Uniform angle distribution in V-shaped bending of ultra-high strength steel sheets having wall thickness distribution

Abstract

Abstract A bending process for improving the angle distribution in bending of ultra-high strength steel sheet having a wall thickness distribution was developed. First, a sheet thickness distribution of ultra-high strength steel sheets was investigated. The sheet thickness distribution in a width direction of rolled ultra-high strength steel sheet was not uniform because of the elastic deformation of rolling mills in rolling, whereas the distribution in a longitudinal direction was uniform. Then the angle distribution of the V-shaped bent ultra-high strength steel sheet having a wall thickness distribution was investigated. A bend angle at the thin end of the bent sheet at the bottom dead centre was larger than that of the angle at the thick end. Springback at the thin end of the sheet was increased by insufficient bending and the thin thickness. The angle at the thin end of the bent sheet was larger than that at the thick end. Finally, the angle distribution in a longitudinal direction of the bent sheet was improved by bottoming using a three-piece die on rubber plates. It was found that bottoming using the rubber plates in bending was effective in improving the angle distribution of the bent ultra-high strength steel sheets having a wall thickness distribution.