How Does Electrical Discharge Machining Work?
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It Is So Small
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Electrical discharge machining, or EDM, works on the molecular level of removing metal. A high voltage is passed across a probe into the work piece, and material is removed. The work piece and probe are immersed in a fluid, generally kerosene. The fluid is passed through a series of filters and cleaned to remove the particles.
The Probe
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The probe can be machined conventionally, on a mill or lathe. This probe, once machined, is attached to a movable head piece so it can be manipulated into the work piece. An electrical current is passed through this probe, and whatever it comes in contact with, that shape will be made--a negative image of the probe.
The Current
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A high-voltage source with a minimum current is required for the work to be accomplished. This electrical source can also be made to change its frequency so more material can be removed at an efficient rate. The higher the frequency or pulses of electrical current, the faster the material removal and the more finite the particles. This can lead to a very precise negative image being created in the work piece.
The Fluid
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The entire operation must be conducted under a fluid so that oxidation does not occur and the hole is burned instead of particle removal at a determined rate. Kerosene is the industry choice due to its economical value and ready availability. The fluid is pumped into a tank where the work takes place. The fluid must go through a series of filters to clean the particles from the tank. A constant flow of clean fluid must be maintained in the process to remove the particles during the operation. If not, a clean "cut" will not be achieved.
Precision
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The work piece can be anything metal or electrically conductive. As the probe advances into the work piece, the material is removed at a small level. The rate of work accomplished fully depends on the probe's size, the fluid rate of particle removal and the constant power supplied to the probe and work piece. A highly precise negative image can be created from the probe. Looking under a microscope, the EDM piece is smooth, while conventional methods may look ragged or have jagged edges.
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