In 2014, NASA’s Jet Propulsion Laboratory (JPL) awarded Ohio-based Fabrisonic seed funding to develop its hybrid Ultrasonic Additive Manufacturing (UAM) process for improved metal heat exchangers. With continued support from JPL over the years and with in depth development and testing, Fabrisonic has successfully developed pumped fluid loop heat exchangers which are lighter, more efficient and faster to produce than traditional epoxy tube heat exchangers.
The joint project, detailed in a recent white paper published by Fabrisonic, sought to find a more efficient way to produce higher quality heat exchangers for rovers and other aerospace applications. Heat exchangers play a critical role in NASA’s interplanetary rover missions, as the components are essential for regulating temperatures for the sensitive electronics of the device.
Traditional heat exchangers, such as those integrated into the Curiosity Rover on Mars, are built using bent metal tubes which are glued onto the vehicle’s outer structure. More specifically, the process of producing heat exchangers at JPL has relied on epoxying aluminum tubing along a CNC milled structural orthogrid. Though robust and long standing, this method for producing heat exchangers does come with its limitations. For one, epoxy is a poor heat conductor. Second, the heat exchangers are very heavy (adding to the payload for space launches) and it can take up to nine months to build a single system.
For these reasons, JPL wanted to find a better solution for manufacturing heat exchangers for which it turned to Fabrisonic and its UAM technology for help.
Ultrasonic Additive Manufacturing
Fabrisonic’s UAM process is a hybrid manufacturing process that uses high frequency ultrasonic vibrations to “scrub metal foils together” additively building up a net shape. This metal 3D printed structure is then selectively machined to integrate internal channels and the final part shape. The process, says Fabrisonic, is capable of manufacturing complex internal geometries which would be impossible with traditional production processes.
One of the features that sets UAM apart is that it is a solid-state process, meaning that it does heat the metal material beyond 121°C (250°F) which allows it to retain the metal’s chemistry, grain structure and material properties. This feature makes it possible to work with typically challenging aluminum alloys such as 6061 and 7075.
Testing the heat exchangers
Working closely with NASA’s JPL, Fabrisonic produced a wide variety of different heat exchangers using its UAM process. After much development and testing, three identical 3D printed heat exchangers were subjected to ground-based qualification tests. The qualification process consisted of various stringent tests including:
- Thermal cycling from -120°C to 120°C (-184°F to 248°F)
- Proof pressure testing to 330 PSI
- Thermal shock testing by submersion in liquid nitrogen
- Vibe testing to simulate a Saturn V launch in x, y, and z orientations while
- bolted to a dummy mass to mimic a typical hosted electronics package
- Burst testing greater than 2500 PSI with 0.030” wall thickness
- CT scans of each heat exchanger before and after mechanical testing
- Helium leak testing
In the end, all three 3D printed heat exchangers passed the mechanical qualification testing and showcased promising results.
In a separate study against the traditional epoxy tube exchangers, the 3D printed specimens also had a range of benefits. While the epoxy tube specimen was made from 40 or more parts, the 3D printed heat exchanger was a single unit. The 3D printed version also saw a slight weight reduction from 1.82 kg to 1.26 kg. Importantly, the lead times for the 3D printed heat exchanger were much lower at two weeks compared to at least two months. Finally, the UAM heat exchangers displayed improved thermal conductance of about 25-35%.
“The methods developed under the NASA JPL funding has been quickly extended to numerous commercial production applications,” reads Fabrisonic’s white paper. “To help with technology adoption, the team is working to explore other key areas. For instance, the solid-state nature of UAM allows integrating multiple metals into one build. Thus, copper may be integrated as a heat spreader in critical locations improving thermal performance with a small weight penalty.”
UAM, it adds, also has the ability to embed sensors into solid metal parts because of its low temperatures. For heat exchanger applications, this could mean improved control and monitoring.