Anvil with rolling elements for friction stir welding

In a Friction Stir Welding process a load, applied through a rotating tool, frictionally heats, plasticizes and commingles selected regions of the workpieces while translating along the length of the joint. The load is supported by an anvil. The applied load inhibits relative motion of the workpiece and conventional anvils due to friction which requires application of higher translation forces and could lead to undesired surface blemishes. Thus conventional practice is to employ bulky, stationary anvils. Compact, moveable anvils comprising freely-rotating or freely moving elements in contact with the workpieces and capable of reducing workpiece-anvil friction are described. Particular benefits of this anvil design are illustrated for the process of assembling inner and outer sheet metal components into an automobile assembly, a portion of which is visible to a vehicle customer.