Development of the Bus Frame by Flexible Roll Forming

Nowadays, the roll forming process is being widely applied in the whole industry. This roll forming process is cost effective as well as high productive technology compared with the conventional stamping method, because of its in-line forming process to manufacture the final part starting from a coil material. Especially, various automotive parts can be manufactured by the roll forming process using a conventional mild steel as well as an advanced high strength steel (AHSS). Door frame part is the best example for the roll forming process using conventional mild steels. Also, automotive structural parts, such as a bumper beam, a side sill, et al, are being manufactured by the roll forming process using AHSS.Although the roll forming process is one of useful forming technologies especially for AHSS, it can only make the part having a uniform cross-sectional profile. In order to overcome this limitation, POSCO multi-directional Roll Forming (PosRollForm) technology was suggested. PosRollForm popularly referred to the flexible roll forming process. It can make a roll formed part having a variable cross-section along the longitudinal direction using a relative motion of each forming roll. But it is still under research and development.In this work, PosRollForm process was applied to the bus frame part having a variable cross-section along the longitudinal direction with SPFH540 in length of 7m and in thickness of 4.5mm. Forming rolls with the flower pattern and process parameters were optimized for the PosRollForm process by numerical analysis. Finally, the bus frame proto part was successfully developed by our own machine.