The Need

Friction stir welding (FSW) and friction stir processing (FSP) are solid-state processes that utilize the heat generated from a rotating pin tool to soften the base metals for fusion and repair, respectively. However, keyhole defects are inevitably left after retracting the tool pin, which can generate stress concentrations and result in corrosion issues in service. Most keyhole refill techniques are based on spot welding or specially designed tools, increasing equipment costs and limiting applications to certain welding configurations and lowering process temperatures.

The Technology

Researchers at The Ohio State University have developed an FSP/FSW tool consisting of a non-consumable shoulder and a replaceable/consumable pin that is compatible with the workpiece. The pin has cutting features that facilitate the initial plunge stage as the tool moves into the workpiece and enhance material flow in the stirring nugget. The replaceable pin is inserted into a pocket in the shoulder that matches the profile of the pin root. The non-consumable shoulder is made of more refractory materials and can have features that guide the metal flow. During the FSP/FSW process, the pin is worn down and fills into the stirring region such that no keyhole is left on the surface of the workpiece after pin retraction.

Commercial Applications

Metal joining for various applications, including aerospace, automotive, shipbuilding, rail, energy, and telecommunications
Low-cost manufacturing of metal assemblies
Joining of dissimilar metals
Metallurgical processing and manufacturing

Benefits/Advantages

Fills the undesirable keyhole that remains at the end of the FSW/FSP process using low-cost tooling and standard equipment
Pin and shoulder dimensions and features can be customized for the specific application
Extra material added to the stirring nugget from the pin creates compressive stresses, which improve fatigue life and alleviate other issues such as stress corrosion cracking

Patents

Patent application 17/943,748