What is the process and application of Electrical Discharge Machining

When traditional machining methods reach their limit, electric discharge machining can be the answer. The EDM process allows for high accuracy and is applicable for any conductive material.

The EDM process

“EDM involves the direction of high-frequency electrical spark discharges from a graphite or soft metal tool, which serves as an electrode, to disintegrate electrically conductive materials such as hardened steel or carbide.”

To put it more simply, electrical discharge machining is a manufacturing process that precisely removes material from conductive materials using an electrode. Similar to pushing a form into soft material, the electrode leaves a negative imprint in the workpiece. The physical process is a little more complicated: In a small gap between workpiece and electrode, a discharge occurs that removes material through melting or vaporizing. For this process, the electrode and the workpiece have to be submerged in a dielectric fluid.

The principle behind this process is the ability of controlled electric sparks to erode material. The workpiece and electrode do not touch during this porcess. In between is a gap that is roughly as thick as a human hair. The amount of removed material with a single spark is small, yet the discharge occurs roughly several 100,000 times a second.

While the electrode is moved closer to the workpiece, the electric field in the gap, also known as spark gap, increases until it reaches the breakdown volume. For this process, it is necessary that the fluid in which this discharge occurs is not conductive, or dielectric. The discharge causes strong heating of the material, melting away small amounts of material. This excess material is removed with the steady flow of the dielectric fluid. The liquid is also useful for cooling during the machining. Moreover, it is necessary for controlling the sparks.

Why Use Electrical Discharge Machining

Given that our molding process is centered on speed, EDM is only used in circumstances where design compromises can’t be made. Most often this means parts with sharp corners on contoured surfaces, or sharp V-shape features, that otherwise can’t be formed using our high-speed milling process. Examples of sharp features include: energy directors, gear teeth, crush ribs, or piercing features. We also use EDM to fabricate steel molds for high temperature resins like PEEK and PEI (Ultem).

We recommend a minimum of 0.020 in. (0.5mm) by 0.020 in. (0.5mm) sharp triangular features for energy directors used in ultrasonic welding assembly. Another helpful tip is to maintain a 1:1 (width:depth) ratio on any feature smaller than 0.04 in. (1.0mm).

The surface finish on features formed with EDM will be PM-F2, which falls between our standard SPI-C1 (600 grit stone) and PM-T1 (light bead blast) finishes. Some customers have even used EDM as a way to get a frosted finish only on certain areas of their parts, when geometry prohibits using a standard custom finish.

Advantages of EDM

The main advantage of electrical discharge machining is that it can be used on any material as long as it is conductive. It is therefore possible to machine workpieces made from tungsten carbide or titanium that are hard to machine with traditional cutting methods. Another advantage of electrical discharge machining is the lack of mechanical force put into the workpiece. Fragile outlines are easier to produce because there is no high cutting force needed to remove the material.

EDM also allows for shapes and depths that are impossible to reach with a cutting tool. Especially deep processing where the tool length to diameter ration would be very high, is a usual application for EDM. Sharp internal corners, deep ribs and narrow slots are other specialities of electrical discharge machining. Another argument for using EDM is that the surface finish is usually better than with traditional methods. Electrical discharge machining produces surfaces with a fine finish and high precision.

Moreover, EDM allows users to machine hardened workpieces. Whereas other machining techniques need to be executed before the workpiece is hardened with heat treatment, electrical discharge machining can be applied on the hardened material as well. Thus, any potential deformation from heat treatment machining can be avoided.

However, there are numerous examples where electrical discharge machining is not the right solutions. EDM is a high precision machining method. EDM is a rather slow method compared to traditional machining. High-volume tasks are therefore not suited for this method. At the same time, the electro thermal process requires high power consumption.

Similar to traditional chipping methods, the tool life in EDM is not endless. In sinker EDM, the electrode is also vulnerable to erosion. Because of the tool wear, the electrode has to be replaced regularly. In sinker EDM, it is also necessary to produce the correctly shaped electrodes before the workpiece can be machined. This is an additional step compared to machining processes with traditional cutting tools.

Applications of Electrical Discharge Machining

EDM is particularly famous in small-volume production, which makes several processes possible. These processes include milling, turning, small hole drilling, and more. This unique process is also valuable for a wide range of industries ranging from automotive to the aerospace industry.

Being able to create unique and precise shapes, this technique helps in the following applications:

Injection Molding
Achieving the right dimension, depth, and shape of a mold is usually dependent on EDM. It is the major injection molding process used by mold manufacturers. Wire EDM is the main type used in this case.

injection molding applications of electrical discharge machining
Since injection molding requires various delicate and complex workpieces, this is usually the best method to use. Moreover, it often produces high precision and fine EDM surface finish.

Small Hole Drilling
Electrical discharge machining is a quick and unique way to create accurate deep small holes drilling in materials, regardless of their hardness.

using edm for small hole sinking
The hole drilling process involves using a brass electrode tube to channel the electrical discharges onto the material. This helps to create holes of various small dimensions. The exciting thing is that it can make holes on inclined faces and other challenging positions.

Die Casting
EDM is also very suitable for die-making applications. Manufacturing highly tailored dies require extreme accuracy. These dies feature sharp internal corners, deep ribs, and other intricate features.

electrical discharge machining for die casting
Also, dies are often made from very hard steel alloys. These alloys are usually harder to machine with traditional methods. The hard steel alloys may require finishing prior to heat treatment, which may reduce the accuracy of details. Therefore, employing the EDM process is more appropriate.