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Currently in field testing, 3M’s new structural adhesive is expected to be commercially available in February. (Ryan Gehm)

3M, GM collaborate on aftermarket adhesive for multi-material structures

According to Dan Wittek, Technical Service Supervisor at 3M, aluminum vehicle bodies are not all that complicated to repair, reminding that “trucks have been made out of aluminum for a really long time.”

The company’s product lineup such as adhesives, body fillers, and abrasives all apply not just to steel- but aluminum-intensive vehicles as well.

“We’re not starting from scratch with aluminum repair; it’s not a whole new lineup of products,” Wittek said. “It’s just technique and how you use them is slightly different.” For example, repair shops need to be mindful of “cross-contamination”—i.e., galvanic corrosion—that can occur by using the same set of tools on aluminum and steel vehicles.

3M’s standard 08115 panel bonding adhesive, which has been on the market since the late 1990s, has already been approved by Ford for use on the new F-150 pickup truck, according to Wittek. “This is our standard product for steel, and it’s going to be standard for aluminum—but [only] for outer body, nonstructural sheet metal.”

The real challenge, according to Wittek, comes from repairing multi-material structural applications. The Cadillac ATS and CTS cast-aluminum strut tower attached to a high-strength-steel frame rail—on display at 3M’s booth during the recent SEMA Show—is the perfect example of such a challenge.

“You can’t weld them together; it has to be mechanical or with adhesives, so General Motors came to us [for a solution] to meet this spec,” Wittek explained to Automotive Engineering. 3M and GM worked collaboratively on a new structural adhesive that is currently in field testing and is expected to be commercially available in February.

“There hasn’t been anything like it before. We already have GM’s stamp of approval for their vehicles, and we’re working to add other OEMs to that as we go,” Wittek said.

As a result of vehicle lightweighting and the use of thinner-yet-stronger materials, OEMs are using adhesives and under-coatings more often to reduce NVH, improve ride quality, and enhance the feeling of quality, particularly in luxury vehicles such as those in the Cadillac lineup.

“General Motors [in some cases] is bonding almost the whole car and welding it. Even if it’s all steel, they’re using a structural adhesive…because there’s still some flex,” Wittek said. “So that’s where this [new product] is going to be deployed for the aftermarket because today there isn’t something for that aftermarket repair in structural applications.”

Carbon fiber is a “different animal,” according to Wittek, because of its unique layup construction.

“There’s a big difference in carbon fiber between a cosmetic outer body panel and a structural inner panel,” he explained. “If it’s a structural inner panel and it’s damaged, today OEMs like BMW with their i3 structural carbon fiber just replace it. Things can change as technology advances, but today because of the weave and the way that it’s designed and engineered…it’s going to be a weak spot.”

Carbon-fiber outer body panels, however, are repairable with current adhesives.

“We have solutions today, but we’re still working on perfect solutions,” Wittek said. “Our panel bonding adhesive actually works really well for carbon fiber; the challenge with it is that it’s slow-drying, it’s a 4-h cure. It’s designed that way so you have enough time to get a body panel onto the car, but if you’re just doing a small crack in a [carbon fiber] fender, you don’t want to wait 4 h. So when I say we’re working to improve that, it’s not that we can’t do it, it’s just there isn’t a system designed for carbon fiber…We’re getting there.”

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