A Step-change in the Cost of CFRP

Williams Advanced Engineering reveals secrets behind its innovations aim to move carbon fiber into the mobility mainstream.

May 1, 2019

Stuart Birch

The new CFRP processes were used to create the FW-EVX electric-vehicle chassis. (Image credit: WILLIAMS ADVANCED ENGINEERING)

A joke in the auto industry about CFRP (carbon fiber reinforced polymer) is that the “C” stands for “costly.” So, any manufacturing process that solves this significant drawback of the ultra-lightweight material’s use outside of Formula One racing and exotic supercars, could change the vehicle-production game.

Engineers at Williams Advanced Engineering in the U.K. are confident they have developed two complementary solutions to the cost hurdle. Revealing details of both, the company stated these solutions could be applied to high-volume production by 2021.

The patent-pending innovations are respectively called 223 and Racetrak. They are claimed by Williams to deliver “a step-change in the affordability of composite materials,” while offering comparable performance to existing composite solutions. This potentially brings the cost within reach of mainstream applications and will be a timely arrival for autonomous vehicle applications. Other innovations in the development pipeline are aimed at delivering savings in process time, skilled labor, materials and capital investment — all “unlocking the benefits of CFRP,” stated the company.

Given the cautious and conservative nature of the automotive business, Williams has taken the unusual decision to reveal much of the detail technology and processes that support 223 and Racetrak, and the development that could lead to high volume production.

Racetrak layered content consists of 80% recycled carbon fiber. (Image credit: WILLIAMS ADVANCED ENGINEERING)

Iain Bomphray, the company’s chief technology specialist for lightweight structures, is the innovator of both new technologies, fitted to the company’s FW-EVX electric-vehicle (EV) platform concept. Revealed in 2017 and previously described by AE, the two CFRP technologies have essentially remained secret until now.

As a cost-effective means of creating three-dimensional composite box-like structures from a two-dimensional form, 223 is claimed to be ideal for a variety of applications, from battery containers for EVs to potentially complete vehicle monocoques. The use of the name 223 derives from the folding of a 2D component into a 3D structure.

Describing 223’s “wide array” of capabilities, Bomphray says it particularly suits structures that are currently assembled from many separate components and where access for fitting-out adds time and cost. For example, a vehicle body-in-white (BIW) typically consists of around 300 metal stampings, made with perhaps 600 different tools. A vehicle hood may require four different press operations. Using 223, the number of stampings “could be reduced to around 50, all created on a single machine, bringing a significant reduction in the capital expenditure for tooling,” he said. A monocoque structure made using 223 could be up to 30% lighter than an aluminum-intensive structure.

Racetrak and 223

Racetrak is a process for creating extremely high-strength CFRP structural members that link two or more points. Suspension control arms/wishbones are an example. “The technique draws on a proven design concept: a continuous loop of unidirectional material (in this case carbon fiber) to provide extremely high hoop strength,” Bomphray explained. “This localization of high embedded strength allows substantial cost reduction. When combined with high levels of automation, this allows an affordable component that is dramatically lighter than traditional alternatives.”

A finished wishbone could be some 40% lighter than an equivalent forged aluminum component, he said, and up to 60% lighter than steel. It could be cost-competitive with a premium aluminum forging and in line with the global auto industry’s budget for weight-saving technologies estimated at up to 7 euros/kg in a recent McKinsey & Co. report.

223 is based on what Bomphray calls “a radically different [and therefore partly still confidential] process for the integration of woven, dry fiber reinforcement sheet with a separately-prepared resin matrix. The technique provides “unprecedented freedom” to optimize both elements to the specific requirements of a design across a component. For example, a design may employ high-strength carbon fibers as reinforcement in structurally critical areas, while low-cost glass fibers could be used in others.

Costly materials are used only where their benefit is required, and local strength can be provided without the expense of additional reinforcing components. “The process allows the full benefits of the anisotropy (variations in physical properties along various axes) of the material to be exploited,” he explained.

The construction of an EV battery box begins with an automated cutter trimming the flat sheet of woven fiber into near-net shape. The excess material from this process is dry, untreated fiber, which is substantially easier and more cost effective to recycle than traditional pre-impregnated (“pre-preg”) materials. At this stage, other components such as printed electronics and energy-absorbing materials can be easily embedded, Bomphray stated.

The matrix then is applied using an automated process that facilitates the composition of the resin to be specified locally across the part. This allows properties such as toughness and thermal conductivity to be varied across the component. At this stage, the preform is still a flat, two-dimensional sheet, like a cardboard box before being folded.

50X faster

The 2D to 3D CFRP forming process as envisioned in a factory rendering. (Image credit: WILLIAMS ADVANCED ENGINEERING)

Bomphray estimates fiber deposition rates of up to 500 kg (1,102 lb) per hour. Overall, including other areas of process-time saving, 223 is said to be as much as 50 times faster than traditional aerospace-grade methods, which lay down material at roughly 10 to 20 kg (22 to 44 lb) per hour. The preform is fed into an industrial press for application of carefully controlled force and temperature. This cures the sections that are destined to form the faces of the battery box, while leaving the hinge areas between them flexible.

Using snap curing resins and a high degree of automation, the pressing process can be accomplished in around three minutes. Energy, cost and time savings are also evident from the ability to maintain the press at a constant temperature; otherwise, the auto-clave or press would traditionally go through a temperature cycle, adversely affecting the operational efficiency.

Once removed from the press, the cured areas have sufficient structural strength for additional manufacturing steps to be performed. Finally, the part is placed in a jig, where it is folded into its finished three-dimensional form. It then undergoes a final curing stage, which solidifies the hinges and seamlessly joins the edges of the adjacent panels to create a perfect three-dimensional shape.

223 has been designed to allow transportation to an external facility in intermediate flat-pack form, potentially reducing the cost of logistics. Williams Advanced Engineering sees the process being suitable for introduction into many aspects of the auto industry including defense.

“We imagine that vehicle bodies would generally be made in factories, but other 223 products such as parts or simple storage or cargo boxes could be stored flat and completed in the field.

“Components can be held in the intermediate flat-pack form for relatively extended periods of up to 12 months (currently this is days, with extended times in development) allowing complex tasks to be performed before the final curing stage is carried out,” Bomphray said.

On an automotive BIW, it could potentially provide scope to fit trim, run electrical harnesses and install heating ventilation and cooling (HVAC) components with easier, quicker access and fewer additional tools, he explained. With the 223 process, automation ensures repeatability, removes the need for skilled labor, reduces cycle times and minimizes the quantity of premium material that is required for unidirectional lay-up.

Bomphray said each tool costs around one tenth that of a steel tool, making smaller production runs more affordable. The same tool also can make similar shaped components of different specifications, simply by changing the composition of the cartridge.

Additional benefits include the ability to embed components such as thin-film sensors (which can be just 6 μm thick) and bearings, effectively removing another step from the current production process. Thin film sensors could, for example, be used “to measure torque or to identify internal failures resulting from out of tolerance stress,” he said.

Racetrak: How it’s done

The Racetrak process takes its name from the continuous loop of fiber around the load bearing area, regarded as resembling a race track when viewed from above. For maximum strength, carbon fibers are specified for this loop, but other fibers could be used. Fibers such as glass could be incorporated in the resin matrix to provide additional strength and toughness.

There are three main components: a core of low-cost, non-woven bulk material, a loop of unidirectional carbon fiber and, on both sides of this, a protective shell made from die-cut woven fiber sheet. Manufacturing is fully automated, with the unidirectional loop robotically wound to create precise, repeatable tailored fiber placement, Bomphrey said.

The reinforced material preform is then placed dry into a tool, which applies a light shaping pressure to create a removable cartridge to be placed into an industrial press. A vacuum is applied and the resin is injected into the heated mold. Under these conditions, the resin takes approximately 90 seconds to cure. It is then ejected from the machine and a fresh cartridge loaded.

“With a cycle time currently at just 120 seconds, a single press using this process can produce more than 500,000 units a year” added Bomphray. “The composition of the system also contributes to an attractive price/performance ratio as the most costly materials, notably the unidirectional carbon fiber, are used only where their unique mechanical properties are required to deliver high local strength, for example to link anchorage points. The woven shell increases load distribution across the component and enhances both shear strength and damage tolerance,” he claimed.

The system allows a choice of resins, polyurethane, perhaps, instead of the more-conventional epoxy, increasing the toughness of the system as well as reducing the cost. There is an option to further increase energy absorption by adding ductile materials such as ground end-of-life CFRP. Polyurethane resin also is an effective adhesive, allowing in-mold integration of fixings and other components. For increased resistance to high temperatures, a phenolic resin could be specified.

Adding sensors to capture data

Automated driving could also emphasize the need for affordable composites in the automotive sector. More mass means substantially more energy consumption to offset. It also begs the question of how this technology will be integrated into the platform. The use of composite processes such as 223 and Racetrak bring the prospect of more flexible design, while both these technologies support the use of embedded thin film sensors.

One possibility is turning wishbones and other CFRP components into calibrated load cells that could transfer road-load data back to the vehicle via wireless electronics. This would not only allow a vehicle manufacturer to capture anonymized usage data, it would also have practical applications at a vehicle level, measuring real-time loads applied to a component. An example is a wish-bone providing data that can be used to infer lateral grip, for use by the stability control input.

Explained Paul McNamara, Williams Advanced Engineering’s technical director: “As tools for efficiency improvement, these [223 and Racetrack] are all synergistic, considering them as an integrated system allows us to increase significantly the total benefits.”