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What is Electrical Discharge Machining (EDM)?
by Ron Bargman
Electrical discharge machining (EDM) is a type of machining operation used for shaping conductive workpieces into geometrically complex parts. Electrical discharge machines are particularly ideal for machining components that 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 with the workpiece, which is completely immersed in a dielectric fluid bath. This proximity causes the electrical field intensity between the tool and workpiece to overcome the strength of the dielectric fluid, and produces a series of electrical discharges between them. These electrical discharges remove material from the workpiece, and the pattern or shape of material removed is dependent on the shape of the tooling electrode. After the machining operation, the dielectric fluid is replaced between the electrodes. Apart from acting as a dielectric between the two electrodes, the fluid also plays a key role in the machining process, as it is used to flush away the removed material and cool the machined area. The nature of the process is such that, while material is being removed from the workpiece; the tooling electrode is also gradually eroded, making periodic replacement necessary.
The electrical discharge machining process is extremely precise and generally used in the production of components that are typically complex and require extreme accuracy. In addition, another area of application that EDMs perform above par is 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 that it can be only be used 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 known as a ram EDM uses a shaped tooling electrode to facilitate the machining process. This tooling electrode is formed by conventional machining into a shape that is specific to the application it is used for and an exact reverse of the shape to be machined into the workpiece. The tooling, typically machined from graphite, is used with an insulating fluid such as oil or other dielectric fluids. This shaped tooling is connected to a power supply and made to approach the workpiece electrode, creating electrical discharges between them, which cause erosion in the desired shape. This type of EDM is typically used for precise machining of complex 3D parts, such as injection molding, die tooling, and other components that require exceptional accuracy.
The wire EDM, on the other hand, is an electrical discharge machine that uses a fine 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 both supplied with electricity and when the wire approaches the workpiece, electrical discharges occur between them. These discharges remove material from the workpiece in a shape that is similar to a cutting or slicing action. As 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 made from diamonds, each placed above and below the workpiece electrode. These guides are movable on a 2-axis x-y plane and are CNC controlled for cutting. The cutting operation occurs on a workpiece that is completely immersed in a dielectric fluid bath, normally de-ionized water, which is used as a coolant and to flush away the removed material. This machining process is used to cut 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, and other parts that need to be intricately cut out. However, the advent 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.
About the Author
Ron Bargman, president of Zycon.com, has been fascinated and involved with the engineering and manufacturing processes required to turn ideas into products for over 30 years. Mr. Bargman is a regular contributor of manufacturing theme articles, and his rich industry history provides insight into manufacturing and engineering events and changes that are timely, poignant, and relevant. Through Zycon, he is able to transfer his passion for the industry by assisting engineers, designers and inventors find the services, parts and components that they need to succeed.
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