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Electrical discharge machining, EDM is a non-traditional method of removing material from a work piece by means of heat energy. Like processes such as laser cutting, EDM process does not need mechanical force in the removal process. This is the reason why it is considered non-traditional, unlike, for example, machining with cutting tools.
Electrical discharge machining or briefly say EDM, is a very popular process in the production of tools and molds due to its use especially for hard materials such as titanium, or for particularly complex shapes that are difficult to achieve by conventional milling measures.
"An EDM process involves directing high-frequency electrical discharges from a graphite tool or soft metal that serves as an electrode to break down conductive materials such as hardened steel or carbide."
Simply put, electrical discharge machining is a production process that precisely removes materials from conductive materials using an electrode. Similar to pressing the mold into a soft material, the electrode leaves a negative impression on the work piece. The physical process is a bit more complicated: a small gap between the work piece and the electrode discharges, which removes the material by melting or evaporation. In this process, the electrode and work piece should be immersed into a dielectric fluid.
The key factor of EDM machines is the ability of controlled electric sparks to erode the materials. The work piece and electrode do not touch during EDM process. Between them there is a gap as thick as human hair. The amount of materials removed using one spark is small, but the discharge occurs roughly several hundred thousand times per second.
While the electrode is moved closer to the work piece, the electric field in the gap, also called the spark gap, increases until it reaches the puncture volume. In this process it is necessary that the fluid in which this discharge occurs is not conductive or dielectric. The discharge causes high heating of the material, melting small amounts of materials. This excess materials are removed with a constant flow of dielectric fluid. The liquid is also useful for cooling effect during processing. In addition, it is necessary to control the sparks.
There are three different types of electrical discharge machining. The one described above is called sinker EDM. It is also known as die sinking, cavity-type EDM, volumetric EDM, traditional EDM or frame EDM. Die sink EDM machines allows users to create complex shapes. This method requires electrodes (often made of graphite or copper) that are pre-treated to obtain the necessary shape. This electrode is then embedded in the work piece, creating a negative version of its original shape.
The second type of electrical discharge machining is wire discharge and it is also known as wire erosion, wire burning or sparks discharge. In Wire EDM process, thin wire is used to cut the work piece. In this case, the wire acts as an electrode. During processing, the wire always comes from the automatic spool feeder. If the cut is to be made in the center, not outside of the work piece, the EDM drilling small holes is used to make a hole in the work piece, through which the wire is then threaded. The wire is held with diamond guides. Usually de-ionized water is the fluid. The wire is often made of brass or copper.
The last type of EDM machines is called hole drillingEDM. As the name implies, the way of electrical discharge machining is used to drill holes. Compared to traditional drilling methods, EDM machines are able to process extremely small and deep holes. Additionally, drilled EDM holes do not require de-burring. The electrodes in this process are tubular, and the dielectric fluid is fed through the electrode itself.
In general, any conductive material can be treated by EDM machines. Typical materials include metals or metal alloys such as hardened steel, titanium and composites can be treated by this effective method.
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