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U.S. Air Force researchers have developed what they say is the first nondestructive technology to measure the thickness of specialty paint coatings as they are applied.
An Air Force Research Laboratory materials engineering team has 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, the Air Force announced Friday (Sept. 24).
“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,” the statement said.
Development and Testing
Aircraft maintainers commonly apply specialty coatings via robot or by hand, the Air Force notes. Measurement of coating thickness—a critical component in material performance—has traditionally used destructive tests, witness coupons, or other measurement systems—all of which require contact with a dry coating surface.
To address the issue, AFRL partnered with Northrop Grumman and Picometrix, of Ann Arbor, MI, which manufactures terahertz instrumentation. The team conducted initial testing and demonstration of a noncontact TD THz instrument for in-process cure monitoring of specialty material coatings.
That instrumentation had been 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.
Spray Challenges
Key to development success was the capacity to mate the sensor to the spray system without altering the production spray path or qualified procedures, the Air Force said. Although the system had performed successfully in lab demonstrations, achieving comparable results in a production environment was critical to complete the program and transfer the technology.
“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,” the Air Force said.
Additional data collection, validation tests, and system deployment activities are slated to occur under a SBIR Phase II extension effort through Fiscal Year 2011.
Operational Plans
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, CA.
Recent testing demonstrated the 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,” the Air Force reported.
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