Researchers at the U.S. Army Armament Research, Development and Engineering Center (ARDEC) successfully fired the first grenade created with a 3-D printer from a grenade launcher that was produced the same way. 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.
The printed grenade launcher, named RAMBO (Rapid Additively Manufactured Ballistics Ordnance), was the culmination of six months of collaborative effort by the U.S. Army Research, Development and Engineering Command (RDECOM), the U.S. Army Manufacturing Technology (ManTech) Program and America Makes, the national accelerator for additive manufacturing and 3-D printing.
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. Additive manufacturing (AM) is an enabling technology that builds successive layers of materials to create a three-dimensional object. 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 (DMLS) 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 purpose of this project was to demonstrate the utility of AM for the design and production of armament systems. A 40 mm grenade launcher (M203A1) and munitions (M781) were selected as candidate systems. 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.
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. 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. This would expedite researchers' advancements and system improvements: Instead of waiting months for a prototype, researchers would be able to print a multitude of different prototypes that could be tested in a matter of days.
AS SIMPLE AS PRINT AND DONE?
Depending on a part's complexity, there can be numerous steps involved before it is ready for use. For instance, in the case of RAMBO, the printed aluminum receiver and barrel required some machining and tumbling. After printing, the components were cut from the build plate, and then support material was removed from the receiver.
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. 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.
PRINTING 40 MM AMMO
Beyond AM fabrication of the weapon system, ManTech also requested that a munition be printed. Two RDECOM research and development centers, the U.S. Army Edgewood Chemical and Biological Center (ECBC) and the U.S. Army Research Laboratory (ARL), participated in this phase of the project to demonstrate RDECOM's cross-organizational capabilities and teaming. 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 PROJECTILE BODY
In current production, the M781 projectile body is made of zinc. Zinc is used because it's easy to mass-produce through die-casting, it's a dense material and it's relatively soft. The hardness of the projectile body is critical, because the rifling of the barrel has to cut into the softer obturating ring of the projectile body. The rifling imparts spin on the round as it travels down the barrel, which improves the round's aerodynamic stability and accuracy once it exits the barrel. Currently, 3-D printing of zinc is not feasible within the Army. Part of the beauty of AM is that changes can be made quickly and there is no need for retooling, so four alternative approaches were taken to overcome this capability gap:
--- The first approach was to print the projectile body in aluminum as an alternative material. The problem with that approach is that aluminum is less dense than zinc; therefore, when fired, the projectile achieves higher speeds than system design specifications call for. Interestingly, even though the barrel and projectile body were printed from the same aluminum material, because the printed barrel was hard-coat anodized, it allowed for proper rifling engagement with the softer untreated printed aluminum projectile body.
--- The second approach was to print the projectile body in steel, which better meets the weight requirements, and then mold a urethane obturating ring onto it. The obturating ring is required to ensure proper engagement and rifling in the aluminum barrel. We couldn't keep the obturating ring as steel, like we did with the first approach, because steel is a lot harder than aluminum, and even with the hard-coat anodization it would have destroyed the grenade launcher's barrel. So for this approach, the projectile body's design was modified to take advantage of design for AM. The original projectile body designs did not consider AM fabrication and processing. For this AM technology demonstrator, the design was modified to take advantage of AM design rules to reduce the amount of post-machining required. This approach also used 3-D printing to fabricate a "negative" mold and then create a silicone positive mold to produce an obturating ring onto the printed munition bodies.
--- The third approach also utilized a groove and obturating ring, but instead of overmolding, the plastic was printed directly onto the steel projectile body using a printer with a rotary axis.
--- The fourth approach used a wax printer to 3D-print projectile bodies. Using the lost-wax casting process, plaster was poured around the wax bodies and allowed to set. Once set, the hardened plaster mold was heated and the wax melted away. Molten zinc was then poured into the plaster mold to cast the zinc projectile bodies.
ARDEC researchers used modeling and simulation throughout the project to verify whether the printed materials would have sufficient structural integrity to function properly. Live-fire testing was used to further validate the designs and fabrication. The printed grenade launcher and printed training rounds were live-fire tested for the first time on Oct. 12, 2016, at the Armament Technology Facility at Picatinny Arsenal, New Jersey.
Testing included live firing at indoor ranges and outdoor test facilities. The system was remotely fired for safety reasons, and the tests were filmed on high-speed video. The testing included 15 test shots with no signs of degradation. All the printed rounds were successfully fired, and the printed launcher performed as expected. There was no wear from the barrel, all the systems held together and the rounds met muzzle velocities within 5 percent of a production M781 fired from a production-grade grenade launcher. The variation in velocities were a result of the cartridge case cracking, and the issue was quickly rectified with a slight design change and additional 3-D printing. This demonstrates a major advantage using AM, since the design was modified and quickly fabricated without the need for new tooling and manufacturing modifications that conventional production would require. More in-depth analysis of material properties and certification is underway. The RAMBO system and associated components and rounds are undergoing further testing to evaluate reliability, survivability, failure rates and mechanisms.
THE WARFIGHTER WEIGHS IN
Before the live-fire testing, the U.S. Army Natick Soldier Research, Development and Engineering Center (NSRDEC) gathered warfighter input from the 2-504 Parachute Infantry Regiment of the 82nd Airborne Division. The regiment was consulted on features and capabilities it would like to have available on the M203A1 grenade launcher. Using that feedback, NSRDEC created the standalone kit for RAMBO. The M203 grenade launcher is typically mounted under other Soldier weapons. NSRDEC researchers took advantage of AM and rapidly created prototypes and kits that included custom handgrips based on warfighter requests and specifications--customization made possible because of the design freedoms and rapid turnaround afforded by AM.
3-D COMMUNITY OF PRACTICE CHIPS IN
The concept and funding for this project initially came from ManTech and ARDEC. ARDEC managed and executed the project with collaboration from other RDECOM AM community of practice and associated member organizations. Some of that collaboration was ad hoc and need-based--the need to find certain printing capabilities that ARDEC lacked, for example--and other collaborative efforts represented a concerted effort to leverage the experience and expertise of the community of practice.
Key organizations included ARDEC, Army ManTech, ARL, ECBC, NSRDEC, America Makes, DOD laboratories and several small businesses. ARL worked with ECBC for development of printed glass-filled nylon cartridge cases, and with NSRDEC for designs and fabrication of the printed standalone kits with Soldier-requested variations.
The Army Special Services Division at Fort Meade, Maryland, expeditiously printed aluminum barrels and receivers to complement ARDEC's capabilities for additive manufacturing of metals. America Makes developed and printed finely tuned AM barrels and receivers. The project also included services from several small businesses and service houses for AM. The cross-organization teaming between government and industry illustrated the current state of the art for AM and the robustness and manufacturing readiness of AM as an enabling technology for current and future U.S. production.
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 Armywide adoption of AM, demonstrations like this one show the technology's advances. Successfully firing an AM-produced weapon system validates AM maturation and applicability in armament production.
By using AM, researchers and developers will be able to build and test their prototypes in a matter of days rather than months. Designs and parts previously unachievable can now be realized. Complex designs that lighten, simplify and optimize armaments are now feasible and manufacturable. These advancements will improve products and facilitate faster and more efficient transition from the labs to the field, further enabling our warfighters.
This article is scheduled to be published in the April -- June 2017 issue of Army AL&T Magazine.