Abstract: The invention illustrates and describes an apparatus for friction stir welding, having a pin (3) and a first friction surface segment (4), the pin (3) and the first friction surface segment (4) being rotationally driven about an axis of rotation (6), and the first friction surface segment (4) having a first friction surface (5) for resting on a workpiece (2). The object of providing a friction stir welding apparatus which can be used to better set the energy which is introduced into the workpiece by way of the friction between pin and friction surface, on the one hand, and workpiece, on the other hand, is achieved by virtue of the fact that a first inner segment (7) is provided, having a first inner friction surface (8) for resting on a workpiece (2, 2?), that the first inner segment (7) surrounds the pin (3), that the first friction surface segment (4) surrounds the first inner segment (7), and that the first friction surface segment (4) is rotationally driven independently of the first inner segment (7).

Abstract: The invention illustrates and describes an apparatus for friction stir welding having a pin (3) and a first friction surface segment (4), the pin (3) and the first friction surface segment (4) being driven in rotation about an axis of rotation (6), and the first friction surface segment (4) having a first friction surface (5) for resting on a workpiece (2), as well as a friction stir welding process. The object of providing an apparatus and a process for friction stir welding which allow better setting of the properties of the weld seam is achieved byvirtue of the fact that there is a feed device for introducing a filler material into the weld seam.