When it comes to lean manufacturing, the Hummer H2 plant in Mishawaka, Ind., stands in there with the best of them. There is typically no more than two hours of materials and parts at any point along the assembly line. And in staging areas, there's no more than four to eight hours of replenishment inventory.

To make that happen, a heavy emphasis is placed on having the right information tools to maximize efficiencies, says Deborah Cafiero. She's the executive director/chief information officer of AM General, a vehicle assembly contractor for General Motors that produces the Hummer H2 sport utility vehicle.

Needless to say with inventories so tight, time is of the essence in the general assembly and body shops. There, two wireless systems (WhereNet), one to manage replenishment of parts and the other to track individual vehicle locations and movement, play a pivotal role in getting the right items to the right places at the right times.

The wireless replenishment system ensures new parts arrive at the line less than fifteen minutes after the call goes out. In addition, the replenishment system maximizes lift truck utilization, trimming costs. Meanwhile, the tracking system not only identifies the location of vehicles but monitors process efficiencies to ensure production is within specifications, says Alan Walker, director of materials.

But these wireless systems are not alone in the plant, explains Cafiero. Also operating is a voice data communication system using in-plant cellular technology, and a wireless local area network for laptops and handheld computers.

Those two systems each operate on their own infrastructure. A third system manages the data from both the replenishment and tracking systems. All three feed data to a centralized routing and tracking system that coordinates the exchange of information between the three as needed, says Cafiero. Combined, the three systems provide a highly efficient data acquisition system with the software handling data management, she adds.

"I wanted our information systems to be as impressive and high impact as the advanced manufacturing technology we have out on the lines," says Cafiero.

Until just last month, the plant produced daily 148 of the H2 model of sport utility vehicle. It has now added a second model, a sport utility truck, and will produce an additional 47 vehicles a day.

While the numbers are not large by automotive production standards, this is a plant that has been willing to spend on information systems and related infrastructure to maximize production efficiencies and provide a platform for continuous improvement.

In the 350,000 square foot general assembly shop, all 150 workstations are outfitted with the wireless parts replenishment system. Simply by pushing a button on a workstation call box, which sends a radio signal at 2.4 GHz, a team member calls for additional parts.

Each call box is dedicated to a single part number, and transmits its identification number. Virtually all parts weighing more than 40 pounds, a total of nearly 600 or about one-third of parts going into the vehicles, are managed by the system.

The call is picked up by one of 18 antennas in the plant and then transmitted to routing and tracking software (see layout box on page 28 for details). The software selects a lift truck for replenishment and sends a signal wirelessly to its onboard wireless tablet computer. According to Walker, lift truck utilization has improved 15% with the system as it speeds new inventory to the line and eliminates deadheading. A lift truck performs up to 85 replenishments a shift.

In addition, the system monitors lift truck operator turnaround times. This allows Walker to identify inefficiencies and conduct additional driver training as needed. It also helps to avoid line downtime due to poor parts replenishment. The routing and tracking software collects all pertinent data.

Just last month, an additional 70 call boxes were added to the system to accommodate the new sport utility truck and as part of the model year changeover for the H2, says project manager Tim Kurtz. In addition, 150 part numbers were modified on call boxes.

"The wireless nature of the system made the changeover not only quick but inexpensive. If it were a wired system, it would have cost us at least $1,000 a call box to make the changes," says Kurtz.

AM General recently added a real-time locating system (RTLS) to 35 workstations along the assembly line. This system uses active wireless tags to identify and track carriers with specific vehicles on them through the assembly process.

The system works on the same wireless antenna infrastructure as the parts replenishment system.

Each tag carries the unique identification number of the vehicle on the carrier. A tag attached to each carrier sends out a radio signal at 2.4 GHz when it is activated by fixed-position communication devices as the carrier enters a track zone or buffer. The tag's signal is then collected by one of the antennas in the plant, which passes the data to a programmable logic controller for data capture and management.

"This way, we know exactly where each carrier and its vehicle is at all times," says Walker. This is especially important for those rare times when a carrier is taken out of sequence on the line and needs to be reintegrated at some point in the future.

Beyond that, the system allows AM General to collect build data so it is known what happened and when to each vehicle during production. This information can be used to identify manufacturing problems and expedite solutions as part of continuous improvement at the plant. "In the best of situations, the system let's us anticipate problems before they crop up," says Walker.

With the initial success of the tracking system, Cafiero says the company is now looking to extend its use to other locations and even out to the yard where finished Hummers sit prior to shipment.