The following is a calculation method, there is no case, I hope it will help you. Taking U-section bending as an example, the relationship between the length expansion of non-flat bending (such as angle steel and channel steel bending) and the bending degree, bending scheme and die structure is discussed. Through theoretical derivation and experimental verification, the calculation formula for reference in design is obtained. 1. When the bending degree is small (R/H= 10), the locus of the strain neutral layer coincides with the cross-sectional center of the bending blank. That is to say, the formula l = π (r+b-z0) (180-β)180 can be used when bending inward at any angle, and the formula L = π (r+z0) α/ 180 can be used when bending outward at any angle. Where Z0 = ey = (1+π R2-L2-4R2-δ/4l1+2l2+2π R2+π δ) δ+2 (l1+R2) 2+(π-3) R22/4l/kloc. 2. When the bending degree is large (r/h < 10), the strain neutral layer moves inward without passing through the section center of gravity. The displacement coefficient x' of this bending neutral layer can be replaced by the displacement coefficient x of the corresponding plate bending obtained from the value of R/H or R/(2Z0). The expanded length is l = π (r+2z0x) α/ 180. The unfolded length when bending at any angle is l = π [r+h-2z0 (1-x)] (180-β)/1803. According to the distance of the center of gravity, the bending length of the profile under the scheme of flanging first and bending later is calculated. Firstly, the value of r/h is calculated, and then the corresponding calculation formula is selected according to the bending degree. The calculation of the bending development length of the profile in the scheme of bending first and then flanging should be based on the calculation method of sheet bending, but when determining the position of neutral layer, the relationship between neutral layer and bending degree should be considered, that is, different determination methods should be considered when the relative bending radius r/t is ≥ 5 and the relative bending radius r/t is < 5. 4. When the die structure is blank-free, its bending mode is flanging bending, and the flanging bending should be calculated step by step. When the die structure is pressed, the appropriate calculation formula is selected according to the comparison between the pressing force and the free bending force. 5. By analyzing the mechanism of bending springback, the influencing factors of springback value are pointed out. At the same time, the calculation basis of how to determine the bending rebound angle of sheet metal is analyzed, and the calculation method and steps of determining the bending rebound value of sheet metal are put forward.