Amorphology has made strides in the advancement of Bulk Metallic Glass (BMG) for gears. What makes BMG an industry material to watch?
BMG is a relatively new class of metallic alloys that is now transitioning out of academia and into industry. NASA is responsible for pulling BMG into the world of gears as they faced a pretty unique challenge for long-life precision motion at the cold temperatures of space. As temperatures drop, wet lubricants increase in viscosity, requiring powered heaters to make sure the steel gears are adequately lubricated. For NASA, not every situation where they would like precision motion has an abundance of available power.
Through testing and validation at low temperatures, they found that gears made out of BMG last significantly longer than steel under these demanding conditions. Even though the steel is coated with a dry lubricant, it wears off, and the stiffness of the steel results in high contact stresses that accelerate wear to unacceptable levels and give poor gearbox performance. Precision BMG gears that do not require heaters allow for lighter weight structures and systems that can expand the capabilities of satellites and rovers.
The gears we make with BMG may be quite small for some readers of Gear Solutions. To obtain the amorphous character of BMG, we must cool the molten liquid quickly enough to bypass crystallization altogether.
While this does limit the size and thickness of gears that we mold, it is also a key manufacturing advantage. Because the liquid does not crystallize, it doesn’t shrink dramatically, and small low-module gears can be molded with high precision in permanent metal molds with smooth surface finish thus eliminating traditional expensive post-processing steps.
In essence, this is an exciting new material that offers different properties to complement existing gear technologies. They address challenges in areas such as space where lubrication or relubrication is difficult. They also enable the manufacture of gears with very fine teeth with minimal steps — eliminating some of the more expensive processes.
What Earth-bound applications do you see this being used in?
Terrestrial use cases include small precision gears for motion control, strainwave gears in robot and cobot arms, and other small complex precision components. There are also many unusual environments on Earth that could benefit from the material properties of BMG including corrosive environments, food handling, medical applications, vacuum environments, and extremely cold environments.
We also see a gap to address in applications where the raw strength of steel is not required, but the strength of aluminum and plastic is not enough. These use cases may also leverage the unique manufacturing techniques allowing for efficient production of small, low-module gears.
I believe we’re in the sweet spot of properties for the material and also for efficient processing where there’s going to be interesting applications.
Robots require extremely precise and difficult-to-make gears — especially if they’re working side-by-side with humans. You need the confidence that these machines will behave and move as advertised, and the gears required have very small-shaped teeth.
Our strategy is to mold these difficult, expensive gear components. If we cut and inspect the cavity very carefully, we remove some of the quality burden by making sure you have a really good permanent mold then reproducing that precision across large numbers of parts.
How do quality assurance and factor into the material quality as well as the molds and the final parts?
It’s extremely critical. My background is in the science and manufacturing of BMG, but I am a recent arrival to the world of precision gearing. It has been incredibly challenging, yet fun, to bring BMG into such a demanding field. The tooth widths range from a half millimeter to several millimeters with micron requirements for the tooth profiles. It is exciting to push the boundaries of BMG technology and alloy innovation in this space. The dimensional tolerances of the gears we are making demand extreme accuracy in the mold, and the desired performance levels require stringent material quality standards.
Amorphology has invested in its own machining and inspection center to verify the dimensions of the molds and resulting parts. Having this capability in-house allows us to rapidly inspect, machine, and iterate on molds or parts as necessary.
We also have our own full metallurgical characterization laboratory so we can ensure high-material quality and correlate it with the full gearbox performance, which is measured on our gearbox test bench.
Because the material is different from steel, we are exploring the broad number of gear-design parameters that can be adjusted. Our BMG alloys have a modulus about half that of steel; they are lower density and still relatively hard. We have a unique opportunity to take advantage of those properties to innovate in the gear space.
What should we stay tuned for coming out of Amorphology’s lab?
Just directly, NASA is responsible for pulling BMG into the world of gears and doing the initial validation. Their work gave other customers the confidence to approach us and try it for themselves.
And while we will absolutely continue working in the space sector, we are also in the process of developing the first commercial Bulk Metallic Glass strainwave and planetary gearboxes to validate with industry leading partners here on Earth.
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