Casting Around for Lightweighting Solutions

A large and complex molding for the innovative sand casting techniques that are a Grainger & Worrall forte. (Grainger & Worrall).

“Get more [efficiency] from less [weight, time, cost],” is a mantra that will be chanted sotto voce by many an automotive designer and engineer facing the latest list of a new vehicle’s “requirements.”

A complex multi-process casting created by U.K. casting specialist Grainger & Worrall. (Grainger & Worrall)

Many propulsion solutions are possible, some of them subtle developments of established processes and methods that can bring new opportunities for application within a rapidly-changing industry. But they are not all focused on the design of pure EVs; the internal combustion engine will remain a mainstay of production vehicles—the majority used hybrid configurations—for many years to come, but there are crossovers between the two competing solutions.

Keith Denholm, technical director of Grainger & Worrall, U.K.-based specialists in the design and manufacture of complex castings, is confident that major developments in aluminum casting technology are leading to what he calls “new and imaginative solutions,” facilitating more-efficient vehicles to be brought to market faster, with reduced technical risk.

“The days of producing a prototype component which had little in common with the final part except its dimensions, are firmly over. We are now able to achieve production-quality structural castings during the prototype and ramp-up stages of production which closely mimic the intended production part in all essential characteristics.”

Denholm is a believer in the “Make Like Production” concept (pioneered by the Warwick Manufacturing Group, based at the U.K.’s University of Warwick) in which the finished part behaves like a production component, enabling useful validation to be carried out—even though the manufacturing process and materials used may be quite different. This is underpinned by using quality systems more akin to production than prototypes, enabling verification and traceability of all parts.

Cost effectiveness

The battery pack for an EV typically forms an integral part of the vehicle structure and requires very effective sealing to optimize battery cooling. While a production part may be made from extrusions, or hydroformed using expensive tooling, modern precision sand casting can quickly produce cost-effective prototype volumes with representative functional performance, said Denholm.

“In the case of a battery pack, structural requirements necessitate wall thicknesses of at least 2.5 mm (0.1 inch) which is comfortably within the casting process capability. Satisfactory crashworthiness may require elongation properties of up to 15%, so we have developed a number of material specifications and heat-treatment procedures to achieve this.”

Grainger & Worrall technical director Keith Denholm. (Grainger & Worrall)

Explaining the crossover of ICE and EV technologies, he said Grainger & Worrall has developed 30 in-house specifications—mostly for aluminum/silicon and aluminum/copper alloys—tailored to suit specific applications. As ICE engine temperatures have increased, the company has developed alloy grades that it claims outperform the commercial grades, retaining their mechanical properties in temperature-critical applications.

“For vehicle body structures such as crumple zones, temperature is not the concern, so we have prioritized ductility over strength to achieve the required elongation properties,” Denholm said. “It’s through extending the performance of sand castings in this way that we are able to supply prototype components which behave just like production parts.”

One word: sand

In 2016, Grainger and Worrall acquired Coscast, home of the famous Cosworth Casting Process known for high-precision, high-quality sand castings. While still in demand globally for ICE engine components, Grainger & Worrall Coscast is increasingly supplying the EDU (Electric Drive Unit) market for hybrids and EVs. The process is equally valuable as a means of producing complex-shape vehicle structural components such as subframes, because it yields sand-cast parts that resemble the shapes and behavior of production pieces.

The relentless need to reduce the time-to-market for new products also has meant adopting innovative new techniques to speed up prototype production, such as digital sand manufacture. This is an additive manufacturing process where sand grains are fused together using a binder jet printing system that is quicker and more flexible than traditional processes.

Grainger & Worrall regards the process as vital for the timely development of new structural components and major castings for EDUs, now a significant growth area for the company.

“Often, OEMs and Tier 1 suppliers are less familiar with major casting design than their opposite numbers in the ICE engine field, plus there is massive potential for design integration and optimization by incorporating the motor, transmission, cooling and control elements. By working with us from the initial concept design stage, we can help them take maximum advantage in terms of packaging and weight reduction.”

CT validation

Grainger & Worrall has invested in computer-simulation methods for casting design, including Magma software packages for various materials. Aimed at producing right-first-time castings without extensive and time-consuming practical trials, more than 500 simulation projects have been completed—validated by x-ray, CT (computerized tomography), micro examination and tensile testing.

Other in-house capabilities include engineering (providing design support through to product launch), a materials lab, metrology lab and extensive machining facilities such as a flexible manufacturing system (FMS) cell comprising three 6Mazak 5-axis machining centers and a fully integrated pallet loading system. “Machining is an essential part of the value chain,” Denholm asserted.

The company is set to expand into engineering analysis and joining technologies, but has no plans to become a high-volume supplier. Added Denholm: “By supplying components which speed up development, we can help our customers begin meaningful testing earlier and shorten their time-to-market for new products. For fledgling companies, of which there are many in the EV sector, this reduces the financial burden prior to revenues coming on stream by generating better products from a finite initial investment.”