What’s EDM (electrical discharge machining)?

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Electrical discharge machining (EDM) is a method used for hard, conductive metals to create intricate shapes using electrical discharges between an electrode and workpiece. Two methods, ram and wire, are used with a fluid bath to wash away material and prevent damage. Wire EDM uses a computer-controlled wire to cut complex shapes and is commonly used for dies, molds, and prototypes.

Electrical discharge machining (EDM) is a machining method used primarily for hard metals or metals that would be impossible to machine with traditional techniques. One critical limitation, however, is that it only works with electrically conductive materials. This method is particularly suitable for cutting intricate contours or delicate cavities that would be difficult to produce with a grinder, router or other cutting tools. Metals that can be EDM machined include hastalloy, hardened tool steel, titanium, carbide, inconel, and kovar.

This method is sometimes called “spark machining” because it removes metal by producing a rapid series of repetitive electrical discharges. These discharges are passed between an electrode and the work piece of metal. The small amount of material that is removed from the workpiece is washed away with a continuously flowing fluid. The repetitive relief creates a series of successively deeper craters in the workpiece until the final shape is produced.

There are two main methods of machining EDM: ram and wire. The main difference between the two is the electrode used to perform the machining. In a typical piston EDM application, a graphite electrode is machined with traditional tools. The now specially shaped electrode is connected to the power source, connected to a piston, and slowly inserted into the workpiece. The entire machining operation is usually performed while submerged in a fluid bath. The fluid serves the following three purposes:

washes away the material, acts as a coolant to minimize the heat affected zone, thus preventing potential damage to the workpiece, and acts as a conductor for current to pass between the electrode and the workpiece.

In wire EDM a very fine wire serves as an electrode. Specialty brass wires are typically used; the wire is slowly fed through the material and the discharges actually cut the workpiece. This method is usually done in a water bath.
If someone were to observe the wire EDM process under a microscope, they would find that the wire itself does not actually touch the metal being cut; the electricity actually removes small amounts of material and allows movement of the wire through the workpiece. The path of the wire is typically controlled by a computer, which allows for extremely complex shapes to be made.

Perhaps the best way to explain this method is to use the example of a thin metal wire stretched between two hands, slipped through a block of cheese, cutting into any desired shape. Hand positions can be changed on either side of the cheese to define complex, curved shapes. Wire EDM works in a similar way, except it can handle some of the tougher materials used in industry. In dragging a wire through cheese, of course, the wire actually moves the cheese as it cuts, but in EDM, a fine cut is created by removing tiny metal particles.

This form of machining is often used to make dies and molds. It has recently become a standard method of producing prototypes and some production parts, particularly in low-volume applications.

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