Performance Impacts of Metal Additive Manufacturing of Very Small Nozzles

Metal Additive Manufacturing for Satellites and Rockets

“…Tommila et al investigated laser powder bed fusion of a nickel alloy for the production of very small nozzles with diameters below 1 mm, as they are used in electrothermal or chemical thrusters of small satellites [67]. They found typical printing-derived surface features of the as-printed nozzles to cause shock wave reflections and other thrust losses in comparison with conventionally produced nozzles of similar surface roughness, and suggest postprocessing of the nozzle exit cone to avoid such shock-inducing protrusions.…”

Understanding Flow Characteristics in Metal Additive Manufacturing

“…SpaceX has experimented with printing thrust chambers and flown printed oxidizer valve housings to reduce lead time and expense (Howell 2014). Large flow structures like this would be less sensitive to the tens of micrometer-scale roughness expected from AM (Tommila et al 2021), simply by virtue of their large size, supporting flow for 500 kN of thrust and up. However, small-scale flow devices from this process alleviate constraints that conventional manufacturing can pose.…”

“…According to this method, the printing process yields an estimated sand grain roughness nearing 40 μm; this roughness is in the range of commercial steel tubing (46 μm, presumably hot rolled, welded seam tubing or similar) values commonly used for the calculation of friction factors and pressure losses in flow devices (Bergman et al 2011). However, previous research by Tommila et al (2021) indicates that these values may not be accurate in reflecting the actual effective roughness that should be used in design predictions. Their work on additively manufactured rocket nozzles found that loss predictions using this methodology were well short of the experimental losses experienced, although some of these losses were due to compressibility effects, likely including shocks within the nozzle (Tommila et al 2021).…”

“…However, previous research by Tommila et al (2021) indicates that these values may not be accurate in reflecting the actual effective roughness that should be used in design predictions. Their work on additively manufactured rocket nozzles found that loss predictions using this methodology were well short of the experimental losses experienced, although some of these losses were due to compressibility effects, likely including shocks within the nozzle (Tommila et al 2021). Some difference was expected, as the Adams et al (2012) formula was based on average roughness for calculating the sand-grain texture.…”

“…This microscale manufacturability has implications for the design and fabrication of flow devices. Devices such as injectors, nozzles, and heat exchangers are capable of being printed using AM (Petrovic et al 2011;Anilli et al 2018;Townsend et al 2016;Anderson et al 2020;Waters 2018;Steitz et al 2013;Durkee et al 2020;Tommila et al 2021) while reducing part and labor complexity. SpaceX has experimented with printing thrust chambers and flown printed oxidizer valve housings to reduce lead time and expense (Howell 2014).…”