A wrinkle for mixed materials: High cost

The growing interest in using mixed materials to hit new-vehicle lightweighting targets has a significant challenge, say manufacturing experts and proponents of the trend: Mixing materials in automaking will require added manufacturing processes and additional investment in joining techniques.

Those additional factory costs are the biggest hurdle for mixed-material solutions, agree Brian Krull, global director of innovation for Magna International's exteriors group, and Mari Chellman, chief engineer for Magna's body and chassis group.

"There's a continued pull for lightweighting," Krull said of the industry trend. "For the most part, that's based on changing powertrain architectures going to electrification.

"We see the biggest demand for lightweighting in areas high up in the vehicle," he said, referring to vehicle roofs.

If suppliers can help automakers take weight out of the roof and rear body area, the gain "allows for downsizing of the powertrain and can offset the new features being added to vehicles," he said.

A recent study from the Center for Automotive Research in Ann Arbor, Mich., concluded that by using a mixture of materials in the construction of the roof, automakers could reduce a vehicle's weight by up to 30 percent.

The study calculated that using aluminum and carbon fiber roof panels would achieve a 40 percent reduction in mass.

Abhay Vadhavkar, co-author of the study and the center's director of materials and manufacturing technology, told Automotive News that a 40 percent mass reduction of the roof subsystem would translate into an overall weight reduction of 25 to 30 percent for the body in white.

Chellman, an expert in multimaterial joining, said that larger body-in-white panels, such as the roof, are now being targeted for lightweighting by some customers.

"The next obvious step is mixed-material joining," Vadhavkar said.

But there is a catch, Chellman acknowledged. Using multiple materials in vehicle construction will require manufacturers to add barriers between some metals, meaning an extra coating or material layer that wouldn't be needed if a single material was used.

The industry is searching for new methods of joining and new processes to apply them on manufacturing lines.

An industry consortium called Lightweight Innovations for Tomorrow, funded by the American Lightweight Materials Manufacturing Innovation Institute and the U.S. Department of Defense, is testing mixed-material joining methods to provide guidelines for manufacturers for production. Hadrian Rori, chief technology officer at the consortium, told Automotive News that a study that began this year has developed 19 fastening methods to be tested for their structural integrity and how they might work in production.

Those methods include adhesives, epoxy, spot and solid-state welding, and spot riveting.

Rori said results from that study will be released next year.

"It's clear that OEMs are evolving to a multimaterial solution in vehicles," Rori said. "We're going to see different types of steels but also an introduction of other materials like aluminum, magnesium and composite materials."

Magna has been working on a low-volume vehicle with magnesium sheet, which is "challenging to form" and "not mainstream by any means."

Rori believes that changes in vehicle construction will represent business opportunities for suppliers of subsystems, chassis parts and structural components by making use of new joining techniques. But Tier 1 suppliers might be slower to embrace the change because of the expense of deploying new tooling for large volumes.

But he also predicted there will be upstream opportunities if Tier 1 companies outsource those new approaches.

"I can see the Tier 1s needing Tier 2 and 3 suppliers to help with these new applications," Rori said of the advent of mixed-material solutions.

"A lot of it depends on what the manufacturers will try to do with the vehicles from an efficiency perspective," he said.

Krull said holding down costs remains critical for Magna, "and that's where innovation is needed in the joining processes.

"We don't see any relief from the request for lightweighting," he added.