H-46 Sea Knight production line at Naval Air Depot Cherry Point, N.C.
Steve Campbell, Naval Air Depot Cherry Point welder, uses a gastungstenarc welder and 0.030-inchdiameter wire filler to make spot weld repairs on the 0.064-inch-thick wire mesh air intake of an H-46 Sea Knight helicopter.
Replacement mesh patches (left) are carefully sized and welded into place to repair the damaged air intake sections (right) of the H-46 air intake.
This 0.080-inch-wide hand weld was done on 0.014-inch-thick Nimonic 75 sheet metal, part of the reaction control system for the AV-8B vertical/short takeoff and landing jet flown by the U.S. Marine Corps.
Cracks in a J79 engine combustion holder assembly for an Air Force F-4 jet require time-consuming manual welds during the repair process. The combustion chambers made of L-605, a metal alloy with high cobalt content, have an average of 100 cracks in each assembly. Repairs on each assembly require an average of 10 hours of labor.
U.S. Marine Corps Lance Cpl. Ryan Rodriguez uses sandpaper to clean metal edges to ensure a proper weld.
David Webber (left) goes over aluminum welding techniques with U.S. Navy AM3 Daniel Maiso. Webber is Naval Air Depot Cherry Point's welding instructor for fleet training.
J.R. Uzzell, welding work leader, uses an automated plasma welder to build up T64 air seal "teeth."
An artisan points out wear damage to a pylon clamshell frame.
Naval Air Depot Cherry Point engineer and artisans discuss repairs for a GE T58-16 main engine harness. The T58 engine powers the H-46 helicopter in the background.
An engineer and artisan at Cherry Point discuss vibration issues related to the forward avionics closet in a CH-46E Sea Knight helicopter.
How many commuters drive cars that last 30 to 40 years or use the same computer for 15 years and have both operating as they were designed because a professional preventative maintenance program has kept them up to date? Every time a military helicopter that has gone through the Naval Air Depot Cherry Point is flown on a new mission, its flight is proving the viability of the Navy's preventative maintenance program.
At Cherry Point, N.C., 4,000 employees work within 1.5 million square feet of production space to keep helicopters flying as designed. Cherry Point opened in 1943 as an aircraft assembly and repair department, and ranks as one of the largest industrial employers in eastern North Carolina. Civilian, military and contractor personnel, working in a variety of skilled technical and professional positions, provide maintenance and engineering support to Navy and Marine Corps aviation units, and to the other armed services, federal agencies and foreign governments. The craftsmen at Cherry Point know how to maintain, rebuild and refurbish 30- to 40-yearold helicopters. These artisans are the type of people who go home from work to revive trucks, tractors, steam engines or Model A Ford cars. The Naval Air Systems Command operates two air vehicle repair depots, one in Jacksonville, Fla.; the other in North Island, Calif. The air vehicle repair depot in Cherry Point is under the command of the Navy's Marine Corps, and specializes in the repair and maintenance of hovering and short-take-off-and-landing (STOL) and vertical-take-offandlanding (VTOL) vehicles.
"If it hovers, we repair it," says Mark Sapp, materials engineer at Cherry Point. "We service all models of H53 helicopters for all services — Marines, Navy and Air Force. These are the largest helicopters flown by the U.S. military for troops and cargo. We support the 'war fighter,' the person on the front line of battle."
When a helicopter arrives — either flown in by a crew or shipped in a box — workers strip it to its skin and search for cracks, corrosion and wear, and they determine the required repair work. Then the journeymen begin the process of rebuilding components, including machining parts, welding engine components and sheet metal, and perform tests and inspections. They reassemble the three-dimensional jigsaw puzzle then test some more. After a Marine pilot gives it a test flight and airworthiness is documented, the aircraft is ready to be returned to service.
A multitude of skills, time, effort, cost and dedication is needed to repair or remanufacture each component to keep aircraft such as a $30 million H-53 helicopter flying.
This drive for perfection becomes evident in the care taken in sheet metal forming, part machining and welding, and places Cherry Point among the elite rebuilders of helicopters in the U.S. military.
Support the "War Fighter"
Cherry Point's personnel perform major airframe modifications and repairs for a wide variety of aircraft used by the Department of Defense including the AV-8B Harrier, the VTOL tactical attack jet flown by the Marines, the medium-lift transport H-46 Sea Knight helicopter, the H-53D Sea Stallion helicopter, the H-53E Super Stallion helicopter, the Air Force's MH-53J helicopter, the AH-1 Cobra helicopter and the UH-1 Huey helicopter. "We can rebuild 80 percent of these aircraft," says Sapp, who earned a welding engineering degree from The Ohio State University. "We need these capabilities because some planes are no longer manufactured, some for the current war were brought out of storage, or we can't locate the parts. Sometimes the lead-time is too short or the price is too high to have the original equipment manufacturer make a single part, compared to repairing the part.
"Each welder approaches a repair in his or her own manner or with the assistance of engineering to determine the best or most capable method to repair an item," says Sapp, who has experience as a welder in the Navy, the Air Force Reserves and with the Seabee Reserves. "They work with alloy steel, nickel, stainless steel, cobalt, titanium, aluminum and magnesium."
At the depot, sheet metal 'artists' use a range of methods from laserbeam cutting to hand tools to form the metal precisely to the shape needed. The welder puts forth his or her best skill to 'stitch' the part back together, much like a quilting bee, to form a seam that blends into the sheet metal.
Work at Cherry Point is unique because the craftsmen repair 30-yearold aircraft and auxiliary equipment, where the designed-for life of the aircraft is long past. Some replacement parts are not available, yet the aircraft must be certified for airworthiness. The original manufacturers rarely repair their own components, so the depot is genuinely self-sufficient.
"Our welders are tasked with making tedious repairs," says Sapp. For example, Steve Campbell, with 17 years of service, repairs air inlet screens made from 0.064-inch 302 stainless steel wire mesh welded with 0.032-inch-diameter 302 stainless steel weld wire. The original mesh was spot-welded. When the wires cracked some were repaired with silver braze. Pieces of fractured wires can wind up inside the engine, sometimes with catastrophic consequences.
The engineer, the artist
Military pilots demand plenty from planes and components, so repairs must be accurate and reliable. As engines and parts are removed from the aircraft, they are routed to the various in-house shops for maintenance.
This includes gutting an aircraft and routing hundreds of parts for examination and evaluation. Each part has a route document that corresponds to a technical manual for repair. When a part does not have a repair established, either through legacy original equipment manufacturer repairs or through local engineering repairs, then engineering finds other resources for the repair or buys the equipment to make the repair. The craftsmen specialize in the manufacture and repair of frames and sheet metal, engine repair, and engine blade and vane repairs.
Engineering personnel work sideby-side with depot production artisans to ensure a quality product is produced the first time. Engineers also develop overhaul, repair, test and troubleshooting procedures when needed. The repair also may require materials engineering services, such as metallurgy, chemistry, and engineered polymers, or testing and related specialized instrumental analyses.
"Because of our operating conditions, we rely on our experience and state-of-the-art equipment to redesign and build replacement parts to meet engineering specifications and quality," says Sapp. "We do little textbook work. Our team members are artists who meticulously re-create parts via machining and welding."
The deport has millions of dollars of CNC and robotic equipment to overhaul, and U.S. Navy, Marine Corps and Air Force helicopters and Marine Harriers (jump jets), and is gearing up to make repairs to the Marine Corps V-22 Osprey.
"We can translate drawings into computer programs to manufacture form blocks. We even have a small foundry for making Kirksite form blocks," states Sapp.
"Manufacturing includes tube bending and welding or silver brazing of fittings from three-inch-diameter aluminum down to 0.125-inch titanium tubes, plus work-hardened manganese stainless steel tubes for hydraulic lines," states Sapp. "We have patterns for every tube on every aircraft that we work on. We can make a pattern from parts of existing tubes with our portable, articulatingarm coordinate-measuring system."
The sheet metal department uses metal forming technology to make one or two parts to maintain these planes and inventories include most original equipment manufacturer tooling and forming blocks. If the tooling is not available, teams replicate the original. The facility's material storage inventory includes at least one piece of all material and thickness used on the planes.
Welders work in three shops with glass-bead cleaning machines, manual welding machines, an eight-axis robot gas-tungsten-arc welding cell, three GTAW automatic welding machines, two resistance welding machines, orbital welding equipment and oxyacetylene torch welding for silver brazing. They have even done gold brazing.
One weld booth is dedicated to welding only magnesium thorium, a metal used to weld a limited number of airfoil pieces for the Air Force.
There are six vacuum brazing machines for nickel braze repairs, two thermal spray shops with robotic oxyfuel gas and plasma units, and a computerizedshot-peening machine-for surface conditioning.
To verify weld quality, the staff can inspect and test with every conceivable nondestructive inspection (NDI) method available including magnetic particle inspection (MT), penetrant testing (PT), meandering wave magnetometer (MWM), radiographic testing (RT), and ultrasonic testing (UT).
There is a heat-treat shop, with furnaces reaching 2,400 F, and complimenting those furnaces are ovens to process sermatel and pack aluminde. The depot has a fully functional surface treatment building for nickel, silver, cadmium and chrome plating.
All steel, aluminum and magnesium components that are processed through the deport go through clean shops and prime and paint shops for some form of metal conditioning.
"The welder's sense of responsibility shows as he takes on ownership of each part," says Sapp. "The welder knows that the aircraft worthiness --the life of the flight crew and the effectiveness of the plane - depends on his skills. He cleans and preps the parts, selects and applies the correct filler metal, and performs in-process visual examinations of the weld to meet the engineering instructions."
While many types of repairs are repetitive, welders often face new challenges. Welders can analyze the issues and submit documentation requesting alternate welding methods or weld filler metals be used to improve the repair or the workflow. One such challenge had welder Terry Jones and apprentice Daniel Selby working to program an eight-axis GTAW robot to weld with a high nickel wire because the workpiece — made of PK-33, a British nickel alloy — is sensitive to heat.
"With manual welding we would have many starts and stops, each generating heat stress," says Jones, with 23 years of service. "Manual welding would take six to eight hours compared to 15 minutes with the robot." The team has minimized manual welding to a few 0.094-inch tack welds needed to hold a maximum 0.002-inch gap in the weld joint.
Using the robot to weld the piece provides a single start and a single stop, and produces a continuous isotherm that relieves stress. For proper penetration they use the recommended amperage and a slow feed rate, using as much of the base metal as filler as they can. They also use a robust copper chill block ported with argon gas for faster cooling of the heat-affected zone.
The skilled pair is seeking a solution to another welding problem: They are experimenting with programming the robot to weld a butterfly insert on a three-dimensional weld joint, saddled within a large three-way exhaust duct, also made of PK-33. With limited access for the torch, the challenge is to program the eight axes and make the torch head reach the various weld joints axes. As they get closer to the correct program the team can "feel" the solution is just a few experiments away.
"The welding skill level here is shown by a recent co-op who wanted to join our apprentice program," says Sapp. "He was completing a welding program at a two-year college. I asked him to weld a six-inch bead on the edge of a 0.032-inch-thick piece of aluminum. He put five beads on that edge barely wider than the workpiece. I knew he earned a place in our 3,000-hour apprenticeship program that runs for four years."
Deviating from the routine aircraft repairs, Sapp took on the task of repairing the cast-iron air compressors used in the shops, and saved the depot six months time by welding and machining them in-house rather than sending them back to their manufacturer. Welders used a nickel weld metal to eliminate corrosion, which was the cause of the air leaks.
"By nature we try to make parts better. "We've been repairing a fuel nozzle used on the T-64 engine. We use an induction-brazing machine to reweld the tip on the nozzle. If the nozzle tip comes off, it can damage or destroy an engine. So we experimented to find a better fix," states Sapp.
To improve the repair, Sapp decided to machine longitudinal " fingers" or grooves on the nozzle to give more "grip" for the silver braze and to minimize shearing at the braze joint. For good measure, they put a resistance spot weld on the nozzle tip.
Since these steps were added, none of the repaired nozzles have failed in testing. These extra steps have likely kept helicopters in battle, rather than down for engine repairs.
Tax dollars at work
The people at Cherry Point are responsible for a variety of aircraft, engines and components including worldwide engineering and logistics management in both the maintenance and design fields.
Engineers and logisticians identify and resolve supply, maintenance and design-related problems to solve problems and reduce ownership costs. The depot supplies emergency field teams, fleet training, engineering support and calibration to fleet units worldwide.
In one year's time, for example, the depot sent more than 400 teams to 10 countries and 20 states. Several years ago a team salvaged a crashdamaged C-130, buried nearly 17 years in Antarctic snow. The aircraft was repaired and modified at the depot and returned to the Navy.
During Operations Desert Shield and Desert Storm in the early 90s, the depot provided on-site support through aircraft damage repair field teams whose work included interservice aircraft, Cruise and Patriot missiles, electrical calibration and other critical equipment. Civilian engineering personnel worked in front-line areas to assist in aircraft maintenance and repair. Today, artisans, engineers and military personnel from Cherry Point travel to various locations in the Mideast to support the U.S. military's efforts.
"We earn most of our revenue from maintenance, repair and overhaul of engines, airframes and components," states John Whitehurst, common industrial processes director at Cherry Point. "Depending on the needs of the warfighter, we will review the availability of difficult-to-obtain parts and perform a cost-benefit analysis to determine whether we have the capability to manufacture or repair. Usually, because of long lead times to obtain replacement parts and our cost control efforts, our costs end up lower than from other sources."
Engineers and logisticians have worked with prime contractors to set logistics and maintenance requirements for the V-22 Osprey helicopter, slated to replace the H-46 Sea Knight.
The Industrial Engines Repair and Modification Division overhauls and repairs numerous aircraft engines for a wide variety of military aircraft. More than a third of the depot's production effort is dedicated to revamping aircraft subassemblies, avionics and engine accessories. Craftsmen repair thousands of types of avionics and dynamic components, such as pressurization units, air starters, valves, gauges, regulators and pneudraulic components.
"In another area we have cooperative programs between the Navy and OEMs where each partner does a part of the project to save the taxpayers money," says Whitehurst. "Since 1991, we have provided a cost avoidance of $300 million on engine turbine blades and vanes that that can instead be spent to purchase additional parts or repairs. We have been selectively upgrading our equipment for 60 years to meet the needs of the military's aging aircraft. The H-53 helicopter, last built around the year 2000, is our newest plane."
The welders have to learn to read drawings from various manufacturers, each of whom have their own methods of naming or indicating information. The depot deals with more than 80,000 parts for these helicopters, and they have made 30,000 to 40,000 replacement parts because the original manufacturers have stopped making parts for most of the aircraft that they work on. There are efforts to reverse some of this trend through partnerships with the original manufacturers wherever possible.
"We can speculate on what equipment could do to benefit our operation," states Sapp. "We get information from conferences, welding networks and visits to OEMs and other military locations then, we do more R&D so we can stay within tightening budgets.
"One way to measure the value of our operations is the number of foreign air forces that send their helicopters, engines and components here for repairs," says Whitehurst. "We get components from Canada, Italy, Greece and many other countries.
"During our 60 plus years of existence, we have been an integral part of the local community," says Whitehurst. "We have two-year college grads in our apprentice program. We've earned state and national environmental awards. The work ethic of our employees is transferred to local clubs, churches and civic organizations." These artists and craftsmen not only apply their talents to repairing helicopters, but to improving their neighborhoods.
Terry Jones is one of the welding artists at the Cherry Point Naval Air Depot in North Carolina. He has 23 years of experience as a welder, and works with apprentice Daniel Selby.
They are seeking a solution to a welding problem: They have to weld a butterfly insert on a threedimensional weld joint, saddled within a large, threeway exhaust duct for an aircraft engine.
The part is made of PK-33, a vacuum-processed, nickel-base alloy made in Britain.
There is limited access for the torch, and the challenge is to make the torch head reach the various weld joints axes.
Jones and Selby are experimenting with programming an eight-axis robot to do the job, and feel the solution is just a few experiments away.
Training: The Foundation for World-Class Welding
"All of our welders are qualified to MIL-STD-1595 and grandfathered into AWS D17.1, 'Specification on Fusion Welding for Aerospace Applications.' says Mark Sapp, materials engineer at Cherry Point.
Instructors teach students, coming from the Navy, Marine Corps, Coast Guard, Army, Air Force and civilian population, using a licensed course from the Hobart Institute of Welding Technology and modified to aviation-specific training.
"We provide formal training, certification and necessary instruction in basic welding using the gas-tungstenarc welding (GTAW) process on carbon and alloy steels, aluminum alloys, precipitation-hardening stainless steels and precipitationhardening nickel alloys, with additional certifications in magnesium, titanium and cobalt alloy," states Webber. Begin with Clean Metal "The focus of training is clean metal to minimize porosity, then torch angle and feed control," says Dave Webber, an instructor with experience as a welder in power plants and traveling maintenance. "We train welders to a skill level so they can make welds under field conditions using the equipment at hand."
"Classroom topics include metallurgy (material groupings and chemical composition), physical strength and application, mechanical properties of the base metals and alloys, such as ductility without failing, and heat treat conditions," says Webber. Students cover weld symbols, weld terminology, welding requirements, joint preparation and welding procedures. The metallurgical lab evaluates test 2G/2G groove welds by X-ray and 3F position 'Ts' by metallographic inspections — cutting sections of the weld and examining for penetration and porosity.
"Each trainee starts by running stringer beads. Once they learn heat control, travel speed and filler wire dipping skills, they advance to groove welds, then fillet welds in that alloy group," says Webber, who has a reputation for expecting and getting premium quality welds. Perhaps his mix of preacher and motorcycle rider sets the classroom tone.
The primary course runs eight weeks. The training lab includes 16 booths for GTAW, four booths for shielded-metal-arc welding and gas-metal-arc welding, and five portable oxyfuel outfits for silver brazing.
Trainees are certified to weld on metal that is between 0.42- to 0.250-inch thick using 0.063-inch-thick test plates. Certifications cover welding alloy steel 4130, PH stainless steel A286, PH nickel alloy Inconel 718 and aluminum alloy 6061-T6.
The current certification positions are 0.032-inch 2G and 3G for civilians and 0.063-inch 2G, 3G and 3F for civilians and military personnel. The certification program is based on the American Welding Society D17.1, Specification on Fusion Welding for Aerospace Applications.
Through on-the-job training, an apprentice learns how important cleaning a crack is to the process of completing an acceptable weld. The apprentice was repairing cracks — in the 0.0125-inch-long range — that could be repaired under field conditions. These were not always the best welds, but always done well enough to save the plane or to get it back to a shop.
The apprentice's first repair welds failed inspection because he did not thoroughly check for contamination. He quickly learned to take off all of the old weld metal then prep the crack for welding.
Apprentice challenge: How hard is that?
Mark Sapp, materials engineer at Cherry Point, says a student who recently applied for the facility's apprentice program was given the following task:
Weld a six-inch bead on the edge of a 0.032-inch-thick piece of aluminum.
Sapp says the student "put five beads on that edge barely wider than the workpiece," and earned a place in the facility's 3,000-hour, four-year apprenticeship program.