Embracing innovation

Quoted in 1956, Nobel Prize winner Robert Solow said “About 88% of economic growth is created by innovation.” This statement is as true today as it was half a century ago, with the ongoing development of fibre reinforced polymer composites being one of those innovative technologies that continues to drive economic growth.

While the aerospace industry has embraced the advances made in composite technologies since the beginning of the 1970s, the emphasis in their usage has changed over the course of the last 20 years. Whereas previous efforts were mostly focused on structural weight reduction, nowadays economical and ecological considerations are becoming increasingly important. Weight, manufacturing costs, fuel efficiency and other in-service parameters remain core driving factors, but sustainability and component recycling issues are also influencing current development strategies. Thus, modern aircraft design and manufacturing technologies take into account all direct and indirect aspects of operating aircraft.
 
It's all in the design

It is the aim of every major aircraft manufacturer to radically reduce the timescale and cost of the design process for a new product. This has resulted in an increasing reliance upon advanced computational simulation tools, including computational fluid dynamics, manufacturing process simulation and computational structural mechanics, and their associated use within multi-disciplinary design optimisation and virtual product testing.

The QinetiQ Structural Design and Optimisation group specialises in the analysis, design and optimisation of advanced structures, developing novel designs, materials, processes and tools to reduce the mass, cost and process time of composite aircraft structures. For the insertion of a new material system into a structural component, the development of reliable computational models that can predict the material's mechanical and failure behaviour is essential. The applicability and validity of any modelling techniques must be demonstrated at different structural levels. This enables further integration of sub-elements into a more complex component, thus optimising structural weight and reducing assembly steps. For instance, it has been publicised that on the Airbus A310-300 tail fin, a structural weight reduction of 20% and a part count reduction from 2,072 to 96 was achieved by using fibre composite technologies.

Advances made in manufacturing process simulation can also be applied to traditional materials such as aluminium. For instance, the creep age forming process – where the material is heat treated and formed in one step, thereby creating a component with low residual stresses as well as other desirable age-hardened properties – is currently used in the production of Airbus A380 wing panels. Novel computer process simulation and optimisation algorithms were developed at QinetiQ to de-risk the project and to accommodate the creep age forming process into the shift pattern of the work force, thus creating a high quality and cost-effective manufacturing process.

However, deploying latest state of the art design for manufacture processes can lead to highly complex and integrated structures, which consequently require equally complex and expensive manufacturing equipment. For this reason, it is important to find the optimum equilibrium between weight savings and manufacturing costs, recurring and non-recurring, for each individual component. A balanced approach is needed that exploits new materials to their full potential, but avoids pursuing a course of action focused purely on technological benefits without economic and environmental returns.

Manufacturing developments

Over decades, the aerospace industry has gained experience in developing and evaluating manufacturing processes for advanced fibre reinforced composite materials and structures. Considerable knowledge has been acquired throughout the development of advanced composites via the prepreg/autoclave route. However, in recent years, the focus of the industry has been on out of autoclave processing to improve process time whilst maintaining quality and reducing manufacturing costs.

A key focus is on the insertion of new aircraft materials for the dual processing techniques of dry fibre pre-forming and low cost resin infusion. Dry fibre pre-forming avoids the high cost of working with prepreg materials, as the dry fibre can be preformed to near net component shape and the final composite component is then produced by infusing the dry preform with a matrix resin. Advanced fibre pre-forming techniques also offer a highly promising approach for improving the impact performance of composite structures as well as reducing the cost of their manufacture.

To this end, three-dimensional preforms that are manufactured component-specifically using a fully computerised automated robotic 6-axis stitching machine have been developed. These 3D dry fibre preforms can be resin-infused using a number of low cost techniques, including RIFT (resin infusion under flexible tooling), RTM (resin transfer moulding) and Light RTM (also known as VARTM). Light RTM involves the combination of a lower rigid moulding tool (e.g. metal) with a semi-flexible upper tool. This further reduces cost by avoiding the matched rigid tooling used in RTM.

Delamination and debonding are the major failure modes in laminated composites, significantly reducing the performance of a structure under compressive or bending loads. To overcome this problem, new composites with through-thickness reinforcement have been used to improve the inter-laminar strength and damage tolerance of laminated composites.

Recent advances in stitching techniques for composite materials have also included the design and development of special stitching heads, where the head is carried by a multi-axial robot over a static composite fabric to allow large components to be easily stitched. Limitation of access to the fibre part has been overcome by the development of a one-sided stitching technique.

Leading industrial companies are embracing advanced manufacturing through the use of innovative new technologies and state of the art equipment. However, sustained success in manufacturing world-leading products requires continuous development of existing and new technologies, as well as capital investment and a skilled workforce.

Economical impact

The value of state of the art design and automation in high wage economies like the UK is already apparent in today's production plants. Simplifying processes and increasing efficiency is only possible if the diversity of variants can be reduced and similar manufacturing stages can be combined into fewer highly integrated processes. For this development in production to continue will require further R&D efforts, highly skilled people and substantial investment.
 
To this end, it is encouraging to see a concerted effort from universities, R&D organisations, industry, regional development agencies and government to further strengthen the UK's aerospace economy. The fruits of those efforts are already visible, and the recent past has demonstrated that it is possible for such innovative design and manufacturing capabilities to be sustained and grown in the UK.

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