Friction stir welding process

A method of friction-stir welding, FSW, a joint between a first workpiece and a second workpiece, the method comprising:

• performing a first pass of FSW of the joint by moving therealong a first tool, the first tool comprising a first probe rotating in a first rotational direction, in a first movement direction defining a first line, on a first side of the joint, comprising:
• inserting the first probe to a first depth, thereby providing a first welded region;
• withdrawing partially the first probe, thereby providing a first partially welded and/or unwelded region;
• and fully withdrawing the first probe, thereby resulting in a first exit hole;
• performing a second pass of FSW of the joint by moving therealong the first tool or a second tool, the second tool comprising a second probe rotating in a second rotational direction, in a second movement direction defining a second line, on the first side of the joint, comprising:
• inserting the first or second probe to a second depth, thereby providing a second welded region;
• and fully withdrawing the first or second probe, thereby resulting in a second exit hole;
• wherein the second welded region includes the first exit hole;
• wherein the second exit hole is included in the first welded region;
• wherein withdrawing partially the first probe comprises withdrawing the first probe from the first depth while moving the first tool in the first movement direction;
• wherein inserting the first or second probe to the second depth comprises inserting the first or second probe proximal to and/or into the first exit hole;
• and
• wherein the second welded region includes the first partially welded and/or unwelded region.