Metallic Glass Gears Up for ‘Cobots,’ Coatings, and More
From his days at Caltech, which manages JPL, Hofmann was familiar with an emerging class of specially engineered materials called bulk metallic glass, also known as amorphous metals. These are metal alloys that can be rapidly cooled from liquid to solid before their atoms form the crystalline lattice structure that is common to all other metals. Instead, the atoms are randomly arranged like those of glass, giving the materials properties of both glass and metal.
Depending on their constituent elements – often including zirconium, titanium, and copper – they can be very strong, and because they aren’t crystalline, they’re elastic. Most compositions also form a hard, smooth ceramic oxide surface, Hofmann explained, noting that these properties together afford gears made of some amorphous metals a long lifetime with no lubrication. “That’s, of course, really important to NASA, because you can run your gearboxes without lubricating them.”
Currently, the Cold Operable Lunar Deployable Arm (COLDArm), a collaborative effort between JPL and the company Motiv Space Systems for lunar missions, is expected to use bulk metallic glass gears to operate in temperatures down to minus 290 degrees Fahrenheit without the need for a heating source.
Casting for Affordable Robot Parts
But amorphous metals have another property that makes them attractive for gears on Earth: “These alloys are designed to have low melting temperatures, because to make a metallic glass, you have to cool the alloy faster than it can crystallize,” Hofmann said. This low melting point, together with their native strength and the fact that their volume hardly changes upon solidifying, makes bulk metallic glasses easy to use in injection molding, which can dramatically reduce the cost of making parts like gears.
Most high-strength metals have high melting points. They can’t be cast with molds because, in molten form, they would simply melt the mold. And steel needs to be rolled or forged to strengthen it, which also precludes molding. So, gears typically start as steel billets that are “machined” – cut, ground, milled, and drilled – into their final shape. Tiny gears, like those for small cobots, are especially challenging – and costly.
The most difficult, expensive gear component to machine from a steel block is one of the most common in robotic arms: the flexspline, an extremely thin-walled, flexible cup with a toothed rim. This is the centerpiece of what’s known as a strain wave gear assembly, which offers better precision, higher torque, and lower backlash than other gear sets. This eliminates positioning errors that would be compounded in a robotic limb with multiple joints.
“It’s a very strange-looking gear if you’ve never seen it, but it’s the heart and soul of a precision robot,” said Hofmann.
This is where molding with amorphous metals promises the greatest savings: it costs about half as much as machining strain wave gears from steel, Hofmann said.
Molding small, high-performance planetary and strain wave gears became the central business plan for Amorphology, which Hofmann cofounded in 2014. Through Caltech, the company licensed several patents for technology he had developed for NASA.
Meanwhile, he and colleagues continued pursuing new materials for spacecraft at both the metallurgy lab and JPL’s Additive Manufacturing Center. A number of patents and technologies led Hofmann to found a second spinoff company focused on using amorphous metals in coatings, 3D printing, and other non-gear-related applications. Both were backed by the same venture capital group, and in 2020 they merged under the Amorphology name, combining about 30 patents and patent applications for the technology from JPL.
A Market Beyond Mars
That year, the merged company finished its move into a new, 13,000-square-foot manufacturing facility where about 15 people now work, mostly making and testing prototype pieces for small gear assemblies for several customers. Amorphology’s first and largest customer is one of the world’s foremost manufacturers of strain wave gears.
At least one other customer has hired the company to coat consumer electronics parts with metallic glass, making them more durable, indicating another market with immediate potential, said Stephen Ceplenski, chief growth officer at Amorphology.
Hofmann noted that gears that can operate without lubrication are also of interest to businesses like food manufacturing, where lubricants can become contaminants.
Meanwhile, many of the company’s other patents for JPL technology – all licensed from Caltech – are probably still years away from commercialization, although they are in fields that are gaining heavy interest. Among these are new alloys and advanced metal 3D printing technologies, from thermal spray additive manufacturing to ultrasonic welding.
Amorphology is not the first company to commercialize innovations in bulk metallic glass from JPL and Caltech, but Garrett noted that creating a startup based on new materials is notoriously difficult. If lubrication-free gears or low-cost flexsplines find a long-term market, “that would be a huge step towards sustained commercial success for bulk metallic glass,” he said. “The research for the Mars rovers would be directly responsible for that.”
NASA has a long history of transferring technology to the private sector. The agency’s Spinoff publication profiles NASA technologies that have transformed into commercial products and services, demonstrating the broader benefits of America’s investment in its space program. Spinoff is a publication of the Technology Transfer program in NASA’s Space Technology Mission Directorate.