Abstract: An apparatus for welding a workpiece has a welding head and a rotating tool. The welding head has a recessed portion and a welding head end to be placed in contact with a surface of the workpiece. The rotating tool is disposed within the recessed portion of the welding head. The rotating tool is operable to rotate about an axis and to translate along the axis. The rotating tool comprises a rotating tool end to be placed in contact with material of the workpiece. The rotating tool end comprises a shoulder and one or more off-center protrusions. The shoulder has a surface operable to frictionally heat the material of the workpiece. An off-center protrusion is operable to penetrate and displace the material of the workpiece to form a weld.