Build a tractor in less time than it takes to play a round of golf? It's not only possible but an everyday occurrence at the John Deere Commercial Products plant in Grovetown, Ga., not far from the Augusta course where the Masters Golf Tournament is played every April.

The utility tractors built in Grovetown are complex, requiring nearly 3,500 assembly steps. But it takes less than four hours to finish the job with automatic guided vehicles (AGVs), a well-trained, self-directed workforce and advanced flow manufacturing techniques.

The AGVs operate in a fully integrated and networked assembly system. It's a "smart device network," says project manager Chip LaPole. Smart AGVs with onboard computers are precisely routed through assembly steps along what LaPole calls a racetrack. The AGVs then mesh with cross-trained operators using smart tools at workstations.

This is a radical departure from traditional powered assembly line handling techniques used in the past. In fact, computer simulation showed the AGVs to be superior to towlines and conveyors, notes LaPole.

He says AGVs are more flexible and cost effective. Downtime for repair and maintenance is less with AGVs, LaPole adds. Furthermore, guided vehicles offer an ergonomic edge over more manual, traditional methods of transporting tractors through assembly.

Just as important as technology in Grovetown, explains LaPole, is flow manufacturing. "It's a major contributor to our success," he says.

Like all production operations, the facility has peaks and valleys of demand. To compensate for those swings, assembly workers are flexed up and down the line and even between plants (as Deere has a second tractor facility in Augusta). When off the line, they might be involved with additional training, special projects, or various continuous improvement projects or even visiting suppliers with supply chain problems.

In addition, all workers are cross-trained at their home workstation as well as the workstation immediately ahead and behind them on the line. If demand drops 50%, for instance, workers can then work their home station as well as either the one in front or behind them.

There are several advantages to this, explains LaPole. Productivity gains of up to 25% are possible utilizing flexible manning during the assembly process. Furthermore, cross-training allows operators to help others should they fall behind. And just as important, he says, is the attitude shift from "not my job" to team spirit.

To make all of this happen, Deere invested in expanding and upgrading the plant. Included are the 62 vehicle AGV system, smart assembly tools, 106 new workstations and an additional 188,000 square feet of space. Payback is expected to be less than three years.

Although they perform different functions, all vehicles are wire-guided and capable of carrying 7,200 pounds. Each AGV, which serves as a mobile assembly platform, is outfitted with one of three custom fixtures for a tractor chassis, an engine or a transmission.

The three-wheeled vehicles have a forward steer-drive wheel and two fixed rear wheels. An onboard, microprocessor-based system controls each vehicle and communicates by radio frequency with a base control unit. Typical speed of the vehicles is 40 feet per minute.

Fifty vehicles circulate around the main assembly line loop (the racetrack) that is 1,452 feet long. There are also two spur or feeder lines for engine and transmission assembly. Six AGVs work the engine line. Six more are on the transmission line. Those two loops are side-by-side at one end of the racetrack.

After a tractor's engine and transmission are ready to be married with the cab, they are lowered onto a vehicle on the racetrack by an overhead crane and hoist system. At the appropriate station, the tractor's cab is similarly lowered onto the AGV. Those tractors that do not receive cabs are routed as necessary on an inner loop of the racetrack.

Through software and radio frequency communications with the AGVs and the vehicles' onboard computers and transceivers, precise control and tracking of vehicles is achieved. "An AGV will not be allowed to move from a specific assembly station until the work is verified complete by the control system and until process quality parameters have been achieved," LaPole says.

These smart vehicles stop only at stations where assembly is required for the specific tractor on board. Depending on the specific tractor being assembled, labor content varies considerably. As a result, variable routing is important to juggling production scheduling.

The plant is also working to implement a manufacturing execution system (MES). When the MES system upgrade is fully implemented, assembly operators will get their tractor build instructions and quality control information through touch screen monitors.

Operators must perform up to 70 critical steps involving the exact application of a specified level of torque. Computerized smart tools help operators do these jobs and verify that the tool itself has performed the task within pre-set limits. In some cases, LaPole says, "the tool even counts out the number of bolts needed."

Deere operations managers follow the progress of work-in-process (WIP) on computer monitors.

Since startup of the system, managers have gained the ability to monitor dwell time of each AGV at every workstation by tractor serial number. This allows managers to track daily progress at each workstation. It also provides the basis for continuous improvement of the process and station throughput.

There have also been improvements since startup made in inventory flow. Workers now use wireless terminals with built-in bar code scanners to receive inventory from suppliers and to manage the flow of inventory from storage to the line. The information is fed directly to the enterprise resource planning (ERP) system. From there, it is sent on to suppliers for replenishment, and when the MES is completed, to touch screens at the workstations, keeping operators up to date in real time on inventory availability.

LaPole expects that the system software and hardware will be implemented in the next 12-18 months. When teamed with the bar code scanning system, the MES will optimize the sequencing of subassembies to the assembly line.

Just as there is flexibility in routing vehicles, there is also flexibility in modifying the racetrack itself, notes LaPole, even though these are in-floor wire-guided vehicles. "AGV routing is easy to modify, as compared to overhead and tow line conveyor systems," he says. "You just cut a small groove into the floor, lay more wire, fill in the cut with epoxy, and route the vehicles a new way."

This ability to change the racetrack layout is important, LaPole adds. The tractor business "is very dynamic. John Deere is always thinking of a better way to give the customer the highest value products."

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