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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - OASIS (Optimisation of Friction Stir Welding (FSW) and Laser Beam Welding (LBW) for assembly of structural aircraft parts)

Teaser

Summary

With the development of precision laser beam welding (LBW) and friction stir welding (FSW), it is now possible to fabricate welded aerostructures without mechanical fasteners such as rivets and bolts. 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. Upon completion of the projects, two cargo door demonstrators will be produced, one with friction stir welding processes and one with laser beam welding.

Work performed

TWI has developed weld procedures for three different friction stir welding process variants, i.e. tee-joints, butt joints and lap spot joints. Furthermore, weld procedures were developed for laser beam welding of AA7000 series aluminium T-frame onto a 5000-series aluminium skin, without the use of filler material. A detailed testing programme was prepared by VZLU to accomodate all weld combinations. The testing will be performed in accordance with the relevant ISO and aerospace standards to be directly applicable in the aerospace industry. ROMAERO, with the support from ESAB and TWI, has designed a fixture capable of maintaining the skin completely fixed at all times to prevent any movement because of the high forces involved. The fixture is multifunctional to accomodate both technology demonstrator 1 (friction stir welding) and technology demonstrator 2 (laser beam welding). To facilitate the selection of aluminium alloys, University West conducted Varestraint experiments, which show which alloys can be successfully laser-welded. GEONX is developing a simulation model for laser beam welding, to predict the distortion and residual stress in the welded structures. A detailed description of the work performed is provided in the technical report (part B).

Final results

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 â€œredressingâ€ step is required after the rivets are in position. Moreover rivetless assembly will enable the usage of â€œleanerâ€ parts. Delivering a new cost effective manufacturing route for assembly of aircraft parts (cargo door) to the topic manager and the European aerospace industry, will make a contribution to the range of innovations being addressed within the Airframe ITD initiative in Clean Sky 2 that includes:

- The use of SSFSW (including corner welding) and RFSSW of stiffeners and frames to skins in a T-configuration, with material combination of AA2000 and AA7000 series alloys.
- The utilisation of the AA5xxx series alloy, specifically the AA5028 Al-Mg-Sc alloy, welded using LBW without a filler addition which would greatly simplify manufacturing.
- The use of SSFSW to weld curved panels in a butt-joint configuration.
- The development and implementation of numerical modelling to model the welding processes as their effects on structural integrity, distortion and residual stress for welded cargo doors.
- The development of â€œDigital Twinâ€ to accurately predict the associated costs for the rivetless assembly when fabricating using welding technologies.

Overall in the project, the developments here will prove that by using welding techniques (FSW, FSSW and LBW), â€œleanerâ€ parts can be used to fabricate cargo doors. The lightweighting derives more from the utilisation on â€œleanerâ€ parts being used that than the elimination of rivets in this case. With the use of welding techniques to produce rivetless assemblies, joining time can be reduced, by 40%, than when using rivets.
The development of a manufacturing technology, through welding technologies in OASIS when combined with other fuel consumption reduction steps and engine developments being undertaken in the JTI, will result in the existing fleet of civil aircraft being able to be replaced with more fuel efficient alternatives, with lower emissions.