During the processing of bending arm die forgings, the surface quality of forgings is poor and even other defects occur due to the skin oxidation and decarburization of the blank under high temperature conditions; Due to the volume change of the blank and the fluctuation of the final forging temperature, the size control of the bending arm die forgings is uncertain; The side wall of the forging is added with dressings due to the need of die ejection of the forging; Due to the wear of the groove and the inevitable dislocation of the upper and lower dies, the size of the forgings is deviated. For all these reasons, forgings should not only have machining allowance, but also specify appropriate dimensional tolerance of forgings.