Development of Linear Friction Welding to Add External Features to Spacecraft and Launchers Systems

The incorporation of external features on critical aerospace structures is often achieved by machining from solid plates or forgings, sourced to fulfil the envelope of the structure. In addition to lacking design flexibility, this approach increases buy-to-fly ratio, especially when considering products of large magnitude like launch modules or satellite fuel tanks. Aiming to save raw material costs, designers may choose to fabricate these structures using mainstream joining techniques, namely fusion welding, mechanical fastening or adhesive bonding. However, these processes will either add weight or require increasing joint thickness to compensate for an inherent local reduction of parent material strength.

Friction welding is an attractive option for producing solid-state joints, while avoiding the drawbacks of fusion welding. It has been adopted increasingly by the aerospace sector for joining safety critical structures or fabricating nearer-net-shape pre-forms from which the components can be extracted. When considered at a design stage, these processes have provided repeated examples of enabling substantial savings in raw materials and manufacturing costs. Furthermore, new design possibilities have arisen from the ability to join dissimilar combinations or even materials previously considered to be unweldable.

The present investigation is part of an ESA funded programme, delivered by a consortium led by TWI in partnership with Airbus UK and ArianeGroup SAS. The main objective is to demonstrate how Linear Friction Welding (LFW) can be used for two applications:

- Joining bosses onto cryogenic tanks in AA2195-T8 for launcher vehicles;

- Adding connection tabs to satellite fuel tanks in Ti6Al4V.

Preliminary results will be presented including the initial LFW parameter development work, joint mechanical characterisation and preliminary concepts for the technology demonstrators (due to be manufactured later in the programme)