Composite materials, like carbon fibre reinforced plastic (CFRP), are an important part of many modern applications ranging from aircraft to sports equipment. These materials are typically stronger, lighter and more resistant to corrosion than their metal alternatives. Because of this the composites market is growing, with the UK market set to go from £2.2bn in 2015 to £12.5bn by 2030. In order to meet this level of demand the UK will need more people skilled at using composite materials.
Manufacturing with Composite Materials
Composite materials come in an array of fibre types, resin types and forms. The fibres themselves are usually made into fabric-like mats with the fibres either all in a single direction (unidirectional) or woven together to give fibres in multiples directions and some extra stability to the material net. Alternatively, unidirectional layers can be stitched, rather than woven, together to form multi-axial fabrics. The second aspect of a fibre reinforced plastic is the “plastic” element. There is a huge range of available polymers (and even ceramic) materials which can be used as a “matrix” to hold the fibres in place, maintaining their position and orientation. These polymer resins can be impregnated into the fabric with the resulting material referred to as a pre-impregnated, or prepreg, material. If the fabric used does not contain resin, then resin will need to be added or infused at a later stage. Whether using dry or prepreg materials the fabric is cut to shape and size and these plies of material are draped onto a mould. After this step resin is added (if not already pre-impregnated) and the pre-formed part is cured. The curing process varies on the materials used and the process being followed, but this stage is what locks the strong reinforcement fibres into place within the polymer part. This method of manufacture is more complex than using metals because the part’s material is shaped and effectively created at the same time.
The Layup Phase
During manufacture the material plies are laid-up onto the mould surface. In the case of complex parts which have multiple features, curves, corners, ramps etc. the only feasible way to drape the fibres into the right orientation is by hand. Depending on the part this can be a tricky task and requires manual dexterity and understanding of how the material can be shaped. The proper orientation of the fibres is essential to the part both structurally in how it performs and visually in how it looks. In many cases such as in visual carbon fire car accessories, for example, the visual look of the part can determine how it needs to be laid up. In any event, layup is an important step in the process and is in large part done manually. In addition to the physical task of draping the materials, they are also inspected and certified as correct by the person doing the laying up. Once the material is cured there is only limited scope to correct any defects which have arisen during the layup phase.
The people responsible for laying up and, more often than not, inspecting composite parts as they are being made are called laminators or composites technicians. In most instances laminators will have learned how to drape materials and what to inspect for by on-the-job training. The typical process involves following a more experienced laminator and learning by doing. There are some issues associated with training in this way:
- The skills and knowledge are unique to that laminator (operator-dependent skill)
- The underlying skills and knowledge may be difficult to write down, explain or transfer (tacit knowledge)
- The laminator is free to leave, taking their tacit skills with them (mobile)
- The laminators can pick up and pass on bad habits or poor practices (practice transfer)
- Different laminators will train and learn in different ways (lack of repeatability)
- There may be no record of what was learnt by whom and when (lack of traceability)
LayupRITE aims to address the above issues by providing an interactive, digital learning program delivered through the use of Augmented Reality (AR). By doing this the project aims to be able to:
- Train laminators effectively and repeatably
- Provide a record of the training done
- Teach the underlying skills and knowledge of layup
- Increase the rate at which laminators can be trained
This project will do this by leveraging the previous work on material draping and composite manufacture from the Bristol Composites Institute (BCI) and research-backed learning methodologies. Funding for this project has been provided by the Ufi Charitable Trust and the work is being carried out at the National Composites Centre (NCC) in the Bristol and Bath Science Park.