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Formula One affiliate sets out new approach to use of carbon composite structures

Formula One affiliate sets out new approach to use of carbon composite structures
Williams Advanced Engineering has published a White Paper to showcase its proprietary, patent-pending innovations in carbon composites and the benefits they offer to the automotive industry and beyond.

Williams Advanced Engineering has published a White Paper to showcase its proprietary, patent-pending innovations in carbon composites and the benefits they offer to the automotive industry and beyond. The company says it has developed a pair of innovative technologies that promise a step-change in the affordability of composite materials.

Known as 223 and Racetrak (discussed in a separate article), these technologies are said to offer comparable performance to existing composites solutions, but with a range of additional benefits, and at a cost that brings them within reach of mainstream applications. They are described as not simply manufacturing innovations, rather they are end-to-end, whole-life solutions that address every aspect of the manufacture, use and recycling of carbon fiber-reinforced plastic (CFRP) and the way in which its remarkable properties can enable new approaches to vehicle design and manufacture.

Composite battery boxes in the FW-EVX, an innovative lightweight EV platform concept from Williams Advanced Engineering, fabricated using the 223 process.

Despite CFRP’s compelling benefits, and recent process advances from the automotive and aerospace industries, a number of factors have held back the mass adoption of CFRP. Chief among these is cost, with traditional composite production methods involving expensive materials and lengthy process times. They also incur a relatively high scrap rate (typically around 30 per cent), compounded by the challenges of recovering the carbon from pre-impregnated off-cuts, and of finding value from the material at the end of the product life.

These challenges have seen the application of CRFP largely confined to niche applications. In the automotive sector, for instance, a body-in-white structure produced with traditional composite techniques is typically around 60 per cent lighter than one manufactured in steel, yet around 20 times the cost. This has limited its application to expensive vehicles manufactured in low volumes, or where the vehicle manufacturer subsidizes the process as part of their learning around new technologies. The innovations from Williams Advanced Engineering aim to address these challenges to unlock the benefits of CFRP.

The 223 process was conceived as a cost-effective means of creating three dimensional composite structures from a two-dimensional form. It is ideal for box-like geometries, such as battery containers for electric vehicles, or potentially even complete vehicle monocoques.

The name is derived from one of the process’s defining features: while composite components generally have to be laid up in their final geometry, 223™ allows the part to be created initially as a two-dimensional component before being folded into a three-dimensional structure.

In particular, 223 suits structures that are currently assembled from many separate components, and where access for fitting-out adds time and cost. A good example is an automotive body-in-white, which typically consists of around 300 metal pressings, made with perhaps 600 different tools; a vehicle bonnet may require four different press operations. Using 223™, the number of pressings could be reduced to around 50, all created on a single machine with a significant reduction in the capital expenditure for tooling.

It is estimated that a weight saving of around 25 to 30 per cent could be achievable on a car’s body- in-white, compared to an equivalent aluminum alloy structure. With 223™, this could be delivered in higher volumes and at a lower cost than a traditional composite solution. Where less strength is required, further cost savings could be made by specifying lower cost materials, for example glass fibers, while alternative resins can be specified to increase toughness and heat resistance.

The heart of the 223™ innovation is a radically different (and therefore 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 the component. For example, a design may employ high-strength carbon fibers as the 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 cost of additional reinforcing components.  The process enables the full benefits of the anisotropy of the material to be exploited, as opposed to a ‘black metal’ approach.

The process 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 materials. At this stage, other components can be easily embedded, such as printed

Next, the matrix is applied using an automated process that allows the composition of the resin to be specified locally across the part, allowing 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 that has yet to be folded.

Williams Advanced Engineering estimates fiber deposition rates of up to 500 kg per hour. Overall, including other areas of process time saving, 223 is up to around 50 times faster than traditional aerospace-grade methods, which lay down material at roughly 10 to 20 kg per hour.

The preform is then fed into an industrial press, where a carefully-controlled force and temperature is applied. This cures the sections that are destined to form the faces of the box, while leaving the hinge areas between them flexible. Thanks to snap curing resins, the pressing process can be accomplished in around three minutes and with a high degree of automation. Energy, cost and time savings are also evident from the ability to maintain the press at a constant temperature, where otherwise the autoclave or press would traditionally go through a temperature cycle, adversely affecting the operational efficiency. Again, a further benefit of the process.

Once removed from the press, the cured areas have sufficient structural strength for additional manufacturing steps to be performed. 223 has been designed to allow transportation of the product to an external facility in this intermediate ‘flat pack’ form, potentially reducing the cost of logistics. In a defense vehicle application, for example, vehicle bodies could be kept flat in storage, with the correct body for the requirement selected and dispatched quickly and efficiently for assembly in the field.

Components can be held in this intermediate ‘flat pack’ form for relatively extended periods (up to 12 months) – currently days, with extended times in development - allowing complex tasks to be performed before the final curing stage is carried out. For instance, on an automotive body-in-white, it could potentially provide scope to fit trim, run electrical / electronic harnesses and install heating ventilation and cooling (HVAC) components with easier, faster access and fewer additional tools.

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.

TAGS: Materials
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