AMS Spring 2023

NASA Spinoff Deploys Large Format Metal 3D Printing for Space Components

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The space industry is undergoing a gradual evolution wherein additive manufacturing (AM) is deployed to improve the quality of components. According to the “3D Printing in Commercial Space: The AM Ecosystem in the Private Space Industry report from SmarTech Analysis, this will mean a $2.1 billion revenue opportunity by 2026. Already businesses young and old are seeing profit on the horizons as they find new applications for the technology.

This includes Amorphology Inc., a NASA spinoff company that is using technology developed at the Jet Propulsion Laboratory (JPL) and the California Institute of Technology. Together with Additive Technologies (AddiTec), the firm is using directed energy deposition (DED) to 3D print large specialty components for strain wave (also known as “harmonic”) gears made of steel.

Strain wave gears are unique in that they are compact and demonstrate zero backlash, making them ideal for robotic arms and precision-motion mechanisms. Their application is so niche that key examples of their use are the electrically driven wheels in the Apollo Lunar Rover and the Mars Curiosity Rover. Key to the function of strain wave gears is a part called a flexspline, a thin-walled cup, hat, or band through which the gear’s torque is delivered.

Additive manufacturing used to produce a 6-inch diameter strain wave gear flexspline from 17-4 PH steel. The part was manufactured using directed energy deposition and then precision-machined into the final shape. The prototype is compared to a common size-20 flexspline measuring approximately 2 inches in diameter. For larger flexsplines, additive manufacturing can provide significant cost savings and open the ability to tailor material properties. Image courtesy of Amorphology.

Due to the precise gear teeth and flexible wall of these components, producing a strain wave gearbox is not cheap and represents a large chunk of the costs for robotic arms with six degrees of freedom (6DOF). This is because flexsplines are traditionally machined from steel billets, which results in a major waste of material. Therefore, 3D printing presents an attractive alternative. Dr. Glenn Garrett, Amorphology CTO, explains:

“When you look at machining of flexsplines that are 6 to 8 inches in diameter, the large steel feedstock may be reduced to as little as 10% of its original volume. This is a detriment from both cost and sustainability standpoints, as energy and material are wasted to produce a part which is a shell of the original stock.  Additive manufacturing becomes a promising alternative since the machining costs can potentially be dramatically reduced while allowing for the cost-effective use of high-performance steels.”

To showcase the possibilities of AM, Amorphology teamed up with AddiTec, a founding partner of DED manufacturer MELTIO. The Meltio Engine, which can be integrated into existing CNC systems, is a multi-laser deposition head that can process wire or powder metal feedstock for DED 3D printing. Using a Haas CNC machine featuring the Meltio Engine, the group 3D printed a 6-inch flexspline made from 17-4 precipitation hardened steel. Upon removal from the build tray, the piece was CNC machined to its final shape.

Workflow comparing conventional manufacturing of flexspline from billets with manufacturing from near-net shaped 3D printed parts. Image courtesy of Amorphology.

This process demonstrated the ability to produce this specialty part on-demand without the need for warehousing flexsplines with a variety of diameters. However, producing these components in a cost-effective manner is just the beginning of the benefits that AM could bring. Amorphology and AddiTec aim to expand flexspline manufacturing to include multi-material parts, as well as functionally graded flexsplines.

While DED manufacturers have long touted the possibilities of functionally graded parts, few have been shared publicly. By transitioning from one material to another within a single component—a capability uniquely suited to DED—it’s possible to modify properties from one area to the next. For instance, hardened metals could be incorporated into one location for extra durability, while radiation-shielding metal could be used in another for space applications.

JPL is a pioneer in the application, given that it has been researching the technology for at least a decade. Now, it seems that at least one JPL-affiliated business may be nearly ready to bring graded components out of the lab. Where will they go? One guess is Europa. According to a 2018 NASA paper, the cryogenic environment of Jupiter’s moon, confirmed to have water vapor, means that the use of liquid lubricants for strain wave gears may not be possible. Instead, novel materials, such as bulk metallic glasses, may be necessary for the function of gearboxes on a Europan lander.

Image courtesy of NASA.

If this means 3D printed flexsplines from Amorphology and Additec, we may not see it until closer to 2027, when a mission to Jupiter’s moon has been tentatively planned. By then, we may be more interested in the findings of such a lander than what it’s made of because where there’s water vapor, there may be signs of life.

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