When two parts of one phase winding of Dalian motor shell are grounded at the same time, the two parts of the winding grounded are short circuited by the iron core and the base. The more turns of the short-circuit coil, the greater the increase of phase current. If two parts of the two-phase winding are grounded at the same time, it will cause phase to phase short circuit, burn the coil, and even make the variable frequency adjustable speed motor unable to start and run. The workpiece is made of 08F with a thickness of 1.2mm. It not only has good ductility, but also has good magnetic conductivity and less residual magnetism. It is suitable to be used as the shell of small power motor. Stress and strain will cause springback in denaturation, and it is more prominent for workpieces with larger thickness, which should be considered in die design. After the workpiece is rounded, there must be an overlap section of concave convex buckle groove to ensure accurate overlap and fastening. Put the blank with the heat dissipation hole punched after blanking into the rounding die and press the rounding. The die structure is shown in Figure 2. The working process is to put the blank on the die, position it by the positioning block, start the press, after the punch contacts the workpiece, the middle of the workpiece moves down with the punch, and the workpiece bends into a U shape. As the punch continues to move down, it contacts the die, so that the left and right concave dies rotate around the rotating pin, hold the workpiece on the punch to form a circle, roll the circle, and then take out the workpiece after the slider returns, and then buckle it.