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Electrical discharge phenomena in EDM occur in a very short time period and in a very narrow space, thus making both observation and theoretical analysis extremely difficult. For this reason, the material removal mechanism in EDM has yet to be understood clearly. EDM is a thermal process. Thermal energy is generated by a pulse discharge between the workpiece and the tool electrode. It results in melting and evaporating followed by removal of both the workpiece and tool electrode, forming a discharge crater on both surfaces. In this paper, the hydrostatic pressure distribution in melting area was simulated by Molecular Dynamics (MD) methods. The analysis shows that after discharge is ignited, extremely high pressure is generated inside the melting area. The pressure distribution along the central axis of the melting area at different times indicates that during the discharge duration, the hydrostatic pressure quickly increases to a peak value along the depth direction of melting area and then reduced to 0 GPa in the unaffected area. It was also found that with the passage of time, the depth of the point where the pressure peaks increases with the formation of the discharge crater, accompanied by the decrease in the peak pressure. In addition, the ejected material atoms at different times during the removal process were also analyzed. It was found that the material ablation occurs mostly during the discharge duration.

This paper describes micro electrochemical machining (ECM) using the electrostatic induction feeding method. In ECM, electrolytic dissolution can be localized in the area where the gap width is narrow by using pulse durations shorter than several tens of nano-seconds. With the electrostatic induction feeding method which has been developed for micro electrical discharge machining, the current pulse of such short durations can be obtained more easily compared with the conventional pulse generators. In this study, the influences of the pulse voltage of power supply and feeding capacitance on the machining current were investigated theoretically. It was found that the current pulse duration is nearly equal to the rise time and fall time regardless of the pulse-on time of the pulse voltage. Hence, ultra-short pulses can be obtained without a need to use an expensive pulse generator. Micro-hole drilling carried out in a sodium nitrate aqueous solution with current pulse duration of 30ns showed that significantly small side gap of 2μm could be obtained.

In wire electrical discharge machining (WEDM), discharge current is one of the important factors which determine the machining properties, such as machining speed or machining accuracy. Previously developed machining simulators of WEDM, however, neglected the influence of workpiece conditions on the discharge current. Hence, this study developed a simulation tool for analyzing the discharge current in WEDM, where the electromagnetic field analysis around the wire electrode was coupled with the analysis of the equivalent circuit of the entire pulse generator circuit. The simulation results showed that, under the same pulse voltage and duration, the discharge current may change depending on the electromotive force which is determined by material properties, geometry and size of workpiece and wire electrode. In this study, the discharge current was calculated with different workpiece thicknesses. In addition, the discharge current was measured and compared with the calculation results in order to show the validity of the simulation tool.

In this paper, the attempt was made to study dry WEDG (Wire Electrical Discharge Grinding), the differences between dry WEDG and wet WEDG, especially the rods appearance and material removal speed and surface roughness were studied experimentally, the results are as follow: (1) The shape especially the symmetry of the rods fabricated with WEDG using kerosene as dielectric fluid is better than that of dry WEDG only using pure air as dielectric. (2) The material removal speed is obviously higher in wet WEDG than that in dry WEDG. (3) The surface roughness of the rods fabricated with wet WEDG is lower than that with dry WEDG;.(4) The wet WEDG can be used in the roughness machining to improve the speed, and the dry WEDG can be used in the finishing machining to advance the surface quality.

This research aims to develop a reverse simulation method to obtain the shape of tool electrode before machining from the shapes of workpiece before and after machining in sinking EDM. To apply the reverse simulation method to tool electrodes which have large curvatures, a special operation was added to the simulation program to consider the influence of the curvature. The validity of the principle of the modified reverse simulation was demonstrated in the machining of a V-shaped cavity.