In EDM, the tool and work piece is submerged in dielectric liquid. When the two electrodes are supplied with electricity, an intense magnetic field is generated between them. Microscopic particles contained in the dielectric fluid are attracted by the magnetic field and are concentrated in the fields strongest point. The concentration of particles creates a high-conductivity bridge between the two electrodes. As power supplied to the electrodes is increased, the bridge heats up to the point of ionization which turns it into a spark channel. This melts and vaporizes materials from the work piece and the tool. In EDM, the melting and vaporizing action is what shapes the work piece into its final form.
Graphite electrodes are the most widely used type of tool. Graphite has several advantages that makes it preferred by many operations.
Graphite is easy to machine, making it one of the most affordable options. The uniform gradient of graphite makes it resistant to the differential expansion caused by heat which can cause cracks in other electrode materials.
Graphite does not melt but breaks down directly from solid to gas at high temperatures. This minimizes residue which can affect the quality of the machined material.