Welding tool comprising a shoulder, welding method and workpiece

1. A welding tool for connecting at least two workpieces at a connection region by means of friction stir welding, the welding tool comprising:

a probe configured to rotate around a rotation axis, wherein the connection region is softened by friction heat provided by the probe during said friction stir welding;

a shoulder, through which the probe passes without contacting the shoulder, wherein the shoulder separates the connection region from the surroundings,

wherein the shoulder has a projection on or next to a lateral surface of the shoulder,

wherein the projection is arranged on the softened connection region during the friction stir welding process, and

wherein the projection is non-displaceably fixed on or next to the lateral shoulder surface in a direction of the rotation axis,

wherein the projection has a projection surface, which is configured to be arranged on the softened connection region during the friction stir welding process,

wherein the projection surface has a first step and a second step that is set off from the first step in a longitudinal direction that is perpendicular to the rotation axis,

wherein a plurality of projections, including the projection, are formed on or next to the shoulder surface, and

wherein the plurality of projections each have a surface, including the projection surface, facing each other in the longitudinal direction, and wherein a distance between the surfaces facing each other varies in the longitudinal direction.

2. The welding tool of claim 1 , wherein the shoulder is rotationally asymmetric about the probe.

3. The welding tool of claim 1 , wherein the first step is connected to the second step via a slope.

4. The welding tool of claim 1 , wherein each of the plurality of projections comprises a corresponding projection surface having a respective first step and respective second step that is set off from the respective first step in the longitudinal direction.

5. The welding tool of claim 4 , wherein each of the respective first steps is connected to a corresponding one of the respective second steps via a respective slope, wherein each of the respective slopes extend in the longitudinal direction.

6. The welding tool of claim 1 , wherein the shoulder is configured to mold the softened connection region or the at least one workpiece.

7. The welding tool of claim 1 , wherein the shoulder is configured to mold a welded seam formed during the friction stir welding process at the softened connection region.