Friction stir welding bobbin tool

A bobbin tool for friction stir welding, the bobbin tool comprising:

• a top shoulder having a body that provides an annular shoulder end surface;
• a bottom shoulder having a body that provides an annular shoulder end surface, a back surface opposite the annular shoulder end surface, and a side surface that joins the annular shoulder end surface and the back surface of the bottom shoulder, the annular shoulder end surface of the bottom shoulder being spaced from and facing the annular shoulder end surface of the top shoulder;
• an axial pin that extends between the top shoulder and the bottom shoulder along an axis of rotation of the bobbin tool and through a gap defined by the annular shoulder end surface of the top shoulder and the annular shoulder end surface of the bottom shoulder;
• and
• a plurality of blades that extend radially outwardly from, and are circumferentially spaced around, the side surface of the bottom shoulder, each of the plurality of blades being planar and comprising an axial cutting edge that runs alongside the side surface of the bottom shoulder from a peripheral edge of the annular shoulder end surface of the bottom shoulder to a peripheral edge of the back surface of the bottom shoulder.

A method of friction stir welding with a friction stir welding bobbin tool, the method comprising:

• providing a bobbin tool that includes a top shoulder having an annular shoulder end surface, a bottom shoulder having an annular shoulder end surface that is spaced from and faces the annular shoulder end surface of the top shoulder so as to define a gap between the annular shoulder end surfaces, and an axial pin that extends between the top shoulder and the bottom shoulder along an axis of rotation of the bobbin tool, the bobbin tool further comprising a blade that extends radially outwardly from a side surface of the bottom shoulder and which comprises an axial cutting edge that runs alongside the side surface of the bottom shoulder;
• receiving a workpiece assembly within the gap defined by the annular shoulder end surface of the top shoulder and the annular shoulder end surface of the bottom shoulder, the workpiece assembly comprising a first metal workpiece and a second metal workpiece to be joined;
• rotating the bobbin tool about its axis of rotation while the workpiece assembly is received in the gap and the annular shoulder end surface of the top shoulder bears against a top surface of the workpiece assembly and the annular shoulder end surface of the bottom shoulder bears against a bottom surface of the workpiece assembly, the bottom surface of the workpiece assembly including a strengthening rib;
• and
• translating the bobbin tool along a weld path in a forward welding direction while rotating the bobbin tool to intermix plasticized material from each of the first metal workpiece and the second metal workpiece to produce a weld bond in a wake of the bobbin tool as the bobbin tool moves in the forward welding direction, the axial cutting edge of the blade sweeping through an arcuate path in advance of the bottom shoulder as the bobbin tool is translating along the weld path, and wherein, when translating along the weld path in the forward welding direction, the axial cutting edge carves through the strengthening rib when the strengthening rib enters the arcuate path of the axial cutting edge.