Research of Large-Area Electrical Discharge Machining for Insulating Si3N4 Ceramics with the Assisting Electrode Method

Generally, all insulating materials were regarded as the non machinable workpiece for the electrical discharge machining (EDM) method. About twenty years ago, many insulating ceramics turned to the machinable materials for EDM using the assisting electrode method which was proposed by our research group. The machining mechanism was already explained with the surface adhesion phenomena [1]. In this process, many unstable discharge phenomena occurred such as concentrate, short circle and long pulse. It was clarified that they generated frequently on the high electrical resistance surface. The EDMed surface became rough and uneven on the unstable discharged area. In this paper, to obtain the good and even EDMed surface on the large removal area same as small area machining for Sinking-EDM, the effects of electrode size and shape were investigated. Considering the path of discharge supply energy on the high resistivity surface, new machining method was proposed which was named as the scanning machining method, and the ability of this method for practical use was confirmed with Si3N4 insulating ceramics. Using the new proposal method, better surface roughness and the sharp corner edge shape could be machined on the large area EDMed surface.

Simulation on Material Removal during Reciprocating Traveling WEDM of Insulating Ceramics

With the double layer structure model, the material removal of insulating ceramics ZrO2 during the machining process by reciprocating traveling wire electrical discharge machining (WEDM) was simulated and analyzed. The influence of conductive layer (C and ZrC) to material removal volume and crater dimension was compared. And the effect of peak current, pulse duration and the movement speed of wire electrode on discharge craters were researched. The simulation shows that the conductive layer exist has much influence to the material removal volume and crater length and width, but has less influence to crater depth during electrical discharge. The simulation for the effect of discharge parameter tells that, with the boiling removal form hypothesis, the material removal volume during single discharge is increasing with the increment of peak current and pulse duration but decreasing with the raising of wire electrode movement speed. For the variation of peak current, the removal volume of ZrO2 is exceeding the removal volume of conductive layer when Ip is bigger than 24A. Meanwhile, for the variation of movement speed of wire electrode, the removal volume of conductive layer is more than that of ZrO2 when v is over 5m/s.

History and Future Prospect of Electro-ceramics in Japan and Asia

On the background of a long history of Japanese ceramics, various electro-ceramic materials have been studied and many kinds of electronic components using them have been developed in Japan. The first invention of electro-ceramics in Japan should be a ferrite at Tokyo Institute of Technology in 1930, and the mass production of ferrite started in 1937. Then, Japanese electro-ceramic industry has led the world on electro-ceramic materials and components until now, especially in the fields of BaTiO3, PZT, PTC thermistor, ZnO varistor and insulating ceramics. In recent years, new electro-ceramic materials, their processes and new devices using them have been still studied actively in Japan. Currently, R&D activities in Asia outside of Japan, and electro-ceramic industries in those areas have been grown steadily.