Davidson improves materials efficiency and troubleshooting ease.

Davidson Improves Materials Efficiency And Troubleshooting Ease

At its plant in Americus, Ga., the Davidson Exterior Trim subsidiary of Textron Inc. has been moving toward CIM for polyurethane RIM molding and painting processes since the mid-'70s (see PT, Aug. '76, p. 11). The facility has 15 urethane metering/mixing units that service 40 RIM clamps, ranging in size from 75 to 125 tons; and a recently completed R&D lab houses a 250-ton unit. The newest and most advanced production cell of RIM equipment, with eight clamping presses serviced by four metering/mixing units, was built in 1985 in response to a large automotive contract. This cell, and an automated painting line, are electronically linked to host computers, providing a real-time flow of manufacturing information to more than 100 terminals throughout the plant.

Rahul Mukerjee, v.p. of technology, estimates that CIM has resulted in up to a 40% improvement in material utilization efficiency over comparable operations lacking a free flow of real-time manufacturing information. In addition, Mukerjee says CIM has allowed both the quality-control and technical-service groups at Davidson to be integrated into the manufacturing group. Now that process data for each shift are readily available, troubleshooting equipment problems is less of a mystery to the manufacturing staff.

Davidson produces over 3 million RIM fascia and body molding parts per year for the auto industry. These parts are spread over 25-30 vehicles from the three major domestic and some foreign "transplant" automakers. Because the finish of an automotive RIM part is essential to its marketability, Davidson's automated paint line has been made as much a part of the CIM system as the RIM molding cells. Taking into account different paint colors and left/right-side design variations, the company produces nearly 800 different parts, each of which can be traced back electronically to the RIM shot that made it.

PLANTWIDE INFORMATION FLOW

The information on any CIM system originates at the sensors that respond to machinery conditions. In Davidson's advanced RIM cell, this information is received and managed in real time by Allen-Bradley PLC-2/30 programmable logic controllers (PLCs). Each clamp has its own PLC, as does each metering/mixing unit. The PLCs control all critical functions, such as press closing and opening, shot timing, and pumping pressure. In case of a serious malfunction, such as a loss of mixhead pressure, the PLCs will shut the press down.

To detect and solve subtler problems, the process data received by the PLCs during each shot are simultaneously sent to a minicomputer. Some data are measured off-line: RRIM glass content of sampled parts is measured in the q-c lab and sent to the minicomputer from a lab terminal. And each part is weighed at the molding line, the weights being manually entered into the computer database.

Davidson uses a pair of PDP minicomputers from Digital Equipment Corp. as "front ends" for a VAX mainframe. The mainframe stores historical data, while the minicomputers store data from recent shifts and generate SPC/SQC histograms and Pareto charts using RS/1 software from BBN Software Products Corp., Cambridge, Mass. One minicomputer serves the RIM area, while another handles the paint line. In addition to RS/1, the paint-line minicomputer also runs some defect-monitoring software developed in-house.

PC POWER

While Davidson relies heavily on its minicomputers, personal-computer technology has advanced so much in recent years that for certain applications, Davidson has PCs linked directly to the mainframe. For instance, Davidson recently updated an older RIM cell by replacing a bulky piece of control hardware (for which replacement parts were becoming scarce) with a PC. The PC puts data into usable form with software from R & L Engineering, Abany, Ga.

Of the more than 100 terminals at Davidson that have access to real-time processing information, two terminals are customized to serve the unique needs of the monitoring booths for both the RIM and paint lines. On the RIM line, software from Square D Co./Crisp Automation Systems, Dublin, Ohio, is used to provide information such as pressure profiles for each shot, SPC trend data, or a schematic of the plant layout indicating real-time status of each press (closed, filling, curing, open, etc.) by means of different colors or blinking icons.

The paint-line PC terminal uses Allen-Bradley "firmware" (open-ended software customized by the end user) to provide information on what parts are being painted, operating conditions, and SPC analysis. Real-time control of the paint line is handled by six Allen-Bradley PLC-3s.

While the custom terminals serve the plant-floor control rooms, numerous "dumb" terminals are located in offices throughout the plant. The office terminals allow someone to generate an up-to-date SPC report without going down to the plant floor.

Other reports that can be generated from a remote terminal include a defects-per-part report that uses data entered manually by inspectors with a barcode scanner and defect menu at the end of the paint line. Davidson catalogues over 50 potential defects, including surface porosity, air entrapment, flash contamination, paint runs, and dirt content. Data can be displayed in the form of a Pareto chart, showing the frequency of different types of defects, which helps set troubleshooting priorities.

With information originating from in-line flow meters, current usage rates for RIM materials, paint, and other resources can also be quickly generated, allowing the accounting department to reap some benefits from CIM. If fact, there's hardly a Davidson group that has not been affected by CIM. Mukerjee notes that the assembly and packing areas are the latest groups to receive improved CIM involvement.

However, Mukerjee stresses that Davidson's success lies not only with moving forward in CIM, but also with holding onto some conventional manual methods of recordkeeping. For critical variables such as part weight, material temperatures, and glass content, manual SPC charts are kept separately by the press operators. Mukerjee feels that people are more likely to respond to changes in the process if they are intimately involved in data acquisition.

PHOTO : Automotive RIM parts such as bumper fascias and body side moldings are produced for several customers at the Davidson Exterior Trim, sub. of Textron Inc. The processor credits CIM with a 40% improvement in material efficiency.

PHOTO : On the plant floor, this "smart" terminal displays information such as SPC data, real-time press-status schematics, and shot-to-shot profiles (shown) indicating material pressures and the difference between them.