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EXTRApolation and technical and economic study of a LASER beam welding technology (extra-laser)

Final Report Summary - EXTRA-LASER (EXTRApolation and technical and economic study of a LASER beam welding technology (extra-laser))

Executive Summary:
The Extra-Laser project dealt with the possible installation of a Laser Beam Welding Facility for producing integral aersostructures. The first objective was to record/present the two manufacturing processes of joining / fastening aircraft structures, namely the laser beam welding and the riveting process and to perform a more-or-less generic comparison among them (Deliverable 1). The next objective was to present the technical study for a possible installation of Laser Beam Welding (LBW) infrastructure at Hellenic Aerospace Industry (HAI) and the relative installation cost. Recurring and non-recurring costs of the production facility were also be discussed and briefly analysed (Deliverable 2). The next objective was to present the total manufacturing cost and the derived equations for the cost evaluation of both, laser beam welding and riveting processes. A direct comparison of these manufacturing processes based on the individual sub-processes as well as total manufacturing cost was attempted. Finally, the mechanical tests on laser beam welded AA2198 coupons were presented (Deliverable 3). The next objective was to assess the environmental footprint of the new technology coupled with various parameters such as the consumption of all materials, energy consumption and carbon footprint. For comparative reason, we have also calculated the carbon footprint of the riveted process; a comparison of the carbon dioxide emissions of both methods when mass production took place (Deliverable 4). The next objective was to present the technical risks and the risk assessment for a possible production line at Hellenic Aerospace Industry (HAI) to manufacture Laser Beam Welded stiffened panels as well as to present respective contingency mitigation plans (Deliverable 5). The next objective was to investigate on the manufacturing and production planning as well as respective material requirement planning (Deliverable 6). The final objective was to provide to Hellenic Aerospace Industry all the technical requirements and quality assurance provisions so as to fully comply with the existing industrial regulations (Deliverable 7). A small summary of the project is provided in the last Deliverable 8.

Project Context and Objectives:
Recent interest in reducing the weight of aircraft has focused attention on the use of aluminium alloys and associated joining technologies. Laser beam welding is one of the more promising methods for high speed welding of aluminium. Advanced aluminium alloys for aerospace applications can be welded, thus eliminating thousands of rivets resulting in a lighter and stronger integral structure. At present, fuselage structures are joined by mechanical fastening (stiffened panels). These stiffened panels are light and highly resistant metal sheets designed to cope with a variety of loading conditions. Stiffeners improve the strength and stability of the structure and are able of slowing down or arresting the growth of cracks in the panel. Around 50.000 rivets are needed to join these elements, thus increasing the global weight of the structure. Wings also consist in a skin-stringer-frame structure with the different elements joined together mechanically. Apart from adding weight to the aircraft structure, the mechanical fasteners mean a source of galvanic corrosion that limits the life of these elements.

The 1st objective was the study of extrapolation of a LBW system to industrial conditions:
This study was concentrated on an explicit process description and flow incorporating all involved materials as well as tools, peripherals and auxiliary equipment, the exact process steps and the involved parameters in each step, ending up in the final outcome of the process, which were specified by the Topic manager. The B1 demonstrator of the ECO-Design was selected to be the representative structure (4-stringer flat panel). The reference benchmark process was the traditional riveting for the very same aircraft structure. The considered LBW equipment was a typical industrial type, capable of being integrated in a production line.

The 2nd objective of this project was to issue technical and economic feasibility study of LBW technology:
The methodology adopted and the analysis performed addressed the possibility to industrialize the process in a real environment. Issues of man power and training required were also investigated. The path to bring the process to the production phase was evaluated in a formulated implementation plan by taking into consideration the recurring and non-recurring costs. The required equipment/layouts and possible modifications of existing industrial plant and studying the technical and economical impact deriving from its introduction were also dealt with.
The industrial repercussion during the implementation of the process in the manufacturing plant were also coped with.
An essential aspect within this objective was the assessment of the environmental footprint of the new technology, in which the following parameters were recorded: Consumption of all materials, Energy consumption, Consumables, Operating materials and others, Outputs per reference product unit, all sorts of emissions to environment, all sorts of produced waste (material, heat (for recovery)), identification of any hazardous waste, and recyclability of waste.
A risk assessment plan was produced and the manufacturing plan for end item top assembly were elaborated.

Project Results:
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:
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.

Potential Impact:
The project dealt with the possible installation of a Laser Beam Welding Facility for producing integral aersostructures. Extra-laser proposal contributed to top level objectives through the weight reduction aluminium structures and the development of a cost effective assembling technology adapted to the low density Al-Cu-Li materials family. The combination of advanced materials and technologies reduce the manufacturing time and cost as well as and the aircraft structure weight. Laser Beam Welding is a technology that has been first introduced by European airframers. The application of this technology to new alloys and to regional aircraft structures will help consolidating the technological competitive advantage of the European industry in aircraft design and fabrication. More specific, extra-laser will have the following possible impact(s):
a) Greening of air transport. The environmental impact of the extra-laser project results will be to strengthen the use of laser welding as a clean manufacturing process with low or zero harmful emissions. Furthermore, the increased use of laser welding for integral structures development will contribute to reduce the need for riveting, a very noisy and monotonous process and therefore enhance working conditions with a more peaceful working environment being available to workers.
b) Aircraft safety. By replacing riveting with laser welding, the large reduction in the number of fasteners required will enhance safety by eliminating the many ‘hot-spots’ that exist at fastener holes. Most fatigue failures originate at fastener holes, hence their elimination will enhance the overall safety of the structure. The laser welded structures have improved damage tolerance behaviour due to improved material properties and laser welding process.
c) Developing critical know-how for laser welding to achieve the best balance of microstructure, mechanical properties and process efficiency for newly developed Al-Mg-Li alloy in coupons and structures level. The main concerns for the weldability of AL-Li alloys are for porosity and hot crack susceptibility. With proper selection of process parameters and conditions as well with the proposed development work in the extra-laser project, the investigated Al-Mg-Li alloy could be easily welded in practice.
d) Demonstration of industrial implementation up to component level. Laser welding process will be developed for industrial large-scale laser welding facility that is equal to laser facilities by Premium Aerotec with CO2-lasers. Techno-economical feasibility, viability and environmental footprint of the new technology will be calculated for the first time.
e) Employment benefits and new skills. The innovative joining technology LBW developed in the project is based on cutting edge science capabilities reached after years of intensive research and development. Hence, the project will ensure future prosperity and employment in Europe. The project will provide a boost in welding of lightweight Al-Mg-Li alloy after the exquisite calculations of performance to cost of both technologies. There are many SMEs in Europe where the laser welding technologies are nowadays already being developed for industrial maturity and it is expected that this mass market will grow in the future. Therefore, the new optimized advanced technology especially gives SMEs the best opportunities in a new mass market. The use of laser welding in industrial scale requires high qualified employees, due to the automation level of technology, which is important to secure Europe as a leader of high quality and competitive production technologies. For example, when AIRBUS Germany started with producing welded panels for aircraft structures, they shifted jobs from drilling and riveting to Laser Beam Welding and quality control.
f) The project is in line with the current view within the aircraft industry, that there is a need to reduce manufacturing costs of aircraft structures, while maintaining, and even enhancing, aircraft safety. The integral metallic structure, as a result of this project, will have reduced manufacturing costs due to the reduction in manufacturing time. In addition, the nature of integral structures will automatically reduce the “parts count”, thereby reducing assembly time and costs. The large reduction in the number of fasteners required will lower costs significantly, and the improvements in design procedures will result in a reduction in the premature loss of components.

List of Websites:

Prof. Nikolaos ALEXOPOULOS (nalexop@aegean.gr) University of the Aegean, Department of Financial Engineering
Dr. Nikolai KASHAEV (nikolai.kashaev@hzg.de) Helmholtz Zentrum Geesthacht, Section of Mechanics