Tungsten Copper Electrode and Other Materials Comparison — Part I

The using of electrode material has a huge effect on electrical discharge machining (EDM), such as the wastage of tool, MRR (Material Removal Rate), the surface quality of work-piece and so on. Therefore, the choice of electrode material should not be ignored in EDM and it depends on the situation.

First of all, the electrode should have high melting point, good conductivity, low coefficient of expansion and some excellent mechanical properties so that it can be thermal resistance, not easy to deformation and has low wastage in EDM. Theoretically, the micro crystal structure of electrode is beneficial for decreasing the wastage of electrode and properly reduce the size of grain will be better. In addition, the material of electrode should pledge stability, good quality of surface, reasonable price and easily for machining to EDM.

With the development of EDM, the material of electrode and the related manufacture makes a great progress. At present, there are so much electrode materials, such as graphite, tungsten (W), copper (Cu) and some other metal or non-metal elementary substances. In addition, steel, cast steel, Cu-based and W-based composite materials or diamond can be also used as EDM electrode.

1. Graphite

As for the aspect of chemical, graphite is an allotrope of carbon element, which covalently bound covalent molecular bonds. Its has high boiling point and melting point, the melting point up to 3652 ℃, the boiling point of 4827 ℃, insoluble in water. And it also has excellent electrical and thermal conductivity, chemical stability and workability so that it is widely used as EDM electrodes. In addition, graphite also has different kinds, which can be specifically divided by graphite particle density, the size and mechanical and electrical properties.

Fine graphite has small grain, porosity and good mechanical strength, which has low wastage of electrode in EDM. But its MRR (Material Removal Rate) is undesirable. At present, the most of graphite grain size is below 10μm, which depends on the conditions electrode works (finishing, semi-finished or roughing) and its shape when we make a choice. In addition, the roughness of work-piece surface is related with the size of graphite grains, the average particle size below 1 μm is specialized for finishing.

Compared with other materials of electrode, graphite can be used in EDM with large discharge current, which remarkably increasing the efficiency. Although graphite has low proportion and price, it is too fragile to machining into the shape of thin. Therefore, it is limited in EDM and researchers find that high speed milling can be improved to some extent.

Some researchers put graphite electrode into molten metal (such as Cu or Al) in order to improve the properties of graphite electrode in EDM. At the same time, pressing the liquid metal and make Cu or Al fill in the pore of graphite electrode for improving the strength and thermal conductivity of the electrode.

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