DESY’s hydroforming machine. Before being placed in the machine, a 150-mm-diameter tube is, at prescribed points along its length, ‘necked’, or spun, to a diameter of 78 mm. This forms the irises, or narrow parts, of the cavity. The necked tube is then placed in the hydroforming machine, and water in the tube presses against the metal. As a result, the tube between the irises swells to a diameter of 208 mm. Image courtesy of Waldemar Singer.