Manufacturing method of member, manufacturing method of member for vehicle, and die and punch

A manufacturing method of a member for manufacturing a member which includes a specific three-dimensional tubular portion including at least any one of a cross-sectional shape changing portion in which a cross-sectional shape of a tubular portion changes along a centroid line, a circumferential length change rate changing portion in which a circumferential length of the tubular portion changes along the centroid line and a change rate of the circumferential length changes, and a curved portion in which the centroid line of the tubular portion has a curvature, by processing a metal material sheet, the manufacturing method comprising:

• a U-forming step of performing U-forming on the metal material sheet using a U-forming die and punch including a U-forming punch to manufacture a U-formed article having a recessed cross-sectional shape;
• and
• an O-forming step of causing side end portions of the U-formed article to abut each other by an O-forming die to form abutting portions,
• wherein a forming condition ratio a=Du/Do which is a ratio of a punch width Du of a portion of the U-forming punch corresponding to the specific three-dimensional tubular portion to a recessed part width Do of a portion of the O-forming die corresponding to the specific three-dimensional tubular portion is set to 0.85 to 0.95;
• wherein a forming condition ratio setting step performed in one or a plurality of cycles before the U-forming step,
• wherein, in the forming condition ratio setting step, a finite element analysis is performed in consideration of conditions including the forming condition ratio a set in the forming condition ratio setting step in a previous cycle or an initial value of the forming condition ratio a, material properties of the member, a shape and a sheet thickness of the metal material sheet, forming conditions in the U-forming step, and forming conditions in the O-forming step to estimate a shape parameter including a strain amount generated in the U-forming step in a direction along the centroid line of the specific three-dimensional tubular portion, a strain amount generated in the O-forming step in the direction along the centroid line of the specific three-dimensional tubular portion, and relative positions of the side end portions, and the forming condition ratio setting step is repeated until the shape parameter satisfies desired conditions.