EDM Defined

What is Electrical Discharge Machining or EDM?

Electrical Discharge Machining or EDM is a machining process commonly used on hard metals, thin metals, or those that would be impossible to machine with traditional techniques. A limitation of the process is that the material must be electrically conductive. EDM is very useful for cutting intricate contours and deep cavities that would be difficult to produce by traditional machining, grinding or other cutting tools. Close tolerances can be achieved with superior repeatability from part to part. Two big advantages to other machining processes include accuracy and surface quality. Some of the more common metals machined with EDM include hardened tool-steel, carbide, and exotic alloys such as hastalloy or titanium.

EDM removes metal by producing a rapid series of repetitive electrical discharges. These electrical discharges are passed between an electrode or brass wire and the piece of metal being machined. During the EDM process, small amounts of material are removed from the work piece and flushed away with continuously flowing fluid. The repetitive discharges work to remove tiny particles of material from the work piece until the final shape is produced.

Two Process Methods for EDM Machining

There are two EDM process methods: conventional (sometimes referred to as ram or sinker EDM) and wire EDM. The difference between the two involves the electrode used to perform the machining. In a conventional EDM application, a graphite electrode is machined with traditional tools. The machined electrode is connected to the power source, attached to a z-axis head, and slowly fed into the work piece. The machining operation is usually performed while submerged in a fluid bath of de-ionized water that acts as a conductor for the electrical current to pass between the electrode and the work piece. The fluid also helps flush material away while acting as a coolant to minimize the heat-affected zone.

In wire EDM a very small diameter brass wire, usually in the .010" diameter range, serves as the electrode. The wire is slowly passed through the material allowing the electrical discharges to cut the work piece. A thin kerf is created from the wire stemming from the removal of the tiny particles of metal. As with conventional EDM, wire EDM is also usually performed in a bath of de-ionized water to help conductivity, material flushing, and to minimize the heat-affected zone.

During the EDM process, neither the electrode nor the brass wire touches the metal to be cut. The electrical discharges remove small amounts of material and allow the wire or electrode to be moved or sunk through the work piece. The process is typically controlled by computer programming allowing for extremely complex shapes, close tolerances, and repeatability.

The most typical application for electrical discharge machining of parts is found in the tooling industry for manufacturing components for dies and molds. It is also a useful process for making very thin metal parts and producing prototypes that require a short lead time. Small hole drilling is another common application for EDM.

Request for more information on 3-D CNC's EDM precision services and EDM operations.