Showing papers on "Electrical discharge machining published in 2007"

A review on current research trends in electrical discharge machining (EDM)

Abstract: Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. A pulse discharge occurs in a small gap between the work piece and the electrode and removes the unwanted material from the parent metal through melting and vaporising. The electrode and the work piece must have electrical conductivity in order to generate the spark. There are various types of products which can be produced using EDM such as dies and moulds. Parts of aerospace, automotive industry and surgical components can be finished by EDM. This paper reviews the research trends in EDM on ultrasonic vibration, dry EDM machining, EDM with powder additives, EDM in water and modeling technique in predicting EDM performances.

Optimization of wire electrical discharge machining (WEDM) process parameters using Taguchi method

Abstract: Wire electrical discharge machining (WEDM) is extensively used in machining of conductive materials when precision is of prime importance. Rough cutting operation in WEDM is treated as a challenging one because improvement of more than one machining performance measures viz. metal removal rate (MRR), surface finish (SF) and cutting width (kerf) are sought to obtain a precision work. Using Taguchi’s parameter design, significant machining parameters affecting the performance measures are identified as discharge current, pulse duration, pulse frequency, wire speed, wire tension, and dielectric flow. It has been observed that a combination of factors for optimization of each performance measure is different. In this study, the relationship between control factors and responses like MRR, SF and kerf are established by means of nonlinear regression analysis, resulting in a valid mathematical model. Finally, genetic algorithm, a popular evolutionary approach, is employed to optimize the wire electrical discharge machining process with multiple objectives. The study demonstrates that the WEDM process parameters can be adjusted to achieve better metal removal rate, surface finish and cutting width simultaneously.

Near dry electrical discharge machining

Abstract: This study investigates the near dry electrical discharge machining (EDM) process Near dry EDM uses liquid–gas mixture as the two phase dielectric fluid and has the benefit to tailor the concentration of liquid and properties of dielectric medium to meet desired performance targets A dispenser for minimum quantity lubrication (MQL) is utilized to supply a minute amount of liquid droplets at a controlled rate to the gap between the workpiece and electrode Wire EDM cutting and EDM drilling are investigated under the wet, dry, and near dry conditions The mixture of water and air is the dielectric fluid used for near dry EDM in this study Near dry EDM shows advantages over the dry EDM in higher material removal rate (MRR), sharper cutting edge, and less debris deposition Compared to wet EDM, near dry EDM has higher material removal rate at low discharge energy and generates a smaller gap distance However, near dry EDM places a higher thermal load on the electrode, which leads to wire breakage in wire EDM and increases electrode wear in EDM drilling A mathematical model, assuming that the gap distance consists of the discharge distance and material removal depth, was developed to quantitatively correlate the water–air mixture's dielectric strength and viscosity to the gap distance

Calculation of Motor Capacitances for Prediction of the Voltage Across the Bearings in Machines of Inverter-Based Drive Systems

Abstract: The occurrence of high-frequency discharge bearing currents (also called "electric discharge machining (EDM) currents") that can occur in machines of inverter-based drive systems depends strongly on the value of the capacitive voltage divider "bearing voltage ratio" (BVR) of the machine. This paper presents a straightforward approach to calculate the involved motor capacitances in order to predict the voltage across the bearing and, thereby, the likeliness of such EDM currents that are caused by this voltage to occur. The approach is based on the design parameters of the machine and does not involve additional measurements. It combines ease of application and satisfying accurateness, and allows prediction of the risk of endangerment of an inverter-based drive system due to discharge bearing currents

Generating complicated surface with electrolyte jet machining

Abstract: In the electrolyte jet machining (EJM), the electrolytic current is supplied between the anodic workpiece and the cathodic nozzle via the electrolyte which is ejected from the minute nozzle. Only the workpiece material exposed to the jet is removed due to the anodic dissolution, because the electrolytic current is restricted to the limited area by the jet. In this study, an electrolyte jet machining system which can be used to process the complicated three-dimensional surface was constructed. This system is composed of an XY stage, a rotating axis and a high-speed bipolar power supply, all of which are cooperatively controlled by a personal computer. An algorithm was developed to obtain the scanning path and speed of the nozzle to process complicated shape by superimposing simple patterns. The optimized path and speed were thus obtained so that the summation of the squared difference between the superimposed and the required patterns at every checking point becomes minimal. In order to verify the effectiveness of the developed algorithm, simulation and experiment were carried out and the machining accuracy was analyzed. The good agreement between the simulated and produced shapes with the required one proves that the algorithm meets the purpose properly. Besides, the effect of machining conditions, especially the current density on surface roughness of produced patterns was examined. It was clarified that a high current density is not only necessary to reduce machining time but also to improve the surface roughness.

Influence of machining parameters on surface roughness in finish cut of WEDM

Abstract: Surface roughness is significant to the finish cut of wire electrical discharge machining (WEDM). This paper describes the influence of the machining parameters (including pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect, material and dielectric) on surface roughness in the finish cut of WEDM. Experiments proved that the surface roughness can be improved by decreasing both pulse duration and discharge current. When the pulse energy per discharge is constant, short pulses and long pulses will result in the same surface roughness but dissimilar surface morphology and different material removal rates. The removal rate when a short pulse duration is used is much higher than when the pulse duration is long. Moreover, from the single discharge experiments, we found that a long pulse duration combined with a low peak value could not produce craters on the workpiece surface any more when the pulse energy was reduced to a certain value. However, the condition of short pulse duration with high peak value still could produce clear craters on the workpiece surface. This indicates that a short pulse duration combined with a high peak value can generate better surface roughness, which cannot be achieved with long pulses. In the study, it was also found that reversed polarity machining with the appropriate pulse energy can improve the machined surface roughness somewhat better compared with normal polarity in finish machining, but some copper from the wire electrode is accreted on the machined surface.

Trepanning of Al2O3 by electro-chemical discharge machining (ECDM) process using abrasive electrode with pulsed DC supply

Abstract: Electro-chemical discharge machining (ECDM) of electrically non-conductive high-strength–high-temperature-resistant ceramics such as aluminium oxide (Al2O3) by trepanning method (i.e. orbital motion of tool) has shown the possibility of drilling large size holes by comparatively smaller electrodes efficiently and economically. However, at greater machined depth, the conventional electrode configurations and machining parameters show that machining performance gradually deteriorates with increase in tool depth and finally cause micro cracks on the machined surface due to thermal shocks at high voltage. To reduce this problem and to enhance the machining performance during trepanning operation of Al2O3, a spring fed cylindrical abrasive electrode of 1.5 mm diameter has been used under the effect of the three most influential parameters, namely, pulsed DC supply voltage, duty factor and electrolyte conductivity, each at five different levels to assess the volume of material removed, machined depth and diameteral overcut. The results obtained from this study revealed that pulsed DC has reduced the tendency of cracking at high supply voltage compared to smooth DC and the machining ability of the abrasive electrode was better than copper electrode as it would enhance the cutting ability due to the presence of abrasive grains during machining. In addition to this, trepanning provides the scope for drilling bigger holes.

An investigation of tube and rod electrode wear in micro EDM drilling

Abstract: This paper studies the influence of various factors contributing to micro electrode wear during electrical discharge machining (EDM) drilling with micro rod and micro tube electrodes. In this paper, a simple method for calculating volumetric wear ratios is proposed based only on geometrical information obtained from the process. The objective of the research is to investigate the wear behaviour of electrodes and the suitability of electrode wear compensation methods. Electrode shape deformation and random variation of the volumetric wear are studied as the main factors affecting the applicability of wear compensation methods and as an indicator of the accuracy achievable with the micro EDM process.

Effect of machining parameters on surface textures in EDM of Fe-Mn-Al alloy

Abstract: In this work, the surface characteristics caused by EDM were analyzed by means of the atomic force microscopy (AFM) technique. An empirical model of Fe-Mn-Al alloy was proposed based on the experimental data. A qualitative energy dispersive spectroscopic analyzer was used to measure the chemical composition of the specimen. Surface hardness was determined with a microhardness tester. Experimental results indicate that the EDM process causes a ridged surface and induces machining damage in the surface layer, and increases the surface roughness. The depth of micro-cracks, micro-voids and machined damage increase with an increase in the amount of pulsed current and pulse-on duration. The effect of the magnitude of the pulse-on duration on the surface texture of the specimen is more significant than the pulsed current. Furthermore, the AFM method reveals the 3D surface textures of the EDM specimen with a nanometer scale.

Surface quality improvement of wire-EDM using a fine-finish power supply

Abstract: This paper presents the development and application of a new fine-finish power supply in wire-EDM. The transistor-controlled power supply composed of a full-bridge circuit, two snubber circuits and a pulse control circuit was designed to provide the functions of anti-electrolysis, high frequency and very-low-energy pulse control. Test results indicated that the pulse duration of discharge current can be shortened through the adjustment of capacitance in parallel with the sparking gap. High value of capacitance contributes to longer discharge duration. A high current-limiting resistance results in the decrease of discharge current. Peak current increases with the increase of pulse on-time and thus contributes to an increase in thickness of recast layer. Experimental results not only verify the usefulness of the developed fine-finish power supply in eliminating titanium's bluing and rusting effect and reducing micro-cracking in tungsten carbide caused by electrolysis and oxidation, but also demonstrate that the developed system can achieve a fine surface finish as low as 0.22 μm R a .

Geometry prediction of EDM-drilled holes and tool electrode shapes of micro-EDM process using simulation

Abstract: EDM is an efficient machining process for the fabrication of a micro-metal hole with various advantages resulting from its characteristics of non-contact and thermal process. However, this process has a serious problem caused by the tool wear, which significantly deteriorates the machining accuracy. In this paper, a geometric simulation model of EDM drilling process with cylindrical tool is proposed to predict the geometries of tool and drilled hole. The geometries of tool and workpiece are represented by two-dimensional matrix. For accurate prediction of their geometries, the tool motion, the sparking gap width, the spark frequency, the crater made by a single spark, and the tool wear ratio are considered as simulation parameters. To verify the simulation model the prediction results are compared with the actual experimental ones. Consequently, it is shown that the geometry prediction results match the experimental ones well within the error of 13%. Developed model can be used in offline compensation of tool wear in the fabrication of a blind hole. For the purpose of this, a compensation scheme based on the developed model is introduced, it is then demonstrated that the scheme is successfully applied to an actual micro-hole machining.

The behavior of graphite and copper electrodes on the finish die-sinking electrical discharge machining (EDM) of AISI P20 tool steel

Abstract: The machining parameter settings installed at CNC EDM machines are developed under optimum process conditions. Standard workpiece and electrode materials are used traditionally by machine manufacturers to establish the EDM parameter settings. However, this is not the usual situation of the tooling industry, where many different grades of workpiece and tool electrode materials are used. Consequently, the customers are required to develop their own process parameters, which normally demand many experimental tests. According to the aforementioned argument an experimental er finish machining has been carried out. The tests were performed with graphite and copper as tool electrodes. Important EDM electrical parameters that influence the process performance were investigated. The measured technological outputs were the material removal rate Vw, volumetric relative wear ϑ and workpiece surface finish Ra . The main conclusions can be summarized as follows: the best results for material removal rate Vw were reached when EDM with negative graphite electrodes. Graphite and copper tools presented similar results of Vw for positive polarity. For graphite and copper tools the lowest values of volumetric relative wear were achieved for positive polarity. The best surface roughness Ra was obtained for copper electrodes under negative polarity. Keywords : sinking EDM, graphite and copper electrodes, tool steel, process parameters

Effects of powder additives suspended in dielectric on crater characteristics for micro electrical discharge machining

Abstract: The effects of using powder additives suspended in dielectric on crater characteristics for micro electrical discharge machining (PSD micro-EDM) are investigated through the conduct of single RC discharge experiments at low discharge energies of 2.5 µJ, 5 µJ and 25 µJ. Through the introduction of additive particles into the dielectric, results of the single discharge experiments show the formation of craters with smaller diameters and depths, and having more consistent circular shapes than those produced in dielectric without additive. These craters also possess a noticeable morphological difference compared to those generated in dielectric without additive. In addition, discharge current measurements show a smaller amount of charges flowing between the tool electrode and workpiece, and at a slower flow rate when additives are present in the dielectric. Furthermore, based on the experimental results and findings from studies done in nanofluids, a hypothesis is made on the effects of powder suspended dielectric on the crater formation mechanism. The increased viscosity and enhanced thermal conductivity of a powder suspended dielectric lower the plasma heat flux into the electrode and raise the rate of heat dissipation away from the molten cavity. As a result, a smaller-sized crater having a larger amount of resolidified material within the crater cavity is formed.