Graphite EDM Electrode in Mould Manufacturing

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In the 20th century, copper was widely used as electrode material in EDM. At that time, graphite materials would only be considered as an alternative when making large electrodes and the mold machining requirements are not high or rough. Some technicians who have been exposed to graphite EDM electrodes in the early days have a general impression: the graphite material is dirty, easy to slag, the surface effect is not good, and the processing efficiency is not high. With the development of high and new technology, the manufacturing process of graphite materials has been continuously improved, and graphite materials that can meet the needs of different EDM emerge in an endless stream. Graphite high-speed milling machine tools have emerged in the market, and the graphite electrical discharge machine performance of CNC EDM machine tools has also been comprehensive. promote. Today, in Europe, where manufacturing technology is leading, more than 90% of the electrode materials of mold companies use graphite. Aerospace, automotive, home appliances, electronics and other molds have widely used graphite as electrode material. This significant change is attributed to the advantages of graphite EDM electrodes, such as high efficiency and high quality processing. But in China, most mold companies still choose copper as the main electrode material. According to the characteristics of graphite materials, the following comprehensively analyzes the advantages and disadvantages of EDM, introduces how to correctly select graphite materials, the key points of electrode fabrication and EDM, and provides practical application cases.

Graphite EDM Electrode

1. Graphite EDM speed

Graphite is a non-metallic material with a very high melting point, up to 3 650 ℃, while the melting point of copper is 1083 ℃, so the graphite EDM electrode can withstand higher current setting conditions. When the scaling of the discharge area and the electrode size is larger, the superiority of high-efficiency roughing of graphite materials is more significant. The thermal conductivity of graphite is 1/3 of that of copper, and the heat energy generated during the discharge process can be used to remove metal materials more effectively, so its processing efficiency is also higher than that of copper electrodes in medium and finish machining. According to processing experience, under the correct conditions of use, the discharge machining speed of graphite electrodes is 1.5 to 2 times faster than that of copper electrodes as a whole.

2. Graphite EDM electrode loss

Graphite electrodes have the characteristics of being able to withstand high current conditions. In addition, under suitable roughing setting conditions, carbon in the corrosion products produced by the machining of carbon-containing steel workpieces and the decomposition products produced by the working fluid at high temperatures Under the action of the polarity effect, part of the corrosion and carbon particles will adhere to the surface of the electrode to form a protective layer, which ensures that the loss of the graphite electrode during rough machining is extremely small, or even “zero loss”. The main electrode loss in EDM comes from rough machining. Although the loss rate of finishing setting conditions is high, the overall loss is also less because there is not much reserved machining allowance for the part, that is, the amount of machining erosion is small. . In general, the loss of graphite electrode is less than that of copper electrode in high current rough machining, and the loss of graphite electrode may be slightly larger than that of copper electrode in finishing, and the electrode loss of the two is equivalent.

3. Graphite EDM surface quality

The particle diameter of the graphite material directly affects the surface roughness processed by the electrical discharge machine, and the smaller the diameter, the lower the surface roughness value can be. A few years ago, graphite materials with a particle diameter of φ5 μm were used, and the optimal surface of the sparking process could only reach VDI18 (Ra0.8 μm). Today, the particle diameter of graphite materials can reach within φ3 μm, and the optimal surface of EDM can be achieved. Stable to VDI12 (Ra0.4 μm) or finer grades, but graphite electrodes cannot be mirror EDM. The resistivity of copper material is low and the structure is dense. It is easy to obtain a stable processing state in die sinking machine finishing, and it can also be processed stably under difficult conditions. The surface roughness can be less than Ra0.1 μm, and mirror EDM can be performed. processing. It can be seen that if EDM pursues an extremely fine surface, it is more suitable to use copper materials as electrodes, which is the main advantage of copper electrodes over graphite electrodes. However, under the condition of high current setting, the surface of the copper electrode is easy to become rough, and even cracks occur, while the graphite material does not have this problem. For the cavity with a surface roughness of about VDI26 (Ra2.0 μm) Machining, one graphite electrode can be used to complete the machining process from coarse to fine, to achieve a uniform texture effect, and there will be no defects on the surface. In addition, due to the difference in the structure of graphite and copper, the corrosion points on the surface of graphite electrodes are more regular than those of copper electrodes. Therefore, when processing the same surface roughness of VDI20 and above, the surface particle size of workpieces processed with graphite electrodes is more distinct. The seed surface effect is better than the discharge surface effect of the copper electrode.

4. Graphite EDM machining accuracy

The thermal expansion coefficient of graphite materials is small, and the thermal expansion coefficient of copper materials is 4 times that of graphite materials. Therefore, graphite electrodes are less prone to deformation than copper electrodes during electrical discharge machining, and more stable and reliable machining accuracy can be obtained. Especially when machining deep and narrow rib parts, the local high temperature is easy to bend the copper electrode, but the graphite electrode does not. Correct size, which is not required for graphite electrodes.

5. Graphite EDM Electrode Weight

The density of graphite material is lower than that of copper, and the weight of graphite electrode of the same volume is only 1/5 of that of copper electrode. It can be seen that the use of graphite material for larger electrodes is very suitable, which greatly reduces the load on the spindle of the EDM machine tool, and the electrode will not cause problems such as inconvenient clamping and yaw displacement during processing due to its large weight. It makes sense to use graphite electrodes in

6. Difficulty in making Graphite EDM electrodes

The machining performance of graphite materials is good, and the cutting resistance is only 1/4 of that of copper. Under the correct processing conditions, the efficiency of milling graphite electrodes is 2 to 3 times that of copper electrodes. The graphite electrode is easy to clean the corner, and the workpiece that usually needs to be completed by multiple electrodes can be designed as a whole electrode for processing. The unique particle structure of graphite material makes the electrode without burrs after milling and molding, and directly meets the requirements for complex shapes that are inconvenient to remove burrs, eliminating the need for manual polishing of the electrode process and avoiding the shape change caused by polishing. , size error, etc. It should be noted that since graphite is a dust accumulation, a large amount of dust will be generated when milling graphite, so the milling machine must have a sealing and dust suction device. If you need to use cnc die sinker to process graphite electrodes, its processing performance is not as good as copper materials, and the cutting speed is about 40% slower than copper.

7. Graphite EDM electrode installation and use

Graphite material has good bondability. Electrode milling and electrical discharge machining can be performed by using conductive glue to bond graphite to fixture, which can save the process of machining screw holes on electrode material and save working time. Graphite materials are relatively brittle, especially small, narrow and long electrodes, which are easy to break when subjected to external force during use, but it can be immediately known that the electrode is damaged. If it is a copper electrode, it will only bend and not break. This situation is very dangerous and difficult to find during use, and it is easy to cause the workpiece to be scrapped.

8. Graphite EDM Price

Copper materials are non-renewable resources, and the price trend will become more and more expensive, while the price of graphite materials tends to stabilize. In recent years, the price of copper materials has continued to rise, and major graphite manufacturers have continued to improve the process of making graphite to make it more cost-effective. Nowadays, the price of isotropic graphite materials is lower than that of copper materials. Under the same volume, universal graphite electrodes The price of the material is 30%~50% lower than the price of copper electrode material, which is equivalent to the price of ordinary copper material to obtain high-quality fine graphite material.

To sum up, among the eight cnc edm die sinking machine processing characteristics of graphite electrode, its advantages are obvious: the efficiency of milling electrode and electric discharge machining is significantly better than that of copper electrode, large electrode has small weight, good dimensional stability, thin electrode It is not easy to deform, the surface texture is better than copper, and the price is lower. The disadvantage of graphite material is that it is not suitable for fine surface discharge machining below VDI12 (Ra0.4 μm), and the efficiency of using wire EDM to make electrodes is low. However, from a practical point of view, an important reason that affects the effective promotion of graphite materials is that special graphite processing machines are required for milling electrodes, which puts forward new requirements for the processing equipment of mold enterprises, and some small enterprises may not have this condition. . In general, the advantages of SAMMLITE MACHINERY’s graphite electrode characteristics cover most of the processing occasions processed by cnc edm die sinking machine, which is worthy of popularization and application, and the long-term benefits are considerable. The shortcomings of its fine surface processing can be made up by using copper electrodes.

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