Factory Floor: Wireless--Real-Time Part Tracking and Replenishment

Factory Floor: Wireless--Real-Time Part Tracking and Replenishment

In a fast-paced auto assembly plant, knowing what’s where can be a challenge.

The more flexible manufacturing processes become, the more complex is the flow of material to the manufacturing assembly lines. No manufacturing process is more complex than automobile manufacturing and feeding the limited-space assembly lines with a consistent flow of material.

For large manufacturing operations such as Ford Motor Company (Dearborn, Mich.), managing the flow of tens of thousands of items is a major undertaking. Temporarily misplaced items can stop the manufacturing process. Delayed delivery means partially assembled or unfinished products. The result can also be excess or obsolete inventory and lost productivity.

The value of real-time information for every container of inventory flowing through the supply chain toward the assembly line is critical. As companies' implement lean manufacturing processes, inventory management along the assembly line becomes more crucial. Standard data collection applications tell manufacturers what they have. A real-time locating system (RTLS) adds the pivotal element of where the item or container is located.

To meet these challenges, Ford Motor has adopted an active RFID-based RTLS at most of its plants throughout North America and Europe. The program, from WhereNet Corp. (Santa Clara, Calif.), is driven by wireless tags, fixed position antennas and Web-enabled software.

The RTLS locates and tracks inventory headed for the assembly line using extremely low-power radio frequency tags and a communications network. Antennas positioned inside and out-side the manufacturing plant receive tag transmissions, then deliver tracking information to a computer. In turn, the system can identify the location of the tag within 10 feet of its exact position, making it easier for lift truck operators and others to find the needed container among hundreds of similar-looking units.

Ford initially implemented this type of RTLS system in February 1998 to track material within its 250,000-sq.-ft. Van Dyke facility in Sterling Heights, Mich. This plant annually produces more than nine million components for Ford cars and trucks. In addition to reliably indicating where inventory parts are located, the RTLS makes it easier for line workers to request fresh supplies of material. Ford and WhereNet engineers found that by using the same infrastructure of antennas used to track products, along with software improvements, they could develop a wireless "call" system, now known as WhereCall, to bring parts to the line as needed.

Parts replenishment
Most major automakers have adopted some variation of the paper card-based, Japanese kanban system for bringing parts to the assembly line. WhereNet and a Ford subsidiary, Ford Global Technologies (Dearborn, Mich.), jointly developed a special call functionality that has greatly improved the efficiency of traditional material replenishment processes and has enhanced the capabilities of the locating system. Ford placed call button devices at assembly stations all along the line. When the inventory level of a specific part reaches a pre-determined replenishment minimum, the line worker presses the WhereCall button. That action sends a signal to re-stock that particular part.

This process eliminates the need for replenishment workers to travel routes picking up kanban cards. It also eliminates some lag time in the replenishment process, further minimizing line-side inventories.

When the button is pressed by an operator, a light on the unit flashes 10 times to confirm the transmission and a timer begins counting. With multiple parts at some assembly stations, the timers help remind workers which tags have been activated and how much time has elapsed since each call was made. During shift changes, this is extremely beneficial as it eliminates confusion and the potential for overstocking of parts.

Moving data
The infrastructure of antennas mounted in the plant ceiling that are used to pick up WhereTag pings, are used by WhereCall to request parts. The server then determines the location of the call and the parts that needs to be replenished. The data is passed onto Ford's material management system, which in turn displays a message on a touch-screen computer of a lift truck. Drivers never have to leave the cabs of their lift trucks to receive an order to pull parts from inventory.

Ford has achieved impressive results by using the wireless technology, including more efficient use of labor, fast installation and implementation cost savings of $200,000 to $500,000 per facility compared to hard-wired systems.

Strengthening links in the chain
WhereNet has now taken the next step in optimizing the process of just-in-time parts flow into Ford assembly plants. It is in the process of backing the system into suppliers and third-party providers, such as TNT Logistics of Jacksonville, Fla. The program offers closed-loop supply chain visibility as TNT coordinates milk run deliveries from its off-site material sequencing centers to assembly lines at Ford's automotive manufacturing facilities.

The material sequencing centers receive parts from multiple automotive suppliers. At the centers operators build then deliver sequenced shipments in accordance with a vehicle build schedule. TNT Logistics went live with the WhereNet system in November 2005 at its material sequencing center in Dearborn, which serves Ford Motor Company's Dearborn truck plant.

"We expect to gain maximum efficiency in our operations by relying on this real-time locating solution to provide complete visibility of all of our racks—which are constantly moving back and forth between the assembly line at the factory and our material sequencing center," says Terry McIntyre, manager solutions design technology services for TNT Logistics.

At the material sequencing centers, just as at the automotive assembly plants, the replenishment system uses active RFID devices and the local wireless access point infrastructure to provide real-time location and status information for thousands of racks carrying subassemblies and parts. The racks are in constant flow between the parts manufacturer, the material sequencing center and the assembly plant.

An enhancement to the system has been the use of devices located at dock doors of the material sequencing center. These devices trigger the WhereTag to emit a signal when a lift truck loads a rack full of parts on a truck bound for the nearby assembly plant. Through this automatic data collection process, the system confirms that the load has been built and validates its ready-to-ship status. The system can even trigger an advanced shipping notice so that the factory knows what material is en route.

As a third-party logistics provider, TNT Logistics expects to realize several benefits from the real-time locator technology:

  • Improved asset use and rack availability;
  • Reduction of parts shortages at the assembly line;
  • Improved space utilization and throughput at the material sequencing center;
  • Labor savings through elimination of time wasted searching for racks.

In addition to tracking mobile racks, at Ford's Ohio Assembly Plant (Avon Lake, Ohio) TNT is now tracking returnable containers for the automaker throughout the various tiers of its suppliers. Three material sequencing locations have been established near the plant. Steve Kowalkoski, vice president automotive for TNT, says this latest expansion (January 2006) of the RTLS program, has created a live sequencing broadcast, allowing a more efficient flow of commodities into a much smaller plant footprint.

Racks of parts reach the assembly line through Ford's electronic just-in-time replenishment program.


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