Patent ID: 7416102

Claim:
A method for joining curved workpieces by friction stir welding, comprising the steps of: placing a first workpiece having a first thickness in close proximity to a second workpiece having a second thickness thereby creating a joint, wherein the first workpiece and second workpiece each have at least one cooperating curve; plunging a portion of a rotating non-consumable multi-section faced shoulderless variable penetration friction stir welding tool into the joint to be welded to a first penetration depth wherein the tool comprises a cylindrical body portion, a head portion, and a tip section, each integral to the tool, the body portion having a longitudinal axis about which it is rotable, a diameter, a sidewall parallel to the longitudinal axis, a proximal end, and a distal end, the head portion located at the distal end of the body portion having a base with a diameter equal to the diameter of the body portion forming a smooth transition between the body portion and the head portion, and the head portion having a multi-section face with a first face section nearest the body portion and a second face section nearest the tip section wherein the multi-section face converges to the tip section having a diameter and a center wherein the center is located on the longitudinal axis, a height from the distal-most portion of the tip section to the base along the longitudinal axis and the first face section having a first section horizontal projection component with a magnitude of less than fifteen percent of the body portion diameter; traversing the joint and the at least one cooperating curve with the rotating tool ensuring that a portion of the first face section is in contact with the first workpiece and the second workpiece, and no part of the body portion extends into the first workpiece or the second workpiece such that no gouging occurs; and gradually retracting the portion of the rotating tool from the workpieces while traversing the joint so that the tool exits the workpieces at a predetermined exit point leaving a friction stir weld free of an exit hole.