Patent ID: 7219522

Claim:
A production apparatus for a metal tube having an oval cross section comprising: an impact extrusion device which impact-extrudes a disk-shaped metal slug to form a metal tube integrally including a mouth, a shoulder and a body of an oval cross section; and a trimming device which trims a hem portion of the oval body of the tube formed by the impact extrusion device by a turning operation, wherein the impact extrusion device includes a columnar punch having an axis, a press die, and a stripper provided around the punch in an axially movable manner, wherein the punch includes a punch shaft, a punch head provided at a distal end of the shaft and including a punch shoulder, wherein the die includes a die base, and a die ring which retains the metal slug therein, wherein the punch shoulder has an outer surface having an oval cross section, and the die ring has an inner peripheral surface having an oval cross section, wherein the punch shoulder is insertable in the die ring, wherein the punch head includes a base of an oval cross section connected to the punch shaft, the punch shoulder which is provided at a distal end of the base and has a greater diameter than the base, and a first taper surface having an oval cross section which has a diameter progressively decreasing toward a distal end thereof from the punch shoulder, wherein generating lines of the first taper surface on diametrically opposite sides of a major axis of the first taper surface each form an angle of not smaller than 55 degrees and not greater than 65 degrees with respect to the axis of the punch, wherein generating lines of the first taper surface on diametrically opposite sides of a minor axis of the first taper surface each form an angle of not smaller than 43 degrees and not greater than 53 degrees with respect to the axis of the punch, wherein the outer surface of the shoulder and the inner peripheral surface of the die ring are each dimensioned so that a dimensional ratio of a minor axis to a major axis thereof is not smaller than 0.5 and not greater than 0.9.