Improving and enlarging the application field of HSS and UHSS for automotive body components by the integration of innovative technologies based on roll-forming and stretch-bending processes

High-strength steels (HSS) and ultra-high-strength steel (UHSS) offer great possibilities for weight reduction, increased safety and reduced fuel consumption. However, serious problems are connected to production of the high-strength steel parts, especially using traditional technologies (stamping, Hydroforming), mainly related to low formability, spring back and tool wear. This project aimed at enlarging the use of HSS and UHSS for the production of lightweight automotive components by promoting the use of alternative processes and process chains, with higher degrees of flexibility and potentially more suitability for the production of component in UHSS: the roll-forming and stretch-bending processes. The work done was addressed to the understanding of the roll-forming and stretch-bending processes capabilities for UHSS, by the in-depth study of the basic principles which dominate the forming process chain when connected with UHSS, the realisation of predictive numerical tools for process feasibility, of cost estimation tools, and of specific formability tests. A 'roll formability' test has been developed both from a numerical and experimental point of view for several UHSS (600-1 200 MPa). A new numerical damage criterion has been developed and used for creating a ranking for the roll formability of UHSS and a Safety Management System (SMS), made of 2 beams, has been realised with different mix of new UHSS. In-service performance of this SMS has shown a drastic increase in the resistance.