The big composites news in April was Audi’s revelation that it’s next generation A8 would feature a large carbon fibre-reinforced plastic (CFRP) part in its spaceframe. The Volkswagen-owned carmaker joins BMW in a rather exclusive club—those using CFRP in high volumes.
Both Audi and BMW benefit not only from CFRP’s singular set of properties – stiffness, strength and low mass – but also from the material’s bleeding-edge image, which burnishes their reputation for refined luxury and precision engineering.
Ford, on the other hand, has always been known as something of a working-class hero. Truly mass-produced, its vehicles can lack subtly, but usually deliver the goods to those on a tighter budget. However, the US giant could be the most likely candidate to make the next big breakthrough in the struggle to get CFRP into mass-market vehicles.
Ford is no stranger to making bold moves to reduce the weight of its vehicles. Its switch from steel to aluminium for the body of its F-Series pick-up trucks was called its ‘billion-dollar gamble’, but the carmaker felt that eliminating some 300kg of mass from the vehicle was a risk worth taking.
If sales figures are anything to go by, the gamble seems to have paid off, but Ford’s ambitions don’t end with aluminium. It claims to be the first carmaker to mass-produce CFRP wheels. The wheels are almost 50% lighter than their aluminium equivalent, and their increased stiffness improves steering response. The wheels feature on Ford’s Shelby GT350R Mustang and have been developed in partnership with Australian company Carbon Revolution.
Ford is also eying the use of CFRP in structural applications. At JEC World in March, automotive tier-1 supplier Magna International presented a prototype CFRP subframe that it had designed with the carmaker intended for use on a C-segment vehicle – such as Ford’s US Fusion model. The subframe is 34% (or almost 10kg) lighter than a stamped steel equivalent.
The president of Magna’s exteriors business, Grahame Burrow, says: “Lower overall vehicle mass leads to improved fuel economy, but additionally vehicle dynamics are improved as mass is reduced at the front end of the vehicle. As a result, the fore/aft weight ratio moves closer to the optimum 50:50 distribution. Key performance metrics such as noise, vibration, ride harshness, durability and safety are equal to or better than a conventional steel subframe.”
According to Burrow, Magna started working with Ford on this programme in mid-to-late 2016 and the two companies have jointly developed the concept and tooling. He says that Magna brought the tooling into its facility in February 2017 and has started to produce demonstration parts.
“We are close to fully validating the target three-minute cycle time, aiming for 200,000 parts per year,” he continues. “The process is easily scalable.”
The CFRP subframe comprises two moulded parts made from CFRP and four metallic insets—an 87% reduction in component count in comparison with the 45 metallic parts required for a standard steel subframe. These moulded parts are made from EpicBlend sheet moulding compound (SMC), which is compounded by Magna using chopped 50k carbon fibre from Zoltek. Rather than the epoxy resin conventionally used in structural CFRP parts, the matrix used in the SMC is a vinyl-ester modified in-house by Magna. The Magna team says that vinyl-ester adheres well with the carbon fibre and its low viscosity enables it to wet-out the reinforcement effectively, which can be a challenge with 50k fibre.
Short fibre reinforced SMC enables complex geometry to be realised. Three areas of high loading in the part are strengthened with patches made from continuous fibre-reinforced SMC, which are co-moulded with the chopped fibre compound.
Burrow says: “Using this multi-directional fabric and this modified vinyl-ester system provides a boost in material properties where it is needed in the subframe. This allows us to both mould complex geometry, and to increase properties.”
The mouldings are joined using adhesives and structural rivets, although Magna points out that in future this function could be fulfilled using a polyurethane adhesive alone.
The design has passed all performance requirements based on computer aided engineering (CAE) analyses, and vehicle level testing is underway at Ford. The testing phase will evaluate corrosion, stone chipping and bolt load retention, which are not currently measured by CAE.
The team will also develop a design, manufacturing and assembly process with the experience gained during the prototype build and subsequent testing.
Burrow concludes: “We’re taking what we have mastered in the development of Class-A hoods, frontend modules, liftgates and more, and bringing that ingenuity to a structural component, which is the very first mass production capable CFRP subframe.”
Equally interesting is Dow Automotive Systems, which also used JEC World to highlight an epoxy it has developed with Ford and DowAksa for the high-volume manufacture of CFRP parts.
The epoxy (Vorafuse P6300) has been designed to produce prepregs for compression moulding processes, which are tack free, are shelf stable at room temperatures and eliminate the need for costly cold storage. They can be handled, cut, stacked and preformed robotically. In compression moulding, the prepregs can be cured in approximately 120s, leaving 60s of cycle time for tool movement, part ejection and the loading of the next preform.
To demonstrate the viability of Vorafuse P6300, Ford used it to manufacture the front roof header and nose bottom panel of the 2017 Ford GT. Its partners have also used the Vorafuse system in a development project to produce a B-pillar reinforcement for a mass-market vehicles to enable a 6kg weight saving in comparison with metal.
Though Ford’s use of CFRP is currently limited to its high-end models, it has already demonstrated with its switch to aluminium that it has the financial clout and drive to make sweeping changes to the way it produces vehicles. Whether it thinks CFRP is worth the risk remains to be seen, but current indications are encouraging.