Investigation of over-bending defect in the cold roll forming of U-channel section using experimental and numerical methods

Abstract

In spite of product quality increase in the cold roll forming process by previous practical researches for defects prevention, there are some ill-considered defects such as over-bending, which diminished the product quality in the open section products of this process. This defect which happens by superfluous bending of sheet in the forming stand not only lead to defective products, but also trigger other defects such as edge wrinkling. Since in an elaborate process such as cold roll forming, forming parameters play an active role in defect prevention, the effect of some important parameters is investigated on the over-bending defect and product bending angle by doing 68 experimental tests and numerical simulations in the present study. The list of parameters which are investigated includes bend angle increment, flange width, strip thickness, radius of bend, strength of the materials, and inter-distance between successive stands. In addition, the reason behind the effect of each parameter on the accuracy of the bending angle is laid out. Results show that over-bending defect can be compensated or even eliminated by decreasing the bending angle in each stand, a technique called bending angle increment. Increasing the number of forming stands from two to five causes the over-bending to decrease from 6° to 0°. With bending angle increment being the most impactful factor, bending radius, flange width, and strip thickness have a decreasing impact on over-bending. This study also brings forward a reverse relationship between the strength of the material and the intensity of over-bending. The inter-distance between successive stands was found to have the least effect on over-bending. Results highlight the importance of pre-form rolls at the beginning of the roll forming line. Without the usage of pre-form rolls, the folding of strips on a 60° angle, cannot be done in one stand.