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# 2021: springback cause about the profile bending machine

### What factors affect the springback when the profile bending machine works?

When the metal profile is bent, the residual stress will cause the bent metal profile to spring back slightly.

Due to this elastic recovery, it is necessary to overbend the metal profile to achieve the required bending radius and bending angle. The final bending radius and bending angle can be approximated from the thickness of the sheet, the K factor, the yield strength and elastic modulus of the metal profile, and the initial bending angle and bending radius.

The final bending radius will be larger than the initially formed radius, and the final bending angle will be smaller. The rebound coefficient Ks will show the ratio of the final bending angle to the initial bending angle.

1, Higher the yield strength of the material, the greater the rebound.

2, The ratio of the bending radius r to the material thickness T, the greater the value of the r/t.

3. The larger the deformation area, the greater the rebound.

4. Friction between the surface of the material and the surface of the die affects the stress state of the parts of the embryo. In most cases, the tensile stress in the bending zone will be increased, and the rebound is reduced.

## Calculation of bending springback

In the bending process of the profile bending machine, the profile has gone through three stages: pure elastic loading stage, elastoplastic loading stage and elastoplastic unloading stage (rebound stage).

The resilience of the profile bending machine has a great influence on the bending accuracy and production efficiency.

Before deriving the general expression of the rebound radius, in order to simplify the mathematical operation and analyze the problem, it is necessary to make certain basic assumptions. Plane assumptions, that is, any cross-section along the longitudinal direction is a plane before plastic bending, and it is still a plane after plastic bending; The plastic bending of the profile belongs to pure bending, that is, the influence of shear is not considered.

According to the theory of elastoplasticity, the springback in the profile bending process mainly depends on the elastic modulus, yield strength, thickness and pre-rolling radius of the profile. After theoretical deduction, the springback of the profile can be established. During the bending process, the radius of curvature of the part mainly depends on the distance between the upper roller and the side roller.

Because the position of the upper roller is fixed, the forming curvature of the part can be controlled by adjusting the stroke of the side roller.

Before calculating, first determine the coordinate system. Because the upper roller is fixed, the center of the upper roller establishes the reference coordinate system of the lower roller and the two side rollers, and the relative coordinate system of the rollers is established with the center of each roller.

The four-roller bending process In fact, there are only 3 working rolls involved, and its mechanism is the same as the forming mechanism of asymmetric three-roll coiling. The value of the straight edge parameter B can be based on the asymmetric three-roll coil, taking B=2t.