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Thursday, 22 August 2019
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Understanding EDM – Electric Discharge Machining

Imagine an inconceivably powerful thunderstorm, with hundreds of thousands of electrical discharges per second. A continuous barrage of lightning flashes, each single one leaving its traces. Where this lightning strikes, the temperature rises to dizzy heights. Even the hardest steel melts like butter, vaporises after the explosion into a whirl of gas, metal particles, ions and electrons. What remains is a crater on the surface.

Everything takes place in the tiniest dimensions
Scaling down to reality, however, the machine has everything under control.

The lightning flashes, at the most as long as a diameter of a hair – the discharge, sharp, hardly perceivable spark – the thunder, a subdued buzzing – and the devastation, a carefully targeted, high-precision recess in the metal surface.

Everything is regulated by sophisticated electronic and mechanical systems. Depending on the intensity, frequency, duration, length and polarity of the discharges, the results are very varied.

How do the sparks come about?

Two metal parts, submerged in an insulating liquid, are connected to a source of current which can be switched on and off at will. When the current is switched on, an electric voltage builds between the two metal parts.

If the two parts are brought together to within a hair’s breadth, the voltage is discharged and a spark jumps across. Where it strikes, the metal is heated up so much that it melts.

Innumerable such sparks spray one after the other (never simultaneously), and gradually shape the desired form in the piece of metal. Several hundred thousand such sparks must fly per second for efficient EDM.

Two processes are differentiated
  • Wire-cut EDM
  • Die-sinking EDM



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