Williams Advanced Engineering has published a White Paper to showcase two proprietary, patent-pending innovations in carbon composites and the benefits they offer to the automotive industry and beyond. The first process, 223, was conceived as a cost-effective means of creating three dimensional composite structures from a two-dimensional form is discussed in a separate article. Here, PlasticsToday looks at the second process: Racetrak.
|A composite wishbone made with the Racetrak process used in the FW-EVX.|
Racetrak is a novel process for creating very high strength structural members that link two or more points, such as automotive wishbones or the link arms of aircraft landing gear. The technique draws on a proven design concept, where a continuous loop of unidirectional material — in this case carbon fiber — provides extremely high hoop strength. This localization of very high embedded strength allows substantial cost reduction which, when combined with high levels of automation, allows an affordable component that is dramatically lighter than traditional alternatives.
In the case of a wishbone for an automotive application, the finished part could be around 40 per cent lighter than the equivalent forged aluminum item and up to 60 per cent lighter than steel, making it cost — competitive with a premium aluminum forging. This puts it in line with the automotive industry’s budget for weight saving technologies, estimated at €5 to €7 ($5.65–7.90) per kg in a recent report by McKinsey & Company. Further, up to 80 per cent of the material can be drawn from recycled sources, helping to solve the growing challenge presented by end-of-life carbon composite components.
Racetrak parts consist of three main components: a core of low cost, non-woven bulk material, a loop of unidirectional carbon fibre and on both sides of this, a protective shell made from die-cut woven fibre sheet. Manufacturing is fully automated, with the unidirectional loop robotically wound to create precise, repeatable tailored fibre placement. This reinforced material preform is then placed dry into a tool, which applies a light shaping pressure to create a removable cartridge.
This is placed into an industrial press, where 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. The composition of the system also contributes to an attractive price/performance ratio as the costliest 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 sheer strength and damage tolerance.
The system allows a choice of resins, for example polyurethane instead of the more conventional epoxy resin, increasing the toughness of the system as well as reducing the cost, with the option to further increase energy absorption by adding ductile materials such as ground end-of-life CFRP. Polyurethane resin is also an effective adhesive, allowing in-mold integration of fixings and other components. For increased resistance to high temperatures, a phenolic resin could be specified.
The Racetrak process takes its name from the continuous loop of fibre around the load bearing area, said to resemble 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.
As with the new 223 process, automation ensures repeatability, removes the need for skilled labour, reduces cycle times and minimizes the quantity of premium material that is required for unidirectional lay-up. Each tool costs around one tenth the cost of a steel tool, making smaller production runs more affordable. The same tool can also make similar shaped components of different specifications, simply by changing the composition of the cartridge.
Williams Advanced Engineering proposes that with savings in process time, skilled labour, materials and capital investment, Racetrak will allow high strength, light weight composite components to be used in applications where CFRP was previously too costly.
Like 223, Racetrak also brings additional benefits, most notably 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 sensor could, for example, be used to measure torque or to identify internal failures resulting from out of tolerance stress.
Racetrak is also environmentally attractive because it requires little energy, and because the bulk material used in the core can be created from the multidirectional carbon created from 223 and Racetrak manufacturing scrap. It can also use a high proportion of ground material created from end-of-life recyclate, helping to solve the current challenge of how to recover and re-use carbon components from end-of-life vehicles as required by legislation, such as the European End-of-Life Directive.