Air Force Research Laboratory
Wright-Patterson Air Force Base, OH
AFRL 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.
Because the paint is removed with a laser, as opposed to traditional mechanical or chemical methods, 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.
Three areas were of concern because this is a thermal process: Cadmium embrittlement (the formation of intermetallics on the material); thermal damage to the material itself; and thirdly, any relaxation of residual stress due to thermal effects.
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.
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.
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