Abstract: A backing member for a friction stir butt welding apparatus includes a groove in the working surface of the backing member which supports the workpieces being butt welded. The backing member is positioned with the groove aligned directly beneath the butt joint between the workpieces. A rotating friction stir welding pin is introduced at the joint so as to plasticize the material of the workpieces on either side of the joint, and pressure is applied between the stir pin and the workpieces to create a forging pressure which forces plasticized material downward through the root zone of the weld and into the groove in the backing member. A visible bead is thus produced on the lower surfaces of the workpieces indicating total penetration of the weld. Lack of a bead indicates probable failure of the weld to totally penetrate through the root zone.

Abstract: A friction stir welding apparatus includes a C-shaped frame having two opposing jaws which are spaced apart to define a space for receiving workpieces which are to be welded together. One of the jaws supports a rotatably driven friction stir welding spindle, and the other jaw supports a back-up tool. The spindle is supported in a polycrystalline thrust bearing disposed in the one jaw for absorbing thrust forces exerted on the spindle during a welding operation. The C-shaped frame may be an integral one-piece structure, in which case the apparatus and workpieces are relatively advanced to cause the spindle to penetrate the workpieces at an edge thereof and to carry the welding tools along a weld path to a second edge of the workpieces, where the spindle exits and disengages the workpieces.

Abstract: A process for joining two or more overlapping metal workpieces includes providing a fastener which is made of metal having a melting point temperature at least as great as that of the workpieces. The fastener is rotated about its central axis and is axially advanced at a predetermined advance rate into engagement with the workpieces so as to cause plasticization of the workpieces at the interface with the fastener, and to cause the fastener to axially penetrate through substantially the entire thickness of the workpieces. The rotation of the fastener is then stopped, and the plastic zone which surrounds the fastener cools to form a metallurgical bond with the fastener. The resulting fastened joint is mechanically superior to conventional mechanically fastened joints made by rivets and the like.