Method for producing gun barrels and apparatus for performing such method

A method for producing gun barrels having a grooved or ribbed inner surface (110) with straight or helical grooves or ribs, the method comprising the steps of:

• providing a metallic hollow cylindrical pre-form (10);
• placing the pre-form (10) on a core mandrel (8) being rotatably supported on a free end of a core mandrel extension rod (3) being rotatably supported in a head stock, wherein the core mandrel (8) is a part of a flow forming machine having a main machine axis (A) and a tail stock extension rod (11) being rotatably supported in a tail stock (12) and which is displaceable in a horizontal axial direction (X) parallel to the main machine axis (A) and extending coaxially with the core mandrel extension rod (3) and the core mandrel (8), wherein the core mandrel extension rod (3), the core mandrel (8), and the tailstock extension rod (11) form a unit that is movable in the axial direction (X), the core mandrel (8) being both not driven and freely rotatable about the main axis (A) and having an outer surface comprising ribs (83) or grooves, the ribs (83) or grooves extending parallel to or helically around the main axis (A);
• applying forming rollers (90) comprised in a roller arrangement (9), to an outside surface of the pre-form (10) so as to apply radial (P1) pressure on the pre-form (10) such that material of which the pre-form (10) is made begins to flow;
• and
• as the rollers (90) apply force upon the pre-form (10), performing a relative motion between the pre-form (10) and the rollers (90) by either moving the pre-form (10) in the axial direction (X) parallel to the main axis (A) through the roller arrangement (9) or by moving the roller arrangement (9) alongside the pre-form (10).