The friction heat generated by the high-speed rotating stirring needle and the workpiece causes the material to be welded to be partially plastic, and the shaft shoulder slides (does not rotate) on the surface of the workpiece, and the plasticized material forms a dense weld under the forging press of the shaft shoulder. The static shoulder tool system is composed of five key parts: support cover, tool handle, fastening nut, mixing needle and shoulder.

Because the shaft shoulder does not rotate, greater forging pressure is provided to the weld, and the joint strength can be increased by 5-10% compared to the moving shaft shoulder. At present, it is mainly used in the welding of battery tray and wide profile.