ABERDEEN PROVING GROUND, Md. (Dec. 30, 2014) – The U.S. Army is seeking to implement a new mortar manufacturing process to provide improved weapons at a lower cost, officials said.
The Army introduced a nickel super-alloy called Inconcel to produce mortars in 2008, but its properties make it challenging to manufacture. Researchers have been working on an alternative method to overcome the difficulties, said Chris Humiston, a mechanical engineer with the Armament Research, Development and Engineering Center, or ARDEC, at Watervliet Arsenal, New York.
ARDEC is one of seven centers and laboratories that make up the U.S. Army Research, Development and Engineering Command.
Current processes to manufacture 60mm mortar tubes rely on traditional mechanical cutting and grinding of material to achieve the required geometry, Humiston said. Tough materials that are good for weapons are inherently difficult to machine.
These materials, such as Inconcel, are becoming more common in defense applications because of their high strength, corrosion resistance and high survivability in extreme environments.
“It’s difficult to machine because it’s a strong, tough material that has a very high temperature resistance,” he said. “When you cut it with conventional tools, you get a high amount of tooling wear. It can lead to deficiencies in the component.
“Since the tube is thin-walled, during the machining process, we would get a large amount of residual stress in the wall of the tube. Occasionally it would cause the tube to go out of round, and the part would have to be scrapped.”
The team at ARDEC then turned to electrochemical machining technology, ECM, as a potential solution. Manufacturers have used ECM for decades to work with extremely hard materials.
General Electric, or GE, developed and patented an electro-erosion process called Blue Arc for the production of aircraft engines. ARDEC partnered with GE, licensed the technology and adapted it for use on mortar manufacturing.
“We were looking for an alternative manufacturing process that would not have any of these issues that would contribute to the deficiencies in production. The ECM process reduces the manufacturing variability, which increases the precision of the rounds. This allows for a more consistent process,” Humiston said.
Engineering technician Joe Carter explained how the Army benefits from ECM.
“In conventional machining, you’re pulling the metal off with a lathe or milling machine. That creates stress,” Carter said. “As your tool gets dull, it creates more stress. With ECM, the tool never touches the part.
“It has electrochemically dissolved the metal. You don’t get the stress in the part, which improve quality and production time.”
The ECM process leaves a polished surface without the machining marks and the residual surface stresses produced by mechanical machining. It can achieve extreme precision in geometric parts with complex geometry.
Humiston said the group examined each step of the production process to identify time savings. “We were able to identify certain operations that could be removed from the existing process if we used ECM. We looked at removing nine operations and 12 hours of machining time from the existing process, which is a 30 to 40 percent improvement,” he said.
This technology will enable defense manufacturing centers to meet the machining demands created through the use of these tougher armament materials, Humiston said.
To fund the partnership with GE, ARDEC leveraged the Defense Acquisition Challenge Program, or DAC. The RDECOM Global Technology Integration Team manages the program for the Army.
The Department of Defense established DAC in 2003 in response to a congressional mandate for a program that was innovative, flexible and competitive to integrate mature technologies into the acquisition cycle, said William “Randy” Everett, DAC project officer at RDECOM headquarters.
The Office of the Secretary of Defense Comparative Technology Office evaluated the proposals and selected candidates for funding. DAC was funded through fiscal year 2012.
To resolve the issue of waste as a byproduct of ECM, ARDEC contracted with Faraday Technology to develop an electrowinning process through the Army’s Small Business Innovation Research Program.
“We’re going to eliminate the waste issue altogether,” Humiston said. “We’re making a fully recyclable, fully sustainable manufacturing process when we combine electrowinning with ECM. It falls in with the Army’s sustainable manufacturing initiative to reduce waste, energy usage and water usage.”
Humiston said the objective under DAC was to prove a pilot capability for this effort. He is now seeking additional funding through the Army’s Manufacturing Technology Program to transition the process into the organic industrial base.