Micro-EDM drilling of ZrB2-SiC-graphite composite using micro sheet-cylinder tool electrode

Abstract

The ZrB2-SiC-graphite composite is a promising engineering material for ultra-high temperature applications. However, the fabrication of micro-hole in this ceramic composite is difficult due to the high hardness. This paper presents micro-electrical discharge machining (EDM) drilling of the ZrB2-SiC-graphite composite using the micro sheet-cylinder tool electrode to improve the machining efficiency and quality of micro-hole. The micro-hole is firstly drilled by the sheet segment of electrode under the high capacitance, and then finish drilling is conducted using the cylinder segment of electrode under the low capacitance. The material removal rate, surface roughness, surface microcracks, debris, and material removal mechanisms are investigated. It is found that the material is removed by melting/evaporation and thermal spalling during micro-EDM of the ZrB2-SiC-graphite composite, and the thermal spalling effect produces the large size irregular debris. The electrode with the sheet shape can significantly increase the machining efficiency compared with the electrode with the cylinder shape. Furthermore, the surface roughness is reduced in finish drilling with the low capacitance. The experiment results of micro-holes machined by the sheet-cylinder electrode demonstrate that the presented method can improve the machining efficiency, surface quality, and machining accuracy.