In electrical discharge machining, it is able to work hardened steels with low electrode-wear by means of power control of electrical discharge (which makes a little value of im/τd). But it is unable to work cemented carbide alloys with low electrode-wear by means such as mentioned above. This paper describes, in case of using cemented carbide alloys as a work, decreasing electrode-wear in finish (worked surface has a roughness of about one μmRmax) and improving the characteristics of erosion rate in pre-finish (worked surface has a roughness of about ten μmRmax). Obtained results are as follows :
(1) Low electrode-wear of finish machining seems to be obtained by repeating uni-directional transient arcs which have the arc duration of sub-microsecond.
(2) In repeating transient arcs which have the arc duration of about ten microsecond, erosion rate of cemented carbide alloys (pre-finish) increases by larger discharge current. Particularly, erosion rate of cemented carbide alloys is getting to larger using silver-tungsten electrode than copper electrode. But it seems to be difficult to obtain low electrode-wear.
(3) In order to increase the erosion rate in finish, and to decrease the electrode-wear in pre-finish, it is necessary to develop power electronic technology in sub-microsecond domain.
