EDM characteristics of graphite materials

Electric discharge machining speed

Graphite is a non-metallic material with a very high melting point of 3 650 ° C and a melting point of 1083 ° C. Therefore, graphite electrodes can withstand higher current setting conditions. When the discharge area and the electrode size are larger, the superiority of the high efficiency rough processing of the graphite material is more remarkable. The thermal conductivity of graphite is 1/3 of that of copper. The heat generated during discharge can be used to remove metal materials more effectively. Therefore, in medium and fine processing, the processing efficiency is higher than that of copper electrodes. According to the processing experience, under the correct conditions of use, the discharge processing speed of the graphite electrode is 1.5~2 times faster than the overall copper electrode.

Electrode loss

Graphite electrodes have the characteristics of being able to withstand large current conditions. In addition, under suitable roughing setting conditions, the carbonaceous steel workpieces are processed during the etching and the working fluid is produced at high temperatures. Under the action of the polarity effect, some of the etchants and carbon particles adhere to the surface of the electrode to form a protective layer, which ensures that the loss of the graphite electrode in the rough processing is extremely small, even "zero loss". The main electrode loss in EDM is from roughing. Although the wear rate is higher, the machining allowance is higher, but the machining allowance is less, the machining loss is less, and the total loss is less. . In general, the graphite electrode will have less loss in the roughing of large current than the copper electrode, and the loss in finishing may be slightly larger than that in the copper electrode, and the electrode loss of the two is equivalent.

Surface Quality

The particle diameter of the graphite material directly affects the surface roughness of the EDM, and the smaller the diameter, the lower the surface roughness value. A few years ago, using graphite materials with a particle diameter of φ5 μm, the best surface for EDM can only reach VDI18 (Ra 0.8 μm). Nowadays, the particle diameter of graphite materials can reach φ3 μm, the best surface for EDM. Stable to VDI12 (Ra 0.4 μm) or finer grade, but graphite electrodes cannot be mirrored. The copper material has low resistivity, compact structure, easy to obtain stable processing state by EDM finishing, stable processing under difficult conditions, surface roughness of less than Ra 0.1 μm, and mirror electric discharge machining .

It can be seen that if the electrical discharge machining pursues an extremely fine surface, it is more suitable to use a copper material as the electrode, which is the main advantage of the copper electrode compared to the graphite electrode. However, under the condition of large current setting, the surface of the electrode is easily roughened and even cracked, but the graphite material has no such problem. The cavity with the surface roughness requirement of VDI26 (Ra2.0 μm) is required. Processing, using a graphite electrode to complete the process from coarse to fine, to achieve a uniform pattern effect, the surface will not be defective. In addition, due to the difference in the structure of graphite and copper, the corrosion point of the surface discharge of the graphite electrode is more regular than that of the copper electrode. Therefore, when the same surface roughness of VDI20 and above is processed, the surface of the workpiece processed by the graphite electrode is more distinct. The grain surface effect is better than the discharge surface effect of the copper electrode.


The thermal expansion coefficient of the graphite material is small, and the thermal expansion coefficient of the copper material is four times that of the graphite material. Therefore, in the electrical discharge machining, the graphite electrode is less likely to be deformed than the copper electrode, and a more stable and reliable processing precision can be obtained. Especially in the processing of deep and narrow ribs, the local high temperature tends to bend and deform the copper electrode, but the graphite electrode does not. For a copper electrode with a large aspect ratio, it is necessary to compensate for a certain thermal expansion value during processing. The size is corrected, and the graphite electrode is not required.

Electrode weight

The graphite material has a lower density than copper, and the same volume of graphite electrode weighs only 1/5 of the copper electrode. It can be seen that the larger volume of the electrode is very suitable for the use of graphite material, which greatly reduces the load on the main shaft of the EDM machine. The electrode does not cause inconvenient clamping and yaw displacement during processing due to the large weight, which can be seen in the processing of large molds. It makes sense to use a high power graphite electrode.

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