Trial production results of spur gear (sun gear)

The combined die is the key component for continuously extruding the external teeth of spur gear. The combined die adopts a three-layer prestressed ring structure. The materials of die core, middle ring and outer ring are cemented carbide YG15, die steel H13 and 42CrMo respectively. Because the core of the combined die is made of cemented carbide, it needs to be pressed from inside to outside in the heating state. The pressing sequence is reversed, which is not only very difficult to press, but also may damage the cemented carbide insert. The core cavity of the combined female die is processed after press fitting. The tooth shape of the die core (forming area and degassing belt) is processed by the slow wire cutting machine. Firstly, 2mm machining allowance is reserved for rough cutting of the tooth shape, and then fine cutting to the size requirements. The die core splitting and extrusion area adopts EDM, and the coarse, medium and fine electrodes with discharge gap of 0.08mm, 0.05mm and 0.02mm are used to complete the machining respectively. Finally, the core cavity is polished to remove the corrosion layer of EDM, and the surface roughness reaches Ra0 2。 The combined die and die base are shown in Figure 1.

The trial production of continuous cold extrusion of external teeth was carried out on 630t four column hydraulic press. During trial production, MoS2 grease lubricant is applied on the surface of the die to reduce the friction resistance between the blank and the die. By adjusting the press down stroke of the equipment, the continuous cold extrusion process of external teeth is realized. The optimized die was used for production trial production, and there was no tooth breakage and cracking during the use of the die. Figure 2 shows the comparison between the simulation results of continuous cold extrusion external teeth and the production trial production results. It can be seen that the outline of the production trial production parts is very consistent with the simulation results. The lower end face of the parts is convex, the upper end face is concave, and the tooth top of the lower end face is not fully filled, resulting in collapse angle.

(a) Simulation results of external tooth forming
(b) Trial production results of external tooth forming

The accuracy of tooth profile and tooth direction of external tooth parts formed by continuous cold extrusion is measured by three coordinates. The accuracy of tooth profile is 7 ~ 8, and the unstable accuracy of tooth direction is 10 ~ 12. After turning the end face, inner hole and outer circle of the continuously extruded external tooth parts, shaving is carried out. After shaving, the tooth profile and tooth direction accuracy of the spur cylindrical gear (sun gear) can reach grade 7. After normalizing, broach the formed internal teeth. Fig. 3 is the part drawing of the machined spur gear (sun gear).

The continuous cold extrusion production of spur gear (sun gear) was trial produced by using the optimized die and process scheme. The blank preparation, production equipment, machining and assembly process of combined die are briefly introduced. The contour of the external tooth formed by continuous cold extrusion is in good agreement with the simulation results. For the external tooth parts formed by continuous cold extrusion, picking the teeth after machining can significantly improve the accuracy of straight cylindrical gear (sun gear), and broaching the internal teeth after normalizing, so as to obtain products that fully meet the requirements of quality and accuracy.

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