Specific design process
　　The mould of refrigerator is usually made of 45# steel in the top material core, backing plate and upper and lower formwork. Its modulation hardness is between 40 and 46 HRC. Besides, the other concave and punch dies, upper and lower wedges of the mould are also made of Cr12AMoV steel. Its hardness can reach 58 to 64 HRC. The guide copper plate is used between the two measuring bending punches, where the pins, screws, springs and other parts are made of copper materials permitted by the national standards. In the design, the gap ratio between the bending die and the punch should be 1-1.5 times the thickness of the material. Among them, the interference fit between the fixed plate and the bending die is between 0.03 and 0.06 mm, while the gap fit between the bending die and the ejector core is between 0.06 and 0.12 mm.
　　We take a refrigerator door shell mold with a dimension of 1000 x 700 mm as an example. When the upper die is only 200 mm away from the end of the mold movement, the lower oblique wedge will first contact the upper bending punch, thus driving the upper bending punch to the left. The upper die will move about 40 mm downward, and the upper bending punch will also contact the upper bending punch. The distance between left and right movements will be about 25mm. After moving to the specified position, the upper curved punch will stop and move to the left. On the other hand, the upper die will stop moving after running to a specified distance of 200 mm, its upper bending punch and side bending punch will start U-bending, the ejector core will also start moving, so that the lower die spring is compressed by force. When the upper die runs 40 mm away, the upper bending punch and the side bending punch can end the first vertical U-bending. After the first bending, the upper inclined wedge moves twice, driving the two sides of the side bending punch to move again, and the upper die causes the spring to compress. Before the side-bending punch stops moving, the upper wedge should keep a distance of 30 mm downward and ensure that the side-bending punch is formed horizontally at a distance of 25 mm. At the same time, the upper wedge will continue to drive the side-bending punch for lateral movement. After 25 mm downward from the upper wedge, the side-bending punch can stop movement after running 30 mm horizontally and completing the lateral horizontal bending. The second and third bending of the die can be completed. At this point, the parts are basically formed, and all parts of the die will leave the mold return to declare the stamping work finished.