By optimizing the cold extrusion process parameters of spur gears, spur gears with high forming quality can be obtained, but the precision of cold extrusion spur gears still does not meet the design requirements. It is necessary to increase the shaping process to improve the gear precision. To solve this problem, firstly, an error model based on the actual test data of cold extruded spur gear is proposed, which is consistent with the actual situation of cold shaping of cold extruded spur gear, and the elastic-plastic finite element method is used to establish the finite element model of cold shaping of spur gear. Secondly, taking the cylinder model as an example, the tooth shape deformation of spur gear during cold shaping is studied, the shaping amount of spur gear cold shaping is preliminarily determined, the stress-strain of spur gear and the stress distribution of shaping die after different cold shaping methods are studied, and the variation law of spur gear accuracy under different cold shaping methods is obtained. On this basis, the effects of different shaping amount and sizing belt length of shaping die on the total deviation of gear profile and helix are studied. Finally, through the verification of process experiments, the best cold shaping method, the best shaping amount and the length of sizing band of shaping die are obtained.
The cold shaping process of cold extruded spur gear is numerically simulated by using the finite element analysis software DEFORM. The metal flow law in the cold shaping process of spur gear under different cold shaping methods and shaping quantities and the influence law on the accuracy of spur gear are obtained. Finally, it is verified by process experiments. The details can be summarized as follows:
① The error model based on the measured cold extrusion spur gear is established, and the cold shaping process of spur gear under different cold shaping methods is numerically simulated. The simulation results show that during full tooth shaping, the tooth surface deformation area is large, the tooth surface deformation is uneven, and the stress at the tooth top of the tooth profile die is large; When only shaping the tooth surface, the deformation area of the tooth surface is small, the deformation of the tooth surface is uniform, and the stress on the tooth top of the tooth profile die is small; The shaping of tooth surface and tooth root is between the two.
The tooth surface reconstruction is carried out for the numerical simulation results under different cold shaping methods. The measurement results of the reconstructed tooth surface show that the accuracy of the straight cylindrical gear after full tooth shaping is grade 10, the accuracy of the straight cylindrical gear after tooth surface root shaping is improved to grade 9, and the accuracy of the straight cylindrical gear after only tooth surface shaping is improved to grade 7, The cold shaping method of shaping only the tooth surface can effectively improve the precision of straight cylindrical gear after shaping.
② The error model is established based on the measured data of cold extrusion spur gear, and the cold shaping process of spur gear under different shaping amounts is numerically simulated. The simulation results show that when the shaping amount is less than 0.1mm, the shaping effect is very limited, and even only elastic deformation occurs on the tooth surface; When the shaping amount is within the range of 0.1 ~ 0.15mm, only slight plastic deformation occurs on the tooth surfaces on both sides of the cold extruded spur gear after passing through the shaping die, and the tooth surface deformation is uniform; With the increase of shaping amount, the deformation area gradually expands to the inner layer. When the shaping amount is greater than 0.25mm, the tooth surface has undergone severe plastic deformation, which can not achieve the purpose of shaping.
The tooth surface reconstruction is carried out for the numerical simulation results under different shaping quantities. The measurement results of the reconstructed tooth surface show that the total deviation of tooth profile and the total deviation of helix increase with the increase of shaping quantity. The shaping quantity on both sides of tooth parts is in the range of 0.1 ~ 0.2mm. After shaping, the precision of cold extruded straight cylindrical gear is the highest, which can reach grade 8 in theory.
The total deviation of tooth profile and the total deviation of helix decrease with the increase of the length of die sizing belt, and reach stability when the length of sizing belt is greater than 10mm. The deformation heat has an obvious influence on the forming accuracy of spur gears. The deformation heat will increase the tooth surface deviation and reduce the accuracy. This is because in the forming process, the blank deformation and deformation heat distribution are uneven, resulting in uneven temperature distribution of spur gear, different coefficient of thermal expansion and elastic modulus of materials at different temperatures, and different elastic recovery after tooth forming, which affects the accuracy of formed spur gear.
③ The process experiment is carried out by using the cold shaping method with bilateral shaping amount of 0.15mm, die sizing belt length of 10mm and only shaping tooth surface. The test results show that the tooth profile accuracy of spur cylindrical gear is improved from Grade 8 to grade 7, the tooth direction accuracy is improved from grade 10 to grade 8, and the bilateral shaping amount is 0.15mm The cold shaping process of shaping only the tooth surface can significantly improve the accuracy of cold extruded spur gears.