Wet Paint No Barrier to Timely, Accurate Measure of Coating Thickness

  • Published
  • By Heyward Burnette
  • Materials and Manufacturing
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  A newly demonstrated technology providing the first-ever nondestructive means to measure the thickness of specialty paint coatings during their application will generate substantial savings for the Air Force. An Air Force Research Laboratory materials engineering team successfully demonstrated the integration of a paint spray robot with a sensor--specifically, a miniature Class I, Division 1-compliant time domain terahertz sensor--for real-time cure monitoring of coating materials as they are applied to aircraft surfaces. By ensuring the application of coatings to the correct thickness the first time, the integrated spray booth/sensing capability will eliminate costly sanding, rework, and/or reapplication tasks, increasing confidence in coating materials and helping to ensure that production schedules--in this case, for the F-35--are met.

Aircraft maintainers commonly apply specialty coatings via robot or by hand. Despite the critical relation of coating thickness to material performance, maintainers have historically relied on destructive tests, costly and inaccurate witness coupons, or otherwise limited and unreliable measurement systems--all of which require contact with a dry coating surface. To address the issue, AFRL partnered with Picometrix and Northrop Grumman to conduct initial testing and demonstration of a noncontact TD THz instrument for in-process cure monitoring of specialty material coatings developed under an earlier, Small Business Innovation Research Phase II effort. With the aid of computer simulations, the AFRL/industry team determined the optimal size of the sensing package, as well as the best location for incorporating the sensor into the automated spray system.

Key to development success was the capacity to mate the sensor to the spray system without altering the production spray path or qualified procedures. While successful laboratory demonstrations of the integrated system occurred earlier in the program, the achievement of comparable results in a production environment was critical for program completion and subsequent technology transition. Ultimately, a production demonstration confirmed that the measurement system could be successfully mounted to the robot and accurately measure wet coating thickness during a spray event. Additional data collection, validation tests, and system deployment activities are slated to occur under a SBIR Phase II extension effort ongoing through Fiscal Year 2011.

Meanwhile, the TD THz instrument is undergoing development for operation in the production line/quality assurance process at Northrop Grumman's paint booth facility in Palmdale, California. Recent testing demonstrated the TD THz system installation concept (i.e., placement of the control unit in the control room, as well as routing of the umbilical cord to the gantry and the robot arm). Researchers achieved sensor operation exhibiting no loss in fidelity or electrical interference with the sensor signal and thus enabling high-quality measurements over the range of sensor-tilt angles of interest.