Abstract: A friction stir welding tool includes a friction stir welding head having a probe and spindle rotatably mounted at a first end. A support supports the stir welding head between the first end and a second end for movement about a pitch axis. A pitch actuator includes an elongated arm coupled to the stir welding head at a point longitudinally spaced from pitch axis to overcome the relatively large forces exerted at the probe. A turntable supports the stir welding head for movement about a yaw axis. A yaw actuator includes an elongated arm coupled to the turntable laterally spaced from the yaw axis, to overcome the relatively large forces exerted at the probe. A controller maintains an angle of attack of the probe with respect to direction of travel of the probe along the work piece.

Abstract: A knock-down anvil assembly provides a rotary anvil ring inside the cylindrical end portions of tank sections to be stir welded together as a butt joint, and an external reactive roller unit is provided which bears against the outer faces of these end portions at a location diametrically opposite from the stir welding tool. The anvil assembly can be disassembled within the finished tank into components which can be individually removed through an access opening in an end cover of the tank.