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Abstract: A new mechanism of cutting pipe combined with electrical discharge machining (EDM) is designed. The mechanism is set up on the working table of electrical discharge machine and used to investigate the effects of machining parameters such as material removal rate (MRR), relative electrode wear rate (REWR) on machining characteristics. The machining variables including machining polarity, peak current, pulse duration and the rotary speed of electrode have been chosen to explore the machining efficiency. The purpose of this study is to confirm the mechanism could not only increase material removal rates but also decrease the electrode wear rates in the EDM process. [Copyright &y& Elsevier]

As previously reported, several insulating ceramics such as Si3N4, SiC and ZrO2 have successfully been machined by sinking electrical discharge machining using the surface discharge modification phenomenon. As unstable discharges occur during the machining of Al2O3 ceramics, inferior machining properties have been obtained as compared to other ceramics. It seems that the formation process of the electrically conductive layer on the workpiece during discharge is much different compared with that of other dissociated ceramics at high temperature. In this study new methods are devised and the electrical discharge machining mechanism of insulating Al2O3 ceramics is researched using high purity alumina and single crystal Al2O3 of sapphire. Machining properties are dependent on the purity and structure of the workpiece, and correlated to its thermal properties. [Copyright &y& Elsevier]

Electrical discharge machining became a commercial process after the discovery of the importance of the dielectric fluid, which affects factors such as productivity and quality. Health, safety and environment are also important factors, particularly when oil-based fluids are used. This paper presents a literature survey on the use of dielectric fluids that provide an alternative to hydrocarbon oil. It has been reported that water-based dielectrics may replace oil-based fluids in die sink applications. Gaseous dielectrics such as oxygen may also be the alternative. Nonetheless, these need further research in order to be commercially viable. [Copyright &y& Elsevier]

In order to achieve high removal rate and low electrode wear in sinking electrical discharge machining (EDM) a stable machining process is required. The process stability is partly influenced by the contamination of the gap between the workpiece and the electrode. Additionally, it also depends on the size of the eroding surface at the given machining regime. When the eroding surface size varies with the depth of machining, the roughing regime has to be selected on-line. The work presented in this paper shows that the average discharge voltage depends on the eroding surface size. Through sets of experiments at constant machining parameters, varying size of the eroding surface and varying geometry of engaged surface were investigated. The average discharge voltages were calculated on the acquired electric voltage signals in the gap. The average discharge voltage is simple for on-line monitoring and it enables on-line detection of the eroding surface size as well as the on-line selection of the rough machining parameters. Thus the average discharge voltage depends on the geometry of the engaged surface, the prototype of the engaged surface has to be presented to the model for successful selection of the roughing regime as well. [Copyright &y& Elsevier]

In this paper, the machining phenomena in the electrical discharge machining (EDM) process are investigated through a new method of in-process measurement of gap distance. The aim of this study is to understand the cause of short-circuiting and to improve the machining rate. A pipe electrode is used and the working fluid is supplied to the gap space though a fixed restrictor and the pipe electrode. Since the pressure between the fixed restrictor and the tip of the pipe electrode (fluid pressure) depends on the gap distance, the absolute value of the gap distance can be determined in-process by measuring the fluid pressure. It is found that the gap distance at the moment when the short-circuiting occurs is more than several micrometers. This result indicates that the cause of the short-circuiting is the bridging of the gap space by collected debris. Based on these results, a new gap control method in which the gap distance is kept constant even when short-circuiting occurs is examined. [Copyright &y& Elsevier]

Electrical discharge machining (EDM) is widely used for manufacturing various kinds of dies and molds. However, EDM has numerous problems such as low material removal rate and generation of heat-affected zones, in which there are numerous cracks and microcraters. Recently, many new machining technologies utilizing EDM have been developed. However, the mechanism of material removal in EDM has not yet been sufficiently explained. In this study, to clarify the mechanism of material removal, first, the impulsive force transitions in an impulse discharge were measured. Second, how the mechanism by which the impulsive forces affect the crater formation by impulse discharge was examined. The following results were obtained: (1) a typical waveform obtained from an impulse discharge in kerosene consists of primary, secondary, tertiary and quaternary waves, and the intervals between the peaks of the waves gradually become smaller; (2) because the shape of the crater is strongly dependent on the polarities under the same conditions in EDM, the effect of the impulsive force acting between the workpiece and the electrode on the crater formation by impulse discharge may be insignificant. [Copyright &y& Elsevier]

In this paper, it is shown that dynamic optimization problems of first-order systems can be transformed into a static parametric programming problem, where the state plays the role of the parameter. Thus, an optimal feedback law is obtained. This concept is applied to the die-sinking electrical discharge machining, a highly time varying industrial process which necessitates adaptation of machining settings during operation. It is shown that the minimum-time operation of this process is equivalent to choosing the manipulated variables that maximizes the speed of machining at every position. [Copyright &y& Elsevier]

Electrical discharge machining (EDM) is used as a precision machining method for the electrically conductive hard materials with a soft electrode material. But recently we succeeded to machine on insulating material by EDM. The technology is named as an assisting electrode method. The EDMed surface is covered with the electrical conductive layer during discharge. The layer holds the electrical conductivity during discharge. For micro-EDM, the wear of tool electrode becomes lager ratio than the normal machining. So the micro-machining is extremely difficult to get the precision sample.In this paper to obtain a fine and precise ceramics sample, some trials were carried out considering the EDM conditions, tool electrodes material and assisting electrode materials. Insulating Si3N4 ceramics were used for workpiece. The machining properties were estimated by the removal rate and tool wear ratio. To confirm the change of micro-machining process, the discharge waveforms were observed. The micro-machining of the Ø0.05 mm hole could be machined with the commercial sinking electrical discharge machine. [Copyright &y& Elsevier]