Tuesday, 14 July 2015
Ford gives Mustang carbon fibre wheels
Ford is using carbon fibre for the wheels for the all-new Shelby GT350R track-ready, road-going production Mustang.
In early testing with benchmark vehicles, prototype wheels showed significant potential – improving suspension response times, chassis dynamics, steering feel and ride quality. When the decision was made to pursue this technology for use in a production vehicle, the engineering team was challenged to develop a wheel that met Ford’s strict standards for durability, quality, craftsmanship and premium finish.
Lowering overall curb weight in general is beneficial to a car’s dynamics, but a reduction in unsprung weight (those components not supported by the suspension) can have a significant impact on handling and performance. Less unsprung weight helps vehicles start, stop and turn faster by reducing wheel rotational inertia, dramatically improving response time to driver input. Lower unsprung weight also translates to suspension components not having to work so hard to keep the tires in contact with the road over undulating or broken surfaces.
Although Carbon Revolution has been the leading manufacturer of carbon fibre wheels, both Ford and the supplier recognized significant innovation was needed to meet Shelby GT350R programme needs.
Ford sets high testing requirements for its wheels. Ford wheels must endure tests that include curb strikes, UV and chemical exposure, and extreme heat durability testing. The GT350R wheels would need to fulfil these demands to proceed to production.
The durability of a carbon fibre product is a feature of the type of resin and design intent of the part. The wheels of Shelby GT350R are designed to be stiff, light and resilient.
One of the most severe tests for wheels in the Ford development process involves striking a curb at speed – a test that, without proper design, can cause serious wheel and tire damage. Because of the light weight, advanced construction methods and resins in the wheels, along with the highly-developed MagneRide dampers, the suspension was able to react so fast that the driver wasn’t sure the test had been carried out correctly and ran it twice to be sure. The suspension response was fast enough to greatly diminish the severity of the impact – that’s the power of minimizing unsprung weight.
During track testing of the braking system, the heat developed created rotor temperatures in excess of 900°C. As a result, the wheel design was elevated from a road car specification to a thermal standard more suitable for motorsports.
For decades aerospace companies have treated turbine blade materials subject to extreme heat with ceramic coatings to help improve durability. The technology is also used in top-tier open-wheel racing environments. A thermal barrier coating system developed by Carbon Revolution uses this same technology.
Carbon Revolution’s thermal barrier coating system uses a multi-stage, multi-material coating formulation to provide a thermal barrier.
Using a plasma arc gun to liquefy a ceramic material, the wheels are coated at critical points around the inner wheel “barrel” and on the back of the spokes.
The result is a thin, nearly diamond-hard coating that reliably shields the resin from heat – reducing maximum wheel temperatures and allowing continuous track use by even the most aggressive drivers.
Also, during extreme exposure to harsh UV environments, corrosive salts and road chemicals, it became apparent that to achieve the durability required by Ford, a special coating would be needed to protect the resin from the environment.
In addition, carbon fibre parts are notoriously challenging when it comes to delivering a flawlessly smooth painted surface – the kind of finish Ford demands for all of its vehicles.
Several proprietary new processes were developed that resulted in a robust, high-gloss black finish that looks good and offers a long life for the wheels.
Manufacturing carbon fibre wheels begins with the creation of the preformed internal carbon structure, composed of precisely manufactured carbon strands arrayed into woven fabrics. The elements are then placed into a mould using state of the art manufacturing techniques.
An RFID chip with a unique tracking number is embedded in this structure, and each wheel is individually entered into a quality assurance system. Once this structure is assembled, it is infused with resin and cured at high temperatures.
This process results in a one-piece wheel that ensures maximum strength – eliminating the need to bond or glue the wheel’s spokes and barrel components together.
As the wheel cures, 61 checks and over 246,000 data points are logged before it’s released from the machine. To guarantee quality parts, the cured wheels are analysed using a 3D computerized tomography (CT) imaging process in which more than 18,000 X-ray images are taken.
If the wheel passes inspection, it undergoes machining for the valve stem and mounting hardware holes before it gets painted, coated, assembled, dimensionally checked and shipped to Flat Rock Assembly Plant for installation on a new Shelby GT350R Mustang.
By cutting the weight of each wheel nearly in half compared to an equivalent aluminium wheel (18lb vs 33lb), both handling and acceleration performance experience serious benefits.
The wheels also provide a reduction in rotational inertia of more than 40 percent, which positively impacts acceleration and braking performance. The wheels are so light, the springs and MagneRide dampers had to be recalibrated because the suspension can respond considerably faster to road inputs.