Method and apparatus for performing double sided refill friction stir spot welding

A method for performing refill friction stir spot welding, comprising:

• providing a first welding head comprising a first probe member and a first tubular shoulder, the first probe member being located inside and axially aligned with the first tubular shoulder along a first head axis;
• providing a second welding head comprising a second probe member and a second tubular shoulder, the second probe member being located inside and axially aligned with the second tubular shoulder along a second head axis;
• locating the first welding head on a first surface of a weld object to be welded such that the first probe member and the first tubular shoulder are in contact with the first surface;
• locating the second welding head on a second surface of the weld object, opposing the first surface, such that the second probe member and the second tubular shoulder are in contact with the second surface and the first head axis is aligned with the second head axis;
• simultaneously rotating the first welding head and the second welding head so as to form a volume of increased plasticity in the weld object proximate the first and second welding heads;
• simultaneously advancing one of the first probe member and the first tubular shoulder, and one of the second probe member and the second tubular shoulder, from an initial position and into the respective first and second surface of the weld object along the respective first and second head axis, while retracting the other of the first probe member and the first tubular shoulder and the second probe member and the second tubular shoulder from an initial position and along the respective first and second head axis;
• returning each of the first and second probe member and first and second tubular shoulder towards the initial position;
• and
• removing the first and second welding head from the respective first and second surface of the weld object.