Riveting has been the state of the art of joining technology for aircraft structures since decades. The necessary overlap joint demands a large amount of material which restricts weight savings. Furthermore, the riveting process is quite intensive in process time. The LIGHTWELD project aimed at developing and adapting LBW and RSW for newly developed more weldable light alloys with the objective of:
- Reducing weight through replacing the use of vast amount of rivets
- Enabling the automation of joining and NDT processes for decreasing process time
The project addressed the comparison of novel welding and conventional riveting processes in terms of fatigue and corrosion performance as well as environmental impact and manufacturing cost enabling the advance towards lightweight and eco-efficiency objectives. Project specific goals were related to:
- Development of robust and optimised LB, RS and FSS welding for the joining Al-Li and Mg;
- Reduction of component weight between 5 and 10%;
- Reduction of operation cost until 20%;
- Corrosion resistance improvement for example by means of new joint designs;
- Inspection time saving due to the possibility of automating that process;
- Knowledge generation in the field of dissimilar joining of Al-Li and Mg alloys; and
- Fabrication cost saving compared to aero-structures made of composite materials.
The singular characteristics of the materials to be welded and weldability problems related to dissimilar metal joining make mandatory big knowledge and expertise, which were in this case provided by IK4-LORTEK as something essential for the good end of the LIGHTWELD project.
The LIGHTWELD project advanced the welding technology for studied alloys, making it cost efficient and feasible for industry manufacturers of different markets. This will mainly open new manufacturing possibilities for European industry. Aircraft industry was the main target market, but other industrial areas were also to be considered in the future exploitation.
Reduction of air transport contribution to climate change is nowadays one of the most challenging objectives for aircraft manufacturers. Weight reduction, manufacture and inspection process improvement are one of the main keys in order to achieve it. Nowadays, riveting is the state of the art of joining technology for aircraft structures. The necessary overlap joint demands a large amount of extra material which restricts weight saving requirements. Furthermore, the riveting process is quite intensive in process time regarding the production chain compared to welding processes.
A considerable lightening is obtained employing newly developed Al-Li and Mg alloys and eliminating the rivets and the extra material needed to ensure a sufficient overlap in the mechanical joint. By means of welded structures it is possible to eliminate the rivets, increase productivity (short production time) and minimizing cost management. Due to those considerations, welded integral structures could be an attractive alternative to usual riveted structures in order to reduce weight and cost.
Within the LIGHTWELD project, all the efforts had been focused on developing welding technologies for Al-Li and Mg alloys. Process parameters have been optimised for laser beam, resistance and friction stir spot welding, in order to ensure joint soundness, achieving a load capability for welded joints, comparable to the reference riveted ones. Laser and friction stir spot technologies had been used on the fabrication of a full-scale curved fuselage demonstrator to joint different Al-Li and Mg components, which result on a component weight reduction up to 10% (estimation) due to rivet removal, lower joint overlap material and lower density of the alloy selected for it. It must be mentioned the operation cost reduction that could be achieved employing laser and friction stir welding technologies, both of them with a high degree of automation, and eliminating manufacturing steps, as the rivet hole drilling.