Friction Stir Welded Low Cost Titanium Propellant Tank

The present work is split in two phases with two main objectives: The objective of the first phase is to develop, characterize and validate 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. In the second phase and provided that the welding parameters and tools are proven to deliver the required quality, repeatability and costs effectiveness, the objective is to manufacture a Friction Stirred Welded Titanium tank. The achieved improvements in terms of of costs reduction, industrial manufacturing aspects, and environmental friendliness compared with a tank made using conventional welding techniques be quantified.  

FSW is considered to be the most significant development in metal joining in decades. In addition it has demonstrated exceptional environmental friendliness.Ti-6Al4V titanium is the baseline alloy for aerospace rocket propellant tankage for many years. These tanks have been made of machined forged Ti-6Al4V titanium alloy. The tanks were normally TIG and EB welded and showed substantially lighter weight than if made of other materials and, furthermore, they show reliable performances. Despite the manufacturing improvements, the tanks are still one of the most costly items in the rocket motor system. High cost is due primarily to excessive machining labour and discard of high quantity of material lost as chips. The evolution of larger motor systems is demanding still larger tankage which threatens to become prohibitively costly if manufactured by traditional methods. The use of the new excellent formable beta titanium Ti-15V-3Cr-3Al-3Sn (Ti-15-3- 3-3) alloy in combination with the Friction Stir Welding (FSW) process would make possible to significantly reduce costs also leading to design simplification and reduction of material wasting. The proposed study is split into two phases: the objective of the first phase is to develop, characterize and validate 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. Extensive characterisation will be performed at sample level. The possibility to scale-up the validated processes will be addressed. In the second phase and provided that the welding parameters and tools are proven to deliver the required quality, repeatability and costs effectiveness, the objective is to manufacture two full-size Titanium tank welded using the FSW welding process; one made of Ti-15-3-3-3, the other from Ti-6Al-4V.Both 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. ESA - Friction Stir Welded Low Cost Propellant Tank