Forming rectangular tubes into complicated 3D shapes by combining three-roll push bending, twisting and rotary draw bending: the role of the fabrication loading history on the mechanical response

Tubular structures find wide application in the automotive context. In particular, rectangular cross-section tubes are used to fabricate structural frames via different techniques, such as Three-Roll-Push-Bending with the addition of twisting component (TRPBT) and the Rotary Draw Bending (RDB). However, whether the accumulated plastic strains, hardening and residual stresses influence the load capacity of the tubular component is still unclear. This paper is intended to shed light on this issue. The load capacity of a tubular mock-up obtained by sequential combination of TRPBT and RDB has been empirically assessed by a destructive compression test. A finite element (FE) model has been devised and validated to analyse the manufacturing processes. This work puts in light the need to correctly model the compliance of the tool set-up for Roll Bending in the numerical calculations. The final shape of the mock-up obtained by FE analysis is the input of the numerical simulation of the compression test. The present modelling has shown clearly that the global resistance of a tubular component is sensitive to plastic strains, hardening and residual stresses resulting from the previous forming processes. Taking into account these three factors greatly improves the capability of the FE to model the mechanical response of the structural part.