Recent developments in the metallurgical field offer now laser weldable Al-alloys of the 2xxx series such as 2198 (Al-Cu-Li) with high structural efficiency index due to their high strength and low density. In the project, butt and T shape welds from third generation Al-Li aluminium alloys were manufactured with the available in-house laser beam welding facilities. Upon the information gained in the project and in-house experience of the manufacturer (HZG) a large, typical aeronautical structure with stiffeners were manufactured and exploited in this project. A similar structure was manufactured by the Topic Manager with the conventional riveting process.
The projects aimed to document the two processes (LBW and riveting), calculate the manufacturing costs of both structures, perform mechanical tests on the structures and finally compare the two structures in terms of the mechanical performance to manufacturing cost index. Besides cost, the environmental footprint of the two different structures were calculated, as well the extrapolation of the LBW process from Laboratory to Industrial environment.
To this end, the intermediate processes were documented, risk assessment was performed and a manufacturing plan of the typical aircraft structure was constructed. Of course, any industrial repercussion during the implementation of the technology in the manufacturing plant was taken into account during calculation of the implementation plan.
It is critical to point out that sensitive data were calculated for the B1 demonstrator of the Clean Sky / JTI platform. To this end, the consortium of the Extra-Laser project have provided and made available to the JTI platform all necessary data for energy consumption of the investigated technology to manufacture such stiffened panels. Worth mentioning is that we, as Consortium, filled in the necessary Life Cycle Analysis (LCA) data that was asked by the JTI in an excel format and actually calculated manufacturing costs and equivalent CO2 emissions of the new technology.
Regarding the Technological Readiness Level (TRL), we assume that the present consortium succeeded to increase the TRL from 3 (analytical and experimental concept) to 5-6, since a representative component, was manufactured and tested in a in a relevant environment. This actually represents a major step up in a technology’s demonstrated readiness.
Among others, the consortium believes that the most important findings of the Extra-Laser project are:
- Weight reduction up to 19% by exploiting only the innovative lower density Al-Li alloys for B1 demonstrator and without changing the structural design of the panel.
- A 25% decrease in yield stress and ultimate tensile strength is noticed, while a 20% decrease is noticed for the fatigue endurance limit of laser beam welded AA 2198-T3. Higher fatigue crack propagation rates were noticed for the LBW specimens.
- B1 demonstrator can be LBW manufactured in 2.17 hours, when 3 work centers work in parallel. This is more than 50% less process time against the respective riveted structure.
- Essentially lower (almost 30%) labor hours are needed to manufacture a LBW B1 demonstrator. More skilled personnel are needed especially for the NDT phase of the structure. By exploiting innovative NDT techniques the time and cost of the last stage could be essentially decreased.
- Total manufacturing cost of LBW panels is significant higher when compared to the conventional riveted structures. This is due to higher purchase price of innovative alloys Al-Li, depreciation charge of LBW equipment and energy cost.
- Although the new process seems to be more energy consuming during the manufacturing phase, it is critical to point out that due to the reduced weight (~20%) of the structure, aircraft fuel consumption will be reduced during the operation phase. Therefore, the lower weight targets on the decrease of the highly pollutant flight phase and this will prove on the long run (life cycle assessment) that the innovative LBW process is an environmentally friendly process.