The purpose of this study is to develop a new type of coated wire electrode for fine wire EDM. Piano wire with a very high tensile strength is coated with an electrically conductive brass layer to achieve high-speed and high-precision wire EDM. In our previous papers, using a thin wire of 50μm diameter, the thickness and quality of the brass coating layer were optimized and the effect of the tensile strength of the piano wire used as the core wire was discussed. In this report, the effect of unevenness of the brass wire electrode surface was experimentally investigated. As a result, it was found that by using wire with relatively large surface unevenness, the machining rate increased because of the high discharge frequency. Also, a more uniform distribution of the discharge location was confirmed by high-speed observation of the working gap during the process. In addition, the electrostatic field in the gap between the wire electrode and workpiece surface was analyzed and the reason for the high machining rate for the wire with relatively large surface unevenness was discussed from the viewpoint of the distribution of electric intensity distribution on the wire surface.
