Method of manufacturing formed product

A method of manufacturing a formed product, the method comprising:

• placing and welding an inner metal plate on an outer metal plate to form at least one first joining portion;
• bending the outer metal plate with the inner metal plate by pressing after the at least one first joining portion is formed;
• and
• forming at least one second joining portion,
• wherein the pressing includes forming a first surface, at least one second surface, and at least one bent portion in the outer metal plate,
• wherein the at least one second surface extends in a direction that crosses the first surface,
• wherein the at least one bent portion couples the first surface and the at least one second surface to each other, and is layered on the inner metal plate,
• wherein the forming of the at least one second joining portion includes welding the outer metal plate and the inner metal plate together after the pressing to form the at least one second joining portion, the at least one second joining portion being three or more portions where the inner metal plate is welded on the at least one second surface, and the at least one second joining portion being arranged so as to be aligned spaced apart from each other along the at least one bent portion,
• wherein the at least one first joining portion is a portion where the inner metal plate is welded on a region of the outer metal plate that is to become the first surface,
• wherein the inner metal plate is disposed on an inner side of the at least one bent portion, and
• wherein spring back of the inner metal plate is greater than spring back of the outer metal plate.