Internally stiffened structure using refill FSSW

Example of an internally stiffened Al-Cu-Li alloy structure joined using refill Friction Stir Spot Welding (refill FSSW). This demonstrates the type of application explored in the 'Development of Refill Friction Stir Spot Welding (RFSSW) for skin-stringer-frame stiffening of Al-CuLi cryogenic tanks 'ESA Discovery project, led by TWI Limited and ArianeGroup. The technique uses friction and pressure to create solid-state welds that join stringers (stiffening ribs) to the skin without melting the metal, enabling cost-effective assembly of lightweight cryogenic fuel tanks for future European launchers.