Automating the assembly of aircraft

Citation

(2006), "Automating the assembly of aircraft", Aircraft Engineering and Aerospace Technology, Vol. 78 No. 2. https://doi.org/10.1108/aeat.2006.12778baf.001

Automating the assembly of aircraft

Automating the assembly of aircraft

Keywords: Aircraft, Assembly, Automation

The European aerospace industry is facing major challenges: on one hand intense global competition, on the other the rapid adoption of advanced new materials and construction methods such as the use of composites. Advanced automation offers a means to improve time-to-market and reduce costs, but to manufacture increasingly complex airframe structures will require new approaches to both design and manufacture, coupled to highly specialised manufacturing machine tools and robotic systems.

Assembly of aircraft in the civil sector is rapidly evolving from the age of manual methods to that of automation: there has been no choice but to change. For the makers of aero-structures market forces such as globalisation, intense competition, reduced time-to-market, faster build rates and the need to reduce costs while maintaining strict quality-assurance are the prime drivers.

These factors are forcing all the large players to move from traditional craft based assembly and dedicated hard tooling jigs towards more agile and flexible solutions. Advanced automation plus new management methods including lean manufacturing are seen as vital means to become more competitive and profitable: in short, to ensure survival. In addition, new materials offer much scope for cost and weight-savings and innovation in construction, but also bring fresh challenges as to manufacture and handling, particularly in relation to the use of automation.

Of course, competitive pressure is not confined to Europe and the USA. World-wide outsourcing of components by the two major players – Airbus and Boeing – means that aero-structure sub-contractors in the UK need to continually find new ways to drive down costs. In China – expected to become the world’s largest aviation market after the US – companies like Airbus are not only selling aircraft in that country, but are also manufacturing there. Regarding sales, witness the recent agreement by the European aircraft maker to supply 150 A320 planes to China in a deal worth almost $US10bn (£5.7bn).

According to Airbus, the company will significantly increase industrial procurement from China in the coming years to reach an annual volume of $US60 million by 2007, with plans to double this volume to $US120 million by 2010, including a substantial amount of A380 work. Further, the company has undertaken to transfer the technology required for the manufacturing of the complete wing of the A320 family of aircraft in China. The process began in 2000 with the first two phases of the plan, including manufacture of the leading and trailing edges. This cooperation will be accelerated in the third phase with the manufacture of the wing box in China and Airbus placing more engineers into the Chinese factories. This is a major project as it is claimed Airbus wings are the most advanced in the world.

The movement of knowledge, competencies and technologies has vital ramifications for the UK. Part of the important European Airbus consortium, the aircraft maker’s centre of excellence for wings is in the UK, and that is where they are currently manufactured. Consequently, manufacturers in this country have much at stake in continuing to develop expertise in design and construction. In order to compete globally, new methods of construction must be found that are faster, less costly, consistently accurate and highly reliable. Since manual methods have reached the limits of their performance, this points to a key role for automation.

The challenge of automation

The design and assembly of aircraft has some parallels with that of the automotive industry. Both are concerned with reducing cost and weight, and improving fuel efficiency; each is under pressure to consider end-of-life recycling, or use of recycled materials, reduced emissions and other environmental factors; and they both use sophisticated automated assembly techniques. But the similarity ends there: the automotive manufacturers have been using automation techniques extensively to build mass-produced products at relatively low cost for a long time, whereas aero-structures are mainly low-volume, large-scale products that cost millions of dollars. Now, however, the use of automation is beginning to extend out of isolated areas.

Although aero-structure manufacturers may learn much by studying their automotive counterparts, automated assembly of aero-structures is somewhat unique. Satisfactory repeatability of build standards is rarely achieved by the use of high accuracy components alone. Critically, success depends more on in-depth process knowledge in conjunction with an ability to deliver innovative manufacturing solutions.

The critical success factor above has a very important bearing in relation to new materials being used in the construction of aero-structures. For example, the use of traditional materials such as aluminium alloy is being increasingly challenged by the adoption of new ones, typically carbon fibre-reinforced plastic (CFRP) composites, often in conjunction with more sophisticated aluminium alloys and titanium.

Significant amounts of composites will be used in the innovative Airbus A350 aircraft wing, a structure that also features the use of the latest aluminium lithium alloys, both materials offering important weight savings. The new A380 555-seat, double-deck airliner, due to begin service with operators in 2006, uses substantial amounts of composites: around 25 per cent of the aircraft is made from advanced materials. CFRP will represent 22 per cent and a glass fibre-aluminium laminate (GLARE) will make up 3 per cent, the first time the latter will have been used in a civil airliner. Other first-time initiatives for the A380 include the use of a composite centre wing-box, a vital primary structure that connects the wings to the fuselage, plus a composite rear fuselage section, behind the composite rear pressure bulkhead. Adoption of composites by Airbus on the above aircraft indicates the way forward for the entire fleet as new models are introduced.

Composite issues

Applying automated techniques to the construction of aero-structures made from composites is very different from making vehicles in the automotive sector. It is not therefore as simple as installing conventional robot systems and raises several issues:

Most composite structures tend to be built-up from a smaller number of larger components than their conventional metallic counterparts. These larger components may themselves be formed from a number of simpler elements before final cure. For example, large skin panels may be co-bonded or co-cured with suitable pultrusions forming stringers or stiffening ribs; or very complex three-dimensional components may be assembled from simple preforms which are then injected with resin during moulding (RIM), or they may be fabricated in the mould from less complex “pre-pregs” – previously resin impregnated fibre parts.

Automated handling and lay-up of flexible materials and parts in the pre-cure state poses problems, and handling of large structures is awkward simply because of their size. One of the advantages of the material, its inherent stiffness, also makes it less conformant to mating structures. This can cause difficulties because composite mouldings are usually very tightly controlled on one critical surface (usually the outer mould line or OML) and less controlled on the opposite face (inner mould line or IML). The resultant local variations in panel thickness may be problematic if they occur where the part locates on the underlying structure.

Machining components made of composites is not easy or desirable, not only because parts may be large and difficult to handle, but also the carbon fibres should not be broken. The material’s strength comes from maintaining the integrity of the fibres. For the same reason, interference fit fastenings cannot be used and if the material is drilled there is a risk of the fibre matrix delaminating, unless the area behind is bolstered by intimate contact with a mating component or application of a sacrificial pad. What is more, “fines” or waste material produced by machining is toxic to human beings, so efficient extraction systems are necessary to prevent risk to operators’ health.

Expert resources available

Fortunately, aero-structure makers need not start from scratch. There is much knowledge and experience to draw upon, gained from several programmes developed to automate assembly tasks. Government and industry initiatives, that have drawn together leading research, development and engineering expertise from international academic and manufacturing organisations, have explored ideas and built groundbreaking, practical solutions.

For example, the automatic wing box assembly (AWBA) project set out to show how automation technology could be applied to low volume manufacture of large airliner wings (Plate 1). The key objectives were: the reduction of costs through flexibility of production equipment that enabled it to be re-used for different wing variants; coupled to efficient, safe handling and assembly of very large structures, needed for a new generation of large aircraft.

Plate 1 A340-600 wing assembly jig

DARWin (drilling automation research for wing manufacture), another innovative project, set out to eliminate “global” accuracy issues in automated machinery for aero-structure manufacture. It addressed the problem of accurately drilling the many holes needed to fix panels on wing structures. Conventional machines for this purpose would have to be designed to feature high accuracy over the entire working envelope to achieve the correct position for each hole.

The developers of DARWin recognised a global accuracy approach was neither feasible nor appropriate for such large aero-structures. Despite what the CAD data might specify, in practice the actual location of holes might be affected by thermal growth, accumulated tolerances and other factors. The developers converted the issue of global accuracy to one of local accuracy and repeatability. Put simply, the automated system identifies local features on the aero-structure and from them establishes datum coordinates to enable the machine to work accurately in that defined local area. The project successfully demonstrated that it was possible to drill holes in metallic or composite wings, precisely in the right place and to the right quality using systems with feature based vision navigation and laser normalisation, and at far lower cost than with traditional machines (Plate 2).

Plate 2 DARWin drilling machine demonstrating “virtual template” drilling

The European Commission (EC) Framework 5 (FP5) project ADFAST (Automation for Drilling, Fastening, Assembly, Systems Integration, and Tooling, with partners: Airbus UK (UK), Saab (SE), Airbus España (E), Alenia (IT), MTorres (E), Leica (SW), Hyde Group (UK), Novator (SE) and Linköping University (SE)) set out to develop the technology to make automation affordable. It targeted: innovative orbital drilling equipment to replace many existing drilling operations, new fastening systems with improved control, novel low-cost reconfigurable tooling, and advanced machine control using high-precision metrology systems.

Amongst the ADFAST outcomes was ART – affordable reconfigurable tooling, a universal tool for aircraft assembly, drawing on ideas from conventional, modular, flexible tooling and CNC-control. The result was a new concept based on having a robot to conduct drilling, riveting and the setting/reconfiguration of flexible tooling. It comprised modular static frameworks carrying adjustable locators that may be rapidly set-up by the robot. Static frameworks are built to surround the work volume from modular beam elements connected together using screws. It is possible to rapidly assemble a framework to suit a new family of parts. Changing the static framework (called rebuild) is relatively time consuming and is carried out infrequently, whereas robotic reconfiguration of the adjustable locators is rapid and can be carried out after each part.

The way ahead

Another EC FP5 project – AHEAD – investigated new ways of manufacturing large semi-flexible aircraft components. The Partners were: Fatronik, Sandvik Coromant, AMTRI, TÜV Rheinland, the University of Bath, Gamesa, the University of Lulea, Saab, and Laboratoire d’Informatique, de Robotique et de Microélectronique de Montpellier (LIRMM). The project critically assessed current and expected component fixturing, handling, machining and assembly requirements and developed concepts for automation equipment. It then went on to develop and adapt key new technologies showing the potential to reduce time-to-market and production costs, integrating these in practical demonstrators.

Within this project AMTRI successfully prototyped a combination of novel developments in robotic aero-structure assembly – using the limbs of a passive, lockable parallel kinematic mechanism (PKM) to both stiffen and provide accurate positional feedback to a conventional (revolute) Kawasaki industrial robot. This deployed a very compact three-axis milling and drilling machine optimised for high-speed interpolation – with help from NUM UK (part of Schneider Electric) – to optimise the low-level trajectory software. This novel unit was able to generate features and provide the fine adjustments to correct the residual, but now known, positioning errors of the robot. It incorporated a compact and cost-effective optical guidance, stand-off measurement and surface-normalisation system based on a CCD camera and structured laser light. The stiffness and accuracy enhanced robot manipulator (SAM) also deployed a compact pulse thermography system developed by the University of Bath – that was able to accurately detect the position of rib feet beneath aluminium and composite skins and so was able to fully support single-sided assembly operations (Plate 3).

Plate 3 A rib foot image produced by a compact pulse thermography system developed by the University of Bath. The system accurately detects the position of rib feet beneath aluminium and composite skins, enabling single-sided assembly operations to be achieved

Much knowledge and experience exists in the UK, fully capable of addressing the issues posed by new materials and developing advanced, automated aerospace engineering solutions. As technological and commercial demands become increasingly sophisticated the primary and subcontracting manufacturers are turning to partnerships with specialist resources. Through close collaboration it is possible to achieve better and far more cost-effective results. A number of aero-structures companies and their suppliers in Europe and the USA have already discovered the benefit of investing in this kind of expertise.

Details available from: AMTRI. Tel: +44 (0)1625 425421. E-mail: sholl@amtri.co.uk; Web sites: www.amtri.co.uk and www.hytri.com

(Phil Sholl is Managing Director of AMTRI, a founding partner of HYTRI, a joint-venture with Hyde Group Ltd, the world’s largest, privately owned aerospace tooling design and manufacturing group. AMTRI is an engineering company that possesses a distinguished record of providing advanced research and advisory services, production machinery and production robotic systems to manufacturing industries in the UK and worldwide, including the aerospace sector.

Located south west of Manchester and aimed at leading international aerospace manufacturers and their supply chain partners, HYTRI was formed to help address changes in the industry and accelerate the drive to find more efficient ways to produce airframe structures. The joint-venture company offers a range of technical consultancy services, backed up by the proven ability to design, make and implement complex special purpose machinery and automation systems for the aerospace industry.)