As manufacturers expand the use of aluminum, titanium, magnesium and other high-strength, lightweight alloys, interest in alternative joining technologies is increasing. One is friction stir welding (FSW), in which a cylindrical shouldered tool with a profiled pin is rotated at high speed and plunged into the joint area between two abutting metal plates or sheets. Frictional heat between the welding tool and workpieces causes the latter to soften without reaching their melting points.
The rotating tool then traverses along the joint line, transferring the softened material around itself as it moves and stirring material from each part together. Plasticized material is pressed downwards by the tool shoulder and transported from the front of the tool to the trailing edge where it is forged into a butt or lap joint.