PICATINNY ARSENAL, N.J. (Oct. 7, 2015) -- Engineers are using ultrasound technology to more easily find defects during the manufacture of ordnance as a way to lower costs, produce more effective ordnance and provide an added measure of safety for Soldiers in the field.
At the U.S. Army Armament Research, Development and Engineering Center, or ARDEC, engineers want to remove the "black box" that surrounds the production of energetic materials. In the context of defense research, "energetics" is a short-hand term for materials such as explosives, propellants and pyrotechnics.
"We have this black box and it's currently hard to see inside with the technology that is available," said chemical engineer Viral Panchal.
"Ultrasound gives us the ability to open up the box, leading to more effective research, development and manufacturing," Panchal added.
ARDEC engineers have been working with Wes Cobb at the University of Denver, who has decades of experience developing ultrasound technology for the food, oil and medical industries.
The ARDEC engineers provide expertise regarding the energetic material, explaining what properties need to be measured, and Cobb develops tools to do so. The technology developed by Cobb allows for faster research and development that will aid in developing better manufacturing models.
Ultrasound technology for energetics research is used as an in-process research and development tool, which ARDEC engineers and contractors are validating in a manufacturing setting.
Advantages of ultrasound is the ability to capture extensive information in real time, easily pass through metal, and operate at low energies, leading to safe use with energetic materials. Ultrasound technology also provides two useful measurements to include measuring the speed of sound and attenuation vs frequency during real-time monitoring.
Project Director Joint Services, which is part of the Program Executive Office for Ammunition at Picatinny, is the main sponsor for the use of ultrasound technology in energetic manufacturing. It has made a significant investment in instruments to examine the melt-castable explosive fills for mortar and artillery shells during the casting process.
The Small Business Innovation Research program provided funds to Applied Sonics Incorporated, which was then able to create key components for the ultrasound equipment. This early investment enabled PM JS to fully support the implementation of the technology to manufacturing lines.
Much of the Army's ordnance items are manufactured as explosive materials cast into shell cases (TNT, Comp B, IMX-101 etc.). The solid explosive materials are first melted in a mixing kettle, stirred and then poured into an empty shell.
Ideally, the casting hardens from the bottom up and evenly fills the case. However, variations in source materials and process conditions can lead to defects such as piping (vertical holes), porosity, and separation between the explosive and the case.
These defects, if found, lead to increased production costs and, if not, can ultimately affect the safety of Soldiers in the field if a loaded projectile with a cast defect is fired.
Currently, there is no way to monitor the quality of the explosive fill at any time during casting.
Recent work has shown that noninvasive ultrasonic sensors can be used to continuously monitor the solidification process during the casting of munitions and detect the formation of defects.
The monitoring technique can use sensors that are explosion-proof, operator friendly, intrinsically safe, and non-destructive to production rounds.
The sensing technology can measure in real time, at a high rate, providing valuable information which will eventually be incorporated into a control system.
"Energetic material manufacturing equipment is out of date, and the origin of flaws are difficult to understand as most available sensors cannot withstand the harsh manufacturing environments," said ARDEC engineer Rajen Patel.
"We had a program started several years ago that examined explosives for internal cracks, density, and viscosity in melt pour formulations. We were able to show that using ultrasound we can collect this information in real time."
ULTRASOUND WITH PROPELLANTS
ARDEC engineers are also currently working with University of Denver to apply ultrasound technology to propellant manufacturing. Propellants are chemical substances that burn rapidly and generate gases, which push bullets or rockets downrange.
Previously, there were a number of methods in place to examine propellants, including X-ray imaging to check for the presence cracks and defects, buoyancy measurements for density, and viscometers to measure viscosity.
These properties are important for the quality of the materials and repeatability of propellant performance.
"Propellants are typically fabricated by mixing both solid and liquid ingredients with a suitable solvent system in batch mixers," Panchal said. After mixing, the product has a tough, dough-like consistency, which is then placed in an extrusion press and squeezed through a die of desired geometry to form strands.
"The strands are then cut into specific lengths to meet ballistic burning rate requirements," Panchal added.
"These cut grains are then blended together to make up the final propellant lot."
The propellants are then thoroughly analyzed afterwards.
"Moving forward, the goals for the project are to reduce the scrap rate and the number of voids in the propellants, while eliminating the blending cycle to reduce lot-to-lot variation.
"This will result in a more consistent product the first time rather than remaking substandard propellant lots at increased time and costs," added Panchal.
"Propellants often have a range of solvent content as they are extruded and this solvent needs to be removed from the final grains through subsequent drying steps," he continued.
"Knowing the solvent level at the extrusion press allows the propellant manufacturer to tailor the diffusion rates of the solvents controlling how they exit the propellant so that the formation of potential voids and cracks in the grains can be reduced.
"If you can detect the solvent levels at the time of extrusion, you can correct manufacturing defects in real time."
REAL-TIME MONITORING
An operator sitting in the control room can monitor the process and the solvent level in real-time so that potential problems can be identified early, reducing production time, saving money and boosting product quality.
"Nothing before could tell you in real time about the product quality," Panchal said.
Ultrasound technology allows the operators to stop at any point during production to address potential problems early on, instead of having to scrap an entire batch.
"We can eventually transfer this technology to our manufacturers to get a higher quality, more consistent product at a lower price," said Patel.
"It will reduce scrap rates and lower production times," Panchal added.
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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.
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