PICATINNY ARSENAL, N.J. -- Using additive manufacturing, Picatinny scientists and engineers have successfully manufactured and fired a grenade launcher and training round, a significant step on the path towards decreasing the time it takes engineers to research, develop, and manufacture ammunition and guns.

Additive manufacturing is the process of printing 3-D objects. An engineer takes a Computer Aided Design model and sends it to a printer with certain specifications. The printer prints the object in successive layers. The printed grenade launcher was modeled after the M203 and the grenade was modeled from the M781 training round.

"For prototyping purposes, there's a lot of advantages to additive manufacturing," explained Sunny Burns, materials engineer at the Armament Research, Development and Engineering Center at Picatinny Arsenal, New Jersey.

One advantage is time. Over 90 percent of the grenade launcher parts were printed on a single build plate in only 35 hours. Except for the springs and fasteners, all of the more than 50 components were additively manufactured.

"Additive manufacturing can potentially allow researchers to build prototypes in days, as opposed to months. This will expedite the acquisition process, allowing engineers to get equipment to warfighters quicker," said Burns. "3-D printing prototypes will allow you to change designs quickly to experiment and test changes."

For instance, rifiling a barrel requires complex tooling and esoteric machining expertise. "It's a pretty tricky process to get the tooling, and things like that take a lot of experience. Only one machinist in our machine shop had any experience doing it and we have around 30 machinists here."
And having a contractor to prototype a single barrel is expensive.

"Just the tooling alone would take around $50,000," he said. "If you're just doing a one-off prototype, or under 10, 3-D printing is definitely the way to go. And you don't need machining expertise -- you just need one of these printers and the software, and you can print it out."

PRINTING TECHNIQUES
Four different additive manufacturing techniques were used to create the M781 training round. The printing involved no energetics -- the energetics were added in at the test area prior to firing. Energetics are the explosives, propellants and pyrotechnics needed to fire ammunition and propel it forward.

"With additional funding we'd like to develop the round further and include something with printed energetics, something that would go boom. That would be the next iteration of the project," said Burns.

"We wanted to demonstrate additive printing's manufacturing applicability. We chose the 40 mm because it's a relatively simple system, with the pressure and speeds involved. It's low velocity and low pressure so it's not as critical as a small caliber system." Burns said.

One challenge has been additive printing the components in the same materials as the original grenade launcher and ammunition.

"We've tried to stay as much one-to-one as possible," explained Burns. "So if a part was aluminum we didn't want to print in steel, we wanted to print in aluminum. Same thing for the round - we tried to stay as close as possible."

While printing the training round, the team encountered some issues.

"The typical grenade training round has a plastic cartridge case and windshield, made of glass reinforced nylon 6. We were not able to print this material, so we printed it in other plastics, which began cracking during firing."

The cracking forced the engineers to alter the geometry of the round, including gussets and reinforcing certain areas because the round lacked structural integrity due to the lack of material properties.

LOOKING AHEAD:
The successful test firing of an AM-produced weapon system validates additive manufacturing's maturation and applicability in the production of armaments.

"In addition, designs and parts previously unachievable can now be realized. Complex geometric designs to lighten, simplify and optimize armaments are 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," Burns said.

"We decided to use the grenade launcher as the platform, but we could have used almost any weapon. We wanted to demonstrate that additive processes are applicable to armament systems," said Jim Zunino, materials engineer at ARDEC.

The team used a variety of different printers and additive manufacturing techniques to include metals, printed polymers, and electronics additive manufacturing.

"The idea is to incorporate 3-D printing into the manufacturing process where it makes sense, and combine it with conventional manufacturing. We're trying to explore what other techniques are out there that could be complimentary to current and future weapon system production," he said.

Zunino said additive manufacturing can allow for mass customization. For instance, the standard weapon parts could be printed using conventional methods, but the finger grooves or butt stock could be customized through additive manufacturing to accommodate for a Soldier's particular height, weight and hand grip.

"Some Soldiers like a 45 degree grip handle in the front on their rifle and some like a 90 degree grip handle in the front. With additive manufacturing we could potentially customize to each Soldier's liking," he said.

Picatinny engineers are researching how to provide forward-deployed teams with "expeditionary kits" to 3-D print spare or customized weapon components.

"You're not going to be able to make a grenade launcher in one of the expeditionary kits we're building, but if you want an additional Picatinny rail or grip we want to be able to give them that ability," he said.

The concept and funding for this project initially came from U.S. Army ManTech and. ARDEC managed and executed the project with collaboration from other RDECOM Additive Manufacturing Community of Practice and associated member organizations. Key organizations included ARDEC, Army ManTech, Army Research Laboratory, Edgewood Chemical Biological Center, Natick Soldier Research, Development & Engineering Center, America Makes, DOD laboratories and several small businesses. ARL contributed with ECBC for development of printed glass-filled nylon cartridge cases and NSRDEC for designs and fabrication of the printed standalone kits with Soldier -requested variations. NSRDEC also interviewed grenadiers and designed customized printed solutions for the warfighters.

The Special Services Division at Fort Meade, Maryland, expeditiously printed aluminum barrels and receivers to complement ARDEC metals AM capabilities. America Makes, the Department of Defense's Manufacturing Innovation Institute for Additive Manufacturing, 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.

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The U.S. Army Armament Research, Development and Engineering Center is part of the U.S. Army Research, Development and Engineering Command, which has the mission to ensure decisive overmatch for unified land operations to empower the Army, the joint warfighter and our nation. RDECOM is a major subordinate command of the U.S. Army Materiel Command.