June 14, 2007 by Fred Hanes Bradley Todd and Tim Eisler
Sequenced part delivery (SPD) allows automotive manufacturers to outsource whole sections of their assembly process, essentially creating a factory without borders.
Automakers that outsource some of their car and truck components to third parties require component products to be delivered to the main assembly plant just in time for the parts to be added into the final car or truck assembly. Suppliers must be able to precisely and reliably track their product flow during manufacturing through shipping so that the order that goods are built and loaded for shipment exactly matches the main assembly plant’s delivery requirements. Absolute synchronization is key.
For SPD to work, supplier execution must be flawless. Heavy penalties may be levied on the supplier any time the automotive production line is held up due to late or incorrect deliveries.
Intier Seating, a Mississauga, Ont.-based automotive supplier, builds the seats for the Ford Edge and the Mercury MKX. To ensure synchronization, Ford sends the SPD schedule to Intier Seating one week before the delivery is due. This information broadcast includes the VIN of the final installed vehicle and the required sequence of delivery. The seats must arrive at the Ford assembly plant in Oakville, Ont., at exactly the right time, in exactly the right sequence.
Intier turned to Escort Memory Systems to help it develop a solution for Ford’s sequenced part delivery requirements. Escort Memory Systems worked with the quality team at Intier to develop a product tracking system for process automation based on RFID technology. The RFID systems are used for both the seat assembly process and for the shipment preparation process.
When a seat build order is started down the line at Intier, the job number is transmitted by the RFID system to an RFID transponder (or tag), which has been embedded in the seat assembly pallet. Once embedded, the tags will remain a permanent element of the reusable pallets. The job number is then read from the tag at each manufacturing workstation to initiate the correct processing as the seat travels from station to station on the production line.
The seat assembly remains with its pallet throughout the build process. After a seat is finished, the pallet is removed to carry another seat through the assembly line, and the tag is re-written with a new job number.
The tags chosen for this application require no batteries. Instead, they receive electrical power from the energy of the RF field when passing an RFID system antenna. These “passive” tags contain digital memory that can typically store from 1,000 to 2,000 bytes of data.
Escort Memory Systems’ Cobalt RFID controllers/antennas are installed on the conveyor system at each workstation to automatically read the job identification data from the tag embedded in the bottom of the seat pallets. Any incorrect (skipped or out-of-sequence) steps are flagged and corrective action is taken.
Shipping the right seats
When manufacturing is complete, the seats are transferred from manufacturing pallets to shipping pallets. These shipping pallets have RFID tags embedded in them as well, so the finished seat assemblies can also be identified for correct staging in the warehouse in preparation for shipment.
Once the seats are on the shipping pallet, weight sensors in the seats are tested according to federal safety requirements to ensure correct functioning of the airbag control systems. This test result is saved to the RFID tag on the shipping pallet. The seat/shipping pallet assemblies are then automatically stored in the automated seat retrieval system (ASRS) to await loading onto trailers bound for the Ford assembly plant.
On the morning of order shipment, the ASRS system pulls the seats based upon the confirmed order. At each staging position for upper and lower seat loading, the RFID tag on the shipping pallet is read to confirm the sequence in which the pallets are placed onto the trailer. A rotation number is written to the RFID tag before the seat is loaded onto the trailer. When the trailer is received at the Ford plant, the rotation number is read from the RFID tag to verify sequencing into the assembly production line.
With only four hours of inventory in the ASRS facility, every portion of the production system must work flawlessly. The key to success for Intier Seatings’ SPD line lies in the reliability of the Escort Memory Systems RFID solution, and the ability of these systems to communicate with standard industrial control equipment.
On the seat production line, RFID controls communicate to Rockwell Automation’s Contrologix PLCs via industrial Ethernet IP. The RFID antennas on the shipping system communicate via Allen-Bradley Remote I/O to a PLC-5 controller and directly through the backplane on an SLC500 interface module. The antennas are multi-dropped into the interface modules via MUX32.
RFID technology is designed to operate in harsh environments. The tags can be used thousands of times, which means the cost of a tag can be spread over thousands of cycles. When you also consider the fact that users can change data by simply writing new data to the tag’s memory, it’s clear that RFID can be the answer to many difficult automation problems. It’s exactly what Intier Seating was looking for.
Fred Hanes is a product manager with Escort Memory Systems. Bradley Todd is the marketing manager, and Tim Eisler is a sales manager.