Advanced Continuous Tow Shearing in 3D (ACTS3D): Advanced fibre placement technology for manufacturing defect-free complex 3D composite structures

Lead Research Organisation: University of Bristol
Department Name: Aerospace Engineering

Abstract

The aerospace industry is the key sector for growth of the UK economy. The potential market share of the UK, which is specialised in the most complicated and high tech aircraft parts, is estimated to be around $600 billion. This enormous market demand was also driven by the environmental issue, which requires the lightweight composite aircraft structures to meet the future CO2 emission regulations.
The automated fibre placement (AFP) process is the core technology that underpins the UK's aerospace industry. This process can lay up carbon fibre tape (or tow) materials on a three dimensional mould surface using a robotic or a computer-controlled gantry machine at high speed, which is mainly used in the aerospace industry to manufacture composite structural components such as fuselages, wings, and spars. The AFP machine's capability of feeding individual tows at different speeds enables steering the fibres within the tows along curved paths, and such fibre steering allows for manufacturing composite structures with complex geometry as well as realising ultra-high structural efficiency beyond the limit of the conventional straight fibre lay-up design. However, it has a few fundamental limitations in fibre steering to produce complex composite components. First, since the AFP machine steers the fibres by bending the tow tape, fibre-buckling defects are always generated. Second, it needs to frequently cut the tows when laying up on a doubly-curved surface that cannot be perfectly tessellated with the finite width tows, which also creates defects such as fibre discontinuity and resin pockets. Such process-induced defects are a critical barrier that reduces the production speed and complicates the design process in the aerospace industry. Furthermore, as the shape of the composite components becomes more complex, the minimisation of such defects in fibre steering process is getting more important.
This project aims to develop a new game-changing fibre placement technology that can produce defect-free doubly-curved composite components, based on fundamental understanding of the impregnation and deformation characteristics of tow materials. The new head mechanism to be developed will be capable of producing variable width tows on-the-fly to cover tessellated sections of a complex 3D surface without gaps. The scientific knowledge on tow-level deformation characteristics will be integrated with an advanced head mechanisms as well as a new head control algorithm in order to realise the buckling free fibre steering using the continuous tow shearing mechanism on complex 3D surfaces. Finally, a prototype head will be tested on a robotic platform programmed using the developed head control algorithm, and the lay-up quality and accuracy will be evaluated using various inspection methods. This establishes a proof-of-concept manufacturing process for complex 3D composite components.
Although the industry is making various attempts to solve the quality problems by modifying the process parameters or the tow material, there are no existing AFP technologies that can either steer the tow without defects or control the tow width. The successful development of this unique and disruptive AFP process will provide the UK aerospace industry with a fundamental solution to the quality problems that they are facing, which enable the UK to be at the forefront of next-generation automated composites manufacturing technology.

Planned Impact

The new AFP process to be developed will be a unique and disruptive automated composites manufacturing technology, which enables manufacturing defect-free complex composite components by using a completely different working mechanism from the current technologies. This game-changing technology will benefit the following groups in different aspects.
1) UK's leadership in automated composites manufacturing
Although the UK has the largest market share in European aerospace industry and is well-known for specialised manufacturing capability of most complicated aircraft parts, the industry is highly dependent on foreign manufacturing technologies in automated composites manufacturing. Especially, the UK aerospace industry is investing multi-million pounds for purchasing the AFP machines from abroad. However, they are still struggling to reduce the defect rate in manufacturing complex composite parts. Without paradigm shift in modern AFP technology, they will face more problems, as more complex components will be required in near future.
The ACTS technology to be developed will deliver great impact to the aerospace industry in many aspects. Its unique capability of steering fibre paths on a doubly curved surface without fibre wrinkling and tow gaps will enable the aerospace industry (e.g. Airbus, BAE Systems, Rolls-Royce) to significantly improve the quality of complex composite components such as wing skins, fuselage panels, spars, and fan blades. Furthermore, such capability will also allow for improving structural efficiency of composite aerostructures through shape and fibre path optimisation. The reduced defect rates will lead to increasing the production rate by simplifying the design process.
2) Industrial research facilitators
Although the AFP technology is essential to the key composites manufacturing process of the UK aerospace industry, there are no UK-based AFP machine manufacturers. The national composites centre (NCC) is a great alternative development route to maximise the national benefit. The new AFP technology to be developed in this project will be transferred to the NCC through their technology pull-through mechanism, in order to establish a manufacturing demonstration cell at the NCC. The NCC could provide the end-users with excellent opportunities to try the ACTS technology for their future products in a de-risking environment. This will attract more international partners to the NCC to exploit various other applications of this advanced AFP technology.
3) Academics working in the field of composites
The AFP process-induced defects are the most critical issues to the researchers working in the field of composites design and optimisation. The ACTS technology will enable them to explore more challenging concepts with wider design flexibility without concerns about the process-induced defects. Furthermore, its completely different working mechanism will motivate the manufacturing researchers to think outside the box escaping from the conventional paradigm in the AFP related research. The ACTS will also derive various research topics on non-conventional mechanical behaviours of fibre steered composites in terms of failure, damage tolerance, vibration, and dimensional stability. Many interdisciplinary researches with other international research groups can be created for the application of this new technology so that the students and researchers can take the opportunities to participate in development process of this cutting-edge technology. The trained students and researchers will contribute to encouraging university and industrial people to understand the new technology and its application to different fields of industries. Their expertise will underpin the value-added manufacturing and knowledge economy that directly benefits the UK. Furthermore, by publishing the research outcomes in high-quality international journals, the UK academia will be able to take the lead in composites manufacturing field.

Publications

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Description The Continuous Tow Shearing (CTS) technology is a world's first automated fibre placement (AFP) process that can steer carbon fibre tapes without defects. The potential of this CTS process has been successfully demonstrated for flat fibre-steered panels, however a significant further technical development needs to be made for 3D complex shapes. A special robot end-effector that can steer and deposit carbon fibre tapes on a mould surface is used, and the robot's movement is the key in achieving high fibre steering quality. For 2D fibre steering, the robot movement is straightforward compared to conventional processes. However, for 3D fibre steering, the movement should be completely different from the conventional way of controlling the robot movement. The aim of this project is to understand the 3D deformation behaviour of the carbon tape material and develop a new robot control algorithm to achieve defect-free fibre steering on complex 3D surfaces, which is not possible with any existing AFP machines.
The key research element is to characterise the deformation of the carbon fibre tape in 3D and find an optimal way to controlling the deformation boundary. The preliminary study founds that the tape could be modelled as a strip comprising elements of 4 bar links, and by detecting the orientation of the bars, the trajectory and orientation of the robot head as well as the trajectories of the tape edges could be predicted. However, the model needs to be fine-tuned based on the material deformation characterisation result, which is being currently carried out in the project.
Exploitation Route The study on the deformation characteristics of carbon fibre tape materials will be extremely useful to other research groups who are focusing on the simulation of the current automated fibre placement process. Since there has been no suitable characterisation method, people have been using the properties of large pre-impregnated carbon fibre sheets, which might not be enough to simulate complicated 'fibre-steering' process. Furthermore, for other research groups working on composites manufacturing could get useful ideas about what the most important material parameters are for achieving high-quality AFP process.
Sectors Aerospace, Defence and Marine,Manufacturing, including Industrial Biotechology

 
Description The designs of the composite components are getting more complex and radical in terms of geometry as well as fibre directions in order to achieve ultra-high structural efficiency beyond the limit of the conventional design paradigm. The process-induced defects in AFP (Automated Fibre Placement) processes have become a critical obstacle for the aerospace industry to develop their future composite products. The Advanced CTS (ACTS) technology, to be developed, will be able to achieve exceptionally complex curvilinear fibre paths on a doubly curved surface without fibre wrinkles and tow gaps. The UK composite industry could use the ACTS to produce advanced composite aerospace components in high-quality; e.g. composite fan blades with an optimal bend-twist coupling effect for maximising the engine performance, new lightweight composite platforms for future unmanned air systems, and civil aircraft wings with improved aeroelastic performance with ultrahigh fuel efficiency. The AFP technology is in the spotlight even in academia since fibre-steered composites can realise a superior structural efficiency to conventional straight fibre composites. However, the quality problems in the fibre steering process have been the most challenging issue for composite designers. The ACTS technology will enable the researchers working in the field of composites design and optimisation to explore more challenging concepts with wider design flexibility without concerns about the process-induced defects. Furthermore, this completely new manufacturing approach will motivate the manufacturing researchers to think outside the box escaping from the conventional design-for- manufacturing paradigm in the AFP related research.
Sector Aerospace, Defence and Marine,Manufacturing, including Industrial Biotechology
Impact Types Societal,Economic