Gear is an important part of mechanical transmission. Its main function is to transmit power and change the speed and direction of movement. Because of its large power range, high transmission efficiency, accurate transmission ratio, long service life, safety and reliability, it is widely used in various projects. Traditional gear production methods include gear hobbing, gear milling, gear shaper, gear planer, gear casting, gear grinding, gear shaving, etc. However, due to the low material utilization and production efficiency, these traditional processing methods can not meet the growing needs of social production. Therefore, people began to explore and develop gear processing technology aiming at net shape or near net shape, such as precision plastic forming, near net shape casting forming, precision forging technology and so on. Among the above near net shape forming technologies, precision forging technology is widely used at present. This method not only has the advantages of high production efficiency, high material utilization and less subsequent processing procedures, but also can form metal fiber structure distributed continuously along the tooth profile with less micro defects, so as to significantly improve the mechanical properties of gears. The precision forging technology of bevel gear with many of the above advantages has been successfully applied in production. However, due to the great difficulty of the precision forging technology of spur cylindrical gear, especially the problems such as insufficient tooth filling, large forming load and serious die wear, the precision forging technology of spur cylindrical gear has not been applied to the actual production. Therefore, the precision forging technology of spur gears has become a cutting-edge topic of common concern to researchers all over the world.
Precision forging technology is a new technology of net forming or near net forming. The parts formed by this method can reach the shape and size of the target parts without or only a small amount of machining. Compared with the traditional forming technology, it not only improves the material utilization and reduces the subsequent processing procedures, but also significantly improves the product quality and production efficiency. Products with complex geometry and good mechanical properties can be manufactured by precision forging technology. The plastic forming process of spur gear is simulated by numerical analysis method, and the deformation of upsetting spur gear is analyzed by energy method and upper bound element method. Aiming at the problems of difficult tooth shape filling and large forming load in precision forging of spur gears, many scholars at home and abroad have put forward different process improvement methods.