AUTOW: Automated Preform Fabrication by Dry Tow Placement

Background

The percentage of fibre reinforced materials, or composites, in primary aircraft structures continues to grow. With this growth comes 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 cure in an autoclave. It uses complex tooling and precludes a high level of part integration, increasing assembly effort. This is therefore a labour and capital intensive manufacturing method.
A novel manufacturing method, often referred to as Liquid Composite Moulding (LCM), uses dry fabric which is pre-formed 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, reducing assembly costs.

Loading of an RTM mould with its preform

So far, the potential advantages of LCM could not be achieved, because preforming is either a manual process or else an automated process with limited scope, such as weaving or braiding.
An innovative technology for the automated fabrication of complex preforms developed would overcome these problems and 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.

Objectives

The aim of the project is the development of manufacturing technology for automated preforming, with a parallel development of a design capability to match.

The AUTOW project will develop the technology by adapting existing automated deposition capability for pre-impregnated materials (prepregs) with the capability to deposit dry fibre tows, allowing the fabrication of complex preforms. These can then be injected with a cost-efficient, automated LCM process. The complexity of the challenge to develop this new technology is in the multi-disciplinary approach required to adapt, develop and explore:

machine capability,
material format,
process window,
an integrated design engineering approach.

Overview of EADS-DAV AFP-machine in ThermoSet configuration

Critical areas that will be developed are:

Advanced machine and materials expertise to develop a material that is compatible with the machine, will stick to the mould or substrate and allow resin injection in a subsequent LCM-process.
Aerospace expertise to determine the scope and constraints of the new fabrication capability with respect to preform shapes, fibre trajectories and processing parameters for relevant applications.
Expertise in materials modelling, process simulation, structural analysis and optimisation to obtain an integrated design engineering approach for the design of components to be made with the new fabrication capability.

Description of work

ThermoSet Fibre Placement of a generic cylinder with fibre path steering

Machine capability for dry tow placement will be developed first by carrying out adaptations of existing machines. The machines will then be used to determine process window and preforming characteristics. Innovative lay-up tooling will be developed, addressing the problem to position the first ply.
Material configurations will be developed and approaches for the activation of the tackiness of the material will be studied. The materials will be tested for compatibility with the adapted machines. Subsequently, the characteristics of the preforms will be determined: (shape-) stability for handling purposes, and compressibility and permeability for injection purposes. A number of preforms will be injected and cured, to evaluate the detailed fibre structure for modelling injection and mechanical performance. A design approach will be developed to match the dry tow placement capability to account for the new options offered, such as fibre steering. The envisaged integrated design environment will not only combine the manufacturing constraints imposed by the tow-placement technology, but fabrication issues associated with the resin infusion process as well.
The new technology will be compared to baseline technology and validated by carrying out the complete cycle of design, analysis, fabrication and test using a suitable component chosen during a workshop.

The enhancement of the state-of-the-art achieved in this project will be summarised and scope and guidelines for the new method will be presented as a manual for future designers.

Expected results

The project will result in:

A new capability for automated preform fabrication for LCM processes.
Aerospace quality, carbon fibre dry tow material configuration with binder, that can be handled by the machine, will stick to the mould and is sufficiently permeable to allow resin injection will be developed.
Processing windows for fabrication and options and limitations with respect to component shape and tow trajectories
An integrated design engineering approach with software capabilities for design of components using dry tow placement
A validated fabrication capability for the complete design-analysis-fabrication-test cycle for representative component.

The proposed research will contribute to realise a validated fabrication technology for automated preform manufacture with advanced dry tow placement machines, which, in combination with automated liquid composite moulding and cure, enables building composite structures for aerospace vehicles in a fully automatic way. This will result in considerable cost and time savings. The possible cost reduction will strengthen the competitiveness of the European Aerospace industry and is in line with the European Vision for 2020.

Overview of task relations