US 5971247 A abstract stir friction welding is accomplished by applying force to plunge a nonconsumable rotating welding post into the region to be welded the rotation creates friction which at least partially melts the material to be welded as the welding post penetrates the force is continued causing the post to continue to penetrate a set of rollers associated with the welding head eventually reaches the surface of the workpiece when the welding post reaches the proper depth and prevents further penetration of the welding post in one embodiment of the invention the rollers have crowned surfaces and the force is applied by a hydraulic cylinder application_number US 3691598 A description in fig1 a 1b and 1c a stir friction welding head 12 is supported by a support element 13 and rotates about an axis of rotation 8 welding head 12 has a distal end 12d which is contiguous with a plane 14 which is transverse or orthogonal to axis of rotation 8 and supports in cantilever fashion the proximal end 16p of a nonconsumable welding post 16 welding post 16 also has a free distal end 16d a portion of welding post 16 projects past a second plane 18 which is parallel with plane 14 and into the unwelded seam lying between flat portions of mutually adjacent workpieces 30a and 30b which are supported by a support arrangement or backing bar illustrated as a bipartite arrangement.