Fri, 24 May, 2019
The development of stationary shoulder friction stir welding (SS-FSW) at TWI has enabled a new range of joint designs, such as tee-joints, which could not be joined by conventional friction stir welding (FSW).
Tee-joints are of particular interest for the aerospace industry, for the fabrication of stiffened skin panels for wing and fuselage applications. The current fabrication method is by riveting an L or Z shaped stiffener onto the skin. Corner SS-FSW joints would eliminate the need for overlapping flanges, rivets and sealant, which could result in significant weight and cost savings.
TWI has implemented Corner SS-FSW on its robotic FSW system. A combination of advanced multi-axis force control and new FSW tool designs allowed welding of both convex and concave curved structures with a minimum radius of 200mm. By minimising the contact area between the stationary shoulder and the work piece, the process forces could be reduced significantly, allowing curved corner joints between a skin and a 3mm thickness stiffener to be produced with a 400kg payload robot. The joints can be produced both with and without a reinforced fillet weld.
Furthermore, SS-FSW offers the ability to join dissimilar materials, e.g. by joining 7000-series aluminium alloy stiffeners to a 2000-series aluminium alloy skin.
You can find out more about friction welding processes at TWI here.