Nov. 16, 2020
As a Graphite Electrodes Manufacturer, share it with you.
Ultrafine graphite is a new type of graphite material developed in the 1970s, mainly used for precision machining electrodes of EDM machine tools.
As an electrode material, it first needs to conduct electricity and heat. In EDM, due to partial discharge, the temperature of the gap between the electrode and the workpiece is 2000-3000°C, so the electrode material needs to withstand high temperatures. If the melting point of the electrode material is low, it cannot be processed quickly with a high current, the processing speed is low, and the processing cost increases. In theory, tungsten or tungsten alloy is the best electrode material. The tungsten electrode has the characteristics of high strength, high density, and melting point close to 3400℃. The actual loss of tungsten electrode in EDM is very small.
However, tungsten electrodes have two problems:
1. Tungsten is difficult to process.
2. The price is expensive. Beginning in the 1960s, fine-structure graphite was used as the electrode material for rough machining of EDM machine tools; in the 1960s, metal materials accounted for 80% of the electrode materials used for EDM machine tools, while graphite materials only accounted for 20%.
Compared with copper electrodes, ultra-fine graphite electrodes have obvious advantages.
The first is to increase the speed. The volume of metal etching per hour is called the processing speed. The processing speed of ultra-fine graphite electrodes is 1.5-3 times faster than copper electrodes. Large area can be processed under high current conditions. However, due to the low melting point of the copper electrode, its processing current is limited.
Moreover, the tolerance of the workpiece contour after processing is the processing accuracy, which is closely related to whether the electrode material is wear-resistant. During EDM, there are several kinds of loss of electrode materials; such as volume loss, end loss, side loss and corner loss. Among the four kinds of loss, the corner loss is the largest, and the size of the corner loss determines the service life of the electrode. Since the final machining wheel is determined by the electrode wear at the corners and edges of the electrode, if the weakest part of the electrode can effectively resist the wear, the electrode has the longest life.
The melting point of ultra-fine graphite rods is 2000°C higher than that of copper. The strength of ultra-fine graphite rods is higher than that of copper, and the corner loss during processing is small. This means that ultra-fine graphite has a long service life and processing costs are lower than copper electrode.
Secondly, it can be processed with high precision. 2813 holes with a diameter of 0.02mm can be drilled on a 13×13mm ultrafine graphite rod. The distance between the holes is 0.05mm, and the strength of copper is lower than that of ultrafine graphite. Processing is powerless.
Also, it is easy to process, ultra-fine graphite is made into electrodes, only 1/3-1/5 of copper electrodes.
Finally, the thermal expansion coefficient of ultrafine graphite is only 1/4 of that of copper, so the original design dimensions of the die will not change due to the heating of the electrode during the processing, and the electrode has good dimensional stability.
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