Page 134 - Module DMV20173

7.0 NON CONVENTIONAL PROCESSES

7.2 ELECTRICAL-DISCHARGE MACHINING

Figure 7.2 Electric discharge machining (EDM): (a) overall setup, and (b) schematic
diagram of arc formation in EDM process (Source : Groover, 2002)

1. The Electrical-Discharge Machining (EDM) process can be used on any material

that is an electrical conductor.
2. This phenomenon has been known since the early day of electricity.
3. However it was not until the 1940s that a machining process based on this

principle was developed.
4. The EDM process has become one of the widely used in industry, especially in
the mold and die manufacturing.

7.2.1 PRINCIPLE OF OPERATION

1. The EDM process involves a controlled erosion of electrically conductive
materials.
2. The process is possible by intiation of rapid and repetitive spark discharges

between the tool and workpiece separated by a small gap of about 0.01 to 0.50
mm.
3. This spark gap is either flooded or immersed in a dielectric fluid.
4. The basic EDM consists of an electrode or tool and the workpiece connected to a
DC power supply and placed in a dielectric fluid (Figure 7.1).

5. Initially the gap between the tool and the workpiece, which consists of electrically
non-conductive dielectric fluid, is not conductive.
6. When the potential difference between the tool and the workpieceis sufficiently
high, the dielectric breaks down and a transient spark discharges through the

fluid, removing a very small amount of metal from the workpiece surface.
BPLK 166 DMV 20173