Wire electrochemical grinding of tungsten micro-rods using neutral electrolyte

A new method, wire electrochemical grinding(WECG), is proposed for machining tungsten micro rods with neutral electrolyte and bipolar current. The inevitable problem of tool wear due to the bipolar current can be eliminated by using a running wire as the tool electrode with this method. In this study, three kinds of wire guides were used for feeding the workpiece rod in the axial direction: cylindrical cemented tungsten carbide (WC) guide, cylindrical zirconium oxide (ZrO2) guide, and disk-shaped cemented WC guide, to investigate the influence of materials and configurations of the guide on the machining characteristics. The experimental results showed that the disk-shaped WC wire guide can realize higher machining accuracy because of less influence of stray current flowing through the gap formed between the machined micro-rod and wire guide. Even if the ZrO2 material has a much lower electrical conductivity than that of the cemented WC, the machining process was still influenced by the stray current between the micro-rod and wire guide. Furthermore, micro-rods were also machined by feeding the rod workpiece in the radial direction. Compared to when the workpiece is fed in the axial direction, the current was higher, which was clarified by the simulation of the current density distribution. However, the machining time was much longer than that with the workpiece fed in the axial direction because more machining steps were necessary to obtain a smooth side surface. With the workpiece fed in the axial direction method, a tungsten micro-rod of 35 pm in diameter was machined to the length of 163 pm. The results confirmed that the new method is capable of miniaturization equivalent to micro electrical discharge machining (EDM).