Development of precision forging technology for Involute Gears

The precision forging of involute gear originated in Germany. In the 1950s, because there were not enough involute gear processing machines, the Germans used EDM to process the forging die cavity and tried to process bevel gear by ingenious hot die forging. German BLW company first obtained the patent of involute gear precision forging. In the late 1950s and early 1960s, Japan, France, Britain and the United States successively introduced German patents. Therefore, the involute gear precision forging technology has been more widely developed. The precision forging of gears in the United States started late, but developed rapidly. In 1975, American TRW company acquired the equity of BLW company, making it a company specializing in the production of precision forging technology gears. Since the 1960s, China began to study the precision forging technology of straight bevel gears. In the early 1970s, it has been able to produce bevel gears with high precision and suitable for automobiles and tractors.

Precision forging technology is habitually divided into; Cold precision forging, hot precision forging, warm precision forging, compound forging, isothermal forging, etc. Cold precision forging refers to the precision forging process at room temperature. Because it does not need to use heating equipment, it is suitable for multi variety and small batch production, and the forging workpiece has high precision and good surface quality. However, due to the large deformation resistance of metal at room temperature, poor plasticity and difficult to fill local details, it is only suitable for forming parts with simple structure. Because of many advantages of cold precision forging, cold precision forging technology has been widely concerned and studied in gear manufacturing.

Yang carried out numerical simulation on the closed cold precision forging process of bevel gear used in Jetta. The results show that the process is reasonable, the die design is correct and the simulation results are reliable. Huang et al. Skillfully studied the grain size, hardness and residual stress of closed cold forged bevel gear with the help of modern metallurgical analysis technology. The results show that the closed cold forging method significantly improves the strength and initial properties of bevel gear, and its residual stress is skin stress. Liu et al. Used the elastic-plastic finite element method and analyzed the strain field, velocity field and die force, studied the metal filling rules of cold closed forging of vehicle conical teeth, and pointed out that there were some phenomena in the forging process, such as insufficient tooth shape filling and obvious differences in the stress of upper and lower forging dies. Dean et al. Studied and analyzed the forging forming of gear parts, described the research background of bevel gear and helical gear forging, paid particular attention to the production of high-precision gears used by land vehicles such as automobiles, and analyzed the relationship between gear forging process parameters and dimensional accuracy by using single tooth die experiment and numerical simulation. Zhang et al. Obtained the instantaneous deformation and stress of vehicle planetary gear through numerical simulation, predicted the forming defects, and provided reference for practical application. Liu et al. Combined with experimental research, studied and analyzed the change of gear tooth size in the cold precision forging process of spur gear, found two main factors affecting the change of gear tooth size, and modified the die according to the simulation results. Through experimental verification, the gear precision can be significantly improved by using the repaired die for gear precision forging. Hot precision forging can significantly reduce the deformation resistance of blank, but the oxidation caused by high temperature leads to poor surface quality and low dimensional accuracy.

Alves et al. Proposed a new flexible tool system for gear precision forging. With the help of numerical simulation and experimental verification, it is pointed out that hot precision forging can significantly reduce the deformation resistance of smart materials, but high temperature and easy oxidation of materials, resulting in poor appearance quality and low dimensional accuracy of products, Therefore, hot precision forging can be applied to parts with low dimensional accuracy requirements or to product pre forging. In order to reduce the blank loss in the hot forging process, Chen et al. Proposed the Cockroft Latham damage model based on the material damage principle, proposed a forging process optimization design method based on the generalized reduced gradient, and used the numerical simulation method to optimize the initial height diameter ratio of the blank. Wang et al. Skillfully used the finite element numerical simulation method to study the microstructure changes of spur gear shaft during hot forging, and obtained the grain size distribution of gear shaft with different sizes by micro weaving simulation and metallographic experiment, The influence laws of different forging parameters (including initial forging temperature and punch speed) on the grain size of gear shaft after forging are given. The numerical simulation of material pre forming is carried out. The results show that pre forming can w make the grain size obviously refined and the grain distribution more uniform. Zhi et al. Put forward the multi-stage hot forging process scheme of roughening pre forging final forging for large-size rectangular gear. Through simulation and experimental verification, the variation laws of temperature distribution, equal effect deformation field and velocity field in the deformation process are obtained. The size of the formed forging is qualified without any folding defects, The feasibility of multistage hot forging process is verified.

Zuo et al. Introduced the tooth shape influence factor into the calculation formula of closed rough forming load, proposed the calculation formula of hot precision forging load of cylindrical gear, and fitted the tooth shape influence factor of gears with different modulus by using the data of finite element simulation of forging process, which was verified by experiment and W. Wang et al. Simulated the hot forging of gear shafts with three different material by material sizes by finite element method Φ The gear shaft with size 36 * 60 has the best formability. The effects of initial blank temperature and friction coefficient on hot forging formability are obtained through simulation and experiment. Finally, reasonable hot forging process parameters of gear shaft are obtained. Warm precision forging is a method of forging at a temperature lower than the recrystallization temperature. Warm precision forging not only overcomes the disadvantages of large deformation resistance and simple shape of formed parts in cold precision forging, but also overcomes the disadvantages of low dimensional accuracy caused by oxidation in hot forging. Therefore, it has attracted attention, but warm precision forging has high requirements for smart materials and forging dies.

In order to reduce the forming force of spur gear, Qiu et al. Proposed the application of a new wet extrusion two-step forming method for ordinary closed die forging and carried out numerical simulation. The results show that compared with the traditional closed die forging, this method can significantly reduce the forming force and ensure that the tooth shape is completely filled. Wang et al. Used numerical simulation and experimental verification methods to improve the forming quality of half shaft telephone wheel by analyzing and optimizing the influencing factors affecting the forming quality of half shaft gear. Wu and other differential bevel gears are made by warm forging and analyzed and developed in combination with the cold swing shaft precision forming process. The results show that the precision of the forming wheel is high, the tooth strength is high, the die life is high and the equipment investment is small, which provides technical support for the localization of differential bevel gears. Luo Shanming et al. Used DEFORM-3D to simulate the wet forging of spur bevel gear, analyzed the temperature distribution in the warm forging process, and pointed out that with the downward movement of punch, the overall temperature of tooth increases, and the humidity change of tooth shape is the most obvious; And the humidity at the tooth top is the highest, which is likely to produce stress concentration. Try to take measures to cool the part of the tooth top.

Scroll to Top