Formulation of cold forging forming scheme of spur gear

Cold finishing process is the last process in compound forming. It is the key point in the whole process to make the tooth surface size of spur gear forging meet the requirements of part drawing and improve the surface quality of spur gear forging. Cold finishing adopts extrusion forming. During processing, the pre spur gear forging is placed at the die inlet of the female die. The spur gear parts enter the female die under the action of the male die and are extruded by the female die. The metal generates radial flow. There is no mandrel constraint at the spur gear hole, which can be shunted.

The metal moves along the axial direction in the process of extrusion, and the excess metal will move from bottom to top and accumulate on the upper end face. Therefore, considering the shape of punch, it can not have tooth shape or tooth shape. If the punch has a tooth shape, the tooth shape of the spur gear should have a large gap with the tooth shape of the sizing belt of the female die, otherwise it is easy to cut off the axial burr of the blank tooth shape and increase the forming force. The punch structure is designed without tooth profile, and the size is slightly smaller than that of the female die. Figure 1 shows the schematic diagram of cold finishing scheme.

The structure of cold finishing die is shown in Figure 2. It is composed of two parts: the mold entry section, which guides the blank into the mold, generally 5 ~ 10 °; The working section is mainly responsible for extrusion. The length of the working section has a great impact on the forming force and forming quality. Increasing the length of the working section will improve the forming accuracy of spur gear, but the same forming force will be improved. Generally, the length of the working section is 5 ~ 8mm.

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