The "other" use of RFID

Most of the news about RFID today concerns how it will, in the next several years, revolutionize supply chains through item-level tracking of goods—involving billions and billions of data points. But a more traditional use of RFID, and one that provides immediate benefit, is on display at the Mishawaka, Ind., plant of AM General, where the HUMMER H2 luxury sport utility vehicle is assembled.

This facility deploys RFID tags that average $50 to $60 apiece. These devices, called active RFID tags, send out signals to wireless access points stationed around the plant. The access points, which essentially are wireless antennas, read messages coming from the tags and transfer the data to the appropriate business applications for processing.

By contrast, passive RFID tags, which can be bought for 20 cents to 25 cents apiece, hold data that only can be read when the tag passes by a reader stationed at a fixed location or by a person using a hand-held scanner.

David Krebs, a director with Venture Development Corp., a Natick, Mass., technology research and consulting firm, says a lot of companies are delaying RFID projects until tag costs drop to five cents or less. But he believes that is a short- sighted view. "You have to look at the total benefits that can be derived from a potential project," he says. "In some cases, tag costs of a dollar or more can be completely justified." (See sidebar for more of Krebs' views on RFID.)

AM General currently has two active RFID applications in place. One manages the kanban-style parts replenishment system that is part of AM General's lean production methodology. The other supports AM General's quality control program by tracking vehicles through various production stages and verifying, among other things, that the correct parts are installed.

"We selected RFID for our electronic pull system when we built this plant, because no other technology would support our lean production initiative," says Tim Kurtz, manufacturing systems coordinator at the HUMMER H2 plant. "After using it for awhile, we began to see that the same infrastructure, technology, and skill sets could be used in other ways." That led to the use of RFID for vehicle tracking and quality reporting in the actual assembly process.

The RFID infrastructure, which AM General purchased from WhereNet, consists of 18 access points, or wireless antennas, that are linked to the plant's data center. WhereNet also supplied the RFID tags.

For the parts replenishment application, the RFID tags are actually call buttons that resemble garage door openers. Several buttons are located at each workstation, and when workers run low on parts, they press the appropriate button to signal that it's time for replenishment. A message—which includes the part type and quantity needed—goes to the nearest access point, which relays the message to AM General's inventory management system. A team member carrying a wireless tablet PC on a forklift sees the request and delivers the needed parts to the appropriate workstation.

Kurtz says this rapid communication of the need for new parts allows the plant to operate with no more than eight hours worth of inventory on hand at any given time, an essential requirement for a lean production facility. He says the vehicle tracking and quality reporting system also supports the lean philosophy by helping to ensure "that we have the right parts at the right stations at the right time," which ultimately leads to vehicles being assembled faster at a lower overall cost.

The vehicle-tracking system starts with an RFID tag about the size of a pager placed on a parts carrier that will hold a specific vehicle as it goes through the production process. The first part loaded in the carrier is a vehicle body, and the RFID tag contains the serial number for that body.

When the body reaches the paint area, it is given a separate number known as a primary vehicle identifier, or (PVI). As the body nears the end of the paint area, it moves past an RFID reader. The serial number from the RFID tag is read and sent, along with the PVI from the body, to AM General's plant monitoring and control application, which is the CIMPLICITY system from GE Fanuc.

At that point, Kurtz says, the body's serial number from the RFID tag and the PVI from the body are considered "married," and they constitute a single record in the CIMPLICITY database. As the vehicle leaves the paint area, a team member looks up its PVI in the CIMPLICITY system to see what other parts are supposed to go on that particular vehicle.

The CIMPLICITY system gets that information in the form of option codes from a program called GM Flex, which transfers dealers' orders to AM General's plant floor systems. Those option codes tell the team member whether the vehicle gets things such as a chrome package.

"As the truck goes down the line, error-proofing mechanisms kick in to tell team members what parts to add," says Kurtz. "If they disregard any of the instructions, the line can be stopped automatically and the team member is asked what happened."

As a truck moves along the line, fixed-position scanners read the RFID tag and relay its location to programs that capture information to determine if the process is operating within quality control specifications. "We also use this system to collect information for bottleneck analysis as we launch new models and introduce new options," Kurtz says.

Running a wireless network also makes it much easier to reconfigure the plant when new models are introduced, or when AM General's continuous improvement program dictates that a particular process be changed.

"A wired system would have added to the expense of moving stuff every time we modify a process or rebalance the line," Kurtz says. "You spend a lot of money moving wires around and hoping that they work right when you connect them. With this system, all we have to do is maintain the batteries inside the tags and make sure the antennas are turned on."