When the hull roof frame with a large bending radius is made with L-shaped steel instead of a square pipe by a press, the die must be designed correctly considering the spring-back in order to ensure high accuracy.
Ri Song Min, a researcher at the Faculty of Mechanical Science and Technology, proposed a method of selecting a reasonable bending radius of the die by considering the stress, strain characteristics and spring-back of work-pieces in the process of bending the L-shaped steel that is used in the manufacture of the roof frames of vehicles including underground trains by means of a press, and conducted a simulation analysis. In addition, by measuring the amount of spring-back at the time of bending with constant force using a press to compare the experimental values with simulation values, he evaluated the accuracy of the simulation analysis, and compared the bending radii of the die to form an L-shaped steel product for roof frames.
He performed a finite element analysis at the ceiling and the corner sections, respectively. The finite element simulation analysis result of the process of bending the L-shaped steel shows that the bending radius of the die must be designed to be 7 782mm and 426mm for the ceiling and the corner sections, respectively.