Electrical discharge machining (EDM) is a process that involves cutting or deforming metal by expelling many hot sparks at a high rate of disbursement along a substrate. The sparks work to shave down layers of the metal until the proper cut has been accomplished. Wire or wire cut EDM employs a wire fed from a spool that is guided along the workpiece, usually while submerged in deionised water. As the wire travels over the workpiece, it rapidly emits the sparks to machine the substrate, while CNC controls guide it in two or more axes. Although a wire EDM machine may be capable of multiple-axis movement and control, the technique is not typically used for complex geometries, but rather holes, punches and simple tools. Because of the strength of EDM, the process can be used to machine pieces as thick as 300 mm.
Wire EDM is a complex process that requires an appropriate amount of space within which to properly operate. However, because of the process’s strengths, it has gained popularity in home shops and at the hobbyist level. Home wire EDM construction requires experience and patience, but can be accomplished and put to use to obtain desirable results.
How Wire EDM Works
A typical wire EDM system features a platform area for the workpiece to sit during machining, over which an arm hands like a gallows. The wire, usually copper or brass, is connected to this arm on wheels to control the wire feed’s speed. Because copper and brass can wear through quickly, the wire constantly unspools along the wire path. When the arm moves along the workpiece, it acts like string cutting clay, but instead of pressure, there is a spark discharge to cut the path. The most commonly used wire is 0.355 mm in width, but both smaller and larger wires are used for different jobs. Any cut made by wire EDM will be slightly larger than the wire’s width, because the sparks will discharge around the wire as it machines. Wire EDM also requires a dielectric fluid, often deionized water, to both control the spark disbursement and flush away debris that gathers as it is cut away from the workpiece. Special dielectric EDM-specific oil is available as well.
Homemade and DIY Wire EDM
Making a homemade wire EDM machine requires patience and safety. There are numerous websites and books that can aid in the process; professionals recommend The EDM Handbook by E. Bud Guitrau (ISBN 1569902429, Hanser Gardner Publications) and Build an EDM by Robert P. Langlois (ISBN 0941653528, Village Press).
There are a few things to keep in mind to avoid dangers or malfunctions before getting started. First, professionals agree that obtaining the kind of precision in a homemade wire EDM machine that is available at a machine shop is incredibly difficult, largely because of the level of adaptive controls relative to the machine. In higher end wire EDM machines, adaptive controls are capable of maintaining a steady rate of movement, factoring in the wire strength, voltage, and machine movement. Additionally, maintaining wire integrity and dielectric flush pressure is performed electronically in modern machines, and designing or implementing the older type of jockey pulley and weight systems used to do this can be difficult. If a wire loses proper tension, it can create abnormal cuts, while it can simply snap if it becomes too taut. Dielectric fluid pressure is important to guide the sparks and ensure safety.
Additionally, because a homemade wire EDM system is unlikely to be as electronically advanced as a newer machine shop system, operating the homemade system requires extra attention. There will be no electronic devices surveying tension, guidance and pattern, so the operator must be experienced to properly move the workpiece or table to properly cut the material. It is important to position the machine in such a way that these movements will be fluid and not hampered by other pieces of machinery.
More technical information is readily available from DIY EDM books and various websites.