Stronger Plug for Friction Pull Plug Welding of Thick Plates

Friction Pull Plug Welding (FPPW) is the process necessary to plug the hole that is left behind as a friction stir weld (FSW) joint is completed and the pin tool of the welder retracts from the joint. FPPW involves a small, rotating part (plug) being spun and simultaneously pulled (forged) into a hole in a larger part. Much work has been done to fully understand and characterize the process and its limitations. FPPW worked very well for building large rocket sections such as the circumferential welds of the upper stages of NASA's Ares rocket, and to repair the external tank. Engineers were challenged to adapt FPPW to accommodate the thicker plates new alloy combinations of the SLS. The new hybrid plug solves the issue of the plugs snapping due to the increase torsion and moment stresses when joining thicker plates. The new hybrid plug, with a steel shank, makes FPPW more practical and robust. The new plug has been used to make space-qualified parts at NASA, and the plug welds are as strong as initial welds. NASA and Geocent, LLC innovators adapted a plug to improve aluminum friction pull plug welding (FPPW). The rugged plug is less vulnerable to snapping off and helps reduce chatter. FPPW is the process that is necessary to plug the hole that is left behind as a friction stir weld (FSW) joint is completed and the pin tool of the welder retracts from the joint. The inventors have replaced the plug support with steel to improve its strength to endure the forces of the FPPW process. NASA adapted the plug to enable FPPW processing for the thicker welds and different alloys needed for NASA&#146s new Space Launch System (SLS). This new plug helps solve the well-known FPPW challenges of plug welding on thicker plates that have caused weld defects in the past such as substantial plug necking and plug rotational stalling. The new plug has been tested and used in building NASA equipment.