Fabrication of high aspect ratio micro-rod using a novel electrochemical micro-machining method

In this paper, a novel electrochemical micro-machining method is proposed to fabricate a tungsten micro-rod with a high aspect ratio. In this method, the periphery of the iron needle is surrounded by an insulator so that only its end face with the diameter of 50 μm is exposed on the electrolyte as the cathode of the tool electrode. A tungsten rod with a diameter of 200 μm is taken as the workpiece and the anode. These two electrodes are immersed to a depth of 3 mm in the electrolyte of 2 wt% sodium hydroxide. This small end face of the tool electrode is against the workpiece in vertically reciprocating motion with a certain stroke to conduct the electrochemical micro-machining under DC electric field. During the machining, since the diameter of the workpiece is gradually reduced, the tool electrode is adjusted so that the gap between its end face and the anode remains 30 μm. The effects of supply voltage or current, rotational speed and stroke of workpiece, and relative position between the end faces of electrodes on the geometry of one end of the workpiece are investigated. This relative position can be used to control the workpiece geometry at one end and its amount of the length reduction. When this relative position is adjusted to a preset position at each stroke, the ratio of the length to the diameter can be increased, but the average decreasing rate in diameter remains invariable. The novel method developed in this paper can fabricate an extremely thin straight rod in diameter of 2 μm with an aspect ratio of 120 from a tungsten rod with a diameter of 200 μm using a tool electrode with an end diameter of 50 μm under two-stage procedure.