Submarines May Dive Deeper Thanks to a New Lightweight 3D Printable Syntactic Foam Filament

In two new papers published in JOM, the Journal of the Minerals, Metals & Materials Society, associate professor of mechanical and aerospace engineering Nikhil Gupta details a process to turn syntactic foams into a 3D printable filament. Gupta and his team of student researchers from the Composite Materials and Mechanics Lab at NYU Tandon developed their new filament and 3D printing process to be compatible with commercially available 3D printers. This will allow for small plastic components with highly complex geometries impossible to manufacture using existing manufacturing technologies to be 3D printed. The filament was made of an environmentally friendly, lightweight, durable composite material that is widely used in the manufacture of submarines, aircraft, watercraft and cars.

Syntactic foams are a material made by mixing an epoxy or plastic resin with billions of microscopic spheres, traditionally made from glass or ceramic. The spheres in the foams are hollow, so any parts or components made using them are considerably lighter than parts made with traditional materials. The shape of the spheres allows for the weight reduction of the part without sacrificing the part’s strength or durability. Syntactic foam parts have been used heavily in the production of state-of-the-art submarines like the new Alvin deep-sea explorer and the Challenger Deep used by James Cameron to make his record-breaking mariana trench dive back in 2012.

These parts are traditionally made using injection molding technology, however this process limits the shape and complexity of the part, with many components needing to be joined together with adhesives or fasteners, a process that can cause weakness or vulnerabilities. The 3D printing process eliminates the need for highly complex parts to be joined as the entire part can be manufactured at the same time. Not only does this reduce the manufacture and production time of the parts, but it improves the overall strength and durability of each component.

“Our focus was to develop a filament that can be used in commercial printers without any change in the printer hardware. There are a lot of parameters that affect the printing process, including build-plate material, temperature, and printing speed. Finding a set of optimum conditions was the key to making the printing of high-quality parts possible,” said Gupta.

When it came to developing their syntactic foam filament, Gupta and his team had several hurdles to overcome, including the tendency of the microspheres to be crushed during the mixing process or to clog the nozzle during printing. The team also needed to find the ideal type of resin to mix with the microbeads. Generally, the greater the number of hollow particles in the resin material, the lighter that the final component will be. However, having more microbeads in the resin mixture increases the number of crushed and broken beads that will result from the printing process, so the researchers had to develop the correct ratio.

They settled on making their filament from a high-density polyethylene plastic, a very strong material often used in the manufacturing of industrial-grade components, rather than a ceramic or a resin, and the microbeads were made from a recycled coal waste byproduct called fly ash. To prevent the microbead spheres from clogging the nozzle they were made with a specific size and shape that allows them to easily flow through the 1.7 mm 3D printer nozzle. Each individual sphere ranges from 0.04 mm to 0.07 mm in diameter. Initial tests of the 3D printed components have revealed that they displayed tensile strength and density comparable to components made using injection molding.

“The results show that the properties of 3D-printed syntactic-foam components are at par with the widely used traditional injection-molded parts of the same material,” explained Ashish Kumar Singh, a doctoral student working under Gupta.

Because the microbeads are made from fly ash, a highly toxic material that is generally buried in special landfills, the 3D printer filament is also considered environmentally friendly. As less than half of all the fly ash in the world is recycled or repurposed, finding more uses for this toxic byproduct could have a significant impact on our environment. The 3D printed parts are also fully recyclable.

The next step for Gupta and his team is to focus on optimizing the material properties for a wide range of applications, including the production of parts used in underwater vehicles capable of functioning at great depths. In addition to his team at NYU Tandon, Gupta also worked closely with his colleagues from the National Institute of Technology Karnataka, Surathkal in India and the project was supported by the U.S. Office of Naval Research.

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[Source: NYU Tandon]