Predicting Plug Weld Quality
Friction plug welding is a process in which there is a small rotating part (plug) being spun and simultaneously pulled (forged) into a larger part to fill or repair a hole or join two pieces (functioning like a rivet). Learning from 1,500+ quality "known" plug welds, NASA’s experts build a load curve that, when combined with the welders’ knowledge of strain size, predicts the properties of a plug weld. The software monitors load, spindle speed, torque, displacement speed and distance, and the material properties and dimensions of the sample. The software correlates changes in the process parameters to mechanical testing of ultimate tensile strength. The software works for several Aluminum alloys such as 2015, 2195, and 2219. NASA is using the technology in its current work for closing out the termination hole of some friction stir welds. FPW is also used for repairs and as a potential replacement for rivets.
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.