How Boeing's lean manufacturing team cut costs, cycle times on the F/A-22 Raptor stealth fighter program
By Patrick Waurzyniak
Aerospace manufacturers face constant pressures to control costs and ensure quality on mission-critical projects while keeping defense programs on track to meet stringent delivery schedules. Faced with tough choices, The Boeing Co. (Chicago) implemented a lean manufacturing program on its project to build the airplane wings and aft fuselage for the US Air Force's next-generation F/A-22 Raptor fighter/attack aircraft, leading to dramatic improvements in cost reductions and cycle times in building those key components for the new stealth fighter plane scheduled to begin service later this year.
With Boeing's lean manufacturing effort, the aerospace giant was able to gain dramatic reductions in both costs and cycle times, boosting productivity and efficiency on its portion of the contract to build the Raptor, the air-superiority successor to the US Air Force F-15 Eagle fighter. Boeing builds the Raptor's wings and aft fuselage, key components with advanced aerodynamic designs and crucial fuel delivery and controls systems.
The F/A-22 Raptor fighter program is shared by several aerospace manufacturers, with Lockheed Martin Corp. (Bethesda, MD) and Boeing being the major contractors, along with aircraft engine supplier Pratt & Whitney (East Hartford, CT), machining supplier GKN (St. Louis), and other subcontractors. Lockheed and Boeing as primary contractors own 67.5% and 32.5%, respectively, of the overall project, and Lockheed Martin Aeronautics Co. plants in Marietta, GA, and Fort Worth, TX, assemble the other major pieces of the aircraft with the jet fighter's final assembly at Lockheed's Marietta facilities.
Lean manufacturing methodologies deployed by Boeing on its Raptor fighter effort included value-stream mapping, high-performance work teams, determinant assembly, and extensive use of an advanced lean manufacturing technique called 3P, Production Preparation Process. Construction of the Raptor wings and aft fuselage takes place at the Boeing Integrated Defense Systems (IDS) Developmental Center, a 710,000 ft2 (66,030 m2) manufacturing facility in Seattle. The facility features large areas for composite fabrication, development prototypes, test labs, quality assurance, and emergent manufacturing, which includes sheetmetal fabrication, tooling, machining, and a tube shop, and it houses the 180,000 ft2 (16,740 m2) area where the F/A-22 wings and aft fuselage assemblies are built.
Key to Boeing's lean effort on the Raptor program was reducing, or even eliminating, the aircraft maker's huge monument tooling, the extremely large fixtures or jigs used to build large aero structures like airplane wings that typically require hundreds of costly, time-consuming crane moves. By implementing new lean techniques, Boeing's IDS manufacturing management was able to eliminate the large jigs for the aft fuselage construction, allowing for much more productive plant layout with improved product flow through the factory.
The Boeing F/A-22 lean program traces its roots to as far back as the late 1990s when Boeing was still grappling with issues traced to its acquisition of aerospace rival McDonnell-Douglas. The lean program started in early 2000, with initial efforts taking on a shotgun approach, putting out fires as needed, according to John C. Dickson, lean manager for the Boeing F/A-22 Raptor program, who notes: "It really started out as a product change--how do we make a product increase its velocity? Ninety percent of our time was focused on enhancing the product, enhancing the tooling, and now 90% of our time is on the people side of lean, which is everything."
Before implementing the lean program, Boeing managers devised a high-level plan on how to increase speed in the Raptor assembly before presenting it to the plant's workers. "We came up with a rough plan, we didn't have all the specifics, but this is where we really started getting our employees involved," Dickson recalls. "This is where the teams started sprouting up. We came from a culture of predominantly firefighting, reacting to fires that were burning. The questions were: 'How do we get more into fire prevention mode? How do we get people ahead of what was coming, and ensure those fires don't start burning?' We had to culturally take a whole group of people and let them focus on that with an innovative product team to define technically where we're going."
By 2001, the F/A-22 management team's lean leaders had crystallized its lean manufacturing philosophy into the Lean Vision 2005 program, which helped managers work with teams of mechanics to lay the groundwork for goals on a successful lean program. The Vision 2005 lean system has since been replaced with a Vision 2008 program, with updated goals for employees and management.
The Lean Vision 2005 plan, made into a poster for the factory floor for visualizing key lean concepts for reducing waste, included 6S (Sort, Simplify, Sweep, Standardize, Self-Discipline, Safety); 9 Tactics (Value Stream, Balance the Line, Standard Work, Visuals, Point of Use, Feeder, Breakthrough Redesign, Pulse Line, Moving Line); and Best Practices. Part of the lean effort also emphasizes pushing work back up the value stream, even back up to suppliers, following Boeing's moves to outsource much of its major metal machining, sheetmetal forming and fabricating to outside suppliers (see the article "A Look at Boeing's Outsourcing Strategy" in the March 2004 issue of Manufacturing Engineering.)
Out on the factory floor, construction of the F/A-22 wing and aft fuselage assemblies previously employed unmovable monument tooling--legacy tooling consisting of giant assembly jigs bolted to the factory floor. The Boeing lean effort jettisoned such hard tools, where possible, in favor of highly flexible, modular, and moveable assembly lines that vastly improve factory flow and greatly reduced the number of crane moves for both wing and aft fuselage assemblies.
Weighing 2000 lb (900 kg) each at delivery, the Raptor wings are constructed using huge cranes and monument tooling. The 16 X 18' (4.9 X 5.5-m) wings feature an integral fuel tank, and construction includes one-piece composite wing skins, structural titanium side-of-body castings, resin-transfer-molded (RTM) sinewave spars, and machined complex titanium parts.
Modular assembly, fewer crane moves, and a balanced pulse line on the wing construction helped Boeing reduce cycle times from more than 75 days to 35 days at the maximum rate. Instead of traveling miles, the wing hardware instead travels feet in the factory using the lean system. "The manufacturing engineers on this team were key members leading our 3P process. We broke down by project and those different modular assemblies were led by manufacturing engineers," notes Dick Dols, Boeing F/A-22 manufacturing engineering manager. "They're the interface between the design engineers and the factory floor."
With its lean teams, Boeing brought together personnel from the shop, engineers, and managers. "We need to engage all of our people out here in this activity," says Tom Kelleher, Boeing F/A-22 assembly center manager, "When I say all of the people, it could be a high-performance work team, or in some places we call it a self-directed team. It consists of not only mechanics, or the individuals touching the hardware, but manufacturing engineers, a manager for the area, a production control person, the quality assurance person, an industrial engineer--they are all part of that team. We don't say the manager of an area has certain targets, the team has a certain target; so they have the ownership, they have the empowerment to make that happen.
"What we're seeing out here, cost is going to be a big issue," he adds. "We want to turn the material, the inventory over, at a faster and faster rate. We want that material, that inventory, at point of use right here for the mechanics. We want our defect rate to be reduced, and that's this team's responsibility. It's an innovative lean manufacturing approach, using high-performance work teams and a lot of different elements of lean."
In the wing assembly, modular assembly and parallel lines have helped speed Raptor wing production. Boeing's wing process previously had 78 parts individually tool located and 120 joints located, drilled, sealed, and fastened on the backbone of the assembly. With the lean effort, the wing assembly features four major subassemblies with 38 joints, removing some work from the backbone.
"In the wing line components, our customer's critical feature is the interface, where the hinge lines mate up to the fuselage," Dols says. "We've taken those features and have established them at the supplier. We index to those features, and then we build off of that index. That alone is probably the most radical concept that we've put in place for the wing, because we took a choke point at the end of the line and moved it upstream as part of a parallel effort.
"It would have taken us, in some cases, three and four weeks to get to the hinge boring operation completed because we had to do it sequentially," Dols adds. "We had to do it side by side by side. The wing is a triangular free-shaped part, so what we're looking at here is our trailing edge. Indexed on the bottom of our tool is the hinge line. That's what our customer indexes to, and it's full size, ready to go into an F/A-22."
On the inboard spar, the wing has a small titanium clevis fittings at the hinge surface locations. "Lockheed Martin puts on those control surfaces--that's the most critical feature," Dols says. "That's the first part that gets loaded into the assembly jig. That's home, and everything else gets built off of it."
Determinant assembly speeds production as well as improves quality. "Many of the components that you see here are piloted, and all we do is locate the holes," Dols says. "That's reducing the amount of time that we have to spend in this position by having those features there already."
Employing 3P techniques enabled the Boeing team to visualize with mock-ups how to best improve what was a time-consuming, stick-build operation in assembling the wings. "What we did was model our time-consuming assemblies to determine how to drastically reduce flow," notes Dickson. "We had to determine how to go from our existing assembly flow and reduce it by two thirds. So what we did in series, we figured how to do it in parallel. We developed a balanced assembly plan. It enabled us to enhance our flow by over 60%, just by more properly, and smartly, putting the structure together."
With 3P lean tools, the IDS team did floor mock-ups, generated seven solutions, and selected the most appropriate, Dols says. Drawing from lean work done by other Boeing facilities, including the 737 commercial airplane group in nearby Renton, WA, and Boeing's Apache helicopter lean line in Mesa, AZ, the team borrowed, or "stole shamelessly," as Dols says, to help improve the Raptor processes. "We tested a whole lot of concepts, building those mockups," Dols recalls. "We had design and manufacturing engineering personnel, the tooling people, and the factory mechanics all working as a unit to develop what those concepts would envision going forward."
The wing AJ, or assembly jig, is the same for the most part, adds Kelleher. "The difference is what gets loaded into that jig. Before the redesign with the 3P, all those parts were pretty much stick-built, one at a time," Kelleher says. "Put one in, put in another, and locate it, then another, then another. Now, these are the modular sub-assemblies. ... Once those modular pieces are put in there, the structural wing box itself is pretty much intact. The crane comes over, grabs onto that, and lifts that entire triangular-shaped AJ out of there with the assembly."
While in the jig, the wings get skin panels installed on the upper and lower surfaces with mechanics applying a liquid compound called moldable plastic shims (MPS) that then hardens. "It's basically a filler, or an epoxy, that we put in," Dols says, "which is part of our design and our process."
After the wing skins are attached, the blue AJ is lifted by crane and dropped into precision drilling machines. "It'll sit there for about nine days while they drill through the skin, through the composite and titanium spars beneath, establishing the fastener holes," Kelleher notes. "There are 3500 holes in the upper, another 3500 in the lower, of each wing, a left-hand and a right-hand wing. A tremendous amount of work has been done to automate the drilling, which is somewhat of a proprietary process. What I can say is that it's highly accurate, with very few if any quality defects on the holes and the countersinking.
"It's a pretty sophisticated system. After the holes are drilled, it gets picked up again, moved on this line, dropped into one of the jigs down there, and they will attach the lower wing skin to that wing box. Then mechanics put fasteners in all those holes and cinch it down. In the next position, they will install the systems that are required--hydraulic, fuel, and a couple small electrical, internal systems. We'll do a FOD [Foreign Object Detection] check, a particle check, before we put the upper wing skin on. You do not want a particle traveling through that system in your engine. When we're done, you will not find any, literally any, particle in that wing. That is the most stringent thing we do, because it could cause a fatality."
In addition to 3P mock-ups, Boeing also uses extensive digital mock-ups with simulation tools from Delmia Corp. (Auburn Hills, MI). Says Dols: "We've invested very heavily with bringing in the Delmia suites that will take the version of software we're using now for our design and allow us to get into the more desirable tool to help us with the simulation."
Loaded with critical aircraft systems including fuel tanks, the aft fuselage measures approximately 12 X 20 X 5.5' (3.7 X 6.1 X 1.7 m) and the large structure houses two Pratt & Whitney F119-PW-100 turbofan engines equipped with afterburners and the two-dimensional thrust-vectoring nozzles that give the Raptor its exceptional maneuverability. Each engine is in the 35,000-lb-thrust class, propelling the warbird at a top speed of Mach 2. The aircraft also features a supercruise mode of Mach 1.5 or faster without using the afterburner, resulting in substantial fuel savings for the stealth fighter.
Featuring integral fuel tanks, doors, systems, and engine attachments, the aft fuselage has contoured titanium/honeycomb structural doors and complex contour composite/honeycomb skin panels. The forward and aft booms have electron-beam weldments, and the components feature complex, five-axis machined titanium die forgings. Previously built with huge monument tooling, the aft fuselage assembly allows shop-floor workers to move the fuselage, weighing 5000 lb (2250 kg) at delivery, around the factory floor during the assembly process using the roller-equipped fixtures.
Aft fuselage factory flow improved most dramatically with the lean effort, reducing multiple crane moves to a single crane move with a greatly reduced floor space and a balanced moving line. Cycle times for the aft fuselage fell from 60 days to 35 days at maximum rate with the changes. Instead of using monstrous "hard tools" with assembly jigs weighing roughly 144,000 lb (64,800 kg), the new system allows virtually unlimited flexibility with smaller fixtures with rollers capable of being moved by factory floor workers.
"We were very heavily dependent on overhead crane moves," Dols says. "If you think of flow and throughput, mechanics are out working on the floor adding value to the product, but if they had to call somebody to get a crane and move a part, that's a major disruption to your flow. We had hundreds of crane moves in our factory. To improve the process, we put the tooling on wheels, and now you have a whole lot more flexibility. You can move by forklifts, or by manpower--it's on wheels, you've got flexibility, and we increased our options there."
Without the monument tooling, Boeing was able to rebalance the work flow throughout the aft fuselage line. "We had what we referred to as monuments, which drive their roots into the ground like Sequoia trees," Dols notes. "Our tools were just like that. Any time you've got a hard fixture that is lodged in the concrete, with a monolithic concrete foundation on things, you become rigid. It is there for a reason--it's intended to be stout and last forever.
"That's the traditional aerospace methodology, which is lag it to the ground, make it weigh about 14 times the weight of the hardware that you're building, be able to withstand earthquakes," adds Dols of the floor-mounted assembly jig. "With the modular assembly approach, the new concept that we brought out that we're using on the aft body right now is where we rely very heavily on advanced technologies like determinant assembly, which was working within the engineering definition."
The Boeing team challenged itself to come up with solutions that fit the existing plant footprint, Dols says. "No brick and mortar can change--you can only work inside those four walls," he says, "and when we add, we have to look at it and see if there's a way to balance the work. We said we have to be modular, have parts coming in subassemblies, rebalance the work, and rely more on manpower than crane power. Everything was designed to be at the disposal of the mechanic on the floor, and ergonomics were part of that."
Since employing the 3P tools, the F/A-22 lean team has had units within the company seek its help on how to use the techniques to improve factory flow at other Boeing manufacturing sites. "Our 3P was a breakthrough, recognized throughout Boeing Co. as just that," Dols says, "and referenced in our Lean Manufacturing Assessment, an internal tool that we use at the Boeing Co. and Integrated Defense Systems."
This article was first published in the March 2005 edition of Manufacturing Engineering magazine.