The content of fibre-reinforced materials, or composites, in primary aircraft structures continues to grow and with this growth comes the demand for continuous improvements in manufacturing technology.
The most common manufacturing technology for composites used today involves manual stacking of pre-impregnated sheets of material, followed by curing in an autoclave. It uses complex tooling, precludes a high level of part integration and increases assembly effort, making it a labour and capital-intensive manufacturing method.
A novel manufacturing method, often referred to as liquid composite moulding (LCM), uses dry fabric which is preformed into the component shape, placed in a mould, subsequently injected with resin and cured. The advantages of this process are that it is possible to use cheaper materials and simpler tooling. It also enables cheaper processing and part integration, thus reducing assembly costs.
So far, the potential advantages of LCM could not be achieved, because preforming is either a manual process or an automated process with limited scope, such as weaving or braiding.
Developing an innovative technology for the automated fabrication of complex preforms would overcome these problems. It could enable cost savings of up to 40% in comparison with current technology, due to cheaper part manufacturing, less scrap, reduced assembly and increased accuracy.
The objectives of AUTOW were to:
- obtain a fabrication capability for automated dry tow placement of pre-forms, by adapting current machines intended for pre-impregnated composite materials and using innovative tooling;
- obtain dry tow material, which can be thermally activated on command to make it stick to the lay-up tool;
- obtain process window and material properties by fabricating and testing pre-forms and test articles;
- obtain a corresponding design engineering approach to satisfy design requirements and manufacturing constraints, and to exploit the new fabrication capabilities;
- obtain an understanding of the benefits of the new capability versus current fabrication methods, with a trade-off design study for several representative components; and
- obtain a validated new technology by design, analysis, fabrication and test of a full-scale component.
Machine capability for dry tow placement was developed first by carrying out adaptations of existing machines. The machines were then used to determine process window and preforming characteristics. Innovative lay-up tooling was developed, addressing the problem of positioning the first ply.
Material configurations were developed and approaches for the activation of the tackiness of the material was studied.
The materials were tested for compatibility with the adapted machines. Subsequently the characteristics of the preforms were determined: (shape-) stability for handling purposes, and compressibility and permeability for injection purposes. A number of preforms were injected and cured to evaluate the detailed fibre structure for modelling injection and mechanical performance.
A design approach was developed to match the dry tow placement capability to account for the new options offered, such as fibre steering. The envisaged integrated design environment not only combined the manufacturing constraints imposed by the tow-placement technology, but also fabrication issues associated with the resin infusion process.
The new technology was compared to baseline technology and validated by carrying out the complete cycle of design, analysis, fabrication and testing, using a suitable component chosen during a workshop.
The enhancement of the state-of-the-art achieved in this project was summarised, and scope and guidelines for the new method were presented as a manual for future designers.
The Project Results are as follows:
Project contribution to Carbon reduction:
Carbon reduction is achieved through weight reduction of the aircraft structural weight using advanced composites and hereby reduction in fuel consumption. Also using innovative fibre steering and optimised fibre paths the weight of the composite structure is further reduced, in turn reducing fuel consumption and use of raw materials.
Project findings and feasibility:
Air transport has become an essential part of economic and social life. Allowing the further anticipated growth in air transport, sustainable solutions are required to limit and eventually reduce the environmental impact. AUTOW contributes to this through further contributing technical advancement helping political and social feasibility of future air transport.
Other positive impacts:
The technology is a significant improvement over traditional, manual preform fabrication, allowing European manufacturers to create cost effective, lightweight structures while improving quality of work of personnel and their qualifications. Less handwork also reduces health risks, in terms of reduced exposure to irritating materials and separation from cutting operations.
Elements of innovation are the fabrication capability for automated fabrication of dry fibre preforms for composite structures through extending the capabilities of automated tow placement machines and developing compatible material system. This was combined with an innovative optimisation design tool, considering manufacturing constraints and using fibre steering capability of AFP.
Low-cost, lightweight structures are the key to achieving efficient aircraft structures and transportation vehicles in general, with minimised impact on the environment. The results from AUTOW are generally applicable to developing and manufacturing the next generation low-cost, lightweight composite structures.
Whereas for large aircraft manufactures like Airbus and Boeing it almost seems default to use composites and a high level of automated fabrication with e.g. AFP, it is also lucrative for the small aircraft industry and the transport industry in general. Both weight and cost reduction can be achieved using automated composite manufacturing like AFP. Further material cost reduction are achieved through use of dry fibers instead of more expensive prepregs, in combination with LCM instead of costly autoclave curing. The reduction in weight and cost supported by novel design and manufacturing approaches will further facilitate and speed up the introduction of composite lightweight structures in aerospace and other transport industries. Lightweight composite structures contribute directly to reducing fuel consumption and hence GHG emissions of aircraft and other transport vehicles, Moreover weight reduction also allows for reduced power system requirements in turn facilitating electrification.
The AUTOW project has shown the tremendous potential of Dry Fiber Placement (DFP). During the project several AUTOW partners started using the knowledge and experience acquired during the AUTOW project in other projects. One of these is for example the EU project ADVITAC, in which an advanced concept for a composite tailcone is being developed using DFP as one of core technologies. Also NLR has developed and manufactured a dry preform for composite landing gear component, which was exhibited on the JEC in Paris 2011.