Improving the service life of cold extrusion die is the key point of precision forming of large modulus spur gear. In the process of cold extrusion forming of spur gear, the blank is plastically deformed, and the die will bear a large extrusion force. The large deformation force puts forward higher requirements for the strength of the cold extrusion die. If the die is not designed properly, it will cause excessive stress and cracks of the die, resulting in die failure. In order to improve the strength of the complex cavity die, the cold extrusion die mostly adopts the prestressed combined die structure. The traditional design method of cold extrusion combined die is to determine the structural parameters of combined die by combining Latin American formula and empirical formula, but it is not suitable for the die with tooth shape on the inner ring.
In recent years, researchers have done a lot of research and achieved remarkable results in order to improve the service life of molds. Hu Chengliang of Shanghai Jiaotong University applied MSC Marc software establishes the cold extrusion finite element model of spur cylindrical gear of three-layer combined die. Combined with numerical simulation and golden section iteration method, the size and interference of each ring of the combined die are optimized. Using the optimized combined die, the maximum equivalent stress on the inner wall of the inner ring is close to the allowable stress of the material. Wang Qiang of Hefei University of technology and others took the non occurrence of tangential tensile stress on the inner wall of the combined die core as the optimization objective, and used the finite element method and golden section iteration method to optimize the design of the combined die for cold extrusion of cylindrical spur gear. The optimization results showed that there was no tangential tensile stress on the inner wall of the die core under the working state. In view of the easy cracking of the combined die of the extrusion part of a perforated cartridge case, Zhang Yu, etc. of Chongqing University, aiming at reducing the maximum equivalent stress on the inner wall of the die core, applied Kriging model and particle swarm optimization algorithm to optimize the pre extrusion combined die of perforated cartridge case, searched within a reasonable value range and determined the optimal combined die size. The actual production shows that, Using the optimized combined die can avoid the premature failure of the die. Lee et al. Studied the influence law of radial interference of bolt cold extrusion combined die on the service life of the die through numerical simulation and process experiment, but its forming die shape is relatively simple, and the failure mode is different from that of complex shape parts, which only has a certain reference value for complex shape tooth parts.
O. Eyercioglu et al. Believe that the stress distribution of the tooth profile combined die obtained from the conventional numerical simulation results is higher than the actual stress distribution, so that the size of the designed combined die is large. Therefore, a modified finite element setting is proposed. The relationship between the radial interference of the two-layer combined die and the maximum principal stress of the tooth profile is studied through numerical simulation and process experiment, The nomograph of interference amount of tooth profile combined die is designed to facilitate the selection of interference amount of cold extrusion combined die of spur gear with different sizes. Ao Wengang of Chongqing University of technology and technology applied the double shear unified strength theory to calculate the structural parameters of the combined die for cold extrusion of cylindrical parts under the consideration of compressive anisotropy. The results show that there are small differences in the radius and interference of each layer of the combined die, and the elastic limit internal pressure is greatly improved. Based on the thick wall cylinder theory, Lu Zhibing and others analyzed the characteristics of die working load of integral and combined die under prestress and working state, optimized the cold extrusion combined die of cylindrical parts by using Lagrange multiplier method, and deduced the optimal diameter ratio, interference amount and die stress distribution of n-layer combined die under preload and working state, However, the inner wall of the mold core is cylindrical, which is too simple compared with the complex tooth shape.