At $200 billion, the F-35 Joint Strike Fighter (JSF) is the biggest defense contract, ever. As such, it represents a tremendous source of revenue, not only for prime contractor Lockheed Martin Corp. (Bethesda, MD), but for subcontractors like Northrop Grumman Corp. (NGC, Los Angeles), which is assembling the aircraft's center fuselage bay at the company's Integrated Systems facility in El Segundo, CA.

The project also represents a tremendous assembly challenge, due to its complexity and the need to produce the aircraft on time, under budget and under safe working conditions. Ultimately, the full JSF program calls for building 3,000 aircraft at the rate of one a day beginning in mid-2008.

The fuselage section that NGC is building falls within the rear bulkhead of the cockpit and the wing. It includes the center fuel tank, the engine air inlet ducts, the lower part of the wing carry-through structure and the fuselage upper skin panels, which are to be installed with many of the electronic, avionic and combat systems in place.

To choreograph what is a tremendously complicated assembly, NGC is using the Envision and Human Solutions simulation software packages from Delmia Corp. (Auburn Hills, MI), a Dassault Systèmes Co. (Paris).

According to NGC manufacturing engineer Dean Hilgenberg, leader of the integrated product team for the JSF's center bay assembly, the software allows his company to coordinate the different assembly tasks and prevent workplace injuries. It also allows NGC to optimize the manufacturing process before committing to expensive tooling, thus avoiding rework costs further down the road.

"Simulations help determine the size of crews working in confined spaces and workstations and whether the mechanics can reach in or get inside if they have to," says Hilgenberg, noting that, because of the high production rates required, some assembly work will be done in close proximity to automated machinery and robots.

"Ergonomics is also a key tool for examining workstation ingress and egress," he says. "Can we eliminate tasks that require squatting down and reaching underneath things by using rollover fixtures? Will there be head bumps?"

According to Hilgenberg, NGC uses the software in a number of different ways, including "quick and dirty" simulations for parts designers along with detailed studies of automated drilling and fastening machines.

"Rough simulations help establish assembly flows within workstations," Helgenberg says. "We are looking for clashes between machine components and fixtures in standard tool usage. We are also using simulation to test tools before they are built. We do this by breaking down the subassemblies to define processes."

According to NGC manufacturing engineer Eric Osborne, the Delmia software was especially effective at targeting problems with a multimillion-dollar mandrel tool for laying up the air inlet ducts. Specifically, the team discovered that the initial mandrel tool design would have resulted in a jig-locked condition. Once the pieces were assembled and joined, they could not be removed because of the draft angles of some mating flanges.

"We found [the problem] with the Delmia clash detection capabilities," Osborne says. "We were two months away from the start of fabrication and this tool had a 28- to 30-week lead time. Without simulation, we probably would not have discovered the problem until we tried to go into production. Then it would have been way too late...[the software] drives the tooling process here. It shaves the time and cost of ergonomics and finds more creative solutions."

A typical JSF simulation has as many as several dozen parts, some of them with dimensions as long as 15 feet, as well as 50 or more smaller parts such as brackets and fasteners. For each, the simulation software demonstrates paths for components through the workstation, around and between previously placed components, and into position.

"Cycle times are so short, that it's more important than ever to plan in advance, and simulation is the key to that planning at NGC," says Mike North, manufacturing engineering manager for Northrop's Air Combat Systems unit. "[Ten years ago] there was no way a defense contract of this scale could have been done in 28 months. Now, simulation gives us insight and understanding of the process so we can avoid doing anything [in engineering and production] that is unnecessary."

According to North, the company is realizing $1 million in savings every year on a one-time $200,000 investment in digital manufacturing. "We can't afford not to do simulation," he says.

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