Electrical Discharge Machining (EDM)

What Is Electrical Discharge Machining (EDM)?

A wire electric discharge machine is a machine tool that processes materials by means of the electrical discharge phenomenon in liquids, such as water or oil, which occurs when the wire that serves as the electrode is energized in the liquid.

The energized wire sparks in the liquid, and the molten metal is repeatedly cooled and dispersed by the liquid to form the external shape of the processed material. Ultra-thin brass (brass) wire with a diameter of about 0.05 to 0.3 mm is used as the wire for processing.

The wire used for processing discharges electricity and does not come into direct contact with the material to be processed.

Uses of Electrical Discharge Machining (EDM)

Electrical discharge machining (EDM) is used when extremely hard materials need to be processed precisely. Examples include the fabrication of press dies and the machining of carbide tool edges.

Electrical discharge machining (EDM) can process any material that conducts electricity. Examples include cemented carbide, titanium, stainless steel, and molybdenum. However, it should be noted that processing time varies depending on the size and material to be processed.

Principles of Electrical Discharge Machining (EDM)

Wire EDM is performed as follows after the work material is immersed in the machine’s processing fluid.

The wire, which is in an insulated state, and the work material approach each other in the processing fluid.
Spark discharges are initiated and pulse currents flow, which generate temperatures of thousands of degrees Celsius, melting the processed material.
The high temperature generated causes a steam explosion of the processing fluid, which blows off the molten metal and removes it.
Water enters the concave areas created by the removed material and cools the material.

By repeating the above process along the shape to be processed, wire EDM processing is performed. The advantages of wire EDM are that “even the hardest materials can be processed” and “precise processing is possible.” On the other hand, because of the above processing method, the processing speed is basically slow, and it is not suitable for mass production.

Another disadvantage is that it is not possible to process the bottom portion of the workpiece or to process in the horizontal direction.

Features of Electrical Discharge Machining (EDM)

Electrical Discharge Machining (EDM) has the following three main features:

1. Various Shapes Can Be Machined With High Precision

Electrical discharge machining (EDM) machines can process even complex shapes with high precision because they process with ultra-fine wires according to a pre-registered program. An example of utilizing this feature is the machining of minute gears.

Due to the characteristics of gears as parts, machining accuracy easily leads to differences in gear performance, such as “the shape of the shaft hole must be close to a perfect circle” and “the tooth tip shape must be correct.” Fine gears may require machining with a dimensional accuracy of φ0.05 mm or less. However, this accuracy is difficult to achieve with ordinary machining methods, such as cutting.

In contrast, wire EDM uses ultra-fine wire, which enables machining of the gear center hole and tooth tip shape as per the dimensions.

2. Machining of Difficult-To-Cut Materials Is Possible

Because the electric energy of the discharge cuts the processed material, it is possible to process any conductive material, no matter how hard it is. An example of utilizing this feature is ultra-precision press die machining. Press dies use a metal material with high hardness as the die material because of the extremely high pressure applied during the pressing process.

Since it is difficult to process complex shapes with high precision using ordinary processing methods, such as cutting, cutting by wire EDM is used.

3. No External Force Is Applied to the Processed Material.

Wire EDM is a non-contact machining process, so no load is applied to the material being machined. Therefore, no burrs are produced on the cut surface and chamfering is not required compared to the cutting process.