Electrical discharge machining (EDM) is a process of metal machining in which a tool discharges thousands of sparks to a metal workpiece.
A non-conventional process, EDM works on parts resistant to conventional machining processes, but only if these parts are electrically conductive; usually, they are non-ferrous, and include steel, titanium, super alloys, brass, and many other metals. Instead of cutting the material, EDM melts or vaporizes it, leaving little debris and providing a very accurate line. Industry-wide acceptance has led to a wide variety of EDM applications, as it is highly versatile, can cut hard metals, and utilizes a relatively compact amount of workspace.
Differences Between Wire Cut and Conventional EDM
There are two main types of EDM: conventional and wire. Conventional EDM, as described above, uses a tool to disperse the electric current. This tool, the cathode, runs along the metal piece, the anode, and the electrical current reacts to melt or vaporize the metal. As a result of the dielectric fluid, what little debris produced washes away from the piece. Wire cut EDM (or WCEDM) discharges the electrified current by means of a taut thin wire, which acts as the cathode and is guided alongside the desired cutting path, or kerf. A dielectric fluid submerges the wire and workpiece, filtering and directing the sparks. The thin wire allows precision cuts, with kerfs as wide as three inches and a positioning accuracy of +/- 0.0002”. This heightened precision allows for complex, three-dimensional cuts, and produces highly accurate punches, dies, and stripper plates.
Wire cut EDM equipment is run by computer numerically controlled (CNC) instruments, which can control the wire on a three-dimensional axis to provide greater flexibility. Whereas conventional EDM cannot always produce tight corners or very intricate patterns, wire EDM’s increased precision allows for intricate patterns and cuts. Additionally, wire EDM is able to cut metals as thin as 0.004”. At a certain thickness, wire EDM will simply cause the metal to evaporate, thereby eliminating potential debris. The wire of a WCEDM unit emits sparks on all sides, which means the cut must be thicker than the wire itself. In other words, because the wire is surrounded by a ring of current, the smallest and most precise cutting path possible is the added diameter of the ring and wire; technicians easily account for this added dimension. Manufacturers continue to produce thinner and thinner wires to allow for smaller kerfs and even finer precision.
Wire Cut EDM Applications
Because of its versatility, manufacturers use wire cut EDM functions for an extensive range of applications. Because the process can cut very small pieces, it is often an ideal choice for the production of small, highly detailed items that would normally be too delicate for other machining options.
Additionally, the process is cost effective for low quantity projects and can prove to be beneficial in prototype manufacturing, even if the actual project is carried out by different means.
It is important to remember that the wire in the process is constantly moving, and not to be reused. As a result, the copper, brass or other metallic wire can be kilometers long, adding to the cost. And, while the process uses no force and thus does not cause burns and can be used on delicate items, the possibility of thermal stress is certainly present.