Rear axle housing forming method

The invention relates to a rear axle housing forming method, which comprises the following steps of: injecting high-pressure gas into a pipe blank, and extruding the pipe blank from two ends of the pipe blank along the axial direction, so that the middle area of the pipe blank is expanded, and a rear axle housing is obtained. Due to the fact that the pipe blank is bulged through the high-pressure gas, the middle area of the pipe blank can be heated before bulging so as to reduce the yield strength of the pipe blank. The pipe blank is extruded from the two ends of the pipe blank in the axial direction while the high-pressure gas is injected, so that materials can be supplemented to the middle area of the pipe blank in the bulging process, and uneven thickness caused by insufficient materials during bulging of the middle area is prevented. In addition, the axial pressure applied to the two ends of the pipe blank can enable the pipe blank to have the trend of expanding in the radial direction, and therefore the