Fundamental study on formation of internal space shapes by EDM

In current mechanical machining technology, it is not easy to form an internal space shape inside a metal workpiece through a small-diameter entrance hole only by removal process. On the other hand, EDM is one of thermal machining methods that removes the material by the high temperature of discharges, and the tool electrode does not contact to the workpiece. The machining force acting on the electrode is very small. Therefore, it is highly expected that internal space shape may be machined if an optimum electrode structure can be designed. This study proposes a new internal space machining method by EDM using a revolution ball electrode consisting of a vertical rotation rod, a tilting rod, and an electrode ball. Experimental results show that the tilting angle between the vertical rotation rod and the tilting one can be changed by the rotation speed, and the electrode ball position can be controlled. Then, machining of some axially-symmetric spacial shapes, such as cylindrical shape and spherical one into a zinc alloy workpiece was succeeded. In addition, machining of internal space shapes by simultaneous two-axis control of the tilting angle and Z coordinate of electrode was possible. Therefore, this method has high possibility to create axially symmetric spatial shapes inside the metal.