Method of sheet forming

A method of sheet forming for manufacturing a sheet-formed part that is formed in an L-shape as viewed in a plan view and includes a top portion, side wall portions formed on the respective both sides of the top portion, and flange portions contiguously formed with the respective side wall portions, by sheet-forming a metal sheet with a sheet forming tool, the method comprising:

• a first sheet forming process in which the metal sheet is arranged on a first sheet forming tool including a first punch, a first die, a first blank holder, and a pad so that a part corresponding to an end portion of a short side of the L-shape in the metal sheet does not overlap with the first die and the first blank holder, a part of the top portion is held by the pad, and the metal sheet is sheet-formed into a first sheet-formed part having an intermediate shape;
• and
• a second sheet forming process in which the first sheet-formed part formed in the first sheet forming process is sheet-formed into a second sheet-formed part having a top portion and a side wall portion whose shapes are identical with those of the sheet-formed part, with a second sheet forming tool having a second punch and a second die, wherein
• the side wall portion on an outer side that includes an L-shaped bent portion in the first sheet-formed part formed in the first sheet forming process is outwardly stretched in an arcuate shape as viewed in a plan view from the side wall portion of the sheet-formed part, a curvature radius of a circular arc of the side wall portion stretched in an arcuate shape is larger than a curvature radius of the L-shaped bent portion of the sheet-formed part, an outside of the top portion of the L-shaped bent portion is stretched from an outside of the top portion of the sheet-formed part, and a curvature radius in a cross section of a shoulder portion contiguously formed with the top portion stretched, as viewed in a side view, is larger than a curvature radius in a cross section of a shoulder portion contiguously formed with the outside of the top portion of the L-shaped bent portion of the sheet-formed part, as viewed in a side view.