# Study on numerical simulation and spread deformation of gear preform

In order to improve the material utilization, the forging of driven spiral bevel gear is generally realized by final forging after the round bar is upset and punched to obtain the annular preform shape with a certain section shape. Rolling (radial rolling) of preformed shape is the key to the precision forming of driven spiral bevel gear, which plays an important role in the subsequent forging process. For the whole forging process, the optimization of rolling blank making process is very important.

When the ring is rolled in the radial direction, the material pressed down along the radial direction of the ring will flow along the circumferential and axial direction of the ring according to the law of minimum resistance on the one hand, and on the other hand, it will also have spread deformation, which is manifested in the increase of the axial size of the ring after rolling. Generally, near the center of the end face, that is, near the average diameter of the ring, the spread deformation in the axial dimension is small, or even negative spread, while near the boundary of the end face, that is, near the inner and outer diameters of the ring, the spread deformation in the axial dimension is large. The axial size of the center of the end face is reduced, and the deformation of the axial size of the end face boundary is increased, as shown in the figure. At this time, the end face shape is similar to fish tail, so it is often called “fish tail”. “Fishtail” is a common defect in ring rolling. Its main reason is that the ratio of ring wall thickness to contact arc length (circumferential arc length of contact surface between ring and roll) is too large, so that the material deformation is mainly concentrated on the inner and outer surfaces of ring, which is accumulated after multi turn rolling, This deformation is similar to the double drum phenomenon caused by the excessive height diameter ratio during cylinder upsetting. If the “fishtail” defect in the ring rolling process is too large, the forging is easy to fold in the final forging process. Therefore, the problems such as spread deformation and fishtail defect in the rolling process must be controlled.

A new forging process scheme of spiral bevel gear is proposed. Based on the analysis of the mechanical principle of ring rolling, the radial rolling process of final forged ring is numerically simulated by ring rolling module of DEFORM software, The distribution and evolution law of important physical fields such as stress, strain and temperature in the ring rolling process and the generation of spread in the ring dairy process were studied. The spread phenomenon of ring rolling in radial direction is caused by the joint action of many factors. Rolling parameters such as feed speed, rotating speed and equipment parameters such as the size of core roll and drive roll have an important impact on the spread of ring rolling. Based on the existing process parameters of ring rolling, by changing important parameters and designing control experiments, the influence of different process parameters on ring radial rolling spread is analyzed, so as to achieve the goal of controlling spread deformation through process parameter optimization.

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