New concepts for friction stir welding of 3D shells

In the shell manufacturing for metallic fuselage structures riveting has been used for decades. Despite the high degree of automation of this process, riveting is correspondingly expensive due to relatively high process times. With regard to the ongoing weight and cost optimization in aircraft manufacturing, an enormous potential for the use of new joining technologies such as friction stir welding exists. In contrast to the riveting process, friction stir welding does not necessarily involve the use of an overlap configuration. The aim is to use friction stir welding also for joining of large-size, non-rigid 3D shells in the fuselage. Classic machine concepts such as CNC gantry systems are of limited suitability for this purpose. Although they have the required high rigidity, they are very costly and regarding to their work space not arbitrarily scalable. In addition, large-sized, thin 3D components require customized intelligent clamping techniques, which ensure a precise positioning of the components relative to the welding system. As part of the aviation research program LuFo IV a new machine concept was developed at the Fraunhofer IWS in collaboration with Airbus Operations GmbH, Airbus Group Innovations and supported by the Federal Ministry of Economics. The concept consists of a combined welding / milling robot which travels autonomously along a three-dimensional rail system that is mounted on the clamping system. The machine concept allows fixing, positioning, milling and the subsequent friction stir welding of large-format, limp 3D shells in one clamping system. In addition to the presented concept, post weld results of the realized 3D seams will be shown.