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Theory

The workpiece, made of electrically conductive material, is connected to one pole of a pulsed power supply. The electrode is connected to the remaining pole of the power supply. A small gap is maintained between the two. An insulating (dielectric) fluid is flooded between the electrode and the workpiece. Its function is to provide a controlled amount of electrical resistance in the gap.

When a pulse of DC electricity is delivered to the electrode and the workpiece, an intense electrical field is created at the point where surface irregularities provide the narrowest gap. As a result of this field, naturally occurring microscopic contaminants suspended in the dielectric fluid begin to migrate and concentrate at the strongest point in this field. A high-conductivity bridge is formed across the gap as a result of these contaminants and particles.

At the beginning of the pulse, the voltage between the electrode and workpiece increases. This lead to an increase in the temperature of the material making up the conductive bridge. A small portion of the dielectric fluid and charged particles in conductive bridge vaporizes and ionizes resulting in the formation of a spark channel between the two surfaces.

At approximately the midpoint of the electrical pulse, the power supply decreases the voltage delivered to the gap, but raises the current. This results in increasing both the temperature and pressure in the spark channel. A small amount of material from the surfaces of both the electrode and the workpiece at the points of spark contact melts and vaporizes due to the extremely high temperature of the spark . Fed by the gaseous byproducts of vaporization, a bubble rapidly expands outward from the spark channel.

When the electrical pulse is terminated, the spark and heating action are stopped instantly. This causes both the spark channel and, consequently, the vapor bubble to collapse. The violent inrush of relatively cool dielectric fluid results in an explosive expulsion of molten metal from both the electrode and workpiece surfaces, resulting in the formation of a small crater in both surfaces. Small, rapidly solidified balls of material and gas bubbles represent the residue from the cycle. The dielectric fluid acts to remove these byproducts from the gap.

This entire sequence takes place in a period of only microseconds to milliseconds. This sequence is repeated from thousands to hundreds of thousands of times each second. The result is a uniform erosion of material from both the electrode and workpiece.

Information source: Benedict, Nontraditional Manufacturing Processes.