The Tunnel 9 team have been consistently expanding their additive manufacturing capabilities over the past few years.

Arnold Engineering Development Complex Hypervelocity Wind Tunnel 9 began with just adding a few 3D printing systems here and there. It recently evolved and become a large part of the manufacturing of components at Arnold Air Force Base in White Oak, Maryland.

“The success of [additive manufacturing] at Tunnel 9 is exciting to say the least,” said Tunnel 9 System and Nitrogen Supply Engineer Samuel Gigioli. “The plastic prototyping is a growing interest here, as more and more people are coming to me with an interest or a need for 3D printing parts.”

Gigioli continued: “We can spit out parts in a matter of hours rather than weeks. Whether it is a test fit piece or a prototype part, the process greater speeds up our operations and can greatly impact Tunnel 9’s mission success.”

The facility acquired its first 3D printer around seven years ago. They used a small filament-based device that could quickly churn out uncomplicated plastic parts. However, the printer soon was put in storage as the prints were not up to the required standard.

During Gigioli’s first summer at Tunnel 9, in 2019, he was tasked with reviving the printer capabilities. This included ordering new parts, filament and materials for the apparatus. The second round with the printer proved more successful than the first.

Following the re-introduction of AM, Tunnel 9 used it to primarily manufacture plastic mounting rigs, fixtures, gauges and other similar components. After this progress, Tunnel 9 subsequently acquired two additional 3D printers.

A resin-based 3D printer, able to print small yet highly detailed and strong parts, alongside a dual filament-based printer capable of consistently printing large and highly detailed parts were brought into the fold at the facility.

In February 2020, a research and development team project involving the additive manufacture of refractive metal hardware launched at Tunnel 9. Gigioli took charge of this effort, aiming to reduce lead time and manufacturing costs for some high-temperature parts used in Tunnel 9.

“These Tunnel 9 parts endure very cyclic, high pressure and temperature conditions, so the lifespan on these parts is significantly shorter than other parts in the tunnel,” Gigioli said. “These parts can experience up to 3,000 degrees Fahrenheit. This is why refractive metals are chosen, as they are metals that can withstand extreme heat with relatively little deformation.”

A significant accomplishment of the research and development program has been successfully manufacturing a component known as the petal orifice liner. The device is integral to high Mach number tunnel runs, and is situated between the two burst diaphragms that Tunnel 9 uses to act as a high-speed valve.

Gigiloi said that the AM liner has outperformed its wrought-built counterpart that has been used for decades in the facility. 

“The part is cheaper to manufacture, quicker to manufacture and deliver, and is more resilient to the cyclic temperature loading,” said Gigioli. “The AM process creates very unique microstructures within the material and as a result, the part’s structural and thermal properties are different than traditional wrought billets metal.”

The team at Tunnel 9 have already begun work on the next 3D printed part to be applied in high Mach number conditions. This component, a particle separator, would act to weed out any airborne particles in the gas flow without hindering any mass flow in the tunnel.

Gigioli revealed that personnel of various Department of Defense (DoD) components have complimented the Tunnel 9 team on the success of the AM work and expressed their astonishment with the technology and its potential. Part of the research effort includes showcasing the potential of AM for the entire DoD.

“Imagine if we scale this process up to multiple tunnel parts or even entire systems,” said Gigioli. “Now some DoD components are interested in printing test models or leading-edge models. I hope to continue leading Tunnel 9 down this path and increase our success through this technology.”

The DoD has been heavily involved in AM as of late, recently becoming a recipient of 3D printing technology through Velo3D's partnership with the Hartech Group.

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