Bonded Nutplate Removal

My first project in the Manufacturing Technology group at Lockheed Martin Aeronautics was to develop a better method to remove bonded nutplates from fiber-reinforced composite parts.

Problem Overview

nutplates bonded in close proximity
Open-type nutplates bonded in close proximity

Nutplates are used extensively in aerospace to secure threaded nuts in place for fastening. Sometimes nutplates are bonded incorrectly and need to be removed; if not heated properly prior to removal from a composite substrate, layers of composite may detach with the adhesive. I was tasked to develop a convenient, reliable method to heat and remove nutplates to prevent further composite damage in F-35 production.

The problem had challenging constraints. Nutplates vary in type/size, and are typically installed in confined spaces and in close proximity. Heat must be localized to the nutplate to protect nearby systems, and temperature must be controlled precisely as overheating can also damage composite.

My Solution

nutplate induction heating prior to removal
Patent application drawing: induction heating of a domed-type nutplate prior to removal

I developed an induction heating solution that worked rapidly, localized heat to just the nutplate within the wire coil, and by bending the wire could reach nutplates in confined spaces. Though less conventional, this proved superior to the conduction and convection-based heating alternatives I tested. Using Design of Experiments (DOE) I analyzed the effects of nutplate type, size, and location on temperature and determined the ideal pulse time. I also evaluated temperature monitoring options (thermocouples, infrared, indicating labels, etc.)

I was also responsible for obtaining approval for my solution and integrating it into F-35 production. Using ultrasonic inspection, I verified that induction heating did not cause internal composite damage. To obtain Environmental Safety and Health approval I measured the electromagnetic field around the the tool. I worked with a vendor to incorporate a time delay relay into their handheld induction heating tool, and sell it in a kit with preformed coils and our chosen temperature probe. Finally, I wrote training materials and oversaw the first production trials.

I submitted a patent application for my solution and received an Inventor Award and Certificate of Achievement from Lockheed Martin.

Patent Application

Neal Seegmiller and Stuart Street, System, method and apparatus for pulsed induction heat removal of components from structural assemblies, U.S. Patent Application Number 12/407,005, Publication Number 2010-0237054, Filed Mar. 19, 2009

Copyright © 2014 Neal Seegmiller