These slides were presented at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

Cold Roll Forming (CRF) is one of the most productive processes for manufacturing thin-walled products with constant cross section. It consists in a continuous bending operation of a long metal sheet. Roll-forming processes gained high interest in the industry to form Ultra-High Strength Steels (UHSS). However, CRF remains a complex process and it is affected by different problems, such as wave, torsion, twist or bow defects and elastic spring back [3]. The aim of the analysis is to predict these defects and optimize the roll-forming process. This work introduces a time-effective numerical methodology for the study of steel sheet cold roll-forming processes. The goal of this roll forming FEA is to predict strain and stress fields occurring during the process for a given roll forming line. The outcome of the simulation are expected to help in designing the process, by predicting the occurrence of defects due to unbalanced springback or excessive longitudinal strain, which is a crucial factor in the quality evaluation of rolls design [4]. Furthermore, the resulting strain field can be used to initialize analysis on final products, and take in account the impact of their manufacturing process. The simulation of a steady-state process of the sheet uncoiling and passing through the rolls would require a great amount of computational power and time. To decrease the process lead time only a small portion of the metal sheet is modelled. The continuity of the process is ensured by guiding the ending rows of nodes of the modelled portion of the studied sheet. The results from the FEA and the model assumptions are compared to the experimental tests. Strain gauges and 3D scan are employed to study the strain field of the flange and the kinematics of the process. Longitudinal strain (z-axis) and sheet geometry are employed to validate the FE model. The roll forming line consists in 6 forming stations, placed at a constant distance of 500 mm to each other. The specimen sheets are 2 meters long and 200 mm wide, with a 3D scanned area adjacent to the centerline and four unidirectional strain gauge on the flange (see fig. 3). The disposition of 3 strain gauges at different longitudinal positions, with the same distance from the folding line, allows to exclude the influence of the blank free edges on the two gauges at the centerline. The maximum value of measured longitudinal strain is 20% lower than the ratio between yield stress and elastic module, and there are no evident defects on the resulting profile. The aim of the project is to create a FE methodology able to give fast and reliable results about the state variables inside part throughout the cold roll-forming process. The outcome of this analysis will be employed to initialize the stress and strain state on existing FE models of parts produced through roll forming. The implementation of effects due to manufacturing is expected to improve the accuracy of structural analysis on final products, which are nowadays studied assuming a zero strain and stress field at the beginning of the analysis. To meet the requirements of the industry, the model is designed to be efficiently set-up and computed in a short time. A script makes the procedure of pre-processing fast and versatile, starting from the roll-forming flower of the line. Furthermore, the commercial FE software LS-DYNA simplifies the initialization of stress and strain states due to manufacturing into existent FE models. The analysis results show a good correlation within a competitive lead time for industrial applications.