Analysis of material behaviour and shape defect compensation in the flexible roll forming of advanced high strength steel

Abstract

Roll forming is a fast and low-cost forming process with the ability to form a wide range of materials, especially advanced high-strength steels (AHSS) that have limited ductility. However, roll forming is only able to form constant cross-sections along the longitudinal direction of the component, while many automotive components are more complex in shape. Flexible Roll Forming (FRF) uses rolls that have the ability to translate or rotate during production, enabling the manufacture of a part that has a variable cross-section potentially useful for the automotive industry.Deakin University is equipped with a flexible forming facility that can prototype parts with variable cross-sections. The machine has been developed, patented and manufactured by dataM Sheet Metal Solutions GmbH. Deakin’s Flexible Forming Facility (DFFF) consists of a single forming stand with two opposing robotic arms connected to forming rolls. The flexibly controlled arms form the clamped sheet along a CNC defined bend line while the sheet remains clamped. This facility is capable of creating changes in the cross-section in both width and depth along the part. Moreover, the Deakin facility can form the part in both forwards and backwards directions along the longitudinal dimension of the part. In contrast, conventional FRF facilities use multiple stands of forming rolls, and the forming sequence occurs in a single direction along the part.The first part of this study compares material deformation in the DFFF in contrast to that of the conventional FRF setup. This study will determine the similarities and differences in the final formed part between DFFF and the forming conditions in conventional FRF. The second step of the study is to investigate the forming properties of the final part when the part has variable depth. An experimental part formed on DFFF was compared to a numerical analysis using COPRA RF FEA to investigate the material flow and the forming defects. The results show that the major shape error is wrinkling. A new forming concept using a blank holder tool was analysed, and it shows promising results in regard to wrinkling reduction.