With great fanfare, supercar manufacturer McLaren announced in January that its second-generation Super Series vehicles would be created around an ultra-lightweight, carbon fibre reinforced plastic (CFRP) monocoque. Immensely rigid, yet weighing less than the CFRP and metal cockpit architecture of the first-generation Super Series, the new monocoque will contribute to an 18kg weight saving compared with a comparable McLaren 650S.
With a six-figure price tag though, it would be more surprising if the car did not feature the extensive use of CFRP. For most of us, it leaves us wondering if cheaper, higher-volume cars will ever really get the benefits that composites offer?
Currently BMW is the only carmaker to be using CFRP in anything approaching high volumes. Other mainstream OEMs have, so far, been put off by the high price of CFRP, the extensive capital investment needing for production tooling and the relatively slow processes used to form parts. The issues are extensive and venture across design, manufacture and skills – and implementation for automotive firms takes some serious investment and belief that this is the way to go.
That belief does exist though, but rather with a single OEM, it is the UK that is trying to position itself to take advantage of the potential opportunity. The Government is currently funding a wide range of projects that are principally seeking to establish a viable supply chain for the mass-production of composites. Heading the charge is the ‘Thermoplastic Overmoulding for Structural Composite Automotive Applications (TOSCAA)’ project.
Led by carbon fibre manufacturer SGL Carbon Fibers, it is backed by a £2 million Innovate UK grant and is slated to take 18 months. In addition to establishing a carbon fibre supply chain, its aim is to develop the affordable use of carbon fibre reinforced thermoplastic (CFRTP) in the manufacture of cars. Eagle-eyed readers will note the slightly different acronym, which marks a move away from conventionally used thermoset resins.
In contrast to thermosets, thermoplastics harden when cooled yet retain their plasticity – allowing them to be remelted and reshaped, and therefore more easily reused and recycled. Once melted thermoplastics harden quickly at relatively low temperatures, meaning that reinforced thermoplastic parts can be produced rapidly in short cycle times.
The vision is that continuous CFRTP blanks will be compression moulded into parts to form a load-bearing structure and then overmoulded to a net shape – imparting extra localised strength or functionality – with cheaper short fibre reinforced thermoplastics using injection moulding.
Chief executive of project partner Surface Generation, Ben Halford, says: “Injection moulding is a phenomenal process because parts just come out right. Composites don’t tend to come out net-shaped; they usually need some post processing.”
Initially this will be a two-step process, but in the future project partners hope to be able to carry this out in one hit.
Jaguar Land Rover (JLR) is also working on the project, and as such TOSCAA will target production volumes in the low six figures, mirroring those of the luxury carmaker. Crucially, the TOSCAA partners are attempting – as much as is possible – to make use of existing infrastructure so that the adoption of their processes are less daunting for OEMs and their suppliers.
AMRC Composite Centre Partnership lead, Hannah Tew, says: “Our role within the research project is to look at how preformed blanks can be made cheaper, faster and stronger, using less material to produce lightWeight composite automotive assemblies.”
The AMRC Composite Centre will also investigate 3D weaving of carbon and thermoplastic fibres to produce preforms, instead of traditional 2D weaves, which commonly fail as a result of delamination.
“The 3D weaving will provide different material properties for the preformed blanks than traditional 2D technology,” says AMRC Composites Centre researcher, Dr Hassan El-Dessouky. “This is set to improve performance and make it cheaper and quicker to produce. It is hoped we prove that less material will be needed making 3D woven CFRP more cost-effective.”
Research will also be carried out to see if the way the carbon fibres are orientated during weaving affects the production and quality of the composite, potentially reducing weight even more than is possible using standard processes.
TOSCAA will also look to exploit Surface Generation’s Production to Functional Specifications (PtFS) process. PtFS encompasses a range of active thermal management technologies that enable localised heating and cooling to be adapted in a mould in real-time during part production.
Using the process, the mould surface is divided up into separate heating and cooling regions known as ‘pixels’, each having an independent circuit of fluid flowing through it, which can be varied on-demand to locally heat and cool the mould face. By altering the pixel fidelity and power density, users can process fully integrated composite structures with highly tailored cure profiles up to 450°C.
“If you think of a chess board, each square is heated and cooled on demand and controlled independently,” says Halford. “It gives you the ability to handle particularly complex structures with different materials and different section thicknesses.”
The process is suitable for single and matched tooling applications, including vacuum bag, resin transfer moulding (RTM), compression moulding and injection moulding using thermoplastic matrices.
PtFS is already being used by global automotive, aerospace and consumer electronics manufacturers to improve the quality and throughput of compression and injection moulding applications, and will be developed further over the course of the TOSCAA project.