Reducing electrode wear ratio using cryogenic cooling during electrical discharge machining

In this study, cooling effect of copper electrode on the die-sinking of electrical discharge machining of titanium alloy (Ti-6Al-4V) has been carried out. Investigation on the effect of cooling on electrode wear and surface roughness of the workpiece has been carried out. Design of experiment plan for rotatable central composite design of second order with four variables at five levels each has been employed to carry out the investigation. Current intensity (I), pulse on-time (t _on), pulse off-time (t _off), and gap voltage (v) were considered as the machining parameters, while electrode wear and surface roughness are the responses. Analysis of the influence of cooling on the responses has been carried out and presented in this study. It was possible to reduce electrode wear ratio up to 27% by electrode cooling. Surface roughness was also reduced while machining with electrode cooling.     

Modelling of surface finish,electrode wear and material removal rate in electrical discharge machining of hard-to-machine alloys

Hard-to-machine alloys are commonly used for industrial applications in the aeronautical, nuclear and automotive sectors, where the materials must have excellent resistance to corrosion and oxidation, high temperature resistance and high mechanical strength. In this present study the influence of different parameters of the electrical discharge machining process on surface roughness, electrode wear and material removal rate have been studied. Regression techniques are employed to model arithmetic mean deviation Ra (μm), peak count Pc (1/cm), material removal rate MRR (mm³/min) and electrode wear EW (%). All these parameters have been studied in terms of current intensity supplied by the generator of the electrical discharge machine I (A), pulse time t_i (μs), duty cycle η and open-circuit voltage U (V). This modelling allows us to obtain mathematical data and models to predict that the most influential factor in MRR and Ra is the current intensity and in the case of EW and Pc is the pulse time.     

Investigating and removing the re-sticky debris on tungsten carbide in electrical discharge machining

Electrical discharge machining (EDM) is an excellent method to machine tungsten carbide with high hardness and high toughness. However, debris from this material produced by EDM re-sticking on the workpiece surface remarkably affects working efficiency and dimension precision. Therefore, this study investigated the re-sticky phenomenon of tungsten carbide and how to reduce the debris re-sticking on the workpiece surface. In general, the polarity in EDM depended on the different electrical parameters of the machine input and the different materials of the tool electrode. The first item of investigation observed the re-sticky position of the debris to study the effect of different polarities during the EDM process. Next, the tool electrode was set at different conditions without rotation and with a 200 rpm rotational speed to evaluate the rotating effect in EDM. Finally, different lift distances of the electrode and different shapes of electrode with rotation were utilized to investigate the improvement for reducing debris re-sticking on the machining surface. The results showed that only negative polarity in EDM could cause the re-sticky phenomenon on tungsten carbide. On the other hand, debris would notably re-stick on any machining position when the tool electrode was not rotated in EDM. Besides, debris significantly stuck on the center of the working area with rotation of the electrode. Additionally, a larger lift distance of the tool electrode could reduce debris re-sticking on the working surface, but this process would decrease material removal rate in EDM. In the end, a special shaped design of the tool electrode resulted in the re-sticky debris completely vanishing, when the electrode width was 0.6 times the diameter of this cylindrical electrode.     

Influence of electrical discharge machining on sliding friction and wear of WC-Ni cemented carbide

Tribological characteristics of fine-grained WC-8 wt%Ni with different surface finishing conditions corresponding to sequential wire electrical discharge machining (wire-EDM) or grinding were investigated by performing dry reciprocating sliding experiments on TE77 pin-on-plate equipment with WC-6 wt%Co as mating material. Surface finishes and wear surfaces were characterized using surface topography scanning, SEM analysis and EDX spectrometry. The decreased wear resistance due to wire-EDM could be linked to flexural strength properties as well as XRD measurements revealing tensile residual stresses on wire-EDM surfaces, in contrast with the compressive stress state on ground surfaces. Substantial improvement of wear resistance was accomplished with finer-executed EDM steps.     

Accretion of titanium carbide by electrical discharge machining with powder suspended in working fluid

A surface modification method by electrical discharge machining (EDM) with a green compact electrode has been studied to make thick TiC or WC layer. Titanium alloy powder or tungsten powder is supplied from the green compact electrode and adheres on a workpiece by the heat caused by discharge. To avoid the production process of the green compact electrode, a surface modification method by EDM with powder suspended in working fluid is proposed in this paper. After considering flow of working fluid in EDM process, the use of a thin electrode and a rotating disk electrode are expected to keep powder concentration high in the gap between a workpiece and an electrode and to accrete powder material on the workpiece. The accretion machining is tried under various electrical conditions. Titanium powder is suspended in working oil like kerosene. TiC layer grows a thickness of 150 μm with a hardness of 1600 Hv on carbon steel with an electrode of 1 mm in diameter. When a disk placed near a plate rotates in viscous fluid, the disk drags the fluid into the gap between the disk and the plate. Therefore, the powder concentration in the gap between a workpiece and a rotational disk electrode can be kept high. A wider area of the accretion can be obtained by using the rotational electrode with a gear shape.     

Effect of processing parameters on structural features of tungsten carbide after electrical discharge machining (EDM)

Abstract

Tungsten carbide (WC) is an extremely hard material which is used extensively in the manufacturing of tools and dies. In the presence of cobalt as a binder its machining becomes a difficult task because of interfacial bonding. In the EDM process, where electrical energy is used for the machining of the substance, the heat generated due to the plasma is responsible for removal of the substance at the interface. The heat generated is conducted differentially because of the composite structure of the tungsten carbide cermet. In order to improve the technological performance it is essential to understand the morphological features of tungsten carbide after machining. The studies have been conducted using different machining parameters. The objective of this study is to analyse the impact of machining parameters on the morphology of tungsten carbide suitable to withstand impact load on press forging for small components during operation. Experiments have been performed with the specially designed fixtures with proper flushing arrangements, to avoid arcing during the process. WC of P20 grade which is one of the most suitable grade substances to withstand load after EDM, has been used as work piece material for the entire study. Copper, graphite and copper tungsten electrodes have been used for the present study. The morphological features were studied with the help of the scanning electron microscope (SEM). It was observed that structural features varied with variation in electrode under similar experimental conditions. Phenomenon of such structures is discussed at length. The formations of cracks on WC have also been studied in detail. The detail of this study is presented in the paper.     

Effect of ultrasonic vibration of tool on electrical discharge machining of cemented tungsten carbide (WC-Co)

This paper deals with the effect of copper tool vibration with ultrasonic (US) frequency on the electrical discharge machining (EDM) characteristics of cemented tungsten carbide (WC-Co). It was found that ultrasonic vibration of the tool (USVT) was more effective in attaining a high material removal rate (MRR) when working under low discharge currents and low pulse times (finishing regimes). In general, the surface roughness and the tool wear ratio (TWR) were increased when ultrasonic vibration was employed. It was observed that application of ultrasonic vibration significantly reduced arcing and open circuit pulses, and the stability of the process had a remarkable improvement. This study showed that, there were optimum conditions for ultrasonic assisted machining of cemented tungsten carbide, although the conditions may vary by giving other input parameters for those which had been set constant in the present work.     

Electrical discharge machining of the AISI D6 tool steel: Prediction and modeling of the material removal rate and tool wear ratio

In this investigation, response surface method was used to predict and optimize the material removal rate and tool wear ratio during electrical discharge machining of AISI D6 tool steel. Pulse on time, pulse current, and voltage were considered as input process parameters. Furthermore, the analysis of variance was employed for checking the developed model results. The results revealed that higher values of pulse on time resulted in higher values of material removal rate and lower amounts of tool wear ratio. In addition, increasing the pulse current caused to higher amounts of both material removal rate and tool wear ratio. Moreover, the higher the input voltage, the lower the both material removal rate and tool wear ratio. The optimal condition to obtain a maximum of material removal rate and a minimum of tool wear rate was 40 μs, 14 A and 150 V, respectively for the pulse on time, pulse current and input voltage.     

Analysis of energy distribution during electric discharge machining of tungsten carbide

Abstract

During electrical discharge machining (EDM) process, electrical energy is used for the machining of the components. Energy distribution in electrical discharge machining process is the distribution of input energy supplied during machining to various components. In order to improve the technological performance during EDM process, it is essential to understand the distribution of input energy in the entire system. An experimental study on the effect of EDM energy distribution parameter for tungsten carbide is presented. The copper tungsten electrode has been used for the study. Experiments have been performed in specially designed dielectric insulated tank. To minimise the energy wastage, workpiece as well as the electrode was covered with Teflon. Current and pulse duration have been selected as variable parameters. The objective of this study is to analyse the amount of electrical energy used for machining effectively. The detail of this study has been presented in this paper.     

Dimensional analysis of tool wear in electrical discharge machining

The erosion phenomenon was analysed by dimensional analysis. An empirical equation was obtained which relates the volume of material eroded from the tool electrode to the energy of the pulse, density, thermal conductivity, specific heat and latent heat of vaporization of the electrode material.     

Influence of electrical conditions on performance of electrical discharge machining with powder suspended in working oil for titanium carbide deposition process

This paper describes the influence of the discharge current and the pulse duration on the titanium carbide (TiC) deposition process by electrical discharge machining (EDM) with titanium (Ti) powder suspended in working oil. Although the influence of the electrical conditions for removal EDM has been investigated, the criteria for deposition have not been discussed. In the experiments, a 1-mm copper rod was used for an electrode to prevent the flushing of working oil from the gap between the electrode and a workpiece. Ti powder reacted with the cracked carbon from the working oil, then depositing a TiC layer on a workpiece surface. A major criterion of the deposition or removal was the discharge energy over a pulse duration of 10 μs. A thickness of the TiC layer became the maximum at a certain discharge current and pulse duration. Larger discharge energy and power promoted the removal by heat and pressure caused by the discharge. The removal was classified further into two patterns; cracks were observed on the Ti-rich surface in removal pattern 1 and a workpiece was simply removed in removal pattern 2. The maximum hardness of the deposition was 2000 Hv. The workpiece about 10 μm beneath its surface was also hardened because of the dispersion of TiC. The machining conditions for the hardest deposition did not coincide with those for the highest one. Therefore, the discharge current and pulse duration should be optimized for the deposition.     

Modeling and analysis of the edge disintegration in the EDM drilling cobalt-bonded tungsten carbide

The characteristic feature of edge disintegration easily appears in the electric discharge machining (EDM) drilling processing of cobalt-bonded tungsten carbide (WC-Co). Such tendency reduces the strength against fatigue and results in a poor assembly tolerance. The objective of this paper was to present the mathematical models for modeling and analysis of the effects of process parameters, including the discharge current, pulse time on, duty factor, and capacitance value, on the disintegration factor at the entrance edge of drilled hole in the EDM drilling process of cobalt-bonded tungsten carbide. An experimental plan of a central composite design based on the response surface methodology (RSM) was employed to carry out the experimental study. The quadratic model of RSM associated with the sequential approximation optimization method was used to find the optimum settings of processing parameters. With the experimental values up to a 95% confidence interval, it is fairly well for the experimental results to present the mathematical model of disintegration factor. The results show that the interaction effect of discharge current with capacitance value has the greatest influence on the disintegration factor, followed by the capacitance value and the quadratic term of duty factor. The optimal settings of processing parameters obtained in this study represent the reduction of the 5.53% disintegration factor, which were compared with the results of initial processing parameters for drilling the cobalt-bonded tungsten carbide in the EDM process.     

超声电沉积制备电火花加工铜电极的研究

电火花加工中,电极是影响加工质量和加工效率的重要因素。电沉积是制备电极材料的有效方法,为了改善沉积层质量,将超声场引入到电沉积中,采用金相显微镜、扫描电子显微镜观察电铸铜层微观形貌,并测试显微硬度和电火花耐电蚀性。结果表明,超声电沉积得到的铜铸层晶粒更加细小、均匀,致密性好;显微硬度比普通电沉积铜提高20%以上;电极相对损耗低,抗电蚀性能得到提高。     

Investigating surface properties of OHNS die steel after electrical discharge machining with manganese powder mixed in the dielectric

Although electrical discharge machining is essentially a material removal process, efforts have been made in the recent past to use it as a surface treatment method. An additive powder in the dielectric medium affects the sparking action and helps in improving the surface properties. It may melt at the high temperature of the plasma channel and alloy with the machined surface under appropriate machining conditions. Breakdown of the hydrocarbon dielectric contributes carbon to the plasma channel. In this paper, changes in surface properties of oil-hardening non-shrinkable die steel after machining with manganese powder suspended in kerosene dielectric medium have been investigated. Results show improvement in microhardness by 73%, and no microcracks on the machined surface. X-ray diffraction analysis of the machined surfaces reveals the transfer of manganese and carbon from the plasma channel in the form of manganese carbide. Quantitative analysis of chemical composition by optical emission spectrometer confirms significant increase in the percentages of manganese and carbon.     

Influence of electrical discharge machining on the reciprocating sliding wear response of WC-Co cemented carbides

A number of commercially available WC-Co-based cemented carbides with 6 up to 12 wt.% Co were machined and surface finished by grinding as well as by wire electrical discharge machining (EDM) in demineralised water through a number of consecutive gradually finer EDM regimes. Comparative dry reciprocating sliding wear experiments on both wire-EDM and ground samples against WC-Co pins were conducted, using a pin-on-plate test rig, in order to investigate the influence of the EDM process on the tribological behavior. The worn surfaces of the investigated cemented carbides were scanned topographically and characterised by scanning electron microscopy (SEM). The post-mortem obtained wear volumes were compared to the online measured wear in order to determine correlations between wear volume and wear rate on the one hand and sliding distance on the other hand. The experimental results revealed a profound influence of surface finish conditions and distinctive EDM regimes on the wear behavior of WC-Co cemented carbides.     

Energy distribution in cool electrode of electrical discharge machining based on wave-particle dualism

This paper studies the energy distribution in cool electrode of electrical discharge machining (EDM) on the basis of the wave-particle duality of matter. First, the movement of electrons and ions in the discharge channel was investigated in this article through the wavelength calculation of particles in a discharge channel. The main characteristic of electrons is wave and the moving form is prioritized for diffraction. Ions are mainly characterized by particles. These ions continuously vibrate in the mean free path. Second, a numerical calculation model is proposed on the basis of particle movement. The temperature field in the discharge channel of the cool electrode in the EDM to the titanium alloy is examined using the ANSYS software and simulation result is validated experimentally. Experimental results show that the diameter of the electric corrosion pit on the cool electrode surface is 355?μm, which is less than the electric corrosion pit diameter of 470?μm on a conventional electrode surface. Eventually, the EDM experiment was carried out under the same processing conditions with the cool electrode and the conventional electrode, respectively. The result shows that using cool electrodes in EDM can reduce electrode wear and increase machining efficiency.     

Thermal simulation of machining of alumina with wire electrical discharge machining process using assisting electrode

Journal of Mechanical Science and Technology - Electrical discharge machining or Wire electrical discharge machining have proven to be an alternate mean for machining nonconducting materials to a...     

Study on effects of electrode material and dielectric medium on arc plasma in electrical discharge machining

In this paper, the arc plasma of electrical discharge machining (EDM) was simulated by coupling the flow field, the heat transfer field, and the electromag     

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.     

Experimental study on micro electrical discharge machining of porous stainless steel

Various cutter strategies have been developed during milling freeform surface. Proper selection of the cutter path orientation is extremely important in ensuring high productivity rate, meeting the better quality level, and longer tool life. In this work, finish milling of TC17 alloy has been done using carbide ball nose end mill on an incline workpiece angle of 30°. The influence of cutter path orientation was examined, and the cutting forces, tool life, tool wear, and surface integrity were evaluated. The results indicate that horizontal downward orientation produced the highest cutting forces. Vertical downward orientation provided the best tool life with cut lengths 90–380 % longer than for all other orientations. Flank wear and adhesion wear were the primary wear form and wear mechanisms, respectively. The best surface finish was achieved using an upward orientation, in particular, the vertical upward orientation. Compressive residual stresses were detected on all the machined surfaces, and vertical upward orientation provided the minimum surface compressive residual stress. In the aspect of tool wear reduction and improvement of surface integrity, horizontal upward cutter path orientation was a suitable choice, which provided a tool life of 270 m, surface roughness (R _a ) of 1.46 μm, and surface compressive residual stress of ?300 MPa.