The stretch bending process of the variable curvature L-section aluminum alloy door column of an electric multiple unit (EMU) was simulated. Based on the relationship between the stress and strain distribution of the cross-section and the spring-back radius at different stages

the factors affecting the precision of stretch bending process were systematically explored for optimizing processing parameters and controlling methods

which were then verified by experiment. Results show that the main forming defects during bending were corss-section distortions and spring-back

where the cross-section distortion defects were web collapse in straight section and concave deformation of vertical edge in arc segment. The defects of cross-section distortions and spring-back could be reduced to some extent

by adjusting the processing parameters such as the stretching amount. The cross-section distortions were mainly caused by different forces on the vertical side during the stretch bending process. By setting back plate and increasing its load

the distortion value of the web plate in straight section could be reduced. The optimization of the profile of the bending die could decrease the distortion value of the vertical edge section in arc segment. Moreover

the spring-back degree in the small arc side was more serious than that in the large arc side

which was mainly due to the asymmetry of both ends of the variable curvature aluminum alloy door column

affecting the part-mold contact gap of the door column. The spring-back could be alleviated via modifying the die surface by spring-back compensation method. The forming accuracy could be greatly enhanced to meet the design requirements when the amount of pre-elongation

wrap-elongation

and post-elongation was 1%

4.5%

and 0.5%

respectively

and the back pressure applied to the straight section was 40 kN.