By Patrick WaurzyniakSenior Editor
A major subcontractor to Lockheed Martin Corp. (Bethesda, MD) on the F-35 JSF program, Northrop Grumman builds composite components for the JSF center fuselage at its El Segundo Manufacturing Center and assembles the system at Palmdale before shipping the completed airframe subassembly to Fort Worth, TX, where Lockheed Martin Aeronautics Co. performs the F-35 aircraft’s final assembly. The JSF program is projected to be among the largest military procurements ever, with approximately 3000 of the F-35 multi-role fighters planned for the US Air Force, Navy, and Marine Corps, British Royal Air Force and Navy, and potentially several allied countries. The first production F-35, an Air Force version, is nearing completion at Fort Worth and will fly later this year.
At the El Segundo facility’s composites center, Northrop Grumman builds the composite structures used on the JSF fuselage, as well as major composite airframe components for the US Navy’s carrier-based F/A-18 aircraft (see “Automating Airframe Assembly” in the March 2003 issue of Manufacturing Engineering). Besides the F/A-18 and F-35 programs, Northrop Grumman also builds composite and metal components and subassemblies for various aerospace/defense projects including the B-2 bomber, the T-38 training jet, the Global Hawk and the CEV (Crew Entry Vehicle) Space Shuttle successor.
Refining critical manufacturing processes can be more easily accomplished with collaboration among key players in the aerospace/defense industry. To solve vexing problems in aircraft manufacturing, Northrop Grumman engineers have been working in conjunction with partners in the Aerospace Automation Consortium (AAC), a group coordinated through Purdue University’s (West Lafayette, IN) School of Technology, on projects to develop new processes including automated burr-less drilling, structural flexible robotic drilling, rapid low-cost tooling for composite fabrication, automated shim application and part loading, automated fastening on assembly systems, and real-time locating systems. Significant contributions have been made to changes in traditional airframe assembly methods by strategic partners such as Comau Pico (Southfield, MI) and Nova-Tech Engineering Inc. (Edmonds, WA).
“Automation in the aerospace industry has been around a while, but more in the fabrication side of the industry,” notes Lance Bryant, director, production engineering, Northrop Grumman Integrated Systems. “In the last 10 years or so, it’s been more common in assembly. But to maintain the tolerances we need, we ended up building large monuments, in order to maintain accuracy in the thousandths of an inch needed for military applications.”
Such investments are costly, and are cumbersome to switch tooling as factory requirements change. For an aircraft like the F/A-18 E/F, there are some 40,000 OML holes to be drilled in Northrop Grumman’s section of the airframe, which can’t be easily done in an automated process, Bryant notes. On the F/A-18, Northrop Grumman builds the aircraft’s center and aft fuselage sections and twin vertical tails as principal subcontractor to Boeing, and then integrates all the subsystems that go into those fuselage sections.
Drilling airframe components constructed of composites with metal substructure such as titanium poses problems when trying to achieve positional accuracy, which is exacerbated by thick material stack-ups. Drilling the composite F-35 engine inlet duct, a bifurcated, serpentine structure, using advanced automation will improve quality and cost, Bryant says, so Northrop Grumman is working on strategic alliances with other aerospace consortium partners such as Comau Pico to develop new automation systems.
“The whole idea was to team up with other companies, instead of trying to do it alone,” Bryant says. “We all have the same issues. The solution was collaboration. If we come up with a low-cost solution, there would be a lot of upside. It’s a smart financial decision to become part of the consortium.”
Automating airframe assembly meant adopting a more modular system similar to the moving lines used by the automotive industry. At Northrop Grumman’s Antelope Valley Manufacturing Center in Palmdale, the F-35 integrated assembly line uses mechanized and automated systems for the aircraft’s center fuselage assembly, with a line that will become capable of producing one complete assembly per day of any of the three F-35 variants. To do so, the production line significantly reduces the use of traditional overhead cranes and larger assembly jigs in favor of an innovative Sequential Universal Rail Fixture, or SURF system, that moves parts and subassemblies between workstations within specific tool systems. The Palmdale factory also employs automated drilling stations that increase positional accuracy and throughput while solving worker-related ergonomic issues.
“Automation is not just a machine, it’s a process,” Bryant says. “That’s even more true today than it ever was. In the past few years, the big thing that has changed is that now there are no more monuments on the assembly floor. That’s what the Aerospace Automation Consortium is about.
“What was found, as we evolve, is that we start locking ourselves into a certain configuration of the assembly line,” Bryant adds, “because of huge machines with their foundations. Then if you come back and say, ‘There’s a better way of doing it now,’ the nonrecurring costs of relocating a massive machine with the foundation is too disruptive to the assembly line. It’s too costly, and not only that, it’s very difficult to do. How do you keep producing product, and make changes in the middle of everything, when relocating automation machinery and assembly tooling is such a massive undertaking?”
To create more modular automation, Northrop Grumman has created alliances with automation integrators, such as Comau Pico and Nova-Tech, looking at automotive industry automation and other methods to see what may work best for aerospace environments. “What we’re really doing is seeing how they’ve done business, and while it’s not all applicable to what we do, much of it is,” Bryant says. “We try to take what they have created and invented, and then try to apply it to our requirements.
“The fact is that with the car industry, their rate is so high that it pays to automate. Our production rate is not as high,” he adds, “so the nonrecurring costs, at times, don’t have the ROI, because we’re not building a thousand a day like the automotive industry. But they have done an amazing amount of development, and we can, and are, using a lot of those innovations to help us automate our assembly lines, and our fabrication houses, where it’s appropriate.”
With its integrator partners, Northrop Grumman has worked toward developing future automated drilling, assembly, and paint systems. “They’re working with us as an integrator to help us try to bring all the talent together to create more modular hole-drilling type of equipment,” Bryant says, “and they’re also working with us to develop an integrated assembly line for the F-35. The idea there is to have a line that is integrated so that it goes from position to position, without cranes, on a rail system, with health monitoring systems that would communicate where the assembly process is from a cost, schedule, and quality view, by embedding the diagnostic equipment into the line. Therefore, you’re verifying that quality is being built in as you go, not inspected in after you’ve built the product, which is defect prevention versus defect detection.”
Automated burr-less drilling, automated shim application, and structural flexible robotic drilling are among the projects Northrop Grumman is working on for future implementation. Drilling methods and technologies may help eliminate burrs created when drilling composite-metal workpieces for many airframe components. Eliminating deburring on metal substructures and liquid shim repair would save time and cost of repairing holes.“If manufacturing can drill a burr-less hole in composite-metal stack assemblies without damaging the liquid shim material, it would save a lot of time and money,” Bryant says. “We’re in the early stages of development and at a low manufacturing-readiness level for burr-less drilling. The industry’s been attacking this for ages. Another way we are trying to tackle this is with determinant assembly, which means that holes are drilled in the skin and substructure separately, and then have to match perfectly when assembled. In the end, determinant assembly might be the better way.”
Along with a more modular moving F-35 assembly line, Northrop Grumman’s working on developing robotic systems with its partners for structural flexible robotic drilling and automated shim application. Automated robotic application of high-tech coatings will enable aircraft like the F-35 and B-2 to maintain a low radar signature, and the application of these coatings requires an automated solution in order to correctly apply the viscous materials at a proper thickness without requiring extensive manual re-work.
With the automated robotics developments, Northrop Grumman is designing solutions before putting out competitive bids to suppliers. “These solutions are still being developed,” Bryant says. “One challenge is to develop the proper head design, packaged small enough so that it can get into tight areas. Kinematics routines are needed to attain the necessary motion analysis and positional accuracy. We also need to overcome rigidity issues inherent in lightweight systems, to make sure they are capable of drilling through thick structures. We hope to have a solution that we can implement in the 2007 timeframe.”
At the composites center in El Segundo, Northrop Grumman fabricates most of the composite workpieces used in its aircraft programs. The company also performs all of the drilling and assembly tasks for the F/A-18 program at the facility, as well as F-35 composite component fabrication. Automatic drilling machines from MTorres Group (Navarre, Spain) are used for holemaking on composite-titanium stacks of components for the F/A-18 E/F aircraft. The systems require extremely high precision on a large quantity of holes, with 2600 holes required for the F/A-18 aircraft’s twin vertical stabilizers alone.
“In my opinion, this embodies all the elements of the aircraft,” notes Nick Bullen, principal engineer, Northrop Grumman Integrated Systems, regarding the F/A-18 twin vertical stabilizers. “This part has elements including composites, steel, aluminum, and titanium, it’s used for fuel storage, and has hydraulics and electronics inside.
“These vertical stabilizer assembly parts are representative of the complexities contained in modern fighter and attack aircraft,” Bullen adds. “It’s one of the most stressed components. The more critical the component, the tighter the tolerances. Positional accuracy here is critical. This Automated Vertical Drilling Machine uses proprietary algorithms and data on the speeds and feeds. It’s a science.”
With a precision milling machine (PMM) from Droop+Rein (Bielefeld, Germany), a unit of Dörries Scharmann Technologie GmbH, the Northrop Grumman facility machines composite parts for the F-35 airframe assembly. “It drills, trims, and mills, to very tight tolerances in the low thousandths, over a large envelope,” says Bryant of the five-axis PMM.
The gantry-mounted PMM is set up in a temperature-controlled room, and the airframe parts are first put through a wash to normalize temperature to within a couple degrees of ambient temperature, Bullen notes. The machine then uses a proprietary volumetric compensation algorithm developed by the manufacturer and licensed for use by aircraft manufacturers to mill, drill, and trim the composite components.
Capable of cutting in X-Y-Z motion as well as pitch and yaw, the PMM has been producing parts at Northrop Grumman for about a year, Bullen adds. The system is outfitted with an advanced composite dust filtration system from Valiant Cleaning Tech GmbH (Aachen, Germany). In order to meet production requirements, the company may need as many as five to seven more of the PMM systems, which can cost $17–$20 million each.
CAD/CAM and simulation help Northrop Grumman engineers at all levels of manufacturing process planning, including toolpath planning simulation, Bryant notes. “We are using CATIA V5 and Delmia in all programs across the sector, which includes the advanced Hawkeye,” Bryant adds. “Our goal, especially in production engineering, is to ‘simulate twice, build once,’ so we’re trying to utilize simulation to design the airplane, design manufacturability, design tools, and design the capacity requirements, and how many tools we need. We use simulation for ergonomics development, to make sure people can reach up and access the aircraft from a tool.”
For toolpath planning, Northrop Grumman uses the Vericut NC verification and optimization software from CGTech Corp. (Irvine, CA). “Vericut has programmed into the simulation model the compensation system, and how the machine will react to certain commands,” Bryant adds, “so when you send the machine from one end to the other and drill a hole, you’ll know how the head is going to rotate and turn to get oriented for the next hole that it’s going to go drill. With this system, you don’t have to go back in and reverse-engineer the path planning like we used to have to do for collision-avoidance. We do it all upfront, and then we download the program into the robot and we’re ready to go.”
This article was first published in the March 2006 edition of Manufacturing Engineering magazine.