When the shearing machine manufacturer forms 16 gauge mild steel with a 1/2 inch opening distance, the bending radius of the part is about 0.078 inches. If the bending radius is almost as small as the material thickness, a bottomed die must be formed. However, the pressure required for forming a bottomed die is about 4 times greater than that of free bending. When free bending is used, the bending radius is 0.156 times the opening distance of the die. During the free bending process, the opening distance of the die should be 8 times the thickness of the metal material.
The forming angle is improved, because the bottomed die has a larger bending tonnage (about 4 times that of free bending), which reduces the stress that usually causes springback in the bending radius. For the bending of bottomed concave mold, the mold angle is generally 86~90°. At the bottom of the stroke, there should be a gap slightly larger than the thickness of the material between the male and female molds. Generally, the springback angle of the free bending die of the shearing machine on the new bending machine is ≤2°, and the bending radius is equal to 0.156 times the opening distance of the die.
When using this group of shearing machine molds, pay attention to the gap between the punch and the die at the bottom of the stroke, and the excessive bending that is sufficient to compensate for the springback and keep the material at about 90°. As far as free bending is concerned, punch and die are processed at 85° or less (smaller is better). If the bending radius is smaller than the thickness of the material, a punch with a front-end fillet radius smaller than the thickness of the material must be used, and the imprint bending method must be used. In this way, 10 times the pressure of free bending is required.
When the bending radius is large, it often does not affect the quality of the finished parts of the shearing machine and its future use. In order to select the tonnage specification, plan for a bending radius larger than the thickness of the material, and use the free bending method as much as possible.
Since the bending machine manufacturer exerts enough pressure (about 10 times of free bending) to force the front end of the punch to contact the material, springback is basically avoided. The imprint bending is the same as the bending of the bottomed die, except that the front end of the punch is processed to the required bending radius, and the gap between the punch and the die at the bottom of the stroke is smaller than the material thickness.
