Internationally, the power transmission gear forging device is developing in the direction of miniaturization, high speed and standardization. The application of special gear forging, the development of planetary gear device and the development of low vibration and low noise gear forging device are some characteristics of gear forging design. In order to achieve the purpose of miniaturization of gear forging device, the bearing thrust of existing involute gear forging can be improved. Hard tooth surface technology is widely used in various countries to improve the hardness to reduce the size of the device; The special tooth profile represented by circular arc gear forgings can also be applied. The main transmission system of Shipborne helicopter developed by Britain and France adopts circular arc gear forging, which greatly reduces the height of reducer. With the trend that ship power is replaced by medium speed diesel engine, it is effective to use high-power planetary gear forging device on large ships; Nowadays, in large transmission devices such as metallurgy, mining and cement rolling mill, planetary gear forgings are more and more used because of their small volume, good coaxiality and high efficiency. Due to the development of large-scale mechanical equipment, the working parameters of gear forgings have been improved. For example, the transmission power of high-speed gear forgings is 1000-30000kw. The circumferential speed of gear forging is 20 ~ 200m / S (1200-12000r / min), and the design working life is 5×104-10×104 hours; The circumferential speed of rolling mill gear forgings has increased from a few meters per second to 20m / s, or even 30 ~ 50M / s. The transmission torque torch reaches l00 ~ 200t m. The service life is required to be more than 20 ~ 30 years. The accuracy grade of these gear forgings is generally grade 3 ~ 8. It also has high requirements for stability and noise. For high-speed gear forgings (including turbomachinery gears). When the circumferential speed exceeds 100M / s, due to the thermal effect in operation, it is required to correct the thermal deformation at the beginning of design to make the gear forging reach a normal meshing state during operation. Especially for high-speed and heavy-duty gear forgings. More consideration should be given. Secondly, for low-speed and heavy-duty gear forgings, such as rolling mill gear, the elastic deformation of the whole gear device system caused by the increase of tooth surface load coefficient after using hard tooth surface gear becomes prominent, so sometimes the elastic deformation reflected on the tooth surface should be corrected. This technology of gear tooth modification is an important trend in the manufacturing of high-power, high-speed and heavy-duty gear forgings. In terms of gear manufacturing technology, the focus is on hard tooth surface machining, especially the development of cutting and heat treatment process of large hard tooth surface gear forgings, such as superhard cutting, internal gear hobbing, forming gear grinding, gear honing of large module gears, elastic grinding wheel polishing, gear tooth modification, deep sand carbon and other new processes are constantly tested and applied in production.
The development of manufacturing technology of gear forgings is largely reflected in the improvement of accuracy level and production efficiency. Since the 1970s, the manufacturing accuracy of various gear forgings has generally increased by about one level. Some even level 2 ~ 3. The accuracy of general low-speed gears has increased from level 8 ~ 9 to level 7 ~ 8. The gear forgings of machine tools are increased from grade 6 ~ 8 to grade 4 ~ 6, and the gears of rolling mills are increased from Grade 7 ~ 8 to grade 5 ~ 6. For small and medium-sized gear forgings with small modulus, due to the development of high-performance hobbing machine and the improvement of tool materials, the hobbing efficiency has been significantly improved. Using multi head hob, the cutting speed can be 90m / s under the condition of large feed and. If the superhard hob is used to process the quenched and tempered steel gear forgings with modulus of about 3, the over cutting can reach 200m / s. improving the gear shaping efficiency is limited by the reciprocating motion mechanism of the tool of the gear shaper. Recently, after developing new structures such as tool unloading, hydrostatic bearing and enhancing the rigidity of tool holder and column, the efficiency has been significantly improved. The stroke number of the new gear shaper can reach 2000 times / min.
Due to the wide application of hard tooth surface gear forgings and the increasing number of gear forgings with high speed and high performance requirements, gear grinding is required to improve efficiency and quality. Generally speaking. Generating method is widely used in gear grinding, while forming method is less. Maag gear grinding method has high precision but low efficiency. Not suitable for regrinding. The single grinding wheel gear grinding machine produced by Niles and hofler has good rigidity, reliable precision, suitable for large feed rate processing and high efficiency. In recent years, grinding methods are also being improved to improve efficiency, such as reducing grinding times, compressing the developed length and shortening the tail cutting stroke; Therefore, the “K” grinding method proposed by Maag company and the “double-sided grinding method” proposed by Niles company have improved the actual grinding efficiency. At present, worm wheel gear grinding machine is preferred for batch grinding of medium and small use gears, with high grinding efficiency. For grinding large modulus gears, in addition to the single wheel gear grinding which can be reground, the forming drawing method is adopted. It is also an effective way of efficient grinding.
In addition, there are some new process methods, such as g-trac no765 track gear cutting machine developed by Gleason company of the United States. It can process 88 gear forgings per hour, which is 3 ~ 4 times higher than that of ordinary gear hobbing machine. High efficiency gear cutting process with double cutter head. The cutting speed can reach 137m / s. It takes only 6 seconds to roughen and finish a helical gear with M = 1.5mm, outer diameter of 24.43mm and tooth width of 19mm, and its efficiency is 5 ~ 10 times that of this gear. The efficiency of multi cutter head gear shaper of Michigan tool company in the United States is 5 ~ 10 times higher than that of ordinary gear shaper. The cold forming process of gear forgings in the automotive industry, cold extrusion, hot rolling and other less and no cutting processes also continue to obtain new development. With the development of self facing gear forgings, people pay more and more attention to the materials and heat treatment of gear forgings.
Development trend of steel for gear forgings; First, low alloy steel containing Cr, Ni and Mo; Second, boron steel; Third, carbonitriding steel; Four is free cutting steel. Due to the lack of Ni and Cr in China, 20CrMnTi carburized steel or boron containing rare earth steel are commonly used. 18CrMnNiMo carburized steel or medium carbon alloy steel is commonly used in heavy machinery. The machine tool industry uses 40Cr, 38CrMoAl and other steels and 25Cr2MoV steel for nitriding of high-speed gear forgings.
The heat treatment processes of gear forgings generally include carburizing (or carbonitriding), nitriding, induction quenching and quenching and tempering. At present, the general trend is to improve the hardness of tooth surface. The bearing capacity of carburized and quenched gear forgings can be 2 ~ 3 times higher than that of quenched and tempered gears. Table 111# shows the gear forgings made by different processing methods. The comparison of center distance, weight and safety factor.
Carburizing and quenching gear forgings can obtain high surface hardness, wear resistance, toughness and impact resistance, and can provide high pitting corrosion and fatigue resistance. The performance of the core and carburized layer mainly depends on the heat treatment process selected. For example, when the gear forging is quenched and tempered to 360hb, its tooth surface contact fatigue limit stress pH. – 750N / mm2, such as when the surface is quenched to hrc56-60 -,
Pj1500n / mm2, if the surface carburized to the same hardness, Yi- 1200n / mm2, for hardened and tempered gears. Due to the improvement of gear tool materials, the tooth surface hardness of pinion has been increased to 360hb and that of large gear has been increased to more than 280hb.
Carburizing of gear forgings mostly adopts gas carburizing method. This method is especially useful for the development of deep carburizing furnace, which can not only reduce the time of carburizing, but also reduce the energy consumption and the cost of carburizing. It is also useful for the development of deep carburizing furnace. It is also useful for reducing the time of carburizing and gas injection, especially for the development of deep carburizing furnace.
Application of electronic computer in various industrial fields; It has promoted the development of various technologies. Similarly, there has been rapid progress in the design and calculation of gear forgings. People can calculate, analyze and compare various possible design methods by using computers, and obtain ideal results through optimization. For example, in analyzing the contact area of tooth surface, calculating the angle between meshing line and relative speed, compiling programs for elastohydrodynamic lubrication calculation and geometric parameter calculation. In addition, there are programs for the modification calculation of gear forgings and the calculation of bearing capacity of gear forgings. China has compiled the program software of gb3480-83 standard for the calculation of bearing capacity of involute cylindrical gears for production application. In gear processing, the whole gear cutting process can be controlled by computer to make the manufacturing quality stable and reliable. At present, China is studying the application of microcomputer to calculate the gear cutting adjustment card of spiral bevel gears, The machining deviation can be adjusted in time, so that the tooth surface contact can reach an ideal position, and the work efficiency is greatly improved. In addition, according to the principle of numerical control, the parabola modification of the helical tooth surface of hourglass worm by microcomputer has been applied to production. Although this work is still in its infancy in China, it is of great significance to improve the manufacturing quality and technical level of gear forgings.