The invention discloses a
friction stir welding tool for an overlap joint. The
friction stir welding tool is composed of a shaft shoulder and a stirring needle. The stirring needle is shaped like a
frustum, the small bottom of the
frustum is connected with the shaft shoulder, the end face of the large bottom of the
frustum is provided with a round concave hole, and the outer surface of the frustum is provided with three arc-shaped grooves distributed in the circumferential direction. Meanwhile, the invention further discloses the stirring needle and the structures and the sizes of all parts of the shaft shoulder. When a stirring tool designed through the
friction stir welding tool is adopted for carrying out friction stir overlap
welding, the stirring needle of the frustum shape generates oblique upward thrust on plasticized
metal around the overlap face, so that the perpendicular motion of the plasticized
metal is reduced, and the perpendicular moving tendency of the overlap face is reduced. Moreover, as the concave hole and the grooves in the side face are formed in the bottom of the stirring needle,
material flow in weld zones is improved, the overlap face is broken completely, and the
weld metal can be mixed fully. Accordingly, the size of the hook-like defect in a weld joint obtained through
welding of the tool is greatly reduced, and the strength coefficient of the joint is remarkably improved.