A robotic laser system was demonstrated at Hill Air Force Base on available aircraft. The robotic laser system utilized 2010 technology with a 6 kW continuous-wave laser. Since that time, many advancements in technology have been accomplished within all critical areas specifically with the laser and sensors. The Air Force Life Cycle Management Center (AFLCMC) planned to develop and procure the next generation robotic laser coating removal system using the qualified 1 kW nano-pulse laser (NPF) on both smaller unmanned aircraft and larger platforms available at Warner Robin Air Logistics Complex. The planned system would have incorporated advancements in laser scanners, surface mapping techniques, color sensors, and control technology. The objective of this project was to validate and qualify a commercially available nano-pulsed 1 kW fiber laser system with a polygon scanner on thin advanced composites coated with traditional and non-traditional military paint colors, such as gloss white.
Using an Air Force purchased commercial IPG Photonics Corporation (IPG) 1 kW NPF laser with a Lincoln Polytek Polygon scanner, validation and qualification testing were accomplished. Pre-screening tests were accomplished using Global Hawk with generic composite and aluminum substrates; in conjunction with associated aircraft surface treatments, primers, and topcoats. Tests utilized an IPG 1 kW NPF laser (Figure 1 IPG 1 kW NPF Laser) with 1.06 um wavelength (IPG YLPN-100-30x100-1000). This laser provided a pulsed output with a maximum pulse energy of 100 mJ. The laser had four nominal operating modes with associated pulse duration, repetition rate, and energy (Table 1 Nominal Laser Operating Modes). All modes provided 1 kW averaged power output. Tests utilized the nominal operating modes.
Laser power was delivered to a scanner by a process fiber (fiber-optic cable) with a 600 um square fiber core and 20m length. The large core size and square cross-section of the process fiber yielded a square beam shape with a flat-top (uniform) intensity distribution on the work surface.
Nano-pulse fiber laser allowed the coating to be removed rapidly at higher peak energy levels. The laser beam moved faster over the surface and allowed for lower substrate temperatures, which is critical for composite materials as well as faster strip rates. There was no cost-benefit analysis accomplished on this project.
A consistent issue with implementing this project was the change in scope. The proposal was for composite panel testing, which then changed to include metallic panels because they were cheaper and faster to purchase for the project. The Lincoln Polygon scanner proved to be too large and cumbersome for use on the end effector and was ultimately replaced with a Galvanometer scanner.