Abstract
The surface generated by electrical discharge machining (EDM) appears to be generally mat. However, the machined surface in EDM with silicon powder mixed fluid becomes glossier and has a smaller surface roughness than that in conventional EDM with kerosine type fluid, which leads to the omission of finish hand lapping of metal mold. The quality of machined surface significantly depends on the kind of workpiece material, but the surface generation mechanism has not yet been made clear sufficiently.
In this study, the effect of silicon powder mixing on the surface generation mechanism is experimentally investigated, analyzing the shape of crater generated by a single pulse discharge, the surface roughness, the machined surface and so on. Main conclusions obtained are as follows:
(1) The gap distance in EDM with silicon powder mixed fluid is larger than that with kerosine type fluid, because of the lower resistivity of the former and the influence of silicon powder arrangement in the gap.
(2) EDM with silicon powder mixed fluid leads to smaller undulation of a crater, because of the smaller impact force acting on the workpiece due to evaporation and expansion of machining fluid.
(3) The more the precipitated carbides in the workpiece are, the larger the surface roughness is, since the carbides come off because of crack propagation due to the frequent heat impact during EDM.
(4) EDM with silicon powder mixed fluid results in the stable machining without short circuit between the electrode and the workpiece.
