Friction stir welding (fsw) apparatus and techniques

An apparatus for performing friction stir welding (FSW) on an interior face of a workpiece, the apparatus comprising:

• a support arm coupled with or comprising a spindle housing;
• a spindle shaft, supported by the spindle housing;
• and
• a tool removably coupled to the spindle shaft, the tool comprising a pin protruding outward from a face of the tool;
• wherein the spindle shaft and tool are oriented to extend laterally outward from the support arm to engage an interior face of a workpiece where a forging force and rotation between a tool and the workpiece are established;
• and
• wherein the support arm, spindle shaft, spindle housing, and tool are sized and shaped to fit within a cross section defined by the workpiece when extended within the workpiece by the support arm.

A tool for friction stir welding (FSW) to plastically deform and mix, in a solid phase, a material, when the tool is subject to a forging force and rotation relative to the material, the tool comprising:

• a shank configured to be engaged by a tool holder;
• and
• a face defined by a body of the tool, the face defining a shoulder extending along the face from an edge of the tool inward toward a center of the face;
• a pin protruding outward from the face of the tool centered at the center of the face;
• and
• at least one spiral feature defined by a protrusion or a recess extending outward or inward from a face of the tool in an axial direction parallel to the forging force, the at least one spiral feature located between the shoulder and the pin.

A method for forming a joint using friction stir welding (FSW), the method comprising:

• positioning a plate against a first face of a base structure, the plate extending outward from the first face of the base structure;
• establishing a forging force and rotation between a tool and a second face of the base structure opposite the first face to plastically deform and mix, in a solid phase, through the base structure, material comprising the base structure and material comprising the plate to form a joint between base structure and the plate;
• and
• contemporaneously with the establishing the forging force and the rotation, establishing translation of the tool relative to the second face of the base structure to define a specified weld path.