Riveting is currently the primary method for joining of complex aluminium structures in aircraft fuselage manufacturing, with large commercial aircraft fuselages containing 100’000s of rivets. Riveting is a time-consuming, expensive and weight-adding operation that places holes and point loads in a cyclically pressurised structure, subject to long-term fatigue loading and corrosion – thus is not an ideal solution for these structures. With the development of precision laser beam welding (LBW) and friction stir welding (FSW), it is now possible to fabricate “rivetless” aerostructures using welding processes. These new processes produce a lighter weight, distributed load path with the potential for enhanced strength and structural stiffness, no holes and a smoother, more aerodynamic surface. In addition to being more structurally efficient, the new processes are cheaper, should reduce inspection & maintenance requirements. Ultimately, they allow manufacture of lighter-weight aircraft, with reduce fuel burn, superior operating efficiencies and reduced emissions of aeroplanes. Achievement of the technical objectives of the project will advance three welding technologies (FSW, Friction Stir Spot Welding (FSSW) and LBW) for manufacturing complex lightweight aluminium structures and will lead to the fabrication of full scale demonstrators for validation. Inspection of these joints will be carried out in accordance with relevant aerospace standards.
In summary, OASIS will develop alternative manufacturing approaches using welding technologies such as FSW, FSSW and LBW that will lead to light weighting and most importantly provide manufacturing cost savings. This will include the development of procedures to weld skins, stiffeners, and frames to produce a cargo door demonstrator. Simulation and modelling of the effect of welding on structural integrity (structural and fatigue analysis of welded joints), residual stress and distortion of the full structure will be studied, with the input data taken from coupon level welding.
The European and global aircraft market will benefit from new cost effective manufacturing routes for aerostructures, ensuring optimal material usage and maintain its competitiveness. The impact of the uptake of the optimised welding techniques (FSW, FSSW and LBW) for assembly of structural aircraft parts will enhance improved aerodynamics and lightweighting which subsequently will improve fuel efficiency and global competitiveness of the industry. Also in terms of productivity, joining using rivets is more time consuming than using welding approaches. In the case of rivets, holes need to be drilled and deburred prior to installing the rivets and a “redressing” step is required after the rivets are in position. Moreover rivetless assembly will enable the usage of “leaner” parts.
The envisaged approach to welding cargo doors will eliminate riveted joints, which is typical in current aircraft manufacture. Via welding of skin, stiffeners and frames, it will enable light-weighting. Impacts of light-weighting are as follows:
- Increased fuel efficiency and increase the cost-effectiveness of operation of the aircraft.
- Reduced aircraft CO2 emissions of the, and with widespread application and use, reduce the emissions output of the aerospace industry as a whole.
- Materials usage savings of up to 30% compared with the mechanical fastening/CNC machining route, and weight savings of 10% for typical airframe structures
- Reducing the working time by 40%
Aircraft parts are joined using various methods (LBW, FSW and riveting). Of these, riveting results in the most significant weight penalties in the final structure. On the A340 aircraft, there are 1 million rivets whereas on Boeing’s 737, there are 367,000 parts; an equal number of bolts, rivets and other fasteners. Airbus reported a saving of 1kg per meter, compared to riveting, when FSW was used to join a A340-600 fuselage panel in trials a few years ago. A huge amount of savings could be achieved in terms of material usage which in turn will reduce weight of manufactured parts and through-life fuel consumption costs. As an example, the Eclipse 500 aircraft, in which ~60% of the rivets were replaced by friction stir welding, is now in production. This offered significant advantages compared to riveting and machining from solid, such as reduced manufacturing costs and weight savings. Automated FSW has reduced manufacturing costs by between €36,500 and €73,000 per Eclipse 500 plane and requires less factory floor space.
Welding of stringers and frames on an aluminium door skin instead of riveting allows savings in consumables such as sealants and reduces the number of protective organic layers needed to ensure a sound protection of the assembly against corrosion.