Showing papers on "Electric discharge published in 2022"

Dynamic characteristics and energy analysis of Microwave-induced metal discharge

Abstract: Small sparks or electric arcs referred to as microwave discharge are generally observed, when the metals are subjected to microwave irradiation. The dynamic characteristics of microwave-induced metal discharge in the work were evaluated by the evolution of discharge intensity, measured using photo-voltage conversion method. An energy analysis method of hydro-thermal exchange was used to measure the generated heat from microwave discharge. The performances of microwave-induced metal discharge were connected to microwave power, metal spices, size and quantity. It was revealed iron exhibited more favorable discharge performance than aluminum and copper. The discharge intensity of iron was 1.66 times and 1.22 times that of aluminum and copper, respectively. The increase of microwave power from 320 W to 480 W led to an enhancement of discharge duration, extending from 5.75 min to 7.25 min. The discharge intensity in the presence of three wires of iron increased by 44.6%, compared to that in the presence of one wire of iron. In spite of an appreciable decrease of discharge intensity with the increase of time, microwave discharge could improve the efficiency from electric energy conversion into heat energy to 48.41%, when utilizing one wire of iron with the length of 4 cm and the diameter of 1 mm at 480 W. The changes of the generated heat with discharge intensity conformed to a stepped attenuation relationship.

Hydrodynamic arc moving mechanism in EDM of polycrystalline diamond

Abstract: ABSTRACT Polycrystalline diamonds (PCD) are difficult-to-cut materials due to their ultra-hardness caused by the diamond particles sintered in the materials’ structure. Electrical discharge machining is a universal nontraditional method to process electrically conductive hard-to-cut materials by using electro-thermal energy without considering the workpiece’s hardness and strength. However, due to the high electrical resistivity caused by the non-conductive diamond particles, EDM machining characteristics of PCD are different from those of metals. Dielectric flushing can disturb the position and shape of the plasma channel, resulting in predictable movements of the sparking spot, which provides the possibility of preventing the discharge from being trapped between the non-conductive particles during each single discharge. This paper explored the potential of improving the processability of PCD by utilizing the moving electric arcs formed by dielectric flushing. Mathematical models were established and simulated to investigate the movement behavior of plasma channels in one single-pulse discharge for the first time. A series of experiments were conducted to investigate the theory and validate the assumptions. The results showed that dielectric flushing stretched the plasma channel and changed the spots of the arcs, which increased the material removal rate and improved the consistency of the processed surface topography.

Influence of Different Dielectrics and Machining Parameters for Electrical Discharge-Assisted Milling of Titanium Alloy

Abstract: The machinability of the hybrid machining method for electrical discharge assisted milling (EDAM) has been validated in previous research. The influence of three different dielectrics (kerosene, EDM oil, and deionized water) on the performance of the EDAM was investigated in this study. An analysis of the discharged signal, surface morphology, and elemental composition of the electrode under different machining parameters reveals the influence of different dielectrics. The results show that compared with deionized water, kerosene and EDM oil have a higher discharge frequency. After long-term discharge, debris and carbides will be generated during processing, which will affect the microhardness and discharge stability of the processed material. Among the result of EDAM, EDM oil produced the best surface integrity, with surface roughness values 34.93%, 87.92%, and 121.68% lower than those of kerosene, deionized water, and conventional milling (CM), respectively. The results show that EDAM reduces the microhardness after machining by reducing the plastic deformation of the surface.

A Novel Flushing Mechanism to Minimize Roughness and Dimensional Errors during Wire Electric Discharge Machining of Complex Profiles on Inconel 718

Abstract: One of the sustainability goals in the aeronautical industry includes developing cost-effective, high-performance engine components possessing complex curved geometries with excellent dimensional precision and surface quality. In this regard, several developments in wire electric discharge machining have been reported, but the influence of flushing attributes is not thoroughly investigated and is thus studied herein. The influence of four process variables, namely servo voltage, flushing pressure, nozzle diameter, and nozzle–workpiece distance, were analyzed on Inconel 718 in relation to geometrical errors (angular and radial deviations), spark gap formation, and arithmetic roughness. In this regard, thorough statistical and microscopical analyses are employed with mono- and multi-objective process optimization. The grey relational analysis affirms the reduction in the process’s limitations, validated through confirmatory experimentation results as 0.109 mm spark gap, 0.956% angular deviation, 3.49% radial deviation, and 2.2 µm surface roughness. The novel flushing mechanism improved the spark gap by 1.92%, reducing angular and radial deviations by 8.24% and 29.11%, respectively.

Study of the Structure and Mechanical Properties after Electrical Discharge Machining with Composite Electrode Tools

Abstract: Our study was devoted to increasing the efficiency of electrical discharge machining of high-quality parts with a composite electrode tool. We analyzed the chemical composition of the surface layer of the processed product, microhardness, the parameter of roughness of the treated surface, residual stresses, and mechanical properties under tension and durability with low-cycle fatigue of steel 15. Our objective was to study the effect of the process of copy-piercing electrical discharge machining on the performance of parts using composite electrode tools. The experiments were carried out on a copy-piercing electrical discharge machining machine Smart CNC using annular and rectangular electrodes; electrode tool materials included copper, graphite, and composite material of the copper–graphite system with a graphite content of 20%. The elemental composition of the surface layer of steel 15 after electrical discharge machining was determined. Measurements of microhardness (HV) and surface roughness were made. Residual stresses were determined using the method of X-ray diffractometry. Metallographic analysis was performed for the presence of microdefects. Tensile tests and low-cycle fatigue tests were carried out. The mechanical properties of steel 15 before and after electrical discharge machining under low-cycle fatigue were determined. We established that the use of a composite electrode tool for electrical discharge machining of steel 15 does not have negative consequences.

Prediction of Kerf Width and Surface Roughness of Al6351 Based Composite in Wire-Cut Electric Discharge Machining Using Mathematical Modelling

Abstract: The machining of composite materials has been an area of intense research for the past couple of decades due to its wide range of applications, from automobiles to air crafts or from boats to nuclear systems. Non-conventional machining, especially electric discharge machining (EDM), is found to be a good machining option for meeting the required outputs. To overcome the challenges of machining complex shapes, wire electric discharge machining (WEDM) was developed. Al6351 composites was observed to be extensively used in nuclear applications. Therefore, identifying the kerf width and surface roughness are important criteria for the dimensional accuracy of the final product. The present work aims at predicting the behavior of the two major machining parameters which are kerf width and surface roughness of Al6351 composites in wire EDM by creating a mathematical model using ANOVA for different combinations of the reinforcements and comparing the variations in the coefficients for different combinations of reinforcements. The developed model has been validated by conducting similar set of experiments in Al6351-5% SiC-1% B4C hybrid composite. From the work, it was identified that pulse on time and current are the major contributing factor for kerf width and wire feed rate was observed to be contributing to the surface roughness. The validation results show an average variation of 8.17% for kerf width and 11.27% for surface roughness. The work can be successfully utilized for prediction of the kerf width and surface roughness of the composites manufactured with Al6351 as the base matrix material.

Surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages

Abstract: Due to the excellent properties, C4F7N/CO2 mixture is the most concerned eco-friendly SF6 alternative gas. For a better understanding of the surface discharge characteristics, the surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages is investigated in this work. The morphology of the surface discharge is obtained by an optical method and a dust figure method. The structure of the surface discharge is established, which from the outside to the inside consists of electron cloud, streamer, streamer stem, and leader. The propagation pattern of the surface discharge in C4F7N/CO2 mixture under negative impulse follows the stepwise expansion pattern. The structure of the surface discharge in C4F7N/CO2 mixtures with different ratios and SF6 has no obvious difference, and the propagation pattern is also the same. The results of this work can help to better understand the surface discharge phenomenon and the insulation characteristics of C4F7N/CO2 mixture.

Processes of Contact Interaction of an Electrolyte Plasma Jet with a Surface

Abstract: In this work, using an example of using current leads of different designs, the process of interaction of an electrolyte-plasma discharge with the surface of a metal anode at atmospheric pressure, at an incoming electrolyte temperature of 4–90 ℃ in the operating voltage range of 20 ℃ –500 V, with an interelectrode gap of 2–30 mm and a volumetric flow rate of electrolyte 2–90 l/h. It is shown that the surface morphology when interacting with an electric discharge varies over a wide range from a polished surface with a roughness parameter Ra of 0.034 μm to critical surface destruction by arc electric discharges. The results obtained make it possible to classify the discharges obtained as glow, spark, microarc, and arc discharges. The use of these discharges allows them to be used to create a technology for processing such complex products as coronary stents and turbine blades.

Enhancement Modelling Based on Electrical Discharge Machining Successive Discharges

Abstract: The surface roughness of Inconel 718 is predicted using a sequential discharge model for electrical discharge machining (EDM). To begin with, the EDM single pulse discharge machining process was accurately simulated using the finite-element method (FEM). The surface topography under various discharge settings, the size, and the characteristic parameters of a single-pulse crater are simulated. Second, the material defines the discharge position as the minimum gap width between the work piece’s starting surface and the electrode in the removal model. The simulation shows that the magnitude of the single-pulse discharge energy influences the crater’s form and size. A difference in discharge energy causes a divergence in the increasing crater radius, depth, and flanging height trends. On the other hand, the ultimate surface morphology of an EDM machined surface is determined by the distribution of discharge locations around the parts in the workpiece; finally, machined surfaces are inspected using the same discharge parameters. The EDM work piece’s surface morphology matches the material removal. Between simulation and experiment, there is a relative error in surface roughness around 8.26%, and there is a relative error in surface roughness.

Analysis of Particle Size and Concentration in Die Sinking Electric Discharge Machining

Abstract: Electric discharge machining with a powder mix dielectric is a promising technique to harden a work piece’s surface using electricity with a high energy density. The quality of the electrical discharge-machined surface is related to its surface integrity in which the surface’s roughness, residual stresses, micro hardness and surface micro cracks are some of the major factors. In this research, graphite powder was mixed in a dielectric with a particle size of 20 µm, 30 µm, and 40 µm, with the concentration of the graphite powder ranging from 2 g/L to 4 g/L. Moreover, the peak current and pulse time on were also coupled with an additive of graphite powder to investigate the effect on the surface quality, i.e., the recast layer thickness, micro hardness and crater depth as well as the material removal rate (MRR) and tool wear rate (TWR). A Box–Behnken design was employed to design the experiments and the experimental results revealed that the graphite powder size and concentration coupled with the electrical parameters (peak current and pulse time on) significantly influenced the recast layer thickness, micro hardness, crater size, MRR and TWR. The crater depth and micro hardness were maximized at a higher concentration and particle size, while the recast layer thickness was reduced with a higher gain size.

Modelling of Surface Roughness and Change in Out-of-Roundness of Tool during Electrical Discharge Machining with Cermet Tool Tip Using Machine Learning

Abstract: Surface roughness of the finished part and profile of the tool electrode are significant factors to assess the functionality of electrical discharge machining process. In this study, EDM was utilized for the machining of hardened EN31 steel. A sintered cermet tool tip with 75% copper–25% titanium carbide was fabricated and used as tool electrode. A data set of 262 such samples was developed with machining variables including discharge current (Ip), gap voltage (Vg), pulse on time (Ton), pulse off time (Toff) and flushing pressure (P). By correlating the machining variables, a machine learning-based regression model was developed for the prediction of surface roughness of the machined surface and change in out-of-roundness of tool during the EDM process. With the help of heat maps and a probability table, it was found that Ip, Ton, Toff and P had significant effect on SR, and Ip, Ton and Toff affected OOR. The machine learning-based regression equation predicted SR with average error of 1.6% and OOR with average error of 0.48%. It was found that machine learning-based regression equation had better accuracy as compared to a DOE-based regression equation.

A Unified Formula for Five Basic Forms of Discharge in an Electric Field Under Short Pulses

Abstract: This study proposes a unified formula for five basic forms of discharge—gas, liquid, solid, and vacuum breakdown, and vacuum surface flashover—under short pulses in an electric field. This formula considers the effects of the number of dimensions and pulsewidth on the electric field. It is verified by using the results of experiments reported at the Aldermaston Weapon Research Establishment (AWRE) and the Northwest Institute of Nuclear Technology. The ranges of application of this formula to different discharge forms are also summarized. The proposed formula can be used to transform experimental data at a small scale under a known pulsewidth into those at a large scale under the application pulsewidth and is thus important for designing insulation.

Measurement of discharge reaction force under different discharge conditions in WEDM using Hopkinson bar method

Abstract: This paper reports the measurement of discharge reaction force with respect to the discharge bubble in wire electrical discharge machining (WEDM) using the horizontal Hopkinson bar method. Using an RC discharge pulse generator circuit which is of the single pulse control functionality, independent discharges are ignited in the gap between the wire electrode and end face of the Hopkinson bar while deionized water is continuously flushed. The reaction force acting on the Hopkinson bar from a single discharge was measured without the interference of subsequent discharges. The peak value of measured discharge reaction force reached several Newtons level in both finishing and roughing. The waveform patterns of discharge reaction force in WEDM were found to be significantly different from that in sinking EDM. The first peak of the force acting on the Hopkinson bar was found to be equivalent to the force acting on the wire electrode based on the observation of the interelectrode gap using a high-speed camera. Moreover, the influences of different discharge conditions on the force were investigated.

High Voltage Electrochemical Explosion in Pulse-Discharge Technologies

Abstract: The analysis and generalization of the results of studies of high-voltage electrochemical explosions (HVECHE) proceeding under various conditions, driven by special aspects and needs of the existing HVECHE based pulse-discharge technologies, was carried out. A methodology to calculate combined energy sources is proposed in relation to the needs of various discharge-pulse technologies using a high-voltage electrochemical explosion. Based on the analysis of the results of experimental studies, the advantage of using a high-voltage electrochemical explosion with a controlled input of electrical energy into the discharge channel was substantiated. An algorithm was developed to calculate the parameters of a combined electric-discharge source of a controlled HVECHE and the required mass of the exothermic composition which provides the energy characteristics specified by a specific discharge-pulse technology. The results of testing the developed calculation algorithm are presented confirming the possibility of its use for engineering calculations of combined power sources with a controlled input of electrical energy into the discharge channel.

Electrodynamic Model of Combustion Chamber With Initiated Subcritical Streamer Discharge

Abstract: Various electrodynamic models of a combustion chamber with an initiated subcritical streamer discharge used to ignite a combustible air/fuel mixture are considered. To localize the discharge in the working chamber, initiators based on half-wave electromagnetic vibrators with resonant properties are applied. The dependencies of the structure of the electric field forming the discharge on the geometric parameters of the discharge initiator are obtained, and integration of the combustion chamber with the generator of microwave radiation is discussed. Calculations are performed for various orientations of the discharge initiator with respect to the optical axis of the chamber. Possibilities for further enhancement of the electric field at the poles of the initiator of a developed streamer discharge are discussed. The results obtained confirm the possibility of using subcritical streamer discharge in high-pressure combustion chambers. The ways of increasing the resulting electromagnetic field at the vibrator poles to form discharge with a developed streamer structure are determined. The results obtained are potentially important to study ignition and combustion of air/fuel mixtures induced by the subcritical streamer discharge.

Experimental optimization of electrical discharge coatings using conventional electrode

Abstract: • Experimental Optimization of electrical discharge coatings (EDC). • Copper coatings on titanium alloy (Ti6Al4V). • Anti-bacterial coating using Electrical Discharge Machine (EDM). • Identification of suitable input process parameters for copper coating. • Usage of readily-available electrodes in market for coating. In the last few years, researchers around the world are working to develop procedures that will allow coating a conductive material on another conductive base material using Electrical Discharge Machine (EDM). This process helps to extend the usage of EDM for the purpose of hard coatings. In this study, 24 experiments were conducted to coat copper on titanium alloy substrate by varying the coating input process parameters and surface treatments and output responses such as material deposition rate (MDR) and electrode wear rate (EWR) were calculated. Wherever it is necessary, L 9 orthogonal array design of experiments was implemented and all the coatings were taken for characterization with scanning electron microscope (SEM). With this characterization, surface morphology, coating thickness, coating-base material interface and surface crack density were studied to select one optimum coating for each case. Selected three coatings were considered for further characterization viz., phase analysis with X-ray diffraction (XRD) and surface topography with Atomic Force Microscopy (AFM). Phase obtained were Cu and TiZn 16 which were further heat treated to stabilize. Line and area profiles from surface roughness analysis was obtained and parameters such as min and max, peak and valley, Ra, Rq, Rz were evaluated.

Influence of Different Dielectrics on Process Performance for Electrical Discharge-Assisted Milling of Titanium Alloy

Abstract: Abstract Electrical discharge-assisted milling (EDAM) is an effective method for machining titanium alloys according to previous research. In this study, the influence of three different dielectrics (kerosene, EDM oil, and deionized water) on the EDAM performance was studied. Experimental studies reveal the influence of different dielectrics by analyzing the discharged signal, surface morphology, and elemental composition of the electrode. The results show that kerosene and EDM oil have a higher discharge frequency than deionized water. After a long discharge time, carbides and debris were generated during the machining process, which affected the micro-hardness and the discharge stability of the machined material. In EDAM, EDM oil can produce the best surface quality, and the surface roughness value was 34.93%, 87.92%, and 121.68% higher than that of kerosene, deionized water, and conventional milling (CM), respectively.