The particle diameter of graphite material directly affects the surface roughness of EDM. The smaller the diameter, the lower the surface roughness value. A few years ago, graphite materials with a particle diameter of φ5 μm were used. The best surface for EDM can only reach VDI18 (Ra0.8 μm). Today, the particle diameter of graphite materials has reached within φ3 μm. Stable to VDI12 (Ra0.4 μm) or finer grades.
Copper material has low resistivity, compact structure, stable machining state easily obtained by EDM, stable processing under difficult conditions, surface roughness can be less than Ra0.1 μm, and mirror EDM .