In this paper, we clarify EDM conditions for shaping a hemispherical tool tip (ball end) via the electrode wear phenomenon. Electrodischarge drilling in brass wire with a rotating tool of tungsten or cemented carbide using an RC circuit and an oil-type working fluid was carried out under various conditions of parameters such as polarity, open-circuit voltage, capacitance, tool feed speed and tool feed. The results obtained are as follows. (1) Rough machining, where the tool is the anode and the wire is the cathode, followed by fine machining, where the tool is the cathode and the wire is the anode, enables the fabrication of hemispherical tool tips of 10μm and 20μm diameters with a shape error of 3%. (2) When boll-end shapes can be fabricated in rough machining, the experimental relation vh
p=c (v: tool feed speed, h: tool feed, p and c: characteristic constants) is found. (3) Estimative v-h relations for fabricating ball-end shapes of various diameters can be derived from the v-h relation experimentally obtained for a certain diameter and the geometrical relation obtained on the basis of the assumption that these shapes are realized when a hemispherical cavity is produced in the wire.
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