Method of producing hollow objects and an arrangement for such method

A method of producing a shaped hollow metal object, the method comprising the steps of:

• a) heating a hollow semi-finished metal product including a central space having an opening to an austenite temperature such that the hollow semi-finished metal product is in an austenite state;
• b) placing the hollow semi-finished metal product into a cavity of a mould, the cavity having a shape corresponding to a desired final external shape of the shaped hollow metal object;
• c) contacting an internal surface of the hollow semi-finished metal product only at a proximal portion of the hollow semi-finished metal product via a sealing feature so as to seal the opening of the hollow semi-finished metal product and the central space, a remainder of the internal surface being uncontacted;
• d) introducing at least one of the water and steam into the central space such that the hollow semi-finished metal product heats the at least one of water and steam thereby increasing pressure in the central space so that the hollow semi-finished metal product attains the desired final shape of the shaped hollow metal object;
• e) unsealing the opening of the hollow semi-finished metal product;
• and
• f) removing the shaped hollow metal object from the cavity,
• wherein steps b)-e) are performed with the respective hollow semi-finished product or shaped hollow metal object being in the austenite state,
• wherein the sealing feature is biased by a spring and step e) includes automatically unsealing the opening when the pressure in the central space generates a counterforce that overcomes a threshold bias force of the spring.