How do you make a heavy liftgate lighter?

A partnership between an industry leader in materials and chemicals and North America's biggest supplier of auto components is attempting to expand on a radical idea they introduced more than a year ago: using adhesives rather than welding to bond vehicle liftgates.

DuPont Transportation & Industrial and Magna International are working on new iterations of the process they jointly developed, to use adhesives to bond liftgates' thermoplastic pieces.

The companies are now trying to simplify their manufacturing process, reduce the required bonding time, accelerate the curing process and commonize adhesives.

The concept also has to be flexible enough to work for different customers with different product specs, said Sid Asthana, Magna's global director of material science.

"The cookie-cutter approach doesn't work," Asthana told Automotive News. "The customer demands change from one liftgate to the next, from one OEM to the next, from one vehicle to the next, depending on the vehicle structure.

"There are a lot of moving parts that we tried to bring together to make it finally work."

Their development work is being driven by the industry push for lighter-weight solutions as vehicle electrification spreads. Liftgates were an obvious target for weight reduction. The closures are typically made of steel and joined by welding processes.

Liftgates could be made using lighter materials, but moving away from metal means welding is no longer possible. The partners' first bonded liftgate appeared on the 2020 Acura RDX and Jeep Cherokee using multiple materials.

"Not every customer is moving toward adopting the thermoplastic liftgate technology at the same pace," Asthana said. "But we clearly see, based on trends from the marketplace and what we are hearing from customers, that the thermoplastic liftgate market is going to grow very big."

Adhesive bonding was one of the only viable joining methods for a construction with thermoplastics, said Frank Billotto, DuPont Americas marketing manager, "especially when you're working with parts that have contoured surfaces and where you have dissimilar mixed materials interfacing together."

Critical to making the new construction work was identifying adhesive and cure properties that met the automakers' performance requirements for durability, he said.

"It really came down to balancing some of the cure properties of the adhesive itself, its elastic properties, its bond strength and also the stiffness of it," Billotto said.

The partners ended up with a bond that provides rigidity and strength to the liftgate's joints, Asthana said. DuPont's Betaseal structural adhesive systems were customized for use on low-surface energy substrates and generally cure faster.

There also is a consideration in their concept for how the resulting liftgate will look. "We have a very clean look around the joints," Asthana said of the first two applications.

"In addition to the aesthetics, we obviously want a water-tight seal so there is no water ingress during the lifetime of liftgate," he added. "The adhesive is not just a bonding feature, but also a sealing feature."

The bonding approach also represents an efficiency gain on the manufacturing side.

"There's flexibility built into the adhesive formulation to enable quick curing speed at room temperature," Billotto said. "But we also have the flexibility to work with external heating sources to accelerate the cure in key areas, to give initial and quick holding ability to the assembled parts."

That's important from a manufacturing perspective, he said, because it determines how many fixtures and tools are required on an assembly line to meet production rates.