Summer can be the best of times and the worst of times. Just ask anyone who's ever used an old-fashioned push mower on a hot summer afternoon how much better the day would be with a little automation.

That's a lesson learned when John Deere automated the production processes at a 260,000 square foot production facility in Greenville, Tenn., where Deere manufactures powered, walk-behind lawn mowers and tractors.

"We expanded from 500 units a day to 1,200 units a day when we added Home Depot as a customer," says Wayne Southall, quality manager. "Our old processes couldn't keep up with the new volume."

The expansion is a tale of two factories.

First, Deere had to rethink a manual assembly line in the plant.

And since Deere outsources parts painting to a factory next door operated by ProCote, the expansion also involved automating the way parts are handled between the two facilities.

The solution is a pair of custom-designed production lines that utilize aluminum pallets as assembly stations to automate the manufacturing process. Meanwhile, an overhead power-and-free conveyor (Jervis B. Webb ) transports parts to and from the paint line, freeing up valuable floor space in both facilities.

What's more, the power-and-free conveyor allows Deere to be more flexible on the production line and more responsive to customer needs.

"Before, if we had to make an unscheduled changeover, we'd have floor space taken up with previously scheduled parts that we didn't need," Southall says. "Now we can make changeovers on the fly. If the production schedule changes, we just put a bar code for the new color on that part and it's handled automatically and with ease."

Prior to the expansion, both the assembly process and the parts painting processes were a lot like that old push mower: they got the job done, but it wasn't always easy.

"We had what I call a manual AGV (automatic guided vehicle) assembly line," Southall explains.

Tractors and mowers were assembled on individual carts powered by air-driven motors. The motors allowed operators to roll them from one work station to the next, and to raise, lower, and rotate a unit during the assembly process.

Frames, fender decks and other parts that needed to be painted were manually loaded onto carts that were then towed next door by lift trucks. There the parts were manually unloaded, coated and cured, then reloaded for transport back to the assembly line.

The process was slow. What's more, the carts took up a lot of valuable space. Finally, the more times the parts were handled, the more likely they were to be scratched or damaged.

The power-and-free conveyor allows Deere to minimize the handling of parts, free-up floor space by hanging parts overhead and keep up with the new production volumes. The system includes nearly four miles of power-and-free that travel between and within the two facilities.

Parts are loaded and unloaded at drop stations in Deere's building. There are four drop stations on each assembly line, plus two stations for service parts for a total of 10 drop stations. Each drop station is serviced by its own spur off the main power-and-free conveyor line.

The system can process 188 carriers of product per hour at full production. Each carrier has an optically read metallic bar code plate for unique identification and control routing.

Since it takes up to three hours to paint parts and less than 75 minutes to build a mower, the paint line runs half a shift ahead of production.

That process begins when production orders generated by Deere's enterprise resource planning (ERP) system are entered into the manufacturing execution system (MES) which manages the production line. The MES builds a production schedule and assigns orders to the two assembly lines.

Production is flexible. It's not uncommon for Deere to build the same or different model lawn tractors on each line depending on demand. In addition, the schedule may also include service parts, grass bagger parts, and parts for Deere products and other brands supported by Deere.

Pre-paint fabrication, welding and assembly are done at a workstation next to the drop station. The part is hung on a carrier on a loadbar that has a permanent metal bar code attached. The bar code identifies the color of the part to be painted and the location where it will be returned.

Once a part is hung on the power-and-free, it won't be handled again until it's ready for assembly.

After a part leaves the drop station, it joins the main power-and-free line and is conveyed through a 75-foot interconnecting tunnel at 60 feet per minute to ProCote's facility. There, an infrared scanner, controlled by Deere's computer system, reads the bar code and determines what processes need to be applied to that particular part.

"We control our coating and painting processes," says Mike Britt, general manager of the ProCote facility. "But Deere's computer system routes the parts."

All parts are cleaned, prepped and electro-coated with a protective black coating. Parts that will be visible, like fenders and mower decks, continue to one of four powder spray booths. Each booth is dedicated to a different color and served by a spur off the main conveyor line. Once the parts leave the powder booths, they rejoin the main line and pass through a cure oven before traveling back to the Deere factory to be assembled.

The line speed varies throughout the plant according to the processes performed. "We have ten separate drive units and three different speeds," says Britt. "The line slows down to 30 feet per minute to go through our pre-treatment and e-coat processes, and to 17 feet per minute through the powder booths. But it's always moving, and that makes us more efficient with our total throughput time."

Back at the Deere factory, the main line delivers the coated and painted parts to an accumulation area.

Raw as well as painted parts can be stored overhead to save clutter on the factory floor in case the paint line goes down. During normal operations, however, the accumulation area acts as a switching area, like a railroad yard. An infrared scanner reads the bar code, and directs the part to a spur that will deliver it to the drop station where it originated.

There it will be manually removed, ready to be assembled on the next available tractor or mower. The operator then places the next part to be painted on the open rung.

In the Deere production facility, the air-driven carts have been replaced with two production lines serviced by chain conveyors.

Mowers are assembled on aluminum pallets that are carried between stations on the chain conveyor. The pallets were custom designed to hold a tractor or mower in place during the assembly process.

At the start of the assembly line, a serial number is applied to each unit. In addition to a unique unit number, serial numbers are also assigned to the engines and transmissions. Together, those three numbers make up the permanent record for that unit which will be tracked for warranty purposes.

Parts coming off the power-and-free conveyor are usually stored within a few feet of an assembly station. That allows an operator to retrieve parts with minimal walking.

That's important to production speeds. The line is timed so that an operator has 45 seconds to accomplish a task before the assembly travels to the next station. In total, each line has 32 workstations plus queuing stations.

When a unit reaches the end of the assembly line, the pallet drops down from the unit and is carried on another powered chain conveyor back to the start of the assembly line, ready for the next tractor assembly.

The tractor or mower is rolled into a "run-in" area for a quality check. If the unit passes inspection, it's banded onto a returnable metal shipping crate. To close out the process, the original three serial numbers are scanned along with the serial number on the shipping crate. That allows Deere to trace the crate in the event of shipping damage.

Once the bar codes have been scanned, the unit is covered with a plastic bag, shipping labels are applied, and the crate is loaded into a trailer for shipment to Deere's warehouse. The whole process takes just over an hour.

After two years of working with the power-and-free conveyor, both facilities have benefited.

"Because the line runs at various speeds, we're more efficient with our total throughput times," says Mike Britt. "And since we no longer manually handle the parts, there are fewer rejects, scratches or defects."

At John Deere, the new assembly lines and power-and-free conveyors have handled the increased production pace with ease. In fact, Deere is about to pump up production volumes again from 1,200 to 2,000 units per day. "The system will handle the output with no problems," says Southall.

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