Effect of bend curve on web warping in flexible roll formed profiles

Abstract

Flexible roll forming is an advanced process for continuous production of variable cross section profiles. In common practice, the cross section width changes in the transition zone by two tangent circular arcs, one of them is stretched and the other is compressed during the forming operation. Web warping is one of the most common defects in variable cross section flexible roll formed profiles. In this paper, the effect of the bend curve on the web warping is investigated to find a cost-effective method for reducing the web warping. For this purpose, different bend curves (circular, quintic, linear, fractional, and Bezier) are designed for a specific variable cross section profile. Finite element simulations are carried out in Abaqus software, and the longitudinal edge strain and the web warping are obtained in the transition zone. An analytical approach is also utilized to calculate the desirable longitudinal edge strain in this zone. The results show that a higher difference between the imposed and desirable longitudinal edge strains leads to a more web warping. Moreover, at each point of the bend curve, this strain difference rises with the increase of the bend curve concavity. For this reason, the profile with linear bend curve has the lowest web warping and is therefore proposed for the variable cross section profiles. Experiments with different bend curves are performed in a flexible roll forming set-up and the history of the longitudinal edge strain and the web warping are measured. The results confirm the accuracy of the finite element model and the capability of the linear bend curve in reducing the web warping.