Friction stir welding (FSW) tools refers to the instruments which adjoin metal substrates in the FSW process. Specifically, FSW welding tools feature a rotating pin to create a butt joint between workpieces, and a shoulder that rests upon the workpiece to maintain uniform joint depth. The workpieces are strongly clamped together, supplied thousands of pounds of opposing pressure, and fed through the FSW tooling to create a metal-to-metal adherence. The main difference amongst FSW tools is the geometry of the pin—which alters the distribution of plasticized metal during operation, the tooling materials, and how the tool exits each joint.
FSW produces numeral advantages and drawbacks. It does not require a consumable or inert gas, and therefore has no chance of molten metal spatter. The weld itself is robust and does not require any post-weld treatment. FSW also typically produces a lower volume of defects when compared to other types of welding. FSW is an excellent option for abutting aluminum materials, but high strength metals, such as titanium, are not susceptible to the FSW process. In order for the tool to be removed from a weld it must be removed while still rotating, which leaves a pin hole at the end of each joint. The clamping forces required are provided by hydraulic machinery, which means welding cannot be completed in situ. The welding process is also somewhat more time consuming.
The tool pin material must exhibit exceptional wear and oxidation resistance, while having low thermal conductivity to insulate the rest of the FSW machine. Longer pin lengths can weld substrates of larger thicknesses. FSW tools include a shoulder which forms the weld seam, and maintains downward pressure and pin depth. Considerate tool selection is evidenced in every joint, as the matrix of significant hydraulic pressures and torque will create a poor joint is improper tooling is used.