Die electrical discharge machining, copper soderberg electrodes or Shijiazhuang soderberg electrodes which is better
Copper is widely used as a material for soderberg electrodes in EDM in mold factories. Many people think that graphite materials will only be considered as candidates when making large-scale soderberg electrodes and the mold processing requirements are not high or rough processing.
Today, in Europe, where manufacturing technology is leading, more than 90% of the soderberg electrodes used by mold companies use graphite. But in China, most mold companies still use copper as the main material for soderberg electrodes. According to the characteristics of graphite materials, the following comprehensive analysis of its advantages and disadvantages of EDM.
EDM characteristics of graphite materials
(1) Electric discharge machining speed Graphite is a non-metallic material with a very high melting point and can withstand larger current setting conditions. When the discharge area and the size of the soderberg electrodes 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 that 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 soderberg electrodes in medium and fine processing. According to processing experience, under the correct conditions of use, the electrical discharge processing speed of soderberg electrodes is 1.5 to 2 times faster than that of copper soderberg electrodes as a whole.
(2) Soderberg electrodes loss Soderberg electrodes have the characteristics of being able to withstand high current conditions. In addition, under suitable rough machining conditions, the erosion products and working fluid generated during processing of carbon-containing steel workpieces are generated at high temperatures. Part of the carbon particles in the decomposition product will adhere to the surface of the soderberg electrodes to form a protective layer under the effect of the polarity effect, which ensures that the loss of the soderberg electrodes in the rough processing is extremely small, even It is “zero loss”. The main loss of soderberg electrodes in EDM comes from rough machining. Although the loss rate of finishing setting conditions is relatively high, because the reserved machining allowance for parts is small, the amount of machining erosion is small, and the overall loss is also relatively large. few. In general, soderberg electrodes will lose less than copper soderberg electrodes during rough processing of large currents, and may be slightly larger than copper soderberg electrodes during finishing. The losses of soderberg electrodes of the two are similar.
(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. 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 electrical discharge machining pursues extremely fine surfaces, it is more appropriate to use copper materials as soderberg electrodes. This is the main advantage of copper soderberg electrodes over soderberg electrodes. But under the condition of high current setting, the surface of soderberg electrodes is prone to become rough and even cracks. Graphite materials do not have this problem. The surface roughness requirement is about VDI26 (Ra2.0 μm). For cavity processing, one soderberg electrodes can be used to complete the machining process from coarse to fine, achieving a uniform texture effect and no defects on the surface. In addition, due to the difference in the structure of graphite and copper, the corrosion points of the surface discharge of soderberg electrodes are more regular than those of copper soderberg electrodes. Therefore, when processing the same surface roughness of VDI20 and above, the surface granularity of the workpiece processed by soderberg electrodes is more clear. This texture effect is better than the discharge surface effect of copper soderberg electrodes.
(4) Processing 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, soderberg electrodes are less prone to deformation than copper soderberg electrodes in electrical discharge processing, and more stable and reliable processing accuracy can be obtained. Especially when processing deep and narrow ribs, the local high temperature will easily cause the copper soderberg electrodes to bend and deform, and soderberg electrodes will not be like this; for copper soderberg electrodes with a large depth-to-diameter ratio, a certain amount of thermal expansion needs to be compensated during processing settings Value to correct the size, soderberg electrodes do not need.
(5) Weight of soderberg electrodes Graphite material is less dense than copper, and the weight of soderberg electrodes of the same volume is only 1/5 of that of copper soderberg electrodes. It can be seen that the larger soderberg electrodes use graphite materials, which greatly reduces the load on the spindle of the EDM machine tool. The soderberg electrodes will not cause problems such as inconvenience in clamping and yaw displacement during processing due to their heavy weight. It makes sense to use soderberg electrodes in mold processing.
(6) Difficulties in making soderberg electrodes The machining performance of graphite materials is good, and the cutting resistance is only 1/4 of copper. Under the correct processing conditions, the efficiency of milling soderberg electrodes is 2 to 3 times that of copper soderberg electrodes. The soderberg electrodes are easy to clean the corners, and the workpieces that are usually completed by multiple soderberg electrodes can be designed as a whole soderberg electrodes for processing. The unique particle structure of the graphite material prevents soderberg electrodes from producing burrs after milling and molding. For complex shapes that are not convenient to remove burrs, it directly meets the requirements of use, eliminating the need for manual polishing of soderberg electrodes, and avoiding polishing caused Shape change, size error, 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 wire EDM to process soderberg electrodes, their processing performance is not as good as copper materials, and the cutting speed is about 40% slower than copper.
(7) The soderberg electrodes have good adhesion between the installation and the use of graphite materials. The method of milling soderberg electrodes and electrical discharge processing can use conductive glue to bond graphite to the fixture, which can eliminate the process of processing screw holes on the soderberg electrodes. Save working time. Graphite materials are relatively fragile, especially the small, narrow and long soderberg electrodes, which are easy to break when subjected to external force during use, but it can be immediately known that the soderberg electrodes have been damaged. If it is a copper soderberg 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 Copper material is a non-renewable resource, and the price trend will become more and more expensive, while the price of graphite material tends to stabilize. In recent years, the price of copper materials has continued to rise, and major graphite manufacturers continue to improve the process of making graphite to make it more cost-effective. At present, different suppliers of world-renowned graphite suppliers have many different grades of graphite to choose from. Graphite materials are usually classified according to the average particle diameter. Those with a particle diameter ≤ φ4 μm are defined as fine graphite, particles with a particle diameter of φ5~φ10 μm are defined as medium graphite, and particles above 10 μm are defined as coarse graphite. The smaller the particle diameter, the more expensive the material, and the appropriate graphite material can be selected according to the requirements and cost of EDM. In summary, among the 8 EDM characteristics of soderberg electrodes, its advantages are obvious: the efficiency of milling soderberg electrodes and electrical discharge machining is significantly better than that of copper soderberg electrodes, with high production efficiency; large soderberg electrodes are very suitable; dimensional stability Good, thin soderberg electrodes are not prone to deformation; disadvantages of graphite materials: milling of soderberg electrodes requires a special graphite processing machine not suitable for fine surface discharge machining below VDI12 (Ra0.4 μm); the superiority of soderberg electrodes Will gradually be recognized and accepted by the domestic mold manufacturing industry. The correct selection of soderberg electrodes materials and the improvement of related process links will bring high efficiency and low cost benefits to mold manufacturers. 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 soderberg electrodes, Shijiazhuang soderberg electrodes, and Datong silicon carbide.