Air Force Research Laboratory Materials Integrity engineers recently played a key role in enabling the safer and more efficient removal of paint from F-16 aircraft through the newly-adopted Robotic Laser Coating Removal System.
At the request of the Air Force Life Cycle Management Center Engineering Division, the research team, part of the Materials and Manufacturing Directorate, contributed technical expertise in the form of test coupon analysis, test procedure development and execution, and many forms of guidance and consultation throughout a seven-year effort that completely reimagined paint removal for certain types of metallic aircraft surfaces.
Through this novel process a laser-equipped robotic arm—mapped individually and specifically to each aircraft—is moved over the vehicle surface, essentially vaporizing paint layer by layer. The process is completely contained, meaning all waste materials as well as potentially harmful chemicals are vacuumed into the tool. A vision system recognizes when the stripping reaches the appropriate stopping point.
It’s a completely automated process that removes the direct human element, both in terms of error and exposure. Instead, operators guide the effort from a computer console in a nearby control room.
“We provided support at the full spectrum and provided expertise so that they could do the right engineering due diligence,” said Structural Materials Evaluation Team Lead Jeff Calcaterra. He explained that the process brought with it challenges never before considered in traditional non-thermal paint removal.
Because the paint is removed with a laser, as opposed to traditional mechanical or chemical methods, Calcaterra said the AFRL team had to take into consideration a whole new set of factors when developing test plans and evaluating the structural soundness of test specimens.
“We had three areas that we were very concerned with because this is a thermal process: Cadmium embrittlement (the formation of intermetallics on the material), the concern of thermal damage to the material itself, and thirdly, any relaxation of residual stress due to thermal effects,” he explained. “None of this is ever considered in any of the non-thermal processes.”
Paint removal is a common maintenance procedure for military aircraft and is performed for a variety of reasons, most notably for inspections and for repainting purposes. Typically, it is performed manually, with maintenance crews applying a chemical solution, performing media blasting, or by meticulously scraping or sanding off the paint. These procedures are time-consuming and create a large amount of potentially hazardous waste material. It is also labor-intensive, requiring teams of maintainers equipped with multiple types of safety gear.
Calcaterra explained that the laser de-paint process is much safer, significantly reducing the environmental hazards posed by chromium-based paint products. The fully-automated process does not require maintenance crews to be in the paint stripping area. And since the process is contained, waste is automatically removed to a collection area, requiring very little cleanup by human maintainers. As an added plus, the process is also faster, saving significant labor hours and associated costs.
Although not every surface material is suitable for laser paint removal, the system is approved for use with specific types of aluminum and graphite epoxy composites with a service temperature greater than 350 degrees Fahrenheit. These materials constitute the outer moldline of the F-16. The system is currently being investigated for a number of other materials and air platforms as well, and AFRL will play a continuing role in these efforts.
The Robotics Laser Coating Removal System has recently been approved for production F-16s and transitioned to the Ogden Air Logistics Complex at Hill Air Force Base, Utah, where it will be incorporated into the regular maintenance toolset for the platform.