As the electrode material, electrical conduction and heat conduction are first required. In the electric discharge machining, the temperature of the gap between the electrode and the workpiece is 2000 to 3000 ° C due to partial discharge, and therefore the electrode material is required to withstand high temperatures. If the melting point of the electrode material is low, it cannot be quickly processed with a high current, the processing speed is low, and the processing cost is increased. In theory, tungsten or a tungsten alloy is the best electrode material. The tungsten electrode has the characteristics of high strength, high density and melting point of nearly 3400 ° C. The actual loss of the tungsten electrode is small in the electric discharge machining.

However, tungsten electrodes have two problems:

1, tungsten is difficult to process.

2, the price is expensive. In the 1960s, fine-structured graphite was used as the electrode material for rough machining of EDM machines. Among the electrode materials used in EDM machines in the 1960s, metal materials accounted for 80%, while graphite materials accounted for only 20%.

Compared with copper electrodes, ultrafine graphite electrodes have obvious advantages.

The first is to increase the speed, and the volume of metal etching per hour is called the processing speed. The processing speed of the ultrafine graphite electrode is 1.5-3 times faster than that of the copper electrode. Large area processing under high current conditions. However, due to the lower melting point of the copper electrode, the processing current is limited.

Moreover, the tolerance of the workpiece profile after machining is the machining accuracy, which is closely related to whether the electrode material is resistant to wear. In EDM, there are several kinds of losses in the electrode material; such as volume loss, end face loss, side loss and corner loss, among the four kinds of losses, the corner loss is the largest, and the corner loss determines the service life of the electrode. Since the final machining wheel is determined by the electrode loss at the corners and edges of the electrode, the life of the electrode is the longest if the weakest portion of the electrode is effective against loss.

The melting point of ultra-fine graphite rod is 2000 °C higher than that of copper. The strength of ultra-fine graphite rod is higher than that of copper. The angular loss during processing is small, which means that the service life of ultra-fine graphite is long and the processing cost is lower than copper. electrode.

Secondly, it can be processed with high precision. On the 13×13mm ultra-fine graphite rod, 2813 holes with a diameter of 0.02mm can be drilled. The hole is 0.05mm apart from the hole, and the copper is lower than the ultra-fine graphite. Processing is powerless.

Also, it is easy to process, ultra-fine graphite is made into an electrode, only 1/3-1/5 of the copper electrode.

Finally, the thermal expansion coefficient of ultrafine graphite is only 1/4 of that of copper. Therefore, the original design size of the die does not change during the processing due to the heating of the electrode, and the dimensional stability of the graphite electrode is good.