Abstract
Recently, tube hydroforming has been appreciated for its features in improving fuel economy and crash safety. Tubular hydroforming parts with a rectangular cross section are typical automotive parts. There are, however, problems in conventional hydroforming. The first problem is that a high internal pressure is necessary to obtain a small corner radius. The second problem is that thickness is largely reduced around corner portions. To solve these problems, the vertical double-action forming method is proposed. This method consists of two stages. The first stage is to form a tube into an elliptic cross-sectional shape. The second stage is to form a square cross-sectional shape by stamping under internal pressure. Experiments on the vertical double-action forming method are carried out. It is clear that, in this method, a small corner radius can be formed with a low internal pressure. The circumferential thickness deviations, furthermore, can be largely reduced by this method. By FE analysis the influences effects of equivalent stress and friction on thickness distribution are discussed in both methods.
