The effect of process and geometric parameters on longitudinal edge strain and product defects in cold roll forming

Roll forming has been used traditionally in the construction and housing industry for the production of longitudinal components but is now increasingly applied in the automotive industry for the manufacture of structural and crash components from ultra high-strength steel (UHSS); the incremental nature of this process allows these hard-to-form materials to be shaped with higher efficiency and less shape defects than observed in common sheet forming processes such as stamping. Tight dimensional tolerances are imposed on automotive components, and this can lead to problems when roll forming UHSS where the high material strength results in shape defect and forming problems. Recent work has therefore increasingly focused on developing process monitoring and control routines for roll forming to improve process robustness and part quality. In roll forming, the longitudinal edge strain is considered to be related to product defects such as bow, twist and end flare. Process and part shape parameters have been shown to significantly influence peak longitudinal edge strain, and the link between process and product parameters, longitudinal edge strain and shape defects needs to be understood for the roll forming of UHSS if routines for process monitoring and control are to be established. Previous studies were mainly focused on traditional roll forming materials used for building products and the like. In this paper, the effect of process and part shape parameters on the peak longitudinal edge strain, longitudinal bow and springback is experimentally and statistically investigated for three different advanced high-strength steel (AHSS) and UHSS commonly used in automotive manufacturing. The results show that there are significant differences in behaviour when forming UHSS and that forming trends differ from those reported for softer steel grades. The experimental data presented in this paper should contribute to the further development of advanced process monitoring and part shape quality control routines in the roll forming AHSS and UHSS.