TWI has been working with astrospace contractor Airbus Defence and Space to satisfy a European Space Agency (ESA) request to investigate cost-effective manufacturing methods for titanium propellant tanks. The project investigated the feasibility of using stationary shoulder friction stir welding (SSFSW) techniques for the cylindrical welding of titanium alloys suitable for launch vehicle propellant tanks. The investigations sought to reduce lead times and costs by developing and validating a system required to weld titanium alloys and also to raise the Technology Readiness Level (TRL) of SSFSW of titanium alloys to prototype demonstrator (TRL6).
Current manufacturing methods for titanium propellant tanks suffer from extremely high cost and long manufacturing lead times. Material wastage from complicated forging, machining, and forming techniques coupled with electron beam (EB) welding makes propellant tanks one of the most expensive hardware items on a satellite launch programme. While friction stir welding (FSW) is capable of welding high strength high temperature materials such as steel and nickel alloys, by using the modified version of FSW, Stationary Shoulder Friction Stir Welding (SSFSW), titanium can also be welded successfully.
The TWI team conducted an extensive review of material and manufacturing processes, with forged and cast titanium both offering the mechanical property requirement. In August 2016 TWI successfully performed the world’s first full circumferential SSFSW of two 420mm cast titanium cylinders. The test pieces were then subjected to full NDT evaluation and mechanical assessment to confirm joint quality and properties.
In winter 2016, TWI fabricated and delivered the first one of four SSFSW cast titanium prototype demonstrator (TRL6) propellant tanks to the European Space Agency, with a delighted response from ESA. The achievement and success of the ESA-TWI-Airbus team was recognised, in March 2017, when they were awarded the Raiser 2017 Award for Friction Welding Innovation.