On-machine process of rough-and-finishing servo scanning EDM for 3D micro cavities

Abstract

Although servo scanning 3D micro electro discharge machining (SS-3D MEDM) can achieve a high discharge ratio, the processing efficiency is still lower than expected because the discharge area at micro-electrode tip is much smaller than the area to machine. In particular, for 3D micro cavities, the processing efficiency and the machining accuracy inherently contradict each other. In this paper, an on-machine process of rough-and-finishing SS-3D MEDM is proposed with consideration that most cavity material cannot affect the dimensional accuracy. In the rough machining process, technological measures such as high discharge energy and large-diameter tool electrodes are applied to maximize processing efficiency. In the finishing machining process, a small amount of material is removed for dimensional accuracy, smooth surface, and clear edges-and-corners by changing multi-factors of machining parameters. The research is concentrated on two key techniques: rough-and-finishing border strategy and micro tool-electrode precision measurement for the process transformation from rough to finishing. Moreover, an online measurement method is proposed by the point electric contact between a micro electrode and a standard thin-rod, and the measurement accuracy was up to ±1 µ m in our experimental system. Machining experiments of 3D micro cavities < 800 µ m verified the proposed methods and the processes including 3D model design, rough-machining, micro-electrode measurement and fabrication, and finishing machining. The experimental results were successfully achieved as follows: the dimensional accuracy < 5 µ m, surface roughness S a0.38 µ m, and the processing efficiency being improved to 2.4 times.