Compared with copper electrode, graphite electrode has the advantages of low electrode consumption, fast processing speed, good machining performance, high processing accuracy, small thermal deformation, light weight, easy surface treatment, high temperature resistance, high processing temperature, and electrode bonding. Although graphite is a very easy cutting material, the graphite material (hot working die steel) used as EDM electrode must have sufficient strength to avoid damage during operation and EDM processing. At the same time, the electrode shape (thin wall, small fillet, sharp change) also puts forward higher requirements for the grain size and strength of graphite electrode, which leads to the easy disintegration of graphite workpiece and the easy wear of cutting tools in the processing process.
Tool wear is the most important problem in graphite electrode machining. Wear not only affects the cost of tool loss, processing time and processing quality, but also affects the surface quality of workpiece materials processed by electrode EDM. It is an important parameter to optimize high-speed machining The main tool wear areas in the processing of graphite gun electrode materials are rake face and rake face. On the rake face, the impact contact between the tool and the broken chip area produces impact abrasive wear, and the chip sliding along the tool surface produces sliding friction wear. Several factors affecting tool wear are as follows.
(1) Tool material tool material (die steel) is the fundamental factor that determines the cutting performance of tools, which has a great impact on machining efficiency, machining quality, machining cost and tool durability. The harder the tool material, the better its wear resistance, the higher the hardness, the lower the impact toughness and the more brittle the material. For graphite cutting tools, the common TiAIN coating with relatively better toughness can be appropriately selected, that is, the coating with slightly higher cobalt content; For the graphite cutter coated with gold erasure stone, the one with relatively better hardness, that is, the one with slightly lower cobalt content, can be selected.
(2) Geometric angle of the cutting tool choosing the appropriate geometric angle of the graphite cutting tool helps to reduce the vibration of the cutting tool. On the contrary, the graphite workpiece is not easy to collapse;
① Front corner. When using negative rake angle to process graphite, j-j has good edge strength and good impact and friction resistance. With the decrease of the absolute value of negative rake angle, the wear area of the flank changes little, but it shows a decreasing trend as a whole. When using positive rake angle to process, with the increase of rake angle, the strength of the cutting edge is weakened, but the wear of the flank is intensified. When machining with negative rake angle, the cutting resistance is large and the cutting vibration is increased. When machining with large positive rake angle, the tool wear is serious and the cutting vibration is also large.
② Back corner. If the rake angle increases, the strength of the cutting edge decreases and the wear area of the flank increases gradually. After the cutting angle is too large, the tool vibration is strengthened.
③ Helix angle. When the helix angle is small, the cutting edge length of cutting graphite workpiece at the same time as all cutting edges is the longest, the cutting resistance is the largest, and the cutting impact force borne by the tool is the largest, so the tool wear, milling force and cutting vibration are the largest. When the helix angle is large, the direction of milling force deviates greatly from the workpiece surface, and the cutting impact caused by the disintegration of graphite material is intensified, so the tool wear, milling force and cutting vibration are also increased.
Therefore, the influence of tool angle change on tool wear, milling force and cutting vibration is the combination of front angle, back angle and helix angle, so we must pay more attention to it in selection. Through a large number of scientific tests on the machining characteristics of graphite materials, para tools optimize the geometric angle of relevant tools, so as to greatly improve the overall cutting performance of tools.
(3) Diamond coated tools have the advantages of high hardness, good wear resistance and low friction coefficient. At present, diamond coating is the best choice for graphite processing tools and can best reflect the superior performance of graphite tools; The advantage of diamond coated cemented carbide tool is that it combines the hardness of natural diamond with the strength and fracture toughness of cemented carbide; However, in China, the diamond coating technology is still in its infancy and the cost investment is very large, so the diamond coating will not have much development in the near future. However, on the basis of ordinary tools, we can optimize the angle and material selection of tools and improve the structure of ordinary coatings, which can be applied in graphite processing to some extent.
The geometric angle of diamond coated tools is essentially different from that of ordinary coated tools. Therefore, when designing diamond coated tools, due to the particularity of graphite processing, the geometric angle can be appropriately enlarged, the cutting groove can be enlarged, and the wear resistance of the cutting edge will not be reduced; Although the wear resistance of ordinary TiAIN coating is significantly higher than that of uncoated tools, compared with diamond coating, its geometric angle should be appropriately reduced when machining graphite to increase its wear resistance. For diamond coating, many coating companies in the world have invested a lot of manpower and material resources to research and develop relevant coating technology, but so far, foreign mature and economic coating companies are only limited to Europe; As an excellent graphite processing tool, para also uses the world’s most advanced coating technology to treat the surface of the tool, so as to ensure the processing life and the economy and practicability of the tool.
(4) The strengthening of tool edge and the passivation technology of tool edge are not generally valued by people, but also very important. There are micro notches (i.e. micro chipping and saw edge) in the edge of cemented carbide tool after grinding with diamond grinding wheel. Graphite high-speed cutting puts forward higher requirements for the performance and stability of the tool, especially the gold cut stone coated tool must go through the passivation treatment of the knife edge before coating, so as to ensure the firmness and service life of the coating. The purpose of tool passivation is to solve the defects of the micro notch on the edge of the tool after grinding, so as to reduce or eliminate its front value, so as to achieve the purpose of smoothness, smoothness, sharpness, firmness and durability.
Graphite is widely used in many aspects due to its good properties.
Graphite has many excellent properties, so it has been widely applied in metallurgical, mechanical, electrical, chemical, textile, national defense and other industrial sectors. It can be used as a refractory. Graphite products retain the original chemical properties of flake graphite and have strong self lubrication properties. The properties of graphite powder are acid resistance, corrosion resistance and high temperature resistance 3000 C and low temperature -204 C. At the same time, its compressive strength is greater than 800kg/Cm2, and the weight loss is 1% at 450 C and the rebound rate is 15–50% (density 1.1–1.5). Therefore, graphite products have been widely used in metallurgy, chemical industry, petrochemical industry, high-energy physics, aerospace, electronics and so on.
Due to its special structure, graphite electrode products have many characteristics such as high temperature resistance, thermal shock resistance, conductivity, lubricity, chemical stability and plasticity. It has always been an important strategic resource in the development of military and modern industry and high, new and sharp technology. Graphite products, such as graphite rings and graphite boats are widely used. Pan, international experts once predicted that “Twentieth Century is the century of silicon, and twenty-first Century will be the century of carbon”.
Qingming Festival, also known as the outing Festival, Xingqing Festival, March Festival and ancestor worship Festival, is held at the intersection of mid spring and late spring. Qingming Festival originated from the ancient ancestor belief and spring festival rituals and customs. It has both natural and human connotations. It is not only a natural solar term, but also a traditional festival. Tomb sweeping and ancestor worship and outing are the two major ritual themes of the Qingming Festival. These two traditional ritual themes have been passed down since ancient times in China, and they have never stopped.
Qingming Festival is an ancient festival of the Chinese nation. It is not only a solemn festival to visit the tomb and worship the ancestors, but also a happy festival for people to get close to nature, go outing and enjoy the fun of spring. Dipper finger B (or sun yellow longitude up to 15 °) is the solar term of Qingming Festival, which is around April 5 of the Gregorian calendar. In this time of year, the vitality is vigorous and the Yin Qi is declining. All things “vomit the old and absorb the new”. The Earth presents the image of spring and Jingming. It’s a good time for youth outing and tomb sacrifice in the countryside. The Qingming ancestor worship period is very long. There are two kinds of statements: before and after 10 days, 8 days and before and 10 days, all of which belong to the Qingming ancestor worship period in the past 20 days.
Qingming Festival is a major traditional festival of Spring Festival. Tomb sweeping and ancestor remembrance is a fine tradition of the Chinese nation since ancient times. It is not only conducive to carrying forward filial piety and family affection, awakening the common memory of the family, but also to promoting the cohesion and identity of family members and even the nation. Qingming Festival is a combination of natural solar terms and human customs. It fully embodies the Chinese ancestors’ pursuit of the harmony of “heaven, earth and man”, and pays attention to the idea of conforming to the natural laws.
Qingming Festival, together with Spring Festival, Dragon Boat Festival and Mid Autumn Festival, is known as the four traditional festivals in China. In addition to China, there are also some countries and regions in the world, such as Vietnam, South Korea, Malaysia, Singapore, etc. On May 20, 2006, the Qingming Festival declared by the Ministry of culture of the people’s Republic of China was approved by the State Council to be included in the first batch of national intangible cultural heritage list.
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2. Poor chip removal
A. Influence of processing depth
The smaller the discharge cross-sectional area and the deeper the machining depth, the more difficult it is to remove the chip. It is the key to improve the chip removal quality for the machining of this type of cavity. When it comes to EDM chip removal, there are two conventional methods at present, one is the flushing method, the other is the immersion method, and the flushing method is used in the immersion processing at the same time, so as to improve the fluidity of the liquid and strengthen the chip removal effect. In terms of machining accuracy and chip removal effect, the immersion method is much better than the simple flushing method. (see Figure) the chip removal mechanism of the immersion processing method is to use the high-speed movement of the spindle to cause the mold cavity to be in a high-pressure or vacuum state and cause the strong disturbance of the liquid to achieve the purpose of chip removal. Imported equipment is very suitable for this chip removal method due to the high running acceleration of the spindle, and the effect is very good. In the flush machining method, due to the uneven flow direction and pressure of the liquid flow, the chip removal may not be complete, and it is easy to form two discharges where the chip removal materials gather, which affects the accuracy of the cavity; Secondly, it is also easy to cause carbon deposition, so the immersion processing method should be used as far as possible when conditions permit.
B. Influence of processing position
It is not necessarily that the discharge stability of open EDM is higher than that of machining blind holes. Sometimes, machining only one surface is easier to cause the deterioration of machining stability than machining all peripheral surfaces at the same time. The reasons are as follows: EDM chip removal mainly depends on the disturbance of machining fluid, or scouring, or extrusion. The stronger the fluidity of the liquid, the more thorough the chip removal. When only one surface is processed, the up and down movement of the electrode can not cause the strong disturbance of the processing fluid. Moreover, if the up and down runout distance of the main shaft is relatively small, the electro-corrosion products can not leave the discharge gap, which is easy to cause the deterioration of processing stability and even carbon deposition. As shown in the figure.
In this case, if the machine tool has good performance and can realize three-axis linkage processing, it is best to adopt lateral servo processing, so that the electrode is slightly away from the processing surface for a certain distance when retreating, so that the electro-corrosion products can be washed away smoothly. If there are no conditions, try to increase the movement range of the main shaft and expose the machining surface to the machining fluid as much as possible, so as to eliminate the electric corrosion.
C. Effect of liquid flow treatment
In EDM, the liquid flow treatment is very important. The liquid flow direction should follow the direction of the generation of electro-corrosion products. For example, in the above example, if the liquid flow direction is not parallel to the discharge gap but perpendicular to the discharge gap, the discharge state may become worse. For example, when processing the above items, but the effect may not be very good by soaking, it is best to supplement it with flushing method.
D. Influence of electrode material quality
Of course, the quality of electrode material is also the main reason for abnormal processing. Generally speaking, the probability of quality problems of graphite material is higher than that of copper. The reason is that the manufacturing process of graphite is complex. In addition, it is a non-metallic material after all, and many characteristics are different from metal materials. The quality problems of graphite are generally manifested in loose material, easy slag falling, uneven discharge roughness, etc., but all these phenomena do not necessarily mean that it is the quality problem of graphite. Poor processing state and improper processing conditions will also cause these problems. We can only consider whether the material problem is solved after eliminating these possibilities. Dongyang carbon provides pure Nissan graphite with stable product quality and guaranteed service. Customers can rest assured to use the graphite products of various brands provided by our company.
1. Improper use of machining standards, exceeding the current density bearing capacity of discharge section, and too small pulse to pulse
The application of discharge energy is not arbitrary. If you want to process faster, you can apply a larger current. In the discharge machining standard, it generally refers to the peak current, that is, the current flowing through the discharge channel when the pulse is on. The action time of the current is very short, which depends on the pulse on time, that is, the pulse width. On the processing equipment, the current value displayed by ammeter or analog ammeter is the average value of pulse current, because the pulse is discharged intermittently. Generally speaking, the peak current is determined by the number of power amplifier elements put into the discharge circuit and the voltage applied by the circuit, which is independent of pulse width and pulse to pulse; In addition to the relationship between the processing current and the peak current, the processing current can also be changed by adjusting the pulse width and pulse to pulse. As shown in the figure.
The discharge current density of graphite electrode is about 6 ~ 8 (a) / cm2. If it exceeds this value, the probability of abnormal discharge and carbon deposition will increase.
The correct treatment method is to correctly estimate the discharge area and select the machining parameters according to the discharge area.
For example, there is a square electrode with a discharge area of 3 × 3 (mm). When selecting the discharge parameters, first select the model number condition of □ 3, and then select a suitable starting machining condition according to the electrode reduction.
It must be noted here that the discharge current should be estimated according to the discharge area. The normal value of the current in this area should be controlled at about 1 / 9 of the current density value. It can be increased appropriately, preferably no more than 2.5A. If it is too large, it is easy to produce carbon deposition. Therefore, for some small electrodes, it is not necessary to reduce the electrode too much. As in the above example, the electrode reduction of 0.1 on one side is basically sufficient.
The processing parameters of imported discharge equipment are relatively complete and scientific, and generally only need to be selected according to needs. However, the processing parameters of some Taiwan machines or domestic medium and low gear spark discharge motors are generally not as detailed as those of imported machines, and there is even no expert library for automatic selection. The processing conditions can only be selected by themselves according to the experience of operators. The principle of selecting processing conditions is the same. First estimate the processing area and determine the discharge current. As mentioned above, the discharge current is related to the pulse width and pulse to pulse, so the matching relationship between the two must also be considered. In particular, it should be noted that setting a reasonable or sufficient pulse to pulse time will make the discharge channel too late to eliminate ionization, and the discharge process has been in the conduction state to form arc discharge (i.e. carbon deposition). In case of uncertainty, it is better to set the pulse gap larger to improve the processing stability
Graphite carbon is a substance with very sensitive chemical reaction. Its resistivity will change in different environments, that is, its resistance value will change, but one thing will not change. Graphite powder is one of the good non-metallic conductive substances. As long as the graphite powder is kept uninterrupted in the insulated object, it will be energized like a thin wire. However, there is no accurate number of the resistance value, Because the thickness of graphite powder is different, the resistance value of graphite powder will be different in different materials and environments.
Cutting graphite is different from cutting metal. When the tool edge is cut to produce curls or chips, the metal will undergo plastic deformation.
When machining graphite, small powder particles will be separated from the workpiece due to the brittle fracture caused by the stress generated at the edge of the cutting tool.
Cutting graphite consumes less energy and generates less heat than cutting metal.
Graphite is an abrasive material that causes rapid wear of metal uncoated cutting tools. Only diamond or carbide cutters can be used to cut graphite.
Graphite and carbon are usually processed and dried without the use of cutting fluid (coolant). If coolant is used in some machining operations (grinding, honing, polishing), the workpiece should be dried at 300-400 ° f (150-200 ° C) to remove the liquid absorbed by the material.
Compared with metal, graphite is processed at higher cutting speed, feed rate and cutting depth:
1. Material fragmentation (fracture) at the exit of the cutting channel can be avoided by limiting the cutting depth to half the length of the insert;
2. Reducing the feed speed at the outlet of the channel can also prevent fragmentation;
3. The chamfering at the end of the workpiece makes the inlet and outlet of the tool easier and reduces fragmentation;
Processing graphite and carbon produces particles with a size of 0.0004 “- 0.005” (10-130 μ m) Dust within the scope. Dust can be removed from the processing area by providing dust removal equipment with a low wind speed of 6 ft / S (20 m / s).
I、 Graphite is selected as the electrode material, and more than 90% of the electrode materials in Europe are graphite. Copper, once the dominant electrode material, has almost lost its advantages compared with graphite electrode.
II、 Reasons for graphite as electrode:
1. Faster processing speed: generally, the machining speed of graphite can be 2 ~ 5 times faster than that of copper; The speed of EDM is 2 ~ 3 times faster than that of copper;
2. The material is not easy to deform: it has obvious advantages in the processing of thin rib electrode; The softening point of copper is about 1000 degrees, which is easy to deform due to heating; The sublimation temperature of graphite is 3650 ℃; The coefficient of thermal expansion is only 1 / 30 of that of copper.
3. Lighter weight: the density of graphite is only 1 / 5 of that of copper. When large electrode is used for EDM, it can effectively reduce the burden of machine tool (EDM); It is more suitable for the application in large molds.
4. Lower discharge consumption; Because the spark oil also contains C atoms, during EDM, the high temperature causes the C atoms in the spark oil to be decomposed, and a protective film is formed on the surface of the graphite electrode to compensate the loss of the graphite electrode.
The supply and demand of high-end materials are unbalanced. Graphite and carbon materials occupy the position of negative electrode materials because of their great resource reserves and excellent performance. The carbon graphite electrode materials in China are still low-end products. If they are used as power lithium batteries, they need to be further improved. With the promotion of new energy vehicles, China’s demand for medium and high-end carbon graphite cathode materials will also expand. China plans to have 1 million electric vehicles by 2015, when the demand for high-end carbon graphite cathode materials will exceed 10000 tons. At present, the production capacity of high-end anode materials in Chinese enterprises is far from enough The bottleneck of localization of lif6 is about to break through.
Power battery is the “energy block” pursued by human beings. The rapid development of battery industry is closely related to the technology and demand of energy utilization and transformation. In the pursuit of “green” energy, the power lithium battery bears the belief of “mobile power, green dream”. We believe that the prospect of power lithium battery industry is very bright. The cathode materials lithium manganate and lithium ferrous phosphate have their own advantages and will coexist for a period of time. Lithium manganate and lithium ferrous phosphate have their own advantages which are very suitable for power batteries, but also have some disadvantages which are difficult to overcome. The biggest requirement of new energy vehicles is safety. As long as the safety of the materials is high, the materials will have a sound foundation for development. At present, the statistical capacity of various companies in China has exceeded 20000 tons, while the global demand is still around 10000 tons. In order to avoid the low-end rough manufacturing, China’s cathode material industry needs to prevent the risk of overcapacity.
At Ray Group, our engineers have been in these industries since 1990. It is combining research, development, production and sales. Backed with expertise garnered from their days at major chemical research institutes, they can offer you the technical understanding you need to get your projects done right.If you have any needs about Graphite Electrodes ,please contact us!
(1) Ordinary power graphite electrode
Allow the use of electric current density of less than 17a/cm 2 graphite electrode, mainly used in steelmaking, smelting silicon, refining of yellow phosphorus, such as ordinary power electric furnace.
(2) Anti-oxidation coating graphite electrode
A graphite electrode coated with an antioxidant protective layer (a graphite electrode antioxidant). Forming both conductive and high-temperature oxidation protection layer, reduce the electrode consumption (19%~50%), prolong the service life of the electrode (22%~60%), reduce the electric energy consumption of the electrode. The use of this technology can bring about such economic and social effects:
Graphite electrode unit Consumption is less, production cost has a certain reduction. For example, a steelmaking plant, according to the whole year does not occur discontinued a LF refining furnace 35 graphite electrode per week, refining treatment 165 furnace consumption calculation, the use of graphite electrode antioxidant technology, can save 373.