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.