Nissan says it has developed a “breakthrough” carbon fibre production process which may pave the way for the material to be used in more mass-market cars. According to Nissan, the process quickens the development of carbon fibre reinforced plastic (CFRP) – carbon fibre that has had a resin applied to it to strengthen it.
CFRP can be up to twice as strong as steel and four times as strong as aluminium, yet is half the weight of steel, according to a Nissan presentation. Lightweight yet extremely strong, the material can be used to make cars safer and more fuel-efficient, and can also lower a vehicle’s centre of gravity when applied to upper body parts.
Currently only using CFRP in the GT-R Nismo sports car, Nissan aims to use the new process to mass-produce CFRP parts and introduce them into more cars. The company says the innovation can cut development lead-time by up to 50 per cent, and cycle time for moulding by about 80 per cent compared with conventional methods.
Carbon fibre is expensive compared with other materials such as steel and aluminium. The company says it costs about 10 times as much as steel parts, blaming the price and difficulty of shaping CFRP parts for hampering the mass production of automotive components made from the material.
Existing methods for making CFRP were quite slow. The conventional process of impregnating carbon fibre sheets with resin and leaving them to cure in a vacuum-sealed autoclave under high pressure takes about 3 to 4 hours.
The invention of resin transfer moulding greatly sped up this process. Instead of using an autoclave, carbon fibre is cut into the right shape and set in a mould. Resin is then injected into the mould at high pressure and left to cure at high temperature. According to Nissan, this process only took 10 minutes – a massive improvement over the autoclave.
Nonetheless, this was still too slow for carbon fibre to be used in mass-production and Nissan attempted to refine the process, ultimately resulting in the breakthrough that the company calls compression-resin transfer moulding (C-RTM). This modified process introduced a gap into the mould between the upper die and the carbon fibre inside. The resin is then injected at the same time the mould is gradually closed and the carbon fibre pressed, while the inside air is drawn out to create a vacuum, causing the resin to rapidly permeate every corner of the carbon fibre. The resin is then rapidly cured at 120°C, resulting in a completed piece of CFRP in just two minutes – the 80 per cent saving the company originally referred to.
Nissan said it originally still encountered problems with this process – some of the carbon fibres would bend when pressed, or some of the resin would harden prematurely before impregnating all of the carbon fibre. Company engineers then developed techniques to accurately simulate the permeability of the resin, creating a transparent die and using temperature sensors to gain better visibility into the behaviour of the resin flow. While it previously took about three attempts to get the carbon fibre to cure properly, the new simulation techniques allowed it to happen properly on the first attempt, turning the new process into a reliable one.
According to Hideyuki Sakamoto, Executive Vice President responsible for Japan manufacturing and supply chain management at Nissan, the company hopes to apply the new C-RTM process to cars that will go on sale around 2024 to 2025. The company was optimistic that it could save as much as 80kg in weight from a typical SUV just by converting its front and centre pillars, as well as the centre tunnel, to CFRP.