Study of precision micro-Electro-Discharge Machining (3rd Report)-Analysis of micro-EDM process with deionized water-

Abstract

The micro-EDM process with deionized water as a dielectric fluid is used for nozzle production because of its high speed and low tool wear benefits. However, this process causes the formation of defects due to the electrolysis corrosion and processing limitation of applicable materials. It was considered that the electrolysis corrosion is induced by the ion produced as a result of the electro-discharge process. The process mechanism is considered in line with the theory indicating that electrolysis occurs in the deionized water when a high voltage is applied. Oxygen and H+ are formed at the anode surface during electrolysis, the carbon in the anode is oxidized, and part of the metal is corroded. For tungsten carbide, the corrosion is severe. A pulse shorter than 40ns can inhibit electrolysis and allow a highly precise micro-EDM to use deionized water with tungsten carbide. The tool wear ratio is 0.025% by volume and the processing speeds that are 150 times higher than those under the same conditions using oil as a dielectric fluid are verified. In addition, the mechanism of the electrolysis corrosion in stainless steel and the capability of the improved surface quality to control the generated electrolysis are explained.