Optimization of post-stretching elongation in stretch bending of aluminum hollow profile

Post-stretching elongation is a crucial process parameter in stretch bending process because of its significant influence on the forming effects. In this paper, the displacement loading method was presented to control the movement of the jaw in order to avoid the instability of tensile force in mechanical loading method. Typical aluminum hollow profile used in high-speed trains was selected as the research object. Stretch bending process with five levels of post-stretching elongations was carried out by finite element (FE) simulation. The simulation results reveal that an increment of the post-stretching elongation leads to smaller shape error and springback but larger cross-sectional distortion and spatial twist. The forming defects index, which is based on normalizing and weighting four forming defects, was put forward to evaluate comprehensive forming effects. Furthermore, the backtracking method was used to obtain the optimal post-stretching elongation. Experimental validation was conducted on stretch-wrap bending machine. The experiment part meets the processing requirements, thereby validating the reasonability of the optimization method. Measured results showed consistency with numerical analysis which verifies the feasibility of using FE simulation to guide the experiment.