3D printing can be used to make anything from small objects to whole houses. Today, we show two projects in which this manufacturing technique can be used to aid the military.

Spare parts
Soldiers on the battlefield or at remote bases often have to wait days or even weeks for vital replacement parts. To help them get many of these parts within hours, researchers found that many of replacement parts can be fabricated with 3D printing, using water bottles, cardboard and other recyclable materials.

Supplies like food, fuel, ammunition and repair parts are not often stocked at front-line locations, so that troops in the area can run out. Many of the units do have 3D printers to produce spare parts, but they rely on commercially available plastic filaments, which have to be supplied.

PET plastic, used for things as water or soda bottles, is on of the most common kinds of waste material found around bases, so this material could be as viable feedstock. The researchers found that PET filament, produced by recycling, were just as strong and flexible as commercially available filaments for 3D printers. They used PET filaments to print a vehicle radio bracket. The process required about 10 water bottles and took two hours to complete.

The researchers also tested other types of plastic, such as polypropylene (PP), used in yoghurt or cottage cheese containers, or polystyrene (PS), used for plastic utensils. By themselves, these plastics were not practical for use in 3D printing. However, by strengthening PP with cardboard, wood fibres and other cellulose waste materials, new composite filaments were made. To make these filaments, the researchers used a process called solid-state shear pulverisation. In this process, shredded plastic and paper, cardboard or wood flour was pulverised in a twin-screw extruder to generate a fine powder, which was then melt-processed into 3D printing filaments.

In addition, PS, which is rather brittle, was blended with PP to generate a strong and flexible filament.

Barracks
The US Marine Corps Systems Command teamed up with Marines from I Marine Expeditionary Force to build the world’s first continuous 3D printed concrete barracks. Using what is said to be the world’s largest concrete printer, they printed a 45-square metre (500 square feet) barracks hut in 40 hours.

While other buildings and large structures have been printed with concrete before, the US military says this barracks hut is the first to be continuously printed on site.

It normally takes 10 Marines five days to construct a barracks hut out of wood. With this printer, however, it only requires 4 Marines and takes less than two days to make a strong structure. In addition to barracks, the 3D printed can also be used to print houses in disaster areas.

Photos: MCSC / Nicole Zander/U.S. Army Research Laboratory