Patent ID: 7140226

Claim:
A multi-stage tube forging method for disproportionally enlarging an end section of an aluminum alloy tube of a bicycle frame part, comprising the steps of: (a) drawing the aluminum alloy tube to form a thin section and a thick end section extending from the thin section, wherein the thin section has a wall thickness thinner than that of the thick end section; (b) radially and proportionally enlarging the cross-section of the thick end section of the aluminum alloy tube by forging the aluminum alloy tube in a first die using a first mandrel in such a manner that the wall thickness of the thick end section after being enlarged is substantially the same as that of the thin section; and (c) disproportionally varying the cross-section of the thick end section of the aluminum alloy tube by forging the aluminum alloy tube obtained in step (b) in a second die using a second mandrel.