2021 年 87 巻 5 号 p. 461-466
Curved hole drilling method by electrical discharge machining (EDM) using suspended ball electrode composed of a metal ball and flexible thin foil has been developed, and it was clarified that curved and bending holes with various curving and bending angles into various workpiece materials could be machined by controlling the workpiece tilting angle during the process. However, the shape accuracy of the holes is not sufficient for practical applications. In order to improve the shape accuracy of bending holes, the bending hole EDM drilling technique using a foil supporting guide was proposed in this study. In EDM drilling into aluminum alloy and carbon steel, the drilling performance was very stable. Without using the foil supporting guide, the bending angle was larger than the designed one at the bending corner. By contrast, bending holes with various bending angles, such as 10 - 100°, could be accurately formed by using the foil supporting guide. Furthermore, practical hole shapes, such as Z-, U-, Y- and T-shapes were successfully formed by combining bending and straight holes.