Manufacturing Processes - EDM Electrical Discharge Machining

Wire Electrical Discharge Machining fits in the category of machining as a manufacturing process. It involves removal of material from a workpiece using spark discharges. This is achieved by connecting the workpiece and the electrode (sometimes in the form of a wire) to an electrical power supply. Clearly then the material for this process to work has to be electrically conductive.

On that basis it is primarily used to machine solid metallic components but in theory it could be used for any conductive material, and because of the nature of the process the hardness of the material is irrelevant.

As indicated the process isn't restricted to the use of a wire, in fact it is probably more common practice to simply bring an electrode, usually formed to the machined shape required, into close contact with the workpiece to generate a high voltage spark, which erodes the material.

The gap between the tool and the workpiece (sometimes known as the over burn) is kept constant by carefully controlling the position of the tooling. A dielectric fluid is flooded over the workpiece and the electrode at the point of contact, serving the purpose of cooling the vaporized material into chips that are flushed away to a filter. Alternatively the workpiece and electrode can be immersed in a bath of dielectric which serves the same purpose. The most common dielectric fluids used for electrical discharge machining are deionised water or light oils.

Note: the electrical field generated must be strong enough to break through the dielectric fluid in order for current to flow between the two electrodes.

Operating costs for the process could be considered to be expensive because dedicated tooling can have high wear rates and investing in electrical discharge machines is not a cheap option. In terms of setting up times, these are usually relatively short, the tooling is dedicated but fairly easy to change out.

The machined surface quality is rather dependent on the rate of material removal, the higher the rate the poorer the quality. Even the faster rates where surface quality is compromised slightly would be considered in general to be quite slow because the rate of material removal depends on the material properties such as latent heat and melting temperature.

It is possible to produce quite intricate shapes to met high tolerance specifications using this process and it is particularly useful for machining hard materials that would be difficult to machine using standard tooling used for single point or multipoint cutting and manufacturing processes.

The electrical discharge machining process has several aliases, it is also known as spark erosion, spark machining, die sinking and wire erosion. But essentially these are all variants of the same manufacturing process and are not to be confused with electrochemical machining.