Patent ID: 7788959

Claim:
A method of producing an ultra thin wall metallic tube by a cold drawing process in which a drawing machine is used, the method comprising the steps of: feeding a mother tube into a solid die, the mother tube having an expanded tube-end portion, an inside diameter, and an outside diameter, the solid die having a diameter that gradually decreases from an engaging inlet side toward a work-ending outlet side; inserting a plug or a tapered mandrel bar into the mother tube, either the plug or the tapered mandrel bar having a diameter that gradually increases in diameter over a corresponding distance from the engaging inlet side of the solid die toward the work-ending outlet side of the solid die; and drawing the mother tube from the engaging inlet side toward the work-ending outlet side by gripping the expanded tube-end portion with a chuck, whereby a wall thickness of the mother tube is reduced to perform elongating while a tube-wall centerline diameter is expanded between the solid die and the plug or tapered mandrel bar, the tube-wall centerline diameter being the mean diameter of the outside and inside diameters of the mother tube, wherein the wall thickness is reduced to perform elongating while the outside diameter is reduced and the inside diameter is expanded, and an expansion amount of the inside diameter being ensured larger than a reducing amount of the outside diameter.