New technologies for welding aircraft structures
For decades, the aerospace industry has exploited riveting to join metals for production of aircraft structures, including the fuselage and wings. Riveting, akin to buttoning a shirt, requires a substantial overlap of materials plus the rivets themselves, both of which increase the load. With a view to reducing the global impact of aviation, the EU funded the project LIGHTWELD (Development of welding technologies for light alloys aircraft structures). Efforts were focused on developing innovative welding technologies for aluminium-lithium (Al-Li) and magnesium (Mg) alloys. Technologies included laser beam welding (LBW), friction stir spot welding (FSSW) and resistance spot welding. These techniques rely on laser heating, frictional heating and electrical resistance heating, respectively, to soften the materials and facilitate joining. Using different material combinations, researchers tested these three welding technologies on a demonstrator model of a real aircraft structural panel with frame and stringer. Process parameters were optimised for all cases to ensure sound joints comparable to the reference riveted ones. For joining the metal intercostals to the skin by FSSW, researchers utilised a robotic arm equipped with a spindle along with a flexible clamping jig system and FSSW holders. For LBW operation, the team utilised a laser processing head guided by an optical fibre, a wire feeder and a gas supply system mounted in a robotic arm. Joints of different Al-Li and Mg components produced by LBW and FSSW demonstrated reduced weight by 10 % due to rivet removal, less joint overlap material and lower alloy density. Researchers used a new inspection technique, called active thermography, which analyses the thermal response of welded samples to a hot or cold source. Results demonstrated no porosity or defect issues of the optimised specimen. The team also conducted different types of tests to assess fatigue and corrosion resistance. Improved welding technologies for advanced lightweight alloys will boost the competitiveness of aircraft manufacturers and open new markets for the cost-effective metal joining methods. Decreasing the weight of aircraft will enhance the position of aircraft operators and reduce the environmental impact of flight. Overall, the socioeconomic impact of LIGHTWELD results will be significant.
Keywords
Welding, aircraft structures, lightweight alloys, LIGHTWELD, laser beam welding, friction stir spot welding
