Development of Friction Stir Welding of Titanium Alloys for Spacecraft Propellant Tanks

FSW is considered to be the most significant development in metal joining in decades, and is now widely used in a variety of commercial applications.

Ti-6Al-4V titanium is the current baseline alloy for rocket/spacecraft propellant tanks. These tanks are usually manufactured from forged feedstock and then welded using a combination of TIG and Electron Beam (EB) welding.  Although the current manufacturing route produces tanks with a reliable performance, tank manufacturing is still one of the most costly items in the rocket/spacecraft motor system. The high cost is due primarily to the extensive amount of machining which is required, coupled with the discard of a high quantity of material lost as chips.  Furthermore, the evolution of larger motor systems is demanding even larger tanks, which threatens to become prohibitively costly if manufactured by traditional methods.

In this collaborative project between TWI, ESA and Airbus UK, alternative methods manufacturing for titanium propellant tanks is being explored.  This includes the use of the new excellent formable beta titanium Ti-15V-3Cr-3Al-3Sn (Ti-15-3-3-3) alloy in combination with FSW.  The project will focus on the development, characterisation and validation a FSW process and tooling system able to weld Ti-15-3-3-3 as well as Ti-6Al-4V Titanium alloys, starting from sheets up to formed shells. Finally the validated processes will be unscaled and full size tanks will be manufactured.  The tanks will undergo a full verification and test campaign to prove the suitability of the materials and technologies.  Their performances will be compared with equivalent titanium tanks welded by conventional techniques including cost, reliability, industrial efficiency and environmental friendliness aspects.

This presentation will discuss the initial work on this 2 year project, and the methodologies that will be used to meet the project deliverables.