Electrical Discharge Machining (EDM) is a machining method primarily used for hard metals or those that would be very difficult to machine with traditional techniques. EDM typically works with materials that are electrically conductive. EDM can cut intricate contours or cavities in pre-hardened steel without the need for heat treatment to soften and re-harden them. This method can be used with any other metal or metal alloy such as titanium, hastelloy, kovar, inconel and to shape polycrystalline diamond tools. EDM is primarily divided into two types: wire cutting EDM and sinker EDM.
Wire cutting EDM, a thin single-strand metal wire, usually brass, is fed through the work piece, submerged in a tank of dielectric fluid, typically deionized water. Wire-cut EDM is typically used to cut plates as thick as 300mm and to make punches, tools, and dies from hard metals that are difficult to machine with other methods. The wire, which is constantly fed from a spool, is held between upper and lower diamond guides. The guides usually CNC-controlled, move in the x–y plane. This allows the wire-cut EDM to be programmed to cut very intricate and delicate shapes.
Sinker EDM, also called cavity type EDM or volume EDM, consists of an electrode and work piece submerged in an insulating liquid such as, more typically, oil or, less frequently, other dielectric fluids. The electrode and work piece are connected to a suitable power supply. The power supply generates an electrical potential between the two parts. As the electrode approaches the work piece, dielectric breakdown occurs in the fluid, forming a plasma channel, and a small spark jumps. These sparks usually strike one at a time. These sparks happen in huge numbers at seemingly random locations between the electrode and the work piece. As the base metal is eroded, and the spark gap subsequently increased, the electrode is lowered automatically by the machine. This process continues uninterrupted. Several hundred thousand sparks occur per second, with the actual duty cycle carefully controlled by the setup parameters.
EDM advantages include:
1. Complex shapes (difficult to produce with conventional cutting tools).
2. Extremely hard material to very close tolerances.
3. Very small work pieces (where conventional cutting tools may damage the part).
4. No contact between tool/work piece (Delicate materials machined without distortion).
5. A good surface finish can be obtained.
6. Very fine holes can be drilled.
7. Pipe or container internal contours and internal corners down to R .001".