CIM raises quality & throughput for American Sheet Extrusion.

CIM Raises Quality & Throughput For American Sheet Extrusion

A mid-sized processor of ABS and HIPS sheet for thermoforming, American Sheet Extrusion Corp., in Evansville, Ind., has seen significantly improved quality and throughput from computer integration of its extrusion lines. The company, which runs 1.2 million lb of product a month on three lines, installed its first computer control system, supplied by NRM-Steelastic Inc., Akron, Ohio, on one extrusion line in August 1988. An identical control system was added to a second line in January 1989, and data from both lines are now collected at a remote, central computer console.

The company implemented CIM to improve process information at all levels, according to president Kenneth Hedges. "We thought we could gain significant reductions in process variations, and be able to control things like head pressure down to [+ or -] 1%." Since its implementation, CIM has provided what Hedges terms a "window on the extrusion process." A base of engineering data allows operators to "cut to the heart of problems faster and get them resolved and the line back on-stream faster."

STARTING SMALL

American Sheet's approach to CIM technology was to start small and progress at a pace that it could afford. The company, which performed its own installation, chose Steelastic controls because they were affordable and flexible, according to Hedges. The company started out with an initial investment of only $25,000. The equipment included paths to upgrade and expand the system, allowing the company to change its control strategy as it learned more about its process.

Hardware for the system consists of two Steelastic Sentry Pro 1000 control systems that each have 32 analog and digital inputs, 24 frequency/count/duty cycle channels, full PID control on all analog or frequency inputs, 16 user-definable cascade control loops, and up to six digital drive interfaces. Both control systems interface with a Steelastic Sentry Master 3000 off-line host computer at a central location, which collects and archives data on a real-time basis. The host system provides automated data capture, selective SQC/SPC process analysis, color trend plotting of historical data, and real-time display of key statistical quality parameters.

On the production floor, each extruder is equipped with a touchscreen monitor on which the operator can make system adjustments. Each monitor may be placed near the polishing roll stand for maximum convenience. The system is user-configurable and can be altered through a menu-driven touchscreen.

The software is fully programmable, an important feature that allowed American to configure its own process-control parameters, says Hedges. The software allowed the processor to set limits, enter PID values, set up cascade loops and experiment with configurations to match the system to the process. The flexibility proved to be a significant part of American Sheet's learning curve.

Since its installation, the company has upgraded the Sentry Master 3000 from DOS to UNIX to handle real-time multi-tasking functions. It also expanded the system to monitor up to four lines. It is also investing in a Command Sentry 1500 control unit, which has about double the capacity of the Sentry Pro 1000 unit, for one of its lines.

SPC IS STRATEGICALLY VITAL

The most important element of the system is real-time statistical process control (SPC) data, which Hedges believes is critical to applying a control strategy. Each variable on the system now can be displayed on a trend chart with a month's worth of data. "We are getting some real-time trending now, and there are more real-time SPC packages that we can add with this new 1500 system," he adds.

His goal is to run everything on a recipe basis. "We will establish capability for the process and the recipe that best supports it for any startup of a new customer or new product. Then we will use that recipe to make sure we repeat that capability. Eventually we will have a library of recipes to draw on." He adds that SPC will aid in troubleshooting because it will narrow the hunt for possible causes of a problem.

Hedges claims that the system makes the operators' jobs easier. "The operators were very skeptical at first. Now they use the system for process conditions, setpoints, and establishing and reading the process all the time. They never look at discreet instruments any more." Consequently, Hedges is removing the old discreet instruments from the line.

TANGIBLE BENEFITS

Although Hedges would not share specific numbers, he says that the company has achieved "significantly" higher throughputs and improvements in quality since the system's installation. Scrap rates over the last 12 months have decreased 45-50%, he claims, largely because of the CIM system.

The control system has enabled the company to maintain the same production rates every day. "If you find you are falling off on rate, the control system will help you find out what your problem is," Hedges explains. "The more variables you can monitor, the easier it is to find a process variable that is out of control."