Modern Technology to Eliminate Sidewall curved Problem on Draw-bending Process against High Strength Steel Sheet

Abstract

Nowadays, side wall curved is one of the most serious problems in bending process of HSS sheest; in general, springback angle increases as the strength of material increases. The aim of this paper is to reduce wall curved problem of workpiece in U bending process. The U-bending consisted of three steps starting with clamping of a sheet between a punch and a counter punch, then U-bending, and finally press flange by using pad pressure. The effect of clamping force was investigated by performing experiments on high strength steel sheets. From the experiment, an appropriate combination of the clamping force can be reduced springback and improve flatness quality of bottom of the sheets. The decreasing of stress at the wall of the sheet can reduced the side wall curved problem of the sheet. To investigate the mechanism of the reduction of springback in the above three-step U-bending process, FE simulation of the bending was also conducted where the FE-simulation was employed. From the result of simulation, it was found that the major mechanism of the side wall curved problem in this process is the decrease of bending moment during the bending.