Metal Removal Mechanism of the EDM Process

Behaviors of Liquid Metal (Mercury) Caused by a Pulse Discharge in Water

Abstract

Behaviors of liquid metal (mercury) caused by a transient arc discharge in water (The maximum current is about 125 A of which duration is about 68μs) are studied in relation to the removal mechanism of the electrical discharge machining (EDM). Photographs are taken with an image converter camera or with a single still camera. It is observed that the small luminous particles scatter away from the vicinity of the arc region at the beginning of a bubble expansion. Small particles of the liquid metal, of which the number increases gradually, are also observed to be emitted from the projections created on the mercury electrode and scatter away during the expansion of a gas bubble. In this manner, they are removed from the mercury electrode. These phenomena vanish suddenly when the gas bubble begins to contract. In the case of a solid electrode, many cavities instead of the projections are observed near its surface in a bubble during the time period mentioned above. They also vanish suddenly after the beginning of the contraction of the bubble. It is apparently suggested that the projections observed in the case of the mercury electrode and cavities on the solid electrode are produced by the same reason; that is, these are created at the regions of partially low pressure on the surface of the electrode. Accordingly, these regions seem to be playing an important role in the removal phenomena of the molten metal on the EDM process; that is, it is concluded that the molten metal in the crater might be removed in the form of small particles from the workpiece showing the same removal mechanism as the case of mercury electrode.