rate and roughness of the electrically machined surface. The developed multiple regression models are flexible, competent and precise in prediction of desired performance measures. The developed regression models were validated and the predicted results from the evolved regression models are closer with the experimental outcomes.