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Posted on Dec 17, 2020
The history of EDM manufacturing has to be traced all the way back to the 1950s, where a team of two Russian scientists were put to the task of finding ways to prevent tungsten from eroding due to sparking contact. This led them to invent the first electrical discharge machining (EDM) machine in 1943, capable of working materials like tungsten that is difficult to machine.
Electrical discharge machining (EDM) is a non-conventional method that is used to remove material from a workpiece using thermal energy. The EDM process is very much like laser cutting, except that the EDM process does not require mechanical force to perform the removal. This is the primary reason why EDM manufacturing is considered non-traditional, for the processes do not necessarily need to be accompanied by cutting tools. EDM process is very prevalent, especially in tool and mold making industries, because it has the capability of working hard-to-machine materials like titanium or other irregularly and complex shaped materials that are hard to machine with milling.
The history of EDM manufacturing has to be traced all the way back to the 1950s, where a team of two Russian scientists was put to the task of finding ways to prevent tungsten from eroding due to sparking contact. This led them to invent the first electrical discharge machining (EDM) machine in 1943, capable of working materials like tungsten that is difficult to machine. At the same time, an American team invented another electrical discharge machining model that is capable of removing broken drills and taps from aluminum castings. Many of the electrical discharge machining methods later were based on their inventions, and we refer to these latter creations as the die-sink EDM.
In the 1960s, wire-cut type electrical discharge machining (i.e., wire EDM), particularly used to make dies from hardened steel, started booming. The die electrode in wire EDM is basically a wire. The electrical discharge machining equipment at this point is capable of avoiding erosion and preventing the wire from breaking. Numerical controlled (NC) systems were first implemented into wire EDM in the 1970s, with the first NC-based wire EDM machine being manufactured in 1967. The wire EDM, later on, evolved into the computer numerical controlled (CNC) models, capable of more automation and programming flexibility. The first CNC wire EDM machine was created in 1976.
During the wire electrical discharge machining process, a metal piece is put into dielectric fluid, and a wire is fed through the immersed metal piece. An electrical current is directed through the metal workpiece to create discharge, or sparks, that will form the intended shape from the original metal piece. When the electrodes come close to each other, the intensity of the electric field grows and the strength of the dielectric fluid enhances consequently. Under these circumstances, the current can pass between the two electrodes more easily, allowing the desired metal shape to be gradually detached from the original metal piece with every spark. After the intended metal shape has been separated out of the metal piece, the process of flushing may be performed which utilizes the dielectric fluid to get rid of the excess material on the metal shape.
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As we already touched base briefly, wire EDM is a more evolved version of the die sinker EDM that uses a thin wire for an electrode. Traditional uses of wire EDM involved making dies, punches, and inserts from hard metals for tooling (die/mold) applications. The uses of wire EDM however have expanded as to part production which is now widely utilized in many industries.
Do note that sinker EDM still exists today despite being one of the earliest inventions. The modern die sinker EDM is mainly used to produce complex cavity shapes in tooling applications, such as plastic injection mold systems or metal stamping dies, but has also found use in a wide array of alternative production applications.
This type of electrical discharge machining process involves the use of a small hollow tube electrode typically made from brass or copper alloys to erode holes into the workpiece. This method is more of a prep-process for the wire EDM by preparing start holes. Over the years it has been developed to have the ability to produce small holes, making it the ideal electrical discharge machining process for niche applications like turbine engine parts manufacturing and medical devices.
The primary benefit of using EDM machines is that the likelihood of damage to the metal due to fixed electrodes is relatively (to other machining operations) low thanks to the continual supply of wire. Moreover, since EDM machines can work with hard material (namely wire EDM), a sub-machine for thermal treatments would not be necessary, thus the surface of the metal shape would be less likely to become distorted due to the absence of heat stress on the metal shape. As a result, smaller and more sophisticated metal shapes can be easily machined with high accuracy.
However, EDM machines do come with certain limitations. For instance, mechanists who are adept at the machining method are not easy to come by. Also, the rate of material removal is sometimes slow, despite being able to retain high accuracy. EDM machines also pose potential hazards correlated with the use of oil-based dielectrics that can easily lead to combustion if not careful. And in the specific case of a sinker EDM, it takes a substantial amount of time and cost just to create electrodes. Furthermore, mechanists often have trouble reproducing sharp corners on the workpiece because of the electrode wear. While power consumption is typically high during electrical discharge machining processes, additional costs may incur, and excessive overcut and tool wear may happen as well during machining.
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