Work stream 1: Technologies framework for Automated Dry Fibre Placement

This core project investigates the rate and quality limiting factors concerned with the manufacturing of components via Automated Dry Fibre Placement (ADFP). It has been established that the fibre deposition rate is typically less than 1m/s for commercial systems, governed by dynamic limitations such as heavy deposition heads and physical limitations, such as low material adhesion.

However, robustness of the technology is also a primary issue, as machine downtime contributes to limiting production rates. There is the potential to build on other work in related fields as some of these factors are not exclusively limited to the ADFP process and are being addressed by automation and machine design within the manufacturing industry, including the drive towards Industry 4.0.

The project work packages have been developed to align with each stage of the manufacturing process.

These include 4 key areas:

1. Using simulation tools to establish the suitability of ADFP for specific components and to optimise processing parameters;
2. Studying the application of the binder to enable low cost tow-based fibres to be utilised;
3. Using high rate data acquisition to accompany closed-loop control to overcome machine and material variabilities;
4. Tailoring the permeability of ADFP materials, by taking advantage of different layup strategies using gaps and data collected during the deposition process.

The overall aim is to understand the rate and quality limiting effects in the ADFP process, by developing numerical models to increase understanding of the critical factors. The project has the following objectives:

1. Developing laboratory scale equipment to determine hardware limitations and ‘course-by-course’ control of the deposition apparatus.
2. Develop real-time data acquisition methods to accompany the construction of the laboratory equipment and to support the development of the numerical models.
3. Investigate the fundamental structure of the tow/NCF, in order to optimise the binder content (type and volume) to provide optimum tack and to prevent fibre fuzzing during deposition.
4. Characterise the binder tack properties with respect to fibre laydown rate and temperature, studying the compaction of single tows or ply stacks and their interactions with the deposition roller.
5. Quantify the permeability of the ADFP fibre architecture post deposition and relate it to geometric features and processing rate.
   

   Figure 1. Finite Element simulation of compliant roller and compliant dry fibre bed. The output from this model is used to provide pressure distribution information for a multi-physics compaction / binder curing preform simulation which ultimately will be used to provide real-time control of the deposition head.

Previous development of the ADFP process has focussed on optimisation of materials to suit the existing deposition heads, this has resulted in a costly material which behaves much like a pre-impregnated slit fabric. This project attempts to rethink the process philosophy from first principles by developing deposition technologies which use materials in their lowest cost raw form. This has required the development of multi-physics models to describe the complex behaviour of the easily deformed materials.

Using a novel real-time control methodology the developed models are able to impact real-time operation of the developed sensor-rich ADFP test rig in order to create preforms with higher quality than existing methods and to build a digital twin of the preform to collect manufacturing data and inform downstream processes.

The developed test rig uses a post-processor-free approach where parts are manufactured direct from the CAD model of the part, this is facilitated by a new data format for storing ply / course data.

A novel method for determining the infusion characteristics of the manufactured preforms is also under development. The permeability of gapless preforms is very low and so the infusion process can be lengthy for complex parts. A detailed study is underway into the optimisation of gaps within the preform which serve to improve the permeability without compromising mechanical properties. In the longer term, computationally efficient models of actual as-deposited preforms will inform the infusion process on the shop floor.

Figure 2. Dry fibre preform showing deposited tows, edge crenulations and evidence of gaps and overlaps. Permeability of the preforms is highly dependent on the gap size making an accurate representation of the as-manufactured fibre architecture important.

Figure 3. Test bench developed for resistance heating trials. Temperature data is gathered via IR thermocouples at 150ms intervals and used to control the power input to the tow in realtime accounting for environmental temperature and tow resistivity changes as well as dynamic nip-point temperature requirements.