01 February 2005
Paint by numbers
By Donald Anspach
System upgrade allows greater productivity from Saturn.
Next time you are on your way to work, try to take notice of the different types of cars on the road—different models, styles, colors. Years ago, there were only a handful of choices and features. Today, consumer choice is a brand differentiator, with automotive manufacturers designing and delivering more variables than ever before.
Inevitably, when there are more variables, there are more opportunities for production inconsistencies, and manufacturers have to work to ensure consistent quality while facing a myriad of challenges. For the manufacturer, this translates to chemical mixing, mixing machines, color recipes, process quality, plus the never-ending tight production schedule.
The Saturn Corp., a wholly owned subsidiary of General Motors, produces an average of 1,000 cars per day at its facility in Spring Hill, Tenn. As Saturn's oldest plant, the Spring Hill campus saw the first Saturn automobile driven off its assembly line in 1990. In the grand scheme of things, the plant is a relatively new manufacturing facility. The Spring Hill site still performs regular equipment updates to stay current with industry-leading manufacturing techniques.
The industrial design specifications for the industrial computers fit perfectly on the shop's heat exchanger platform, where a standard PC wouldn't be able to withstand the heat, noise, and vibration.
Unplanned downtime is never helpful in the manufacturing environment, but it is particularly troublesome in the paint shop, where such problems can pose significant risks in terms of production schedule and safety. Numerous chemicals used in the paint shop warrant a Class 1, Division 1 hazardous location rating. The shop's automated system continuously monitors paint materials to make sure they all remain chemically stable, checking volume levels throughout the system to ensure there are no overflows. Any downtime requires extra staff to manually check each system and maintain safety standards at the plant. With a production schedule that runs 20 hours a day, six days a week, losing even one day's output can have a negative impact on production goals.
Saturn Spring Hill needed a new paint shop control system that would not only meet General Motors' continuous improvement criteria, but also provide the latest control technology that would help improve paint shop operations. After reviewing the system design, they decided on a controls system upgrade using controllers, new I/O, software, and new industrial computers. The new system's interoperability, combined with the multiple communications options, meant Saturn's engineers could use state-of-the-art equipment in the paint shop that integrated seamlessly with other existing plant systems.
With Saturn's rigorous production schedule, it was difficult to find the best time to replace the paint shop controls. Working with Saturn, the installation team found a small window of opportunity near a scheduled downtime period in which Saturn could work to replace the shop's 40 control systems. In order to make the most of the opportunity, the installation team did pull-ahead work in advance of the shutdown. This involved installing components in the heat exchanger control panels, installing new temperature control actuators on all non-operational systems, and terminating all wiring and controls on the non-operational systems. The pull-ahead work represented more than half of the work they needed to do on each of the systems. When the paint shop shut down, two crews working simultaneously on the heat exchanger platform and in the paint mix area completed the task on time.
Retrofitting was a key part of the upgrade. In the predesign, Saturn reviewed the wiring in its existing programmable controller racks and determined it would work with the new modules. This saved Saturn the time and expense of rewiring panels. Saturn was able to install 13 of these racks into the existing footprint, rewiring back to the new modules. The main processor and supporting Ethernet communication modules went on a rack that fit into another existing footprint, leaving enough room to mount power supplies and data switches for Ethernet I/P network connections.
By installing a single platform of programmable controllers, Saturn found they were able to simplify user training. Saturn officials realized over the years that having two different programming languages on a considerable amount of equipment made it much more difficult for workers to gain proficiency in both languages.
Saturn already invested a significant amount of time creating user-defined data tags for their paint mix systems and heat exchanger systems. While engineers worked on code creation only once, they reduced the amount of time spent programming each system by duplicating the code to each system.
"We liked the idea of importing the complete tag database into the (software) application only once," said Jim Barton, paint controls engineer, Saturn Spring Hill. "We had already built the tags to be part of the actual ... program, so simply importing the tags saved time—especially with the size of the tag database we needed for the paint system."
The new industrial computers replaced a multi-function device that provided access to set points, process variables, and alarms. The industrial design specifications for the industrial computers made them a good bet to place them in the shop's heat exchanger platform; where a standard PC wouldn't be able to withstand the heat, noise, and vibration.
Saturn installed four computers in the paint shop—two PCs running in the paint mix area and two industrial computers at the heat exchanger platform. All four computers receive data from the paint mix controller and the heat exchanger controller, in part because the two controllers share portions of the tag databases. One of the PCs in the paint mix location allows operators to monitor the systems remotely. But, since any of the 40 systems are accessible from any of the industrial computers or PCs, operators can make emergency adjustments onsite. The application runs in all four locations, so application changes only need to occur once and then go out to other computers.
A GM first
The Spring Hill paint shop upgrade was the first time the company used EtherNet/IP in a plant. Saturn Spring Hill uses an Ethernet bridge with twisted pair cable (ENBT) modules and a special Ethernet that is dual layered—one for control and one for communication. General Motors had been looking for a specific site application to use this network technology. When Saturn Spring Hill showed how they could use the network to control collision potential, using switches to dedicate ports between the processor and I/O racks, General Motors approved the system upgrade plan.
Over the course of several years, Saturn Spring Hill engineers worked to create a very flexible, automated paint shop. Since installation last December, the new control system has exceeded expectations.
"The old system worked, but the new one is much easier to troubleshoot," Barton said. "We had some glitches in the old system that could take a while to work through, but we've had no problems with the new one. This system has significantly improved our ability to troubleshoot." IC
BEHIND THE BYLINE
Donald Anspach has been with Rockwell Automation since 1989 as a field application engineer and in product marketing for Allen-Bradley industrial computer and electronic operator interface platforms. In 2001, Anspach was named product manager for all Rockwell Automation industrial computers and monitors.
A complete vehicle
Over 6,700 employees at Saturn Spring Hill work together to build three types of automobiles: the Saturn VUE sport utility vehicle, the Saturn ION sedan, and the Saturn ION quad coupe. The Spring Hill campus has three buildings dedicated to building the cars: In the powertrain building, workers build engines and attach transmissions.
In the body shop, workers stamp and mold vehicle frames and various body parts, painting and coating the components for storage until they head out for assembly.
In the assembly building, Saturn employees bring the engine and body parts together to create a complete vehicle.
The process of manufacturing a Saturn automobile at the Spring Hill site begins in the body shop, which creates parts from rolled sheet metal and pre-assembled parts the body shop cannot create onsite. Workers stamp the rolled sheet metal into "blanks," or smaller sheets, that then go to stamping machines. Multi-die transfer machines stamp out parts used to build up vehicle subassemblies: body side left, body side right, motor compartment, rear compartment, and floor pan. The motor compartment, rear compartment, and floor pan ship out to the underbody marriage area, where they join and sides become attached to create a completed frame. The frame then goes through Saturn's phosphate/e-coat system and sealer operation, where all seams are sealed and made watertight. The frame is now ready to go to general assembly to receive its interior fittings.
The polymer area's plastic pellets come to Saturn Spring Hill by rail car and stored in silos. From the silos, they heat up the pellets and then inject them into molding machines used to make plastic panels. The injection-molded panels then go to the paint shop for finishing. These plastic parts, along with steel panels, make a completed panel set of: hood, roof, deck lid, fenders, doors, and rear quarters. At the paint shop, the panel set goes through a washer, is primed, and then inspected. If the set passes inspection, it is washed again and top-coated before undergoing another round of inspections. Once the inspection process is completed, the panel sets travel to an automatic storage and retrieval system, where they sit until general assembly electronically requests a panel set needed for a particular job.