The precision forming technology of cylindrical gear comes from Germany. As early as the 1950s, due to the lack of sufficient cylindrical gear processing machine tools, the Germans began to trial produce bevel gears by closed hot die forging. The main feature is that the very new EDM process was used to manufacture the die forging cavity. In addition, the die forging process was strictly controlled. On this basis, the precision forming technology of cylindrical gear is further applied to the production of spiral bevel gear and cylindrical gear. However, in the plastic forming of cylindrical gear, because the plastic flow direction of metal material is perpendicular to its stress direction, its tooth shape is more difficult to form than bevel gear. The research on die forging of cylindrical gear began in the 1960s and developed greatly in the 1970s. This is mainly due to the pressure from the automobile industry to reduce costs. By the 1980s, the die forging technology was more mature and could achieve higher accuracy and consistency, so that the die forging cylindrical gear can be accurately positioned on the assembly line and suitable for mass production.
In 1984, Kondo K proposed the centripetal flow and centrifugal flow conditions for the cold forging of cylindrical gears with bosses. For the cold forging of cylindrical gears with flush end faces, the measure of setting pressure reducing holes on the blank or die was taken to achieve the purpose of shunt and pressure reduction. The University of Birmingham has conducted extensive research on the precision forging of spur gear. In 1987, the floating die principle of precision forging spur gear with hollow forging blank was put forward, which reduces the material, forging energy and forging pressure consumption of precision forging of spur gear, and the tooth shape is easy to fill, but this die is not suitable for the case of large deformation force. In 1990, battle company of the United States used the principle of “push through” to study the forming of extruded cylindrical gear. Nagai y proposes to take the prefabricated cup-shaped parts as the blank making measures for the cold forging of some cylindrical gears, that is, the cold forging of cylindrical gears with large counterbore can be realized in the four steps of drawing, shaping, thinning, drawing and compression.
Kou Shuqing, Yang Shenhua, etc. studied the cold forging method of high-precision cylindrical gear, put forward the practical process scheme of closed pier extrusion one hole split two-step forming and the modified design method of tooth profile die based on displacement theory, and achieved good results. E. Doege and r. bohnsack use alternating closing devices to separate “die closing” and “deformation”, and successfully forge spur and helical gears, so as to avoid that the pressure higher than that in the traditional closed forging is only used for die closing without deformation.
Liu Quankun and others introduced the concept of flow curve into the tooth cavity, constructed the streamline concave cavity by using the curved surface, and numerically simulated the extrusion process of cylindrical gear. The results show that the use of streamlined concave model cavity is beneficial to improve the filling of corner metal; At the same time, based on the die geometry, a new scheme to change the shape of the end face of the punch and the bottom face of the die is proposed; The better scheme is determined by two-dimensional finite element simulation. On this basis, the new scheme is optimized by the combination of three-dimensional finite element simulation and physical test. The results of numerical simulation are in good agreement with the physical test.