The application of the most efficient cutting tool

The application of efficient tools promotes the development of gear manufacturing technology

-- Mr. Xuan angung, chief engineer of Hangzhou Qianjin gear box group, talks about the application of tools in gear processing

at the "seminar on efficient tool technology", I had the honor to communicate with Mr. Xuan angung, chief engineer of Hangzhou Qianjin gear box group. In order to introduce the problems concerned with the application of tools in gear and gear box processing, And the application of advanced and efficient cutting tools promotes gear processing

: first of all, please introduce the development history of your company

nowadays, the modern theory of forward gear oscillation measurement and analysis and imitation analysis has been established, and the products of the rear box factory cover a wide range, including the whole gearbox. The company has a special powder metallurgy plant, and its friction plate production adopts domestic leading technology, which adopts copper based, iron-based or other powder technology to sinter into friction layer

: in terms of cutting tools, what problems do you think are of concern to gear or gearbox processing

Mr. Xuan angung: in the gear manufacturing industry, gear hobbing technology accounts for more than 70% of the gear processing, and the adoption of high-speed gear hobbing is of great significance. In order to realize high-speed gear hobbing, the gear hobbing machine must improve the rigidity, improve the driving power of the hob head, improve the numerical control and servo functions, realize temperature compensation, etc., and promote the application of high-performance and efficient tools at the same time. In terms of cutting tools, at present, there are fewer and fewer high-speed steel cutting tools, and most of them use cemented carbide. At present, HSS is the main hob material used in production, and cemented carbide insert hobs or integral powder metallurgy cemented carbide hobs are also used. Some tool suppliers in Germany, such as Sandvik croman in Sweden, are particularly good at adapting to processing technology, especially for heavy gear processing

: can you tell us about the new development of gear grinding technology

Mr. Xuan angung: in the past, we used to use the development method. Now, high efficiency molding mills are used. When this technology was proposed in the 1970s and 1980s, there were technical problems that could not be solved. For example, due to the contact of the whole alveolar, it is easy to burn, and the spots formed are easy to become soft spots. The successful development of large pore grinding wheel, the application of large flow cooling device and numerical control technology in gear grinding machine make the forming grinding become a reality. In the past, it was difficult to grind grade 7 accuracy, but now it can reach the highest grade 3 accuracy. Hangzhou gear factory has imported more than 10 German forming mill CNC machine tools

attachment: the application of efficient cutting tools promotes the development of gear manufacturing technology Author: Xuan angung

in the current gear manufacturing industry, the tooth shape processing technology of each company is roughly the same. Gear processing mostly adopts gear hobbing, gear shaving and gear honing after heat, while a few enterprises adopt gear hobbing and gear honing after heat, while the heavy-duty gear transmission industry generally adopts gear hobbing technology

gear hobbing accounts for more than 70% of the share in gear manufacturing, and it is of great significance to adopt high-speed gear hobbing. In order to realize high-speed gear hobbing, the gear hobbing machine must improve the rigidity, improve the driving power of the hob head, improve the numerical control and servo functions, and realize temperature compensation. At the same time, it is also necessary to promote the application of high-performance and efficient tools after users purchase products

at present, the hob materials used in production are mainly high-speed steel, and there are also carbide insert hobs or integral powder metallurgy carbide hobs. High speed steel hobs are usually coated, such as M35, M42, A4 and other commonly used tool materials. With tin coating, the matrix toughness is good, the coating is heat-resistant and wear-resistant, and the edge collapse is prevented. The cutting speed can be increased to 120 ~ 150mmin. The solid carbide hob made by powder metallurgy sintering forming method also has good effect. After coating treatment, the cutting speed of this tool can be increased to more than 250mm, and the axial feed rate can reach 3 ~ 6mmr. And as long as the equipment conditions permit, dry cutting can be realized. The use of dry cutting can reduce the pollution of oil mist caused by the original use of cutting coolant to the environment, and the excellent performance of cemented carbide coated tools can greatly prolong their service life and reduce processing costs

during gear hobbing, the hob and the workpiece are equivalent to a pair of worm and worm gears that mesh with each other. According to the continuous generation method, the linear tooth profile of the hob blade envelope cuts out the involute tooth profile of the workpiece. Hobbing processing should be for subsequent processing, such as shaving before heat treatment or grinding after heat treatment, with appropriate machining allowance, and the tooth root part should be processed in hobbing to the requirements of finished parts. The higher the speed of the hob, the more the number of heads, and the shorter the cutting time. In order to improve efficiency, in addition to increasing the speed and feed speed of hobs, multi head hobs should be used as much as possible. Increasing the number of heads can significantly improve the cutting speed and reduce the cutting times of the cutting edge, which is conducive to the cutting of the hob, reduce wear and improve the tool life. Hobs are usually used with 2-4 heads, and there are also 5-7 heads

increasing the diameter of the hob and the number of grooves can increase the chip thickness and productivity. However, because the hob diameter is limited by the machine tool structure, there is little room to increase. Increasing the number of slots will affect the strength of the cutter teeth in many cases, so there are double tooth hobs or three tooth hobs that combine two or three rows of slots into one. This hob can be used for rough cutting and fine cutting. In particular, after the strength of the cutter teeth is improved, the cutting parameters can be increased, the chip formation conditions can be improved, and the cutting area can be reasonably distributed along the whole blade to meet the requirements of heavy cutting. Compared with ordinary hobs, the efficiency is increased by 4~6 times, so it is often called heavy cutting hobs

in the whole gear hobbing process, while the hob is fed along the axial direction of the workpiece, it also needs to move along the axial direction of the hob, that is, to make the tool channeling movement, so that all the cutter teeth on the hob participate in cutting, balance the wear of the cutter teeth, and improve the durability of the tool. If the roughness of the tooth surface of the workpiece is obviously deteriorated, there are light spots, burrs increase or the sound is abnormal, it should be sharpened in time

the method of Machining Hardened Gears with carbide hobs has been used in enterprises for many years, but in most cases, it is only used to replace rough grinding. This is because when hobbing the hard tooth surface, the elasticity of the hob during cutting in and cutting out causes the sudden change of the tooth shape of the workpiece. In addition, the instantaneous extrusion high temperature causes the annealing of the tooth surface of the workpiece to produce soft spots, which affects the contact strength of the workpiece. Therefore, taking advantage of its high metal removal rate than the grinding gear, it has a better effect to replace the rough grinding tool. There are also examples of successful precision machining of spiral bevel gears with carbide formed scraping and milling cutter heads, but the formed cutters are very expensive, have limited service life, and are not widely used

gear shaping technology is often used for internal teeth, double or multiple gears. Compared with gear hobbing, although both work according to the generating principle, the impact of cutting in and cutting out of the tool and the up and down movement of the tool spindle during gear shaping are affected by the inertial force. Unless the process conditions do not permit the use of gear hobbing, the gear shaping process will not be applied. Because of this, there is little progress in the research of dry cutting gear shaping methods

on the modern large gear hobbing machine, the internal gear milling head can be configured according to the user's requirements. The disc milling cutter is used to replace the interpolation with milling, and the machining allowance of the internal gear ring is cut off by dividing the teeth one by one, and then the final gear shape is obtained by internal gear grinding. Compared with the gear shaping process, the efficiency is improved several times. Of course, due to the limitation of the internal tooth milling head, the inner diameter of the workpiece should be large enough. In addition, when milling internal straight teeth by milling instead of inserting, the cutting edge of the precision milling cutter can be made into the involute shape like the workpiece, and the allowance reserved for grinding teeth after machining can be smaller; When milling internal oblique teeth, although the cutter base can pull an angle according to the spiral angle, the disc-shaped milling cutter cannot make continuous generation like hobbing, so the tooth shape cut is approximate involute, and the allowance left for grinding teeth is slightly larger. The high-power internal gear milling head adopts a preloaded mechanical transmission chain and is driven by a motor or hydraulic motor, which provides the basic conditions for efficient machining. The coating milling cutter or carbide insert milling cutter with optimized cutting parameters can not only improve the metal removal rate and prolong the tool life, but also realize dry cutting. For example, the internal gear with 107 teeth, 9 modulus, 8 degree helix angle, 210 mm tooth width and 42crmos4 material is processed on the P high-efficiency hobbing machine with internal gear milling head, and the air-cooled dry cutting is adopted. The total milling time is 135 minutes (one-time cutting), while the same cutting amount, processed on the ordinary machine tool by gear shaping method, takes at least twoorthree days

users have higher and higher requirements for reducing gear noise, and the traditional hobbing and hot honing process cannot meet this requirement due to its limited capacity. If the hot rolling grinding process is adopted, the decision-makers of enterprises are hesitant because of the high manufacturing cost. For mass-produced vehicle transmission gears, the honing technology of powerful internal gear honing wheel solves this contradiction well, and provides a feasible method for gear finishing. The maximum honing allowance of the traditional honing process is no more than 10 microns, which is only finished on the tooth surface after heat treatment after shaving, so as to improve some surface quality, so it can not improve the tooth profile and direction. Strong internal gear honing is different. After heat treatment, large machining allowance (20~50 microns) can be finished to meet the process requirements; Moreover, it can form a strip texture on the tooth surface, unlike the periodic strip texture obtained when grinding the teeth considering the future global energy, so it can reduce the meshing frequency of the teeth, thus reducing the noise. Honing tools can be resin bonded sand, emery or CBN honing wheels. In order to save costs when machining external teeth, resin bonded honing wheels that can be trimmed are usually used, and diamond dressing wheels are used for trimming. Strong honing technology is mainly used in mass-produced automotive gears. The workpiece modulus is 0.3~6 mm, the diameter is 10 ~ 250 mm when selecting the installation environment, and the tooth width is 20~50 mm. The final gear accuracy can reach level 6 or even higher, and the processing cost is about half of that of gear grinding. (end)