Fine Deep Boring of Carbide by EDM with YAG Laser

This paper deals with fine deep boring of carbide alloys. Fine deep boring by EDM is superior for obtaining a qualitatively machined shape and high surface integrity compared to conventional processes. However, it is difficult to obtain a microhole smaller than 100μm in diameter with an aspect ratio larger than 5, because of remaining bubbles and debris in the small gap between the electrode and workpiece which cause unstable machining. A new fine boring method is proposed in which EDM and laser beam machining are combined. First, a penetrating prehole is machined with a YAG laser. In the next process, micro-EDM boring is carried out on the prehole. By removing the bubbles and debris through the prehole, it is possible to maintain stable EDM. With these two successive processes, a fine deep hole is obtained. The hole made by this method has a good roundness and a high aspect ratio that cannot be achieved using only the EDM process. We applied this method to a superfine grain carbide alloy which is widely used for precise metal molds and cutting tools. The main results of this study are as follows. (1) Using the combined process of EDM and LBM, ∅160μm holes were successfully machined through a 2-mm-thick superfine grain carbide. (2) It is possible to remove the bubbles and debris efficiently by suction flow through the prehole. (3) In the case of EDM boring with a prehole, electrode wear mainly occurs on the side of the electrode. (4) For a 1-mm-thick workpiece, it is possible to bore a microhole with a diameter of 100μm and an aspect ratio of 10.