Source: United States Navy
Recently, artisans assigned to the Fleet Readiness Center Southeast (FRCSE) F-5 Production Line propelled the organization into the next generation of industrial aviation maintenance with the single pull of an electrical discharge machining (EDM) trigger.
After more than a year of careful training and testing on composite structures, FRCSE has finally employed the E-Drill on metallic structures. The event marks the first time the technology has been used on an aircraft within the NAVAIR enterprise. FRCSE’s F-5 Production Line is the first to utilize the E-Drill and if all goes according to plan, every aircraft production line at the command will possess the new technology in the not-too-distant future.
“The E-Drill is a variation of electric discharge machining that has been around the machining industry for 30 years or more,” said Dr. Luis Carney, FRCSE’s senior materials engineer and team lead. “FRCSE has taken a bit longer to introduce this technology because it took time to get our own unit, set it up, write the instructions, develop non-destructive inspection techniques, demonstrate the viability of the operation without harm to the structure, and finally obtain the authority to execute.”
Considering many aerospace rework facilities, including FRCSE, remove aircraft fasteners the conventional way – by hand with a drill and hammer or punch – once fully rolled out, the E-Drill system will significantly reduce the time it takes to remove the thousands of rivets touched during routine aircraft maintenance and repair.
The tool uses a computer-controlled electric arc, or spark, between the device’s electrode and an aircraft fastener. After localizing to a fastener’s shank axis, the E-Drill uses a pulse-cutting technique that measures, cuts, re-measures and cuts a second time — ultimately weakening the fastener, punching out the head and simultaneously flushing the opening with water to reduce the risk of damage from to molten material. The device also vacuums the area to remove foreign object debris (FOD).
The E-Drill was used on the F-5’s Vertical Stabilizer (V-stab), a static part of the vertical tail that stabilizes and balances the aircraft in flight, and the heat shield — or the titanium panels in the boat tail that protect the structural, mechanical and electrical components from the high temperatures produced by the engine and exhaust.
On some aircraft, V-stab removal is required, and its leading edge is full of fasteners – about 130 on the F-5 – and removing them by hand can take upwards of 16 hours. When the E-Drill is used on areas like the V-stab, it will save time – and a lot of it. The device takes a 16-hour job and reduces it to about three – a decrease of better than 80 percent.
Where removing fasteners on the V-stab is straightforward, the heat shield presents complexity.
The heat shields are curved and thin, but what’s more, they are also full of problematic steel fasteners that are difficult to remove because of spinning. When executed by hand, the process takes longer and forces workers to use larger drill bits.
“These steel fasteners have been the source of countless discrepancy work orders,” said Jeff Cavanaugh, FRCSE’s F-5 Production Line Lead. “When drilling, we have to attack these fasteners from various angles because of the spinning, and that can cause damage and deformation of the holes. When artisans punch the fasteners out, it’s not uncommon to crack the heat shields, which are not repairable. Purchasing new heat shields creates delays and further stresses an already strained supply system.”
While the technology is exciting and promising, learning the best way to balance the power of the E-Drill with the complexity of the contours and fragility of the heat shield requires more development before full implementation.
“While we have been slow in our roll-out of this device, it was methodical because understanding the device and making sure each artisan is thoroughly trained is vital,” said Cavanaugh. “FRCSE’s Materials Engineering Lab and Quality Assurance Branch developed a special process certification that’s imperative for artisans handling the E-Drill.”
The introductory training is expected to take about eight hours and will be followed by on-the-job training before artisans are ready to use the device alone, but they are already lining up to learn.
Time reductions are far from the only benefit the command will see. Substantial decreases in FOD, artisan injury, noise exposure and significant cost savings are also expected.
“The E-Drill significantly reduces work-related musculoskeletal disorders and hearing loss risks because, contrary to conventional drilling, there is no vibration or noise,” said Nancy Chung, an F-5 and P-8 process engineer with FRCSE. “It also vacuums all metallic shavings, virtually eliminating FOD.”
Further, FRCSE’s experts also anticipate big savings in consumable and direct labor costs.
Despite the command’s sheet metal artisan’s expert-level skill, the human element is a major factor. One minor misalignment can cost thousands of dollars and hundreds of hours of labor. Even the most frugal carbide-tipped drill bits come in at $2 per hole if everything goes smoothly, but as mentioned, old fasteners are often tough to remove, so it isn’t unusual for drill bits to break during conventional drilling. Whereas the E-Drill is pinpoint precise, and the electrode costs about $1.
While the E-Drill has only begun to make its cautious and calculated FRCSE debut, when it does become commonplace at command, the device is expected to revolutionize how maintenance actions are completed.
“Once the training, process control, and non-destructive inspection methods have been established, E-Drill is destined to be a common part of all aircraft production lines and component repair shops,” Dr. Carney said. “Eventually, I expect fifteen to twenty of these per depot and at least one at every squadron and intermediate-level facility.”
About Fleet Readiness Center Southeast
Fleet Readiness Center Southeast (FRCSE) is Northeast Florida and Southeast Georgia’s largest maintenance, repair, overhaul and technical services provider, employing approximately 5,000 civilian, military and contract workers. With annual revenue exceeding $1 billion, the organization serves as an integral part of the greater US Navy, Naval Air Systems Command, and Commander, Fleet Readiness Centers by maintaining the combat airpower for America’s military forces.