Analysing the reduction in buckling limit of a flexible roll formed flange due to shape imperfection

Flexible roll-forming can form high-strength sheet metals into components with complex cross-sections but widespread application is limited by flange wrinkling. Previous work has suggested that the low buckling limit in flexible roll forming may be due to the local contact of the forming roll with the metal sheet which produces an imperfection in the flange. In this study, a new plate buckling test is presented and applied to study the effect of imperfections on the buckling limit for conditions that represent flange deformation in flexible roll forming. This is combined with a finite element analysis approach to determine the level of imperfection in a flexible roll formed flange and used to estimate the reduction of the flange buckling limit due to shape imperfection. The results of this study provide for the first time experimental and analytical evidence that the theoretical buckling limit in a flexible roll formed flange is significantly reduced by flange imperfections. The experimental plate buckling test combined with the finite element analysis method for estimating imperfection levels enables the analysis of the effect of forming parameters and geometric conditions on flange imperfection and buckling behaviour and therefore provides a promising alternative to conventional finite element analysis for flexible roll forming process optimisation. • First experimental proof that the buckling limit in flexible roll forming is reduced by shape imperfections in the flange. • Development of a new strip buckling test that reproduces the deformation conditions in a flexible roll formed flange. • New approach for predicting the critical buckling limit that can assist in process design and optimisation.