What are the problems in cold bending process?

Cold bending technology is called an "art", and its products are widely used in various fields. At present, scholars have carried out in-depth theoretical research on it, and some researchers have simulated the molding process by computer, and achieved certain results. However, the cold bending process is a very complicated process, and there are still many problems to be solved in design and production, which are often found in debugging and production. Taking wide-section sheet forming as an example, if the design is unreasonable, there will be deformation defects such as side wave, pocket wave, longitudinal bending, corner wrinkle, crack and distortion during debugging. Re-designing the processing roller after problems occur will inevitably lead to great waste of resources such as manpower and material resources. If we can understand the mechanism of these defects, try to avoid these defects in the design process, or make reasonable improvements on the original basis after the defects appear, so as to alleviate or even eliminate these defects, we can still achieve the expected goal of roll design.

The following are some simple analysis of the causes of problems in the actual operation of cold bending forming, please give us your advice!

1. Pocket wave is mainly caused by transverse tensile stress and transverse strain in the bending process of sheet metal, while the strain in the thickness direction of sheet metal is relatively small. According to the Poisson relation of material deformation, longitudinal shrinkage deformation will inevitably occur at the part where deformation is concentrated. In this experiment, this phenomenon mainly occurs at four deformed corners, so the longitudinally contracted part exerts a compressive force on the middle plate, and some areas become unstable under this force, which is what we often call pocket wave. Pocket wave is mainly elastic deformation.

2. Edge wave (hereinafter referred to as edge wave) is a more common defect than pocket wave, and its generation is mainly a combination of two functions: the first one, like the previous pocket wave, produces transverse tensile strain because the bending part of the section is subjected to transverse tensile stress, and when the strain in the thickness direction is not large, it contracts longitudinally according to Poisson relation, while the edge part is subjected to compressive stress, resulting in edge wave; The second is that the material in the edge part is stretched and sheared under the action of external force, and then compressed and sheared to produce plastic deformation, causing edge waves. These two actions are superimposed on each other to form a lateral wave.

3. There are many reasons for longitudinal bending, one of which is that the edge of the section is pulled when bending, trying to lengthen the whole section in the longitudinal direction, but the pulling force is not enough to lengthen the whole rigid section, which leads to the phenomenon that the front end of the rolled piece bends up or down.

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