Investigation of a new incremental counter forming in flexible roll forming to manufacture accurate profiles with variable cross-sections

• A new process combined with flexible roll forming is proposed.
• Longitudinal strain at flange can be controlled by new process to reduce shape error.
• An additional strain at flange works as an excessive strain to worsen shape errors.
• The new process is validated by simulations and experimental results.

A roll-formed profile with variable cross-sections fabricated by flexible roll forming has a shape error, such as warping, because of geometrical deviations in transitional zones of the profile between the initial metal strip and the roll-formed profile. To reduce the shape error, a new process called incremental counter forming (ICF) is proposed. Our investigation of the ICF process shows that the longitudinal strain distribution at the flange of the roll-formed profile can be controlled by combinations of forming parameters of the ICF process. As the forming parameters increase the longitudinal strain distribution in the concave zone, the shape error decreases. However, when the longitudinal strain distribution in the straight zone reaches a critical limit, the additional longitudinal strain works as an excessive longitudinal strain to worsen the shape error. An analytical model, which describes the longitudinal strain at the flange during roll forming, is adopted to reveal that the increase of the longitudinal strain is induced by increasing derivatives of a bending angle, which is controlled by the forming parameters of the ICF process. Finally, the FE simulation has been carried out to compare with the experimental results, which show that the ICF process is effective for reducing the shape error of the profile with variable cross-sections in flexible roll forming.