Development of on-the-Machine Surface Modification Technology in EDM

As a method of processing cemented carbide, sinking electrical discharge machining (EDM) is generally used. However, typical surface defects, such as cracks, microcraters and recast layer, lead to a decreased surface integrity, probably resulting in a short tool life. Under the present situation, the recast layer is removed by polishing. However, this process extends the machining time and increases the cost of production of metal molds. Therefore, it is desirable to eliminate these surface defects by some methods. Thus, an on-the-machine surface modification technology in EDM, for the complete elimination of surface defects, was developed in this study. The surface defects are eliminated using a sinking electrical discharge machine by introducing surface integrity machining for EDM (SIME) after applying finishing EDM. SIME is conducted by applying voltage to the constant gap between electrode and workpiece in deionized water. It can be considered that a recast layer including cracks is selectively eliminated by the dissolution of cobalt based on the electrolytic action during SIME. As a result, the surface defects generated by EDM could be completely eliminated by incorporating SIME into EDM.