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The EDM system consists of a shaped tool, an electrode, and the workpiece. The workpiece is connected to a dc power supply. To create a potential difference between the workpiece and tool, the workpiece is immersed in a dielectric (electrically nonconducting) fluid which also acts to flush away debris.

The material removal rate and surface finish are all factors of the DC voltage supplied, current, discharge rate, and melting point of the workpiece. Material removal rate, ranging from 2 to 400 cubic mm/min, increases as current increases and as melting point decreases. A higher discharge rate gives a smoother surface finish.

The cutting pattern is usually computer numerically controlled (CNC) whereby servo motors position the workpiece as the electrode tool discharges. Some electrodes are designed to rotate about two axis allowing for cutting of internal cavities. This makes EDM one of the few processes that can do so.

EDM comes in two basic types: wire and sinker. Wire EDM is used primarily for shapes cut out of a flat sheet or plate of metal. With a wire EDM machine, if a hole needs to be machined, an initial hole must first be drilled in the material. Then the wire can be cut and fed through the hole to complete the machining. Sinker EDMs are generally used for very small pieces where conventional milling is not practical or very difficult due to the hardness of the material-such as die cast tooling. For example, they can cut a hole into the workpiece without having a hole pre-drilled for the electrode.

	A CNC Wire EDM Machine