Raytheon: Precision in the air and on the ground

As a premier tool in the United States military arsenal, an interceptor missile is designed to travel at thousands of miles per hour to precisely strike another enemy missile from the sky. The automatic guided vehicles (AGVs) used to assemble and transport work in process at Raytheon’s Redstone Missile Integration Facility where these missiles are manufactured are also expected to perform with precision and consistency.

Completed in November 2012, the 70,000-square-foot facility, located on the campus of the Redstone Arsenal Army base in Huntsville, Ala., represents the most modern manufacturing processes in any Raytheon missile operations, says Steve Larson, director of manufacturing innovation. Central to the state-of-the art production is a fleet of custom and fully integrated AGVs, which enable a zero-lift philosophy, significant ergonomic improvements, and traceability throughout the assembly process.

Although labor savings are typically essential to justifying an AGV deployment, Larson says those savings were only a small piece of the pie. “Mission assurance was the real key,” he says. “The missiles must work absolutely perfectly every time, and we need to know they will before they are used. Reworks and defects become very expensive.”

Processes before
Raytheon’s facility specializes in testing and assembling parts of missile systems manufactured at other facilities. Unlike most applications suited to automation, Raytheon’s missile production is a very low-volume application. Missiles can take weeks to assemble and might spend days at any given workstation.

The new facility uses two 24-foot AGVs and one 10-foot AGV (JBT, jbtcorporation.com) for material movement between the testing area and 19 assembly workstations. At other facilities, moving parts between workstations is a time-consuming, labor-intensive process that presents the opportunity for errors and ergonomic strain, says Larson. Manual carts are used to ferry product from place to place, and because of the explosive nature of the product, regulations mandate that assembly areas be kept a certain distance from testing areas. This means manual labor is required to push finished missiles on carts as much as 300 feet, as well as for retrieving parts from storage.

“We had a lot of brute force and machine/human interface to push sections together and move them,” says Larson. “Just to do a simple thing like moving something from one place to another took a lot of planning and people, which was not the most efficient use of time for the people involved.”

Although such moves were infrequent, Larson knew there must be a better way than to use between four and six skilled technicians to manually move materials. “We were moving something that’s very expensive and has explosives using a labor-intensive, paper-based, people-dependent process,” he says. “Now we’re realizing we can error-proof it much better by bringing in some automation.”

The evaluation process
When Larson first considered AGVs, the first concern was the weight of the missile components. Finished missiles weigh in at multiple tons, and Larson simply didn’t know if AGVs were up to the task.

“When you’re carrying multiple tons, that’s an interesting engineering challenge right there,” Larson says. “You need to know what will happen to the load if, for instance, the AGV stops suddenly.” The AGV supplier brought Larson to a facility that uses AGVs to transport toilet paper and other commercial products. Although the products are as different as night and day, the raw materials at the toilet paper test facility often exceeded 10,000 pounds, proving AGVs could handle Raytheon’s missiles.

As in any industry, product damage and defects could result in significant costs for Raytheon. Where Raytheon had previously used bulky overhead cranes for some product movement, the AGVs allowed them to implement a zero-lift assembly process, eliminating both cranes and lift trucks from the assembly area. Missile parts are now lifted just once—from inbound trailers to the loading dock—before the AGVs carry them the rest of the way. The vehicles are programmed to follow a certain path, but feature laser guidance technologies that are aware of obstacles both at floor level and at the top of the unit.

The AGV takes away any opportunity for people to drop things and for errors to be made, Larson says, while allowing the workers to focus on higher priority tasks. Larson had evaluated conveyors at one point, which are often used for smaller assemblies at other Raytheon facilities, but said the AGVs allow for more flexibility.

“The system is more reconfigurable,” says Larson. “Right now it’s set up for two missile platforms, but the hardware, tooling and software are all expandable, modular and adaptable. The cost to adapt a new missile to the factory is very low.”

Design and testing
Having established that the AGVs could handle the weight, the next step was outfitting them to carry their unique payload. Raytheon is working to patent what they call the “sled,” a sliding mechanism that locks onto the rings and cradles of the missile carrier.

The AGVs are only used for product movement; no assembly work takes place with the product on the AGVs. Instead, the sleds move the entire missile or components from the AGV to the workstations. There, the AGV temporarily docks to get its supply of electricity, compressed air and data transfer.
“We don’t have to dedicate an AGV to a particular missile piece, since cycle time for assembly is very long,” says Larson. “Its usefulness is not to serve as a workstation, it’s for product movement.”

Because Raytheon had just one year to build the new building, all factory equipment, workstations and AGVs were mocked up at a test facility in nearby Nashville, Tenn. “It was the only way to work the bugs out,” says Larson. “Once we got into the facility, we didn’t have time to debug because we were installing and starting to build products at the same time.”

Working with an automation integrator (Doerfer Companies, doerfer.com), Raytheon developed the new facility’s workflows over a period of six months. The fully integrated system provides detailed track-and-trace capabilities to every step of the assembly process. An AGV will not retrieve an item from a workstation until all necessary steps and checks have been performed, and will not allow work to be performed by a technician without the proper certifications.

“AGVs are part of the overall system architecture,” says Larson. “For every step, we have history and verification of who did it, how it was done and when it was done, taking the human out of that loop to allow a very thorough verification.”

After a ribbon-cutting ceremony in November 2012, the facility produced its first missile at the end of the first quarter of 2013. As the most modern of Raytheon’s missile integration facilities, the new building will serve as a model for automated product flow. “We’ve scrapped 35 years of production technology to create this factory,” Larson adds. He says plans are in the works to allow the AGV sled to interface with the automated vertical carousel system used for parts storage. This will remove yet another human touch point and further enable accurate, seamless product movement and increased labor efficiency.