Assembly lines are one place that wireless has not made much of an inroad, since most plants have had decades of process improvements to gain maximum efficiency and since their environments can be hostile to wireless signals. But new factories can benefit from the use of wireless on the assembly line, not just in the warehouse and parts yard. Case in point: For contract manufacturer AM General, wireless technology was essential to getting its Mishawaka, Ind., plant built in the first place. Mishawaka is near the company's headquarters in South Bend, Ind., and three years ago the company decided to try to get the contract to make General Motors' Hummer H2 sport utility vehicles. The goal was to bring new jobs to the struggling industrial town, even though it is fairly far away from auto parts makers and its plant sites are smaller than most modern plants require, since they were originally created in an era of smaller, urban factories. But to get the contract, AM General had to build a new plant in a smaller-than-usual space, and that meant minimizing on-site parts storage below the industry's usual 48-hour-inventory levels, relying instead on just-in-time delivery of parts.

But having parts offsite means there can be no delay between noting a low parts inventory and having them delivered. And that's where wireless comes in. Normally, line workers place paper cards, called Kanbans, in baskets that are then collected periodically by employees. These cards are essentially bar codes that are scanned in to trigger a request to the parts maker for a new delivery. But they can easily get lost or delayed, notes Tim Kurtz, the plant's manufacturing systems coordinator. So AM General deployed a WhereNet 802.11b wireless LAN that includes pendant-shaped devices at each assembly station. These pendants can be attached via magnets to any surface, so workers can place them where most convenient. Workers press a button when parts are low, sending a wireless parts-replenishment request. (Each pendant is associated with a specific part number.)

This saved AM General the expense of installing cable at each location and also makes it easier to adjust the assembly line for vehicle changes or even for new vehicles. For example, when it began manufacturing the new H3 sports truck this summer, AM General was able to reprogram existing and add 140 new pendants in over a weekend, versus the usual several weeks. Plus the batteries last at least five years, so maintenance is minimal. "Wired systems are very expensive and hard to maintain, and costly to change," Kurtz says. The wireless system paid for itself in about nine months, he adds.

AM General also gained better tracking capability as a result of implementing a wireless LAN in the assembly facility. For example, the company can track an individual auto body's progression by scanning its bar code as it enter the line and passes various checkpoints, so each stage along the line can be notified of any options that should be installed or not installed for that particular vehicle. Also, Kurtz notes, if there's a gap in the assembly line because of extra work needed at one station, that fact can be immediately noted, other stations down the line can be alerted, and individual stations can be shut down without shutting down the entire line. Over the next several years, AM General expects to enhance the system with radiofrequency identification tags (RFIDs), so larger parts like dashboards can be tracked as they move through the assembly line. That would also permit real-time tracking of delays in the line. Small, hard-to-tag parts like screws will likely be kept in weight-sensitive containers that wirelessly transmit their contents' weight, so the parts-ordering system will be notified automatically as supplies run low.