nipple graphite electrode
The use of nipple graphite electrode EDM
In the 20th century, copper was widely used as a material for nipple graphite electrode in EDM. At that time, graphite materials would become an alternative consideration only when the large-scale nipple graphite electrode was made and the mold processing requirements were not high or rough processing. Some technicians who have been in contact with nipple graphite electrode in the early days have a general impression: the graphite material is dirty, easy to drop off, the surface effect is not good, the processing efficiency is not high, and so on.
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 are emerging in an endless stream. Graphite high-speed milling machine tools have emerged on the market, and the graphite discharge performance of CNC EDM machine tools has also been comprehensive. promote. Today, in Europe, where manufacturing technology is leading, more than 90% of the nipple graphite electrode materials used by mold companies use graphite. A wide range of molds such as aerospace, automobiles, home appliances, and electronics have adopted graphite as the material of nipple graphite electrode. This significant change is attributed to the many advantages of nipple graphite electrode, which can achieve high efficiency and high quality processing.
However, in China, most mold companies still choose copper as the main nipple graphite electrode material. According to the characteristics of graphite materials, the following is a comprehensive analysis of the advantages and disadvantages of EDM, and introduces how to select graphite materials, the main points of nipple graphite electrode production and electrical discharge machining.
EDM characteristics of graphite materials
(1) Electrical discharge machining speed Graphite is a non-metallic material with a very high melting point of 3650 ℃, while the melting point of copper is 1083 ℃, so nipple graphite electrode can withstand higher current setting conditions. When the discharge area and the size of the nipple graphite electrode are scaled larger, the superiority of the graphite material’s high-efficiency rough machining is more obvious. The thermal conductivity of graphite is 1/3 of copper, and the heat generated during the discharge process can be used to remove metal materials more effectively. Therefore, its processing efficiency is higher than that of copper nipple graphite electrode in medium and fine processing. According to machining experience, under the correct conditions of use, the electrical discharge machining speed of nipple graphite electrode is 1.5~2 times faster than that of copper nipple graphite electrode as a whole.
(2) The loss of nipple graphite electrode The nipple graphite electrode has the characteristics of being able to withstand high current conditions. In addition, under the appropriate roughing conditions, the erosion products and working fluid generated during the processing of carbon-containing steel workpieces are at high temperatures. The carbon particles in the decomposition product produced under the effect of the polarity effect, part of the ablation and carbon particles will adhere to the surface of the nipple graphite electrode to form a protective layer, which ensures the loss of the nipple graphite electrode during rough processing Very small, even “zero loss”. The main loss of nipple graphite electrode in EDM comes from rough machining. Although the loss rate of finishing setting conditions is relatively high, because the reserved machining allowance of parts is small, the amount of machining erosion is small, and the overall loss is also less. In general, the loss of the nipple graphite electrode in the rough machining of high current is less than that of the copper nipple graphite electrode, and the loss in the finishing process may be slightly greater than that of the copper nipple graphite electrode. The loss of the nipple graphite electrode of the two is equivalent.
(3) Surface quality The particle diameter of graphite material directly affects the surface roughness of EDM, the smaller the diameter, the lower the surface roughness value can be obtained. A few years ago, graphite materials with a particle diameter of φ5 μm were used, and the best surface for EDM can only reach VDI18 (Ra0.8 μm). Nowadays, the particle diameter of graphite materials can reach within φ3 μm, which is the best surface for EDM. It can stably reach VDI12 (Ra0.4 μm) or a finer level, but the nipple graphite electrode cannot be used for mirror EDM. The resistivity of copper material is low, and the structure is dense. EDM is easy to obtain a stable processing state, and it can be processed stably under difficult conditions. The surface roughness can be less than Ra0.1 μm, and it can be mirrored EDM. . It can be seen that if the electrical discharge machining pursues an extremely fine surface, it is more appropriate to use copper materials to make the nipple graphite electrode. This is the main advantage of the copper nipple graphite electrode over the nipple graphite electrode. However, under the condition of high current setting, the surface of the nipple graphite electrode is prone to become rough and even cracks. Graphite materials do not have this problem. The surface roughness requirement is VDI26 (Ra2.0 μm). For the left and right cavity processing, a nipple graphite electrode can be used to complete the machining process from coarse to fine, achieving a uniform texture effect, and there will be no defects on the surface. In addition, due to the different structure of graphite and copper, the corrosion points of nipple graphite electrode surface discharge are more regular than copper nipple graphite electrode. Therefore, when processing the same surface roughness of VDI20 and above, the surface granularity of the workpiece processed by nipple graphite electrode is More clearly, this kind of texture effect is better than the discharge surface effect of the copper nipple graphite electrode.
(4) Machining accuracy The thermal expansion coefficient of graphite material is small, and the thermal expansion coefficient of copper material is 4 times that of graphite material. Therefore, in electrical discharge machining, nipple graphite electrode is less prone to deformation than copper nipple graphite electrode, and more stable and reliable machining accuracy can be obtained. . Especially when processing deep and narrow ribs, the local high temperature will easily cause the copper nipple graphite electrode to bend and deform, but the nipple graphite electrode will not be like this; for the copper nipple graphite electrode with a large depth-to-diameter ratio, compensation is required when processing settings. A certain thermal expansion value is used to correct the size, but the nipple graphite electrode does not need it.
(5) Weight of nipple graphite electrode Graphite material has a lower density than copper. The weight of nipple graphite electrode with the same volume is only 1/5 of that of copper nipple graphite electrode. It can be seen that the larger nipple graphite electrode uses graphite material very suitable, which greatly reduces the load on the spindle of the EDM machine tool. The nipple graphite electrode will not cause problems such as inconvenience in clamping and yaw displacement during processing due to its heavy weight. It makes sense to use nipple graphite electrode in large mold processing.
(6) Difficulty in making nipple graphite electrode The machining performance of graphite material is good, and the cutting resistance is only 1/4 of that of copper. Under the correct processing conditions, the efficiency of milling nipple graphite electrode is 2 to 3 times that of copper nipple graphite electrode. . The nipple graphite electrode is easy to clean the corners, and the workpiece that is usually completed by multiple nipple graphite electrodes can be designed into a whole nipple graphite electrode for processing. The unique particle structure of the graphite material prevents the nipple graphite electrode from producing burrs after milling and forming. It directly meets the requirements for complex shapes that are not easy to remove the burrs, eliminating the need for manual polishing of the nipple graphite electrode and avoiding polishing. The resulting shape changes, size errors, etc. It should be noted that because 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 EDM wire cutting to process nipple graphite electrode, its processing performance is not as good as copper material, and the cutting speed is about 40% slower than copper.
(7) The nipple graphite electrode has good adhesion between the installation and the use of graphite materials. Conductive glue can be used to bond graphite to the fixture for milling nipple graphite electrode and electric discharge machining, which can eliminate the need for machining screw holes on the nipple graphite electrode material. The process saves working time. Graphite materials are relatively brittle, especially the small, narrow and long nipple graphite electrode, which is easy to break when subjected to external force during use, but it can be immediately known that the nipple graphite electrode is damaged. If it is a copper nipple graphite 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) Price In recent years, the price of copper materials has continued to rise, and major graphite manufacturers have continuously improved the process of making graphite to make it more cost-effective. Under the same volume, the price of universal nipple graphite electrode material is equivalent to that of copper nipple graphite electrode, while the price of fine graphite will be higher than that of copper nipple graphite electrode. In summary, among the 8 EDM characteristics of nipple graphite electrode, its advantages are obvious: the efficiency of milling nipple graphite electrode and electric discharge machining is significantly better than that of copper nipple graphite electrode, large nipple graphite electrode has small weight and dimensional stability Good, thin nipple graphite electrode is not prone to deformation, the surface texture is better than copper, and the price is lower. The disadvantage of graphite materials is that they are not suitable for fine surface electrical discharge machining below VDI12 (Ra0.4 μm), and the efficiency of making nipple graphite electrode by wire EDM is low. But from a practical point of view, an important reason that affects the effective promotion of graphite materials in China is that milling nipple graphite electrode requires a special graphite processing machine, which puts new requirements on the processing equipment of mold companies, and some small companies may Doesn’t have this condition. In general, the advantages of nipple graphite electrode characteristics cover most of the machining occasions of EDM, it is worthy of popularization and application, and the long-term benefits are considerable. The shortcomings of its fine surface processing can be compensated by using copper nipple graphite electrode. When the carbon company was founded, it established the development strategy of “science and technology, innovation, and leadership”, adhering to the business philosophy of “quality first, service first”, through technological improvement, quality improvement, and market development, carbon has become a region in Shanxi, Hebei, and Mongolia. The largest graphitization processing company. The main business includes nipple graphite electrode, Shijiazhuang nipple graphite electrode, and Datong silicon carbide.