Wire Electrical Discharge Machining
The physical principle of Electric Discharge Machining (EDM): In order to generate an electric spark between two electrodes, the voltage between the two electrodes must be higher than the gap between the electrode and the workpiece, while the breakdown voltage depends on:
- The distances between the electrode and the workpiece.
- Insulation capacity of electrolyte (the ratio of water and resistance)
- Pollution in the gap
The discharge occurs at the point where the electric field is strongest, which is a very complicated process; Positive ions and electrons accumulate in the field, and quickly form an ionized conductive channel. During this process, an electric current is formed between the two plates, and it causes numerous collisions between the particles that forms a plasma region. After that, the temperature rises up to around 8000 ° C to 12000 °C, and the materials are melted on the surface of the two conductors while a bubble is formed due to vaporization of the electrodes and the dielectric liquid, and its pressure level is very high at this point. Next, the electric current stops while the temperature suddenly drops as well that leads to the inward blast of the bubble. The power that generated by the blast of the bubble then throws the dissolved materials out of the crater, and then the dissolved materials reforms a small sphere in the dielectric fluid, then it is drained away by the dielectric liquid.
The problem of asymmetry between the electrode and the corroded workpiece depends on the thermal conductivity of the electrode, the melting point, and discharge density. When this happens on the electrode, it’s called loss, and when this happens on the workpiece, it’s called material removal.