The erosion rate in electric discharge machining is remarkably increased by letting the working fluid flow at high speed between an electrode and a work surface Flat work pieces of carbon steel are machined with a cylindrical electrode of graphite. The water-base working fluid mixed with electric-conductive powder is flashed through holes on the surface of the electrode. Use of this kind of the fluid permits not only of very high discharge current without any fear of firing but also of widening the discharge gap. The discharge current and the velocity of the working fluid are varied to 100-400A and 13-18m/s respectively. The experimental results indicate that with increasing the velocity of the working fluid at a constant discharge current the erosion rate increases finally approaching to a constant value over a critical velocity. The maximum erosion rate is shown to be proportional to the discharge current. The erosion rate with the positive polarity is about double as high as that with the negative polarity. Observation of the section of the work surface shows that increase of the erosion rate is due to perfect removal of the molton volume at the discharge point by the action of flow of Working fluid. The maximum erosion effeiciency obtained in the expericlent is 8g/kw min.

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In the electric Discharge machining the bubble grows at the electric discharge point. This bubble consumes part of the electric discharge energy.
We have calculated the percentage of the distributed energy, under the condition that the distributed energy is given by radiation and the bubble is a hemisphere.
Our calculation shows that in proportion as the electric discharge duration becomes shorter, the distributed energy and the gas pressure of the bubble become greater, and that a sudden change is to be seen This result agrees with the experiments.

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