In this study, an electrolytic micro-machining tester is employed to investigate the effects of supply voltage and initial machining position on the geometry of the tungsten needle using the single-point and the reciprocating methods. The tungsten needle to be electrolyzed is dipped in an aqueous electrolyte of 2wt % sodium hydroxide as the anode, and the stainless steel needle with a diameter of 100 £gm as the cathode, and the electrode gap is set to be 10 £gm. Experimental results show that it is difficult to control the diameter of the tungsten needle because the reduction rate of its diameter is quite fast and the bubbles are generated violently to cause the breakage of the tungsten needle at the higher supply voltage. At the lower supply voltage, the tungsten needle can be machined to a finer scale, but it takes a long machining time. Under the single-point machining condition, it can be used to manufacture a short, uniform, and smooth tungsten needle with the diameter of 9 £gm at the supply voltage of 12V and the initial machining position of 75 £gm. Under the reciprocating machining condition, a long uniform micro-cylinder tungsten needle can be manufactured, but its surface becomes rough slightly at the supply voltage of 4V and the initial machining position in the range between -50 and 0 £gm. A tungsten needle with the aspect ratio of 30 and the diameter of 9 £gm can be manufactured using the following process: the machining time of 24 min at the supply voltage of 4V, and then the machining time of 28 min at the supply voltage of 2V. Key words¡Gtungsten needle, sodium hydroxide

In this study, an electrolytic micro-machining tester is employed to investigate the effects of the supply voltage, the immerse depth of tungsten rod, and the machining time on the current waveform, the material removal rate, and the geometry of the tungsten needle. The tungsten rod to be electrolyzed is dipped in an aqueous electrolyte of 10 wt% sodium hydroxide as the anode, and the stainless steel ring as the cathode. The spindle rotating speed and the stirring rotating speed are set to be 100 rpm and 200rpm, respectively. According to analyze the topography of the tungsten needle, four machined regimes have been identified as:¡]1¡^non-machined regime,¡]2¡^incomplete machined regime,¡]3¡^complete machined regime,¡]4¡^over machined regime. In order to obtain the perfect tungsten needle, the experiments are conducted in the complete machined regime. Results show that the tungsten rod becomes a short cone for the immerse depth of 5 mm, and a long cone for the depth of 10mm. When the immerse depth of 10 mm and the supply voltage of 3V, the surface of tungsten needle becomes rough slightly and the tip radius of tungsten needle is about 2£gm. With increasing the supply voltage to 4.5 V, the surface of tungsten needle is uniform with a downward trend in material removal rate, and the tip radius can achieve a submicron. For the supply voltage of 6V, because the material removal rate varies violently, it becomes very difficult to control the diameter of tungsten needle. During the machining time between 0 to 10 min for the supply voltage of 4.5V, the diameter of tungsten rod is decreased from 1000 to 200£gm, but during the machining time between 10 to 12.5 min, the tungsten rod gradually transforms into the needle due to a downward trend in current, and the tip radius is decreased from 200£gm to submicron. Hence, the machining time must be controlled accurately to manufacture the needle in a submicron radius.