Tube bending and hydroforming of aluminium alloy S-rails

Abstract

This research examines the effect of the tube bending and hydroforming processes on the characteristics of aluminium alloy s-rail structures used in crash applications. Tube bending and hydroforming experiments are conducted using a fully instrumented mandrel-rotary draw tube bender and a 1,000 tonne hydroforming press to investigate the effect of bend severity on the thickness and strain distributions within the tube. Finite element simulations of the tube bending and hydroforming process, that consider previous deformation history, are developed to serve as a predictive tool that provides additional insight into the manufacturing of the s-rail. The bending of the s-rail results in thinning on the outside and thickening on the inside of the bend, due to axial strains in those regions. The most significant variable affecting the degree of thickness change and strain in the bend is the bend severity. “Boost” in bending, refers to the technique whereby a compressive axial load is applied to the portion of the tube being bent, and can also increase the overall thickness and work hardening in the bend regions of the s-rail, which has been shown to increase the overall resistance to deformation of the hinge during collapse (Oliveira 1). The low-pressure hydroforming operation induces circumferential strain at the corners of the s-rail cross-section, despite undergoing near zero circumferential expansion.