Electric discharge machining (also known as EDM), sometimes colloquially also referred to as spark machining, spark eroding, burning, die sinking or wire erosion, is a manufacturing process whereby a wanted shape of an object, called work piece, is obtained using electrical discharges (sparks). The material removal from the work piece occurs by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is called tool-electrode and is sometimes simply referred to as ‘tool’ or ‘electrode’, whereas the other is called work piece-electrode, commonly abbreviated in ‘work piece’. When the distance between the two electrodes is reduced, the intensity of the electric field in the volume between the electrodes is expected to become larger than the strength of the dielectric (at least in some point(s)) and therefore the dielectric breaks allowing some current to flow between the two electrodes. This phenomenon is the same as the breakdown of a capacitor (condenser) (see also breakdown voltage). A collateral effect of this passage of current is that material is removed from both the electrodes. Once the current flow stops (or it is stopped – depending on the type of generator), new liquid dielectric should be conveyed into the inter-electrode volume enabling the removed electrode material solid particles (debris) to be carried away and the insulating proprieties of the dielectric to be restored. This addition of new liquid dielectric in the inter-electrode volume is commonly referred to as flushing. Also, after a current flow, a difference of potential between the two electrodes is restored as it was before the breakdown, so that a new liquid dielectric breakdown can occur.
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