What is application of Electrical Discharge Machining ( EDM )

EDM is the thermal erosion process in which metal is removed by a series of recurring electrical discharges between a cutting tool acting as an electrode and a conductive work piece, in the presence of a dielectric fluid. This discharge occurs in a voltage gap between the electrode and work piece. Heat from the discharge vaporizes minute particles of work piece material, which are then washed from the gap by the continuously flushing dielectric fluid. There are two main types of EDMs;  the ram and the wire-cut. Each are used to produce very small and accurate parts as well as large items like automotive stamping dies and aircraft body components. 

The largest single use of EDM is in die making. Materials worked with EDM include hardened and heat-treated steels, carbide, poly crystalline diamond, titanium, hot and cold rolled steels, copper, brass, and high temperature alloys. However, any material to be machined with the EDM process must be conductive.

The benefits of EDM include:

1. EDM is a non-contact process that generates no cutting forces, permitting the production of small and fragile pieces
2. Burr-free edges are produced
3. Intricate details and superior finishes are possible
4. EDM machines with built-in process knowledge allow the production of intricate parts with minimum operator intervention

The limitations of EDM include:

1. Low metal removal rates compared to chip machining  
2. Lead time is needed to produce specific, consumable electrode shapes

In ram EDM, the electrode/tool is attached to the ram which is connected to one pole, usually the positive pole, of a pulsed power supply. The work piece is connected to the negative pole. The work is then positioned so that there is a gap between it and the electrode. The gap is then flooded with the dielectric fluid. Once the power supply is turned on, thousands of direct current, or DC, impulses per second cross the gap, beginning the erosion process. 

The spark temperatures generated can range from 14,000° to 21,000° Fahrenheit. As the erosion continues, the electrode advances into the work while maintaining a constant gap dimension.

The finished EDM ' d work piece can exhibit several distinct layers. The surface layer will have small globules of removed work piece metal and electrode particles adhering to it, which are easily removed. 

The second layer is called the “white” or “recast” layer where EDM has altered the metallurgical structure of the work piece. The third layer is the heat-affected zone or “annealed” layer. This layer has been heated but not melted.

Complete ntpel notes of EDM