Re-engineering the wheel - Alcoa's forged wheel

Materials World magazine
,
1 Jun 2009

The impact of wheel weight is being increasingly felt by today’s vehicle engineers as they strive to reduce CO2 emissions. Better use of materials can meet this reduction and boost performance, says UK-based David Yates, Marketing Manager for Alcoa Forged Specialty Wheels, Europe.

Vehicle stylists crave a larger wheel, and with dimension creep and pedestrian safety legislation raising bonnet lines, wheels have been growing proportionally over time. This has led to compromises in ride, handling, performance and weight. The latter has an adverse affect on CO2 emissions.

Forging a smaller footprint

Alcoa Wheel Products, a business unit of USA-headquartered Alcoa Inc, has been developing, producing and supplying alloy wheels to the global automotive industry for 60 years. With the parent company involved in all elements of aluminium manufacture from mining to recycling, the firm believes it can offer maximum design benefits from extraction to finishing.

According to the company, carmakers seeking simple and cost-effective solutions to lower CO2 on existing and future vehicle programmes should consider simply changing wheels. It suggests that by switching to a forged alloy wheel, makers can achieve an immediate drop in unsprung weight, which can lower emissions. Reduced weight also offers performance and fuel efficiency gains, as well as allowing stylists creative freedom without the engineering compromise.

‘Our analysis shows an optimised forged wheel, as opposed to a cast or two-piece alloy, can actually save up to 39kg per car,’ explains David Yates, Marketing Manager for Alcoa Forged Specialty Wheels, Europe ‘This is based on a 19” US SUV wheel, but a recent programme for a European sports car manufacturer demonstrated a saving close to 10kg over their current cast wheel.’

Alcoa’s engineers calculate that a 45kg decrease in weight equates to a fuel economy improvement of 1.5%. Such reductions, achieved with a change in material or material processing and design, mean engineers are considering an alternative to the traditional cast wheel.

Forging ahead

Casting is the traditional and cost effective method of wheel manufacture. However, Alcoa believes forging offers an immediate solution, even on an existing vehicle platform. As opposed to cast wheels, the alignment of the aluminium grain structure is retained with forged wheels. This offers improved strength and durability that, with appropriate design, can lead to a significantly lighter wheel.

‘Reducing the unsprung wheel weight can improve vehicle dynamics and reduce inertia,’ claims Yates. ‘This is a further way to improve handling or acceleration, with minimal cost and testing, on an existing car.’

The company says a forged wheel offers more design flexibility, allowing for more material to be machined out, creating sharper detailing without diminishing strength and durability. For example, designers push for the spoke rim interface to be as tight as possible. Some manufacturing processes inhibit this, and radii and fillets have to be introduced to allow for draft angles.
The design flexibility is helping manufacturers offer several options from a single blank. ‘[One] single blank can be machined into five or six variants,’ says Yates. ‘We are already offering this in the USA, with a single blank delivering six different SUV wheels.’


Whole life wheel

Alcoa has also been looking at enhancing the wheel’s performance long after it leaves the factory. Research from customer satisfaction surveys suggests that wheel condition and maintenance is important to drivers and should be a design consideration. To achieve this, Alcoa developed Dura-Bright technology to improve the wheels’ perceived quality by making them easy to clean, maintain and keep free from corrosion.

Traditional alloy wheels rely on lacquer as a finish and protection against the elements. During heat cycling, brake dust and grime can penetrate the lacquer to create a yellow discolouration or black specks that cannot be removed. Furthermore, the lacquer is easily damaged by kerbing.

Dura-Bright technology is an integrated surface modification and polymerisation process that aims to improve durability in corrosive environments. Compatibility with the physical microstructure of the alloy maximises adhesion, resulting in chemical bonding and eliminating filiform corrosion. It is, the company says, resistant to dirt, brake dust, oil and road grime, preventing surface dulling.

Further information: Alcoa