Sinker EDM

Electrical discharge machining (EDM) is an interesting process in itself because, unlike other areas of CNC machining, it is not mechanical friction that separates the excess from the work piece, but electrical discharge. The principle is that a positive electrical charge is applied to the work piece and a negative electrical charge to the electrode, and the discharge between the two parts melts the metal over an extremely small surface area, which is then removed from the work piece when the discharge ends. It is, therefore, the only machining process where the material of the tool may be significantly softer than the material of the work piece. As the craters are extremely tiny, down to nanometers in size, the series of craters gives an extremely fine surface. There are two main areas of CNC EDM: wire and sinker EDM.

Now we’ll talk about sinker EDM. While during wire electrical discharge machining, the stretched wire separates the material along a straight line, similar to a ribbon or a jigsaw, the electrode of a sinker EDM electrode sinks into the material as a kind of mold and removes the parts that match the shape of the electrode.

The limits of machining are extended by the fact that the electrode array can also be moved during sinker electrical discharge machining, so that, for example, a rod-shaped electrode can be moved in a circular motion to create a disc-shaped recess.

Sinker EDM has certain prerequisites. One of these is a precisely machined electrode, typically made of copper or graphite – or even tungsten when machining hard metals. Only precisely moldable materials with a good electrical conductivity are suitable as negative electrodes for sinker electrical discharge machining.

The other one is a liquid (dielectric material), in which both electrodes are immersed during the process. Deionized water or oil with a high ignition point may be used for this purpose. Not only does it cool the tool and the work piece during electrical discharge machining, but also removes the resulting material and helps to create a precise spark.

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