Development of Ultra-high-precision Micromachining System using Dry EDM

本研究旨在开发一种利用干电火花加工（dry EDM）的超高精密微加工系统。在干式电火花加工中，借助通过薄壁管电极供应的高压气流，熔化的工件材料可以被移除并冲出工作间隙，而无需重新附着在电极表面上。该技术的最大优点之一是，在任何脉冲持续时间内，工具电极磨损率几乎为零。此外，与传统的以油为介质的电火花加工相比，加工反作用力小得可以忽略不计，加工表面产生的残余应力也很低。因此，干式电火花加工有望成为微加工中最有前途的技术之一。然而，材料的去除率比传统的电火花加工要低得多，因为在连续脉冲放电期间短路的概率高达95%，这是由于极窄的工作间隙。因此，为了降低短路的概率，首先在工作台上安装高频响应压电驱动器，由伺服控制器驱动，该伺服控制器与原电火花加工机床z轴伺服进给机构一起工作。其次，提高开路电压，以获得更长的间隙距离，防止短路；实验结果表明，两种方法均能显著提高材料去除率。为了缩小使用干式电火花加工可以实现的尺寸，应该取消使用管电极，因为管电极的最小直径是有限制的。因此，通过在放电间隙外的喷嘴向放电间隙提供氧气射流的方法，尝试了使用固体电极的干式电火花加工。在氧气条件下，WEDG加工的棒材的最小直径为5 μ m，直径为15 μ m、长度为200 μ m的棒材的畸变比在介质液体中加工的棒材畸变要小得多。此外，与传统的液体微细电火花加工相比，干式微细电火花加工的工具电极磨损率显著降低。少

This research aims to develop an ultra-high-precision micromachining system using dry electrical discharge machining (dry EDM). In dry EDM, with the help of a high-pressure gas flow supplied through a thin-walled pipe electrode, the molten workpiece material can be removed and flushed out of the working gap without being reattached to the electrode surfaces. One of the greatest advantages of this technique is that the tool electrode wear ratio is almost zero for any pulse duration. Furthermore, the process reaction force is negligibly small and the residual stress generated on the surface machined is quite low compared with the conventional EDM using oil as the dielectric liquid. As a result, the dry EDM is expected to be one of the most promising techniques for micromachining.However, the material removal rate is considerably lower than that of the conventional EDM, because the probability of short circuiting during successive pulse discharge ranges up to ninety five percent due to th … More e extremely narrow working gap. Hence, to lower the probability of short circuiting, first a high frequency response piezoelectric actuator was installed on the working table and driven by a servo control which operates together with the original servo-feed mechanism of the Z-axis of the EDM machine. Secondly, the open voltage was raised to obtain a longer gap distance to prevent short circuiting. Experimental results show that both measures are effective to obtain a dramatic increase in the material removal rate.To scale down the size which can be achieved using the dry EDM, usage of the pipe electrode should be eliminated, because there is a limitation in the minimum diameter of the pipe electrode. Hence, the dry EDM using solid electrode was tried by means of supplying oxygen gas jet to the discharge gap from a nozzle which is positioned outside the gap. The minimum diameter of rods machined by WEDG in oxygen gas was 5 mu m, and the distortion of the obtained rod 15 mu m in diameter and 200 mu m in length was much smaller than that obtained in a dielectric liquid. Furthermore, the ratio of tool electrode wear in the dry-micro-EDM was found to be significantly low compared with that obtained with the conventional micro-EDM in liquid. Less