Sheet material press forming method

A method of press forming a formed part from a metal blank, the formed part having a target shape with a cross-sectional shape that includes a top portion having a protrusion with a closed periphery, a side wall portion, and a flange portion, the method comprising:

• performing a press forming analysis step of determining, for the top portion in a region of the protrusion, a preforming shape that is rougher than the target shape and has a surface area that is the same as the target shape according to the following steps S1 and S2, where
• S1:
• discretizing the region of the protrusion having the target shape into two- dimensional elements and nodes for finite element analysis to determine a discretized portion, and
• S2:
• applying pressure to the discretized portion from inside of a cavity formed by the top portion and the side wall portion, in normal directions of the two-dimensional elements, to deform the discretized portion under the following conditions:
• (a) the two-dimensional elements are deformed within an elastic deformation range;
• and
• (b) an angle between adjacent two-dimensional elements is free to change out of the elastic deformation range so that sides connected by the nodes bend freely;
• and
• thereafter, performing an actual press forming step of press forming the metal blank into the preforming shape, and subsequently crash forming, in which bending deformation is applied to the two-dimensional elements and nodes, the metal blank into the target shape.