U.S. Army researchers test fired RAMBO, a 40mm grenade launcher and 40mm grenades that were built using a 3-D printer.
The printed grenade launcher, named RAMBO, which stands for Rapid Additively Manufactured Ballistics Ordnance, was the culmination of six months of collaborative effort by the U.S. Army Research, Development and Engineering Command, the U.S. Army Manufacturing Technology Program and America Makes, the national accelerator for additive manufacturing and 3-D printing.
Additive manufacturing, or AM, is an enabling technology that builds successive layers of materials to create a three-dimensional object.
“This demonstration shows that additive manufacturing (commonly known as 3-D printing) has a potential future in weapon prototype development, which could allow engineers to provide munitions to soldiers more quickly,” according to a March 1 Army press release.
“RAMBO is a tangible testament to the utility and maturation of additive manufacturing. It epitomizes a new era of rapidly developed, testable prototypes that will accelerate the rate at which researchers’ advancements are incorporated into fieldable weapons that further enable our warfighters.”
Every component in the M203A1 grenade launcher, except springs and fasteners, was produced using AM techniques and processes.
The barrel and receiver were fabricated in aluminum using a direct metal laser sintering process. This process uses high-powered precision lasers to heat the particles of powder below their melting point, essentially welding the fine metal powder layer by layer until a finished object is formed. Other components, like the trigger and firing pin, were printed in 4340 alloy steel, which matches the material of the traditional production parts.
The M203A1 and M781 grenades were selected as candidate systems for the project. The technology demonstrator did not aim to illustrate whether the grenade launcher and munition could be made cheaper, lighter or better than traditional mass-production methods. Instead, researchers sought to determine whether AM technologies were mature enough to build an entire weapon system and the materials’ properties robust enough to create a properly functioning armament, according to the release.
“To be able to additively manufacture a one-off working testable prototype of something as complex as an armament system would radically accelerate the speed and efficiency with which modifications and fixes are delivered to the warfighter,” the release states.
AM doesn’t require expensive and time-intensive tooling. Researchers would be able to manufacture multiple variations of a design during a single printing build in a matter of hours or days.
The barrel was printed vertically with the rifling. After it was removed from the build plate, two tangs were broken off and the barrel was tumbled in an abrasive rock bath to polish the surface. The receiver required more post-process machining to meet the tighter dimensional requirements. Once post-processing was complete, the barrel and receiver underwent Type III hard-coat anodizing, a coating process that’s also used for conventionally manufactured components of the M203A1. Anodizing creates an extremely hard, abrasion-resistant outer layer on the exposed surface of the aluminum.
The barrel and receiver took about 70 hours to print and required around five hours of post-process machining. The cost for powdered metals varies but is in the realm of $100 a pound. This may sound like a lot of time and expensive material costs, but given that the machine prints unmanned and there is no scrap material, the time and cost savings that can be gained through AM are staggering, according to the release.
The tooling and set-up needed to make such intricate parts through conventional methods would take months and tens of thousands of dollars, and would require a machinist who has the esoteric machining expertise to manufacture things like the rifling on the barrel.
Two RDECOM research and development centers, the U.S. Army Edgewood Chemical and Biological Center and the U.S. Army Research Laboratory helped build the 40mm grenades for the project.
An integrated product team selected the M781 40 mm training round because it is simple and does not involve any energetics—explosives, propellants and pyrotechnics are still awaiting approval for use in 3-D printing.
The M781 consists of four main parts: the windshield, the projectile body, the cartridge case and a .38-caliber cartridge case.
The windshield and cartridge case are traditionally made by injection molding glass-filled nylon. Using multiple AM systems at multiple locations helped emphasize manufacturing readiness and the Army’s capability to design, fabricate, integrate and test components while meeting tolerances, requirements and design rules. ARL and ECBC used selective laser sintering and other AM processes to print glass-filled nylon cartridge cases and windshields for the rounds.
The .38-caliber cartridge case was the only component of the M781 that was not printed. The .38-caliber cartridge case was purchased and pressed into the additively manufactured cartridge case. Research and development is underway at ARDEC to print energetics and propellants.
ARDEC researchers used modeling and simulation throughout the project to verify whether the printed materials would have sufficient structural integrity to function properly.
Army researchers conducted live-fire testing the printed grenade launcher and printed training rounds on Oct. 12, 2016, at the Armament Technology Facility at Picatinny Arsenal, New Jersey.
The 40 mm AM-produced grenade launcher and components were a highlighted project at the 2016 Defense Manufacturing Conference.
“Although there are still many challenges to be addressed before Army-wide adoption of AM, demonstrations like this one show the technology’s advances,” the release states.