Method for hydroforming and a hydroformed product

A method for hydroforming a metal tube, having two ends and an inside, by feeding a pressure medium into an inside of a metal tube to apply internal pressure, applying an axial pushing action to the two ends of the metal tube, and simultaneously applying an axial pushing action to movable molds in which the metal tube is positioned to form the metal tube into a predetermined shape,

• the method for hydroforming a metal tube comprising:
• a first step of raising the internal pressure with the pressure medium in the metal tube, while maintaining the two ends of the metal tube in a fixed position;
• or
• applying an axial pushing action in an amount of 10% or less of the total amount of axial pushing action, and
• then simultaneously applying an axial pushing action to the two ends of the metal tube and the movable molds while holding the internal pressure at a constant pressure to expand the metal tube near the ends,
• a second step of raising only the internal pressure with the pressure medium to thereby expand a center of the metal tube without applying an axial pushing action to the two ends of the metal tube and without applying an axial pushing action to the movable molds, and
• a third step of lowering only the internal pressure to the value of the constant pressure without applying an axial pushing action to the two ends of the metal tube and without applying an axial pushing action to the movable molds,
• then repeating the first to third steps one or more times, and
• then raising the internal pressure with the pressure medium, while maintaining the two ends of the metal tube in a fixed position;
• or
• applying an axial pushing action of no more than 10% of the total axial pushing action;
• wherein
• the total axial pushing action is the axial pushing action applied while holding the internal pressure at a constant pressure in the first step.