Vibration-assisted servo scanning 3D micro EDM

Abstract

In scanning micro electrical discharge machining (EDM), the machining time for a 3D mould cavity is longer due to the smaller discharge area of a thin wire tool electrode. Moreover, a stable discharge area is hardly kept because of the scanning motion, resulting in a lower discharge ratio. To improve the machining process, a method of workpiece vibration-assisted servo scanning 3D micro EDM is developed. 3D micro structures are machined by tool electrode scanning layer by layer according to the numerical control (NC) code. Micro-amplitude assisting vibration is realized by adopting a piezoelectric (PZT) actuator driven by high-frequency sinewave voltage. Tool electrode wear is real-time compensated in the axial direction by keeping a discharge gap. A number of experiments were carried out to machine a micro rectangular cavity (900 µm × 600 µm), and the process model of vibration-assisted servo scanning EDM was established. In addition, several typical 3D micro structures have been machined. The process-model analysis and the experimental results show that the occurring frequency of the favorable discharge gap increases obviously during the machining process assisted with high-frequency vibration, so that the machining stability and the effective discharge ratio are improved. The machining efficiency increases to 6.5 times at the assisting vibration frequency of 5 kHz and the amplitude of 2.7 µm, and the material removal rate on red copper plate reaches about 1.4 × 105 µm3 s−1 with a tool electrode of 100 µm in diameter.