When bending with CNC automatic pipe bender, the bending radius of the pipe bender is 0.156 times of the opening distance of the die. During the bending process of the free pipe bender, the opening distance of the die should be 8 times the thickness of the metal material. For example, when forming 16 gauge mild steel with a 1/2 inch (0.0127 m) opening pitch, the bending radius of the part is about 0.078 inches. If the bending radius of the pipe bender is almost as small as the thickness of the material, it must be formed with a bottom concave die. However, the pressure required for forming a concave die with a bottom is about 4 times greater than that of a free pipe bender. If the bending radius of the pipe bender is less than the thickness of the material, a punch with a corner radius of the front end less than the thickness of the material must be used, and the bending method of the imprinted pipe bender must be resorted to. In this way, 10 times the bending pressure of the free bender is required. In the case of free tube bending, punches and dies are machined at 85° or less (a little bit is better). When using this set of dies, pay attention to the gap between the punch and the die at the bottom end of the stroke, as well as the excessive bending of the bending machine that is sufficient to compensate for the springback and keep the material at about 90°. Typically, the rebound angle produced by the free bender bending die on the new bender is ≤2°, and the bending radius of the bender is equal to 0.156 times the opening distance of the die. For the bending of the bottom die bender, the mold angle is generally 86 ~ 90°. At the bottom end of the stroke, there should be a gap between the convex and concave dies that is slightly greater than the thickness of the material. The forming angle is improved because the tonnage of bending of the bender with a bottom die is larger (about 4 times that of the free bending), which reduces the stress that usually causes springback within the bending radius of the bender. The bending of the embossing pipe bender is the same as the bending of the bottomed die bender, except that the front end of the punch is processed into the required bending radius of the pipe bender, and the convex and concave die gap at the bottom of the stroke is less than the thickness of the material. Springback is essentially avoided by applying enough pressure (about 10 times the bend of a free pipe bender) to force the front end of the punch into contact with the material. In order to select a low tonnage specification, plan for a bending radius that is larger than the thickness of the material, and use the free bending method as much as possible. When the bending radius of the pipe bender is large, it often does not affect the quality of the finished part and its future use.
