What’s Electrical Discharge Machining (EDM)?


Electrical discharge machining (EDM) is a type of machining operation used for shaping conductive workpieces into geometrically complex parts. Electrical discharge machines are particularly well suited for machining components which have complicated contours or subtle cavities that would be difficult to produce with other conventional machining equipment. The process involves supplying electricity to both the shaping tool as well as the workpiece and then bringing the tool into close proximity using the workpiece, which is completely immersed inside a dielectric fluid bath. This proximity causes the electrical field intensity between the oral appliance workpiece to beat the strength of the dielectric fluid, and creates a series of electrical discharges between them. These electrical discharges remove material in the Electrical Discharge Machine, and also the pattern or shape of material removed relies upon the form of the tooling electrode. Following the machining operation, the dielectric fluid is replaced between the electrodes. Apart from serving as a dielectric between the two electrodes, the fluid also plays a vital role in the machining process, as it is accustomed to eliminate the removed material and cool the machined area. The character from the process is really that, while material is being removed from the workpiece; the tooling electrode can also be gradually eroded, making periodic replacement necessary.

AQ360L electric discharge wire cutting machine (immersion method) (Sodick)  - Joyofuji Kogyo Co., Ltd.

The electrical discharge machining process is incredibly precise and generally utilized in producing components that are typically complex and require extreme accuracy. In addition, another area of application that EDMs perform above par is incorporated in the machining and shaping of hard or exotic materials such as titanium, Hastelloy, Kovar, Inconel, as well as hardened steel. However, the only caveat with the electrical discharge machining process is it could be simply be combined with conductive materials.

There are essentially two types of electrical discharge machines, which differ in the type of tooling electrode that they are outfitted with. They are sinker EDMs and wire EDMs. The sinker EDM, also referred to as a ram EDM uses a shaped tooling electrode to facilitate the machining process. This tooling electrode is created by conventional machining right into a shape that is specific towards the application it is employed for as well as an exact reverse from the contour around be machined into the workpiece. The tooling, typically machined from graphite, is used by having an insulating fluid for example oil or any other dielectric fluids. This shaped tooling is linked to an energy supply making to approach the workpiece electrode, creating electrical discharges between them, which cause erosion in the desired shape. This kind of EDM is typically used for precise machining of complex 3D parts, such as injection molding, die tooling, along with other components that require exceptional accuracy.

The wire EDM, however, is an electrical discharge machine that uses an excellent metallic wire, usually made from brass, which acts as a cutting electrode to accurately shape intricate, complex components from thick metal plates. The wire and workpiece are generally supplied with electricity and when the wire approaches the workpiece, electrical discharges occur together. These discharges remove material in the workpiece inside a shape that resembles a cutting or slicing action. Because the wire electrode is eroding along with the workpiece, it is continuously fed into the workpiece from a spool to ensure uninterrupted cutting operation. The wire is fed through two guides, typically produced from diamonds, each placed above and below the workpiece electrode. These guides are movable on the 2-axis x-y plane and are CNC controlled for cutting. The cutting operation occurs on a workpiece that’s completely immersed in a dielectric fluid bath, normally de-ionized water, which is often used like a coolant and to flush away the removed material. This machining process can be used to chop complex and intricate 2D shapes on thick metal parts, especially components from hard and exotic metals such as Inconel and titanium. Some components commonly machined using wire EDMs are stripper plates, custom gears, along with other parts that should be intricately cut out. However, the arrival of upper guides and multi-axis freedom of movement in the newer wire EDMs, allows these machines to cut intricate tapers and transitional shapes as well.