The advantages of composites are rarely debated. Born mostly from aerospace research, incredibly light but strong creations such as carbon fiber have upended mass-to-strength formulas, changing the way we think about materials and their applications. The often-stunning combination of light weight and enormous strength continues to advance in the composites world, minus two aspects critical for wide application: cost and mass-producibility.
If you want the most astonishing properties of composites, they’re available – but almost invariably, at a prohibitive cost and in small batches. For aerospace or Formula 1, this is rarely an issue. But for high-volume automotive products, one-off, hand-laid, hours-to-bake composite pieces do not jive with vehicles produced in the hundreds of thousands per year. Solving the speed/cost Achilles heel of composites has been the goal of Norcross, Georgia-based WEAV3D, which may have a solution in its woven thermoplastic consolidated lattice.
A doctoral project comes to market
WEAV3D is the brainchild of Chris Oberste, its CEO and the inventor of the technology. The company and its new materials process came out of his Ph.D. research at Georgia Tech in Atlanta, after completing a polymer and fiber engineering degree at Auburn University. WEAV3D was founded in 2017 along with Georgia Tech MBA Lewis Motion, leveraging funding from the Georgia Research Alliance, the National Science Foundation (NSF) and earnings from the Dept. of Energy’s Cleantech University Prize.
One focus for Oberste’s doctoral dissertation was composite manufacturing technologies, and he had first-hand experience with traditional composites, having interned with GKN Aerospace, which produces composite panels for the Sikorsky UH-60 Black Hawk helicopter and a number of composite components for both Airbus and Boeing. According to Oberste, most composite manufacturing processes have matured in the aerospace market in the last five decades with “very high performance requirements and very low production volumes.”
“We're talking hundreds, maybe thousands of parts per year versus the hundreds of thousands that you might look at for an automotive production application,” Oberste said. “The factors that affect the aerospace market have converged most traditional composites into this bucket of batch-production processes.”
Often laid up by hand before the mold is placed in an autoclave, the incremental nature is an anathema to cost and production targets. “You're doing one part at a time, very incrementally, leading to relatively high part cost,” Oberste explained. “These technologies are very bad at scaling. If you're producing 100 parts today and you need to produce 1000 parts tomorrow, you buy 10 more molds and you have 10 more people doing the layup. You're not benefiting from economies of scale.”
Other downsides of having composite processes shepherded by the aerospace industry, according to Oberste, are the often-unnecessary performance requirements around heat resistance, durability for moisture and high-altitude behavior. This has led to chemically curing polymers such as epoxy and vinyl ester resins that can make components very difficult to recycle.
Made for manufacturing
From this current state of composites processes, WEAV3D saw an opportunity to make composites far more suitable for mass production. “We developed this ground up, clean-sheet approach, throwing out everything that we know about how to make composites from the aerospace market,” Oberste said. “We wanted to basically say, ‘Ignore all that. If you wanted to make a composite forming process that could be used for mass production, what would you do?’”
WEAV3D developed a unique process taking a mass-production approach, reducing cost structure by roughly 75%. “Because of how new composites are to the automotive industry, oftentimes automotive engineers think, ‘I want carbon fiber to be X dollars per kilogram,’” Oberste said. “But they're neglecting significant processing costs in converting that fiber into a usable product. Our technology emphasizes reducing the process cost, and by doing that reducing the overall cost of a composite structure so it's scalable for high-volume production.”
Oberste noted that if doing hand layup such as for a Formula 1 chassis structure, it doesn't matter if you're using glass fiber or carbon fiber, the amount of labor hours that it takes to do that layup is a huge portion of overall cost. Moving away from just thinking of the raw material to how is it being applied, and how to apply it for mass production, was the crucial innovation.
“We really focused on the idea of thermoplastics – polypropylenes, nylons, polycarbonates – materials that you can reheat, reshape or recycle, potentially within the same value stream, recycling scrap from one process step into the next,” Oberste continued. “That was fundamental for this concept to make it suitable for high-volume production. Leverage the existing high-volume processes like compression molding and injection molding, because they work well and the industry is familiar with them. If you can augment those capabilities, you have a much better solution.”
Reinforcing common plastics
Focusing so keenly on mass-production capability led WEAV3D to trademark a system it calls “Rebar for Plastics.” This involves using widely available reinforced plastic tapes. These include polycarbonate, polypropylene, nylon, polyethylene terephthalate (PET) and polyphthalamide (PPA), with WEAV3D focusing on commercially available engineering- and commodity-grade plastics tapes reinforced with carbon and glass.
“The manufacturers of these tape products are usually the same manufacturers of high-volume, injection-molded pellet plastic,” Oberste detailed, noting most of the industry has started to consolidate around “one-inch” (25mm) tape widths. “These are the BASFs, the Covestros, the DSMs, the SABICs – all of these companies either currently produce tape or spun off the business recently. It's basically a pultrusion or film-lamination process, so you can make a lot of tape and the actual cost is not huge.”
WEAV3D takes these common tapes and inputs them into a loom-like machine which converts them into a woven thermoplastic consolidated lattice. “Think of it as a combination between a Jacquard loom and a continuous compression process,” Oberste said. “We are weaving the tapes and then melting and compressing them at the weave locations so that they're fully bonded in a continuous roll-to-roll forming process. The advantage of the lattice being thermoplastic is that we can reheat and reform it in complex structures as needed.”
The resulting lattices (comprising multiple layers if needed) can be overmolded into a thermo-forming, compression-molding or injection-molding process, acting as a structural skeleton within a molded plastic component. Currently, WEAV3D can produce the composite lattice in a continuous roll 60 in. (1.5 m) wide, but will soon be scaling up to an 80-in. (2-m) width.
“Unique from a traditional loom approach is we're able to vary the density of the lattice on the fly, where the tapes get closer or farther apart,” Oberste said. “We can also ‘tune’ the tapes in the structure. Maybe for cost reasons, you want the majority of your lattice made from glass tapes, but you need certain areas of the part to be stiffer or stronger. We can selectively insert carbon tapes where we want them.”
“The overall goal is taking these molded plastic parts that are currently non-structural and making them structural, at a fraction of the cost of what it would take to do with a traditional composite,” Oberste explained. “That has always been the historical yank on the chain. Whenever you try to present a lightweight solution out of traditional composite forming processes, you can make it work at maybe the tens-of-thousands range. That's why you see it on the [BMW] i3 and the Corvette. But as soon as you start going into the hundreds of thousands, you're basically out the window.”
In earlier, greater benefits
The trick, Oberste explained, is putting the right material in the right spot, permitting cost reduction by creating a lattice with needed properties only where required. “It's really about the design freedom that this allows, because traditionally, you have a layer of carbon fiber reinforcement that's going to be everywhere in the part,” he said. “So the idea that you can selectively choose where your reinforcement is and how dense lets you optimize part thickness and geometry in parallel with the lattice geometry, allowing new configurations that you couldn't do on their own while using a homogenous material.”
An aspect of automotive production showing strong potential for the WEAV3D process is cosmetic interior trim, often molded polypropylene panels for doors, dash and trunk. These panels often require an underlying collection of metal brackets or stiffeners for support. “The idea is by putting this lattice into the molded plastic part, now you don't need all those brackets and stiffeners,” Oberste said “The plastic part can become a structural element in the assembly. You've eliminated part count and cost, and you've eliminated mass just by changing how the load is being carried.”
According to WEAV3D’s principal, being as close as possible to the design phase will create the greatest benefits, as the lattice can be tuned based on the part’s stress profile, permitting the lowest-cost solution for the application. “The later we come into the process, the more the component has been locked down in terms of geometry, part thickness, material selection,” Oberste claimed. “All those features eliminate some of the advantages, because we can only iterate within those boundaries. The wider the design space that we're allowed to play with, the more benefits we can show.”
Oberste said he hopes WEAV3D products become as common a choice as selecting a material from a sheet-metal supplier, but key interest has come from the opposite end of the materials spectrum: natural fibers. “Historically, one of the big challenges with natural fibers has been that they are worse than glass fiber in terms of their mechanical properties, so you're limited in what you can use them for. But once we start looking at putting a [composite] lattice within that natural fiber structure, now we can outperform the glass-fiber structure.”
Enabling smart surfaces
One of the most intriguing use cases for woven thermoplastic lattices is upcoming “smart surfaces,” interior panels with screens or other haptic-control technologies built in. By weaving in tapes with inherent electrical or data properties, the structural reinforcement can provide a conduit to enable such features. “Great, you have a smart surface on this panel, how are you going to get power and data to that smart surface?” Oberste described. “You're going to drill a hole in the bottom of the panel and then have someone hand solder it, or have a robot trying to solder it into the panel structure? It's a kind of a nightmare.”
“One of the areas we have IP around is functional structures,” he said. “The lattice becomes a carrier for a transmission material like metallic tape or optical fiber. Now you've created a plastic panel that has integrated power, data or heat-sinking capabilities. This lets you eliminate certain aspects like wiring harnesses or metallic heat-sink brackets that are normally necessary when you're working with interior plastic assemblies. There's a lot of opportunity there for making the manufacturing process way more streamlined.”
Leveraging an NSF Small Business Innovation Research Phase II grant, WEAV3D currently is assembling an automotive, commercial-scale machine designed to support 200K to 500K units of production per year for a component roughly the size of an automotive door panel. According to Oberste, though the process is still new, they’re already meeting mass-production targets.
“Currently, if you want to do automated tape placement for an injection-molded preform, you usually have three tools,” he said. “One that's being laid up, one that's being consolidated and one that's waiting to go in. Your tooling costs to hit the rate production is way higher than if we're just producing the lattice at the high volume that it needs – just blanking it out and putting it in the mold. We can produce parts faster than a single machine can mold them.”Continue reading »