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Spark Erosion is a recent machining technique with lot of advantages in particular when machining difficult pieces with intricated shapes. The principle of spark erosion is uncomplicated. A workpiece and tool are placed in a working position in such a way that they do nor touch each other. The workpiece and the tool are conected to a DC source via a cable. The voltage applied between the electrode and the workpiece and the discharge current have a time sequence. The voltage builds up an electrical field throughout the space between the electrodes. They are separated by a gap which which is filled with an insulating fluid.
The cutting process therefore takes place in a tank. The workpiece and tool are connected to a D.C. source via a cable. There is a switch in one lead. When this is closed, an electrical potential is applied between the workpiece and tool. At first no current flows because the dielectric between the workpiece and tool is an insulator. However, if the gap is reduced then a spark jumps across it when it reaches a certain very small size. In this process, which is also known as a discharge, current is converted into heat. The surface of the material is very strongly heated in the area of the discharge channel. If the flow of current is interrupted the discharge channel collapses very quickly. Consequently the molten metal on the surface of the material evaporates explosively and takes liquid material with it down to a certain depth. A small crater is formed. If one discharge is followed by another, new craters are formed next to the previous ones and the workpiece surface is constantly eroded.
(Ref:http://www.unl.edu/nmrc) |