EDM of Tool Steel

Electrical Discharge Machining or EDM, as it is commonly known, is the process of machining tool steel through the use of an electrical current used to erode the surface of the tool. An electrical charge is passed between the anode, made of copper or graphite, and a cathode, the tool steel. The process takes place under a dielectric fluid.

EDM processing is a very efficient and economical method of producing tooling. This manufacturing process allows for the production of tooling with very intricate shapes that may not be produced by any other means.

There are two types of EDM processing, wire and conventional, or sinker. The main difference between the two types is the shape of the anode. In wire EDM machining, a small diameter wire (.005-.016”) typically made of copper or brass, carries the electrical current to the cathode, or tool. In the conventional EDM machining process, a copper plate or graphite block electrode is used. This electrode is fabricated into the reverse of the desired shape of the finished tool section and is used as the anode.

EDM white layer of tool steel caused by excessive exposure during the EDM process
Heat affected zone of tool steel depicting the resolidified, rehardened, retempered and unaffected base layers left behind after the EDM machining process.

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