The US Army’s Armament Research, Development and Engineering Center (ARDEC) has successfully fired the first 3D-printed grenade from a 3D-printed grenade launcher. Part of a demonstration of how such technology can be used to greatly speed up prototyping and modification of weapons while lowering costs, the grenade launcher, called RAMBO (Rapid Additively Manufactured Ballistics Ordnance), was based on an M203A1 grenade launcher and every component, with the exception of the springs and fasteners, was manufactured using additive manufacturing.

Although the parts used to create RAMBO were made using 3D printing, some additional processing was required based on the material and complexity of the individual components. For example, the aluminum barrel and receiver were made using direct metal laser sintering (DMLS), where a layer of aluminum powder is laid down, then fused into solid metal with a laser beam guided by a digital CAD file. A second layer is them laid down and the process continues until complete. The excess powder is blown away, any support structures are removed, and the part is buffed smooth. However, for the barrel and receiver, some additional machining and tumbling was needed.

One of the advantages of this approach is that the rifling in the barrel was printed directly into the barrel instead of milled out later. The barrel and receiver were then hardened by applying hard-coat anodizing to form a hard, abrasion-resistant outer layer.

ARDEC says that the cost of producing the barrel and receiver was about US$100 per pound. The agency conceded that this is not cheap, but pointed out that the process only took 75 hours, that there was no scrap, and a skilled machinist wasn’t needed to fabricate the parts, resulting in considerable cost savings.

In addition to the grenade launcher, the researchers also printed M781 40mm training rounds. This particular munition was selected because training rounds don’t require explosives, which have not yet been approved for printing. Because the round consists of a windshield, projectile body, cartridge case and a .38-caliber cartridge case, each had to fabricated separately with a special printing process for the glass-filled nylon cartridge cases and windshields. The 38-caliber cartridge case was the only component of the M781 that was not printed because of lack of approval to handle propellants using 3D printing.

Another problem with fabricating the projectile body was that it was made out of zinc, which doesn’t lend itself to 3D printing. This required the engineers to come up with four alternate designs for the body to replace the zinc, yet still allow it to fulfil the function of forming a gas seal in the barrel and engaging the rifling lands.

This involved a projectile body made of aluminum, one of steel with a urethane ring, another steel body with a plastic ring printed directly onto it, and a fourth that printed a wax projectile body, which was then set in a plaster mold into which molten zinc was poured to melt away the wax and replace it to form the final structure.

ARDEC says that RAMBO was test fired at indoor and outdoor facilities in October at the Armament Technology Facility at Picatinny Arsenal, New Jersey. Using a remote control system for safety, the grenade launcher fired 15 test rounds successfully with no signs of degradation of the barrel or other parts. However, there was some cracking of the cartridge casing – a problem that was quickly resolved.

The team emphasizes that the purpose of the experiment was not to produce a less expensive or superior grenade launcher, but to demonstrate how 3D printing can produce entire weapons of the required quality that can work properly. In addition, it’s hoped that 3D printing will allow for faster prototyping and modifications that will allow engineers to do in hours or days what now takes months.

RAMBO was developed as part of six-month project in cooperation with the Research, Development and Engineering Command (RDECOM), the Manufacturing Technology (ManTech) program, and the national accelerator for additive manufacturing and 3-D printing, America Makes.

Image credits: US Army/Sunny Burns/ARDEC

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