Replacing the material of automobile body panels from steel sheets to aluminum alloy sheets is an approach to reducing the automobile weight. In the press forming of panel parts with aluminum alloy sheets, it is necessary to smooth stepped linear marks of about 5 μm to 50 μm generated during press forming to satisfy the surface quality of the panel parts. These linear marks are called shock lines, which are generated when the blank sheet slides on the die corner radius during press forming. In this research, the protrusion shape of forming dies that enables us to smooth a shock line is investigated using a 1.2-mm-thick 6000 series aluminum alloy sheet. The shock line is smoothed by applying a trapezoidal surface pressure to the blank sheet near the shock line at the bottom dead center. We propose a method of using finite element analysis to calculate the protrusion shape from the amount of elastic displacement of the dies that occurs when the target surface pressure is applied to the dies surface. The protruding shape calculated by the proposed method has been applied to the forming dies for the door inner panel of the 6000 series aluminum alloy sheet. As a result, in our experiments, the shock line has been smoothed by using these forming dies.
