Electrical Discharge Machining (EDM)

Electrical discharge machining, or EDM, is a non-contact process that can machine parts regardless of their hardness. It involves placing an electrode or wire and an electrically conductive workpiece into a circulating dielectric fluid. The fluid acts as an insulator until a specific spark gap and voltage ionizes it and enables a spark to travel to the workpiece.

Using a CNC, the operator moves the electrode or wire as needed and rapidly turns the current on and off. This accommodates the flushing of molten material (often called “swarf”) from the workpiece.

Source: Machining 101: What is Electrical Discharge Machining?

The two main types of EDM machines are sinker EDM machines and wire EDM machines.

Source: Machining 101: What is Electrical Discharge Machining?

Sinker EDM uses an electrode as its “cutting” tool, with the shape of the electrode serving as a mirrored, slightly smaller image of the finished form it will produce in the workpiece. The electrode makes one spark at a time — but the frequency of the current means the tool could produce anywhere between 500 and 30,000 sparks per second.

Electrodes for sinker EDM are typically either copper or graphite.

Source: Machining 101: What is Electrical Discharge Machining?

Wire EDM feeds a strand of wire from a supply spool to the workpiece via a wire drive system. The wire is energized by electrical contacts and passes through the workpiece at a specific velocity determined by the operation at hand. A stream or bath of deionized water surrounds the wire, and sparks are continuously emitted along the length of the wire. Rollers pinch the wire and provide tension, while guides above and below the workpiece position the wire on its path — helping it to achieve complex shapes on the workpiece.

The wires used in this process commonly have diameters of 0.010 to 0.012 inch, with finer wires at 0.001 to 0.004 inch. The material of the wires also holds great influence over the operation’s success, as hard wires that have insufficient tensile strength for an operation are liable to break under sudden shock. Softer wires prove more desirable for high-taper cutting operations.

Source: Machining 101: What is Electrical Discharge Machining?

During the EDM process, the operator moves the electrode or wire as needed and rapidly turns the current on and off. This accommodates the flushing of molten material (often called “swarf” or “chips”) that is removed from the workpiece.

Source: Machining 101: What is Electrical Discharge Machining?