Patent ID: 7931185

Claim:
A welding device for friction stir welding of parts comprising a first shoulder and a second shoulder facing the first shoulder, each of the first shoulder and second shoulder comprising an internal ring and an external ring adjacently bordering on and arranged concentrically around the internal ring, the internal rings configured to compress stirred material of parts to be welded during an advancement of the welding device, each internal ring and each external ring consisting of a continuous support surface extending entirely within a two dimensional plane, the support surfaces extending parallel to one another, the support surface of each internal ring separated by the support surface of the adjacent external ring by a step transition, the support surfaces of the internal rings spaced apart by a first distance, and the support surfaces of the external rings spaced apart by a second distance, the first distance being less than the second distance, and the difference between the first and second distances corresponding to a maximum compression of parts to be welded, each external ring forming a sink-in stop for the adjacent internal ring that it surrounds to limit the sinking of the internal rings into the stirred material by supporting the external rings on the parts to be welded on both sides of a weld.