Study on precision forming process of bevel gear by cold rotary forging

As a typical transmission part, gear is widely used in many industries, such as aviation, aerospace, automobile, instrument and so on. The quality of gears directly affects the performance level of related products. It can be said that the level of gear processing technology has become one of the important symbols to measure a country’s machinery manufacturing level. At present, domestic gear processing is still dominated by traditional machining technologies such as gear hobbing, gear shaping, gear shaving and gear grinding. These conventional cutting processes have the advantages of low material utilization, high energy consumption and low productivity. Especially, the metal streamline of the material is cut off in the machining process, resulting in the decline of gear tooth strength and fatigue life. Therefore, in recent years, the application of plastic forming technology to replace the traditional mechanical cutting methods has been paid more and more attention.

Precision forming technology overcomes the shortcomings of low material utilization and low productivity in cutting process, especially the low strength caused by cutting off metal streamline. It has become one of the main methods of gear machining reform with its high efficiency and high precision. As an advanced manufacturing technology, precision forming technology is gradually developed on the basis of traditional die forging technology. At present, the generally accepted definition of precision forming process is “at least the dimensional accuracy and shape accuracy of some surfaces of forgings can be directly used for assembly or can be assembled only by grinding”. Using precision forming technology to produce gear parts not only has the significant advantages of material saving, energy saving, reducing machining processes and man hours, low cost and high efficiency, but also can greatly improve the internal and appearance quality of products, which is in line with the development trend of advanced manufacturing technology in the 21st century, which is efficient, precise, green and clean. It is one of the main methods of gear processing reform in the future.

Cold rotary forging of bevel gear is an advanced gear processing technology. This process is to form the tooth shape by plastic deformation of the profile. It has the significant advantages of high material utilization, high productivity and low production cost. Moreover, the tooth surface forms a complete metal streamline, which can greatly improve the mechanical properties and service life of the gear. At the same time, as a type of rotary forging process, this process also has the advantages of labor-saving, high forming size and shape accuracy, less and no cutting, high service life of rotary forging die, good labor environment, easy mechanization and automatic production.

At the same time, the cold rotary forging precision forming process of bevel gear is a complex system engineering, which involves a series of process processes, process theories and methods, such as softening treatment of raw materials, lubrication treatment, flow law of metal in die cavity, forming die structure, die cavity design and tooth profile accuracy compensation method, electrode design of machining cavity and electrode tooth profile correction method, The technology is very complex. In order to improve the technical and economic level of auto parts production in China, enhance the market competitiveness of auto gear products in Hubei Province and fill the gap of car gear products in Hubei Province, Wuhan University of technology and Hubei car Co., Ltd. jointly applied for the key science and technology development plan project of Hubei Province “Fukang car gear cold swing rolling precision forming technology” in 1999, Approved by the science and Technology Commission of Hubei Province. After nearly two years of process theoretical analysis and experimental research, the cold swing rolling precision forming technology of Fukang car gear has been successfully developed and put into trial production. The product is matched with Fukang car of Shenlong Automobile Co., Ltd.

Based on this project, the cold rotary forging precision forming process of bevel gear is systematically studied, tested, analyzed and summarized, and the process is applied to computer-aided design to develop a targeted computer-aided design system.