Friction Plug Welding Process for Repair and Exit Hole Closure

This paper will focus on development of the Friction Plug Welding (FPW) process and equipment used to close the exit hole from a Self-Reacting Friction Stir Welding (SR-FSW). SR-FSW is a solid state welding process that offers an innovative solution to the challenges associated with conventional Friction Stir Welding. The SR-FSW technology is being implemented by NASA for the fabrication of the SLS Upper Stage and Orion crew exploration vehicle. FPW is used to seal the exit hole that remains from a circumferential SR-FSW using a rotating plug that pushed or drawn into a hole in the welded hardware. Friction plug welding can also be used as a repair process.

The data presented in this work was obtained from welds produced using a purpose build servo-hydraulic controlled weldhead capable of both push and pull friction plug welding. This advanced head assembly includes a motor and spindle with an integrated forge axis. The forge axis provides the linear motion of the plug as well as the force required to complete the friction plug welding process. While executing a friction pull plug weld, the forge axis and the external anvil attached to the weldhead create opposing forces to provide the necessary process loads while transferring no loads to the hardware. The friction pull plug weld process eliminates the need for reaction structures inside the flight hardware.

The range of plug and test piece material combinations tested to date are aluminum alloys 2195, 2219, and 2024 using several different plug geometries and hole diameters. Some analysis and results of welds completed will be presented along with the implementation plans for this unique technology.