Forming device and forming method

A forming device for forming a metal pipe having a pipe portion, the forming device comprising:

• a pair of dies comprising:
• a first die that comprises a first flange forming surface,
• a protrusion portion inside an outer end portion of the first flange forming surface, and
• a second die that comprises a second flange forming surface;
• a driver configured to:
• move, so that the first die and the second die constitute a first cavity portion which forms the pipe portion and a second cavity portion which communicates with the first cavity portion, the first die or the second die in a direction in which the dies are joined to each other;
• and
• a gas supplier configured to:
• supply, so as to form a flange portion of the metal pipe, a gas into a heated metal pipe material while the heated metal pipe material is held between the first die and the second die,
• wherein, when the driver joins the first die and the second die to each other:
• the protrusion portion protrudes from the first flange forming surface toward the second flange forming surface,
• the first flange forming surface faces the second flange forming surface to constitute the second cavity portion, and
• inner surfaces of the flange portion face each other,
• wherein, when the gas supplier supplies the gas into the heated metal pipe material:
• the protrusion portion forms, inside the flange portion, a gap portion where the inner surfaces are separated from each other and a proximity portion where the inner surfaces of the flange portion are close to each other compared to the gap portion.