The building of a spacecraft requires a rigor and level of invention beyond anything needed for earthbound machines. Engineers tasked with building machines for space travel often require custom parts which traditional manufacturing techniques are incapable of delivering. Due to the unique stresses placed on spacecraft, some of those parts need to have the properties of multiple metals to properly function.
So when the tools and the materials needed to accomplish a difficult mission don't exist, engineers have to create them.
Researchers at the NASA Jet Propulsion Laboratory in Pasadena, California, have now designed a printing process capable of transitioning from one metal or alloy to the next all within the confines of a single object as it's constructed.
John-Paul Borgonia, a mechanical engineer at JPL, says that while these so-called "gradient alloys" have, in the past, been created in research and development, this discovery marks the first time such composite materials have been used in making actual, practical objects.
Borgonia says engineers might need, for example, a metal part where the ends of the part need different characteristics than the middle. One side might require a high melting temperature, while the other has low density. Perhaps one side of a given part might be magnetized and the other side, not.
While both halves of a given part might be made separately from different materials and then welded together, weakness could be introduced at the site of the weld itself. The scientists at JPL say they've been developing this technique to address the problem for the last four years. The Mars Science Laboratory mission, which landed the Curiosity rover back in 2012, served as the inspiration for their 3D printed, multiple-alloy components.
"We're taking a standard 3D printing process and combining the ability to change the metal powder that the part is being built with on the fly. You can constantly be changing the composition of the material," says Douglas Hofmann, a researcher in material science and metallurgy at JPL.
The technique involves depositing layers of metal on a rotating rod, This method allows engineers to transition the metal materials from the inside out as opposed to the usual AM method of adding layers in a bottom to top process as a laser melts the metal powder to create the layers.
"You can have a continuous transition from alloy to alloy to alloy, and you can study a wide range of potential alloys. We think it's going to change materials research in the future," said R. Peter Dillon, a technologist at JPL.
The researchers say that future space missions will almost certainly incorporate parts made with their new technique, and they add that they see applications of the technique in the auto industry and the commercial aerospace industry.
The findings of the team were published in Scientific Reports, and the coauthors of the work include Douglas Hofmann, Scott Roberts, Joanna Kolodziejska and Andrew A. Shapiro from Caltech and JPL, R. Peter Dillon, Jong-ook Suh, and John-Paul Borgonia from JPL, and Richard Otis and Zi-Kui Liu from Pennsylvania State University.