Automated molding & testing facilities aid resin quality control.

Resin producers are making use of high-tech injection molding and robotic testing to improve the quality and consistency of their materials. The latest example of this is a new automated cell for molding test-bar specimens at the headquarters of Hoechst Celanese Corp., Chatham, N.J. It's the first installment of a far-reaching, computer-networked system that will manage quality for resin production at all the firm's North American facilities.

The purpose of the automated molding cell (detailed below) is to produce test bars under precisely reproducible molding conditions, in order to ensure validity of subsequent property test data. Plans calls for the molding cell to be linked to an automated sample testing system, creating a quality-management blueprint that will be duplicated at the company's resin production sites throughout the country.

Ultimately, data from the system will be networked via computer modem with a central data-management facility in Summit. The system also will be linked to quality management and testing operations of Hoechst AG, the German parent firm.

A KEY TO ISO CERTIFICATION

Company executives say the new system also will create an ISO/ASTM testing database for resin customers. ISO standards spell out not only how samples are to be tested, but also strict definitions of how they are made and types of equipment used. Donald Shatinsky, support services supervisor at the Summit technically facility, says injection molding operators can improve resin properties to boost performance for certain tests by making adjustments to molding machines. The ISO standards, however, spell out machine parameters and molding guidelines for producing specimens that must be followed, he says.

Shatinsky says the test data generated from the automated system will be used internally by Hoechst Celanese to monitor and improve the quality of the company's various polymer grades, which will result in more consistent resin products for molding customers.

The test data also will be employed as a permanent, ongoing source of quality-assurance data, which the company will need to document in order to be certified under the ISO 9000 international quality standard (see PT, Jan. '91, p. 53 for an explanation of ISO 9000).

Certification under ISO, which must be renewed periodically through planned and unannounced inspections by independent auditors, requires a firm to demonstrate that it has an ongoing quality-management program in place. As explained by company officials, the new automated system will become the centerpiece of the company's quality-management program for resins.

Compliance with international quality standards as laid out by the International Organization for Standardization (ISO) in Geneva, Switzerland, is seen as a critical certification for resin producers as well as processors, given the demands of globalized business for major OEM manufacturers, and the advent of the unified European market in 1992. One example of this is Ford Moto Co. having recently advised its suppliers that all its materials will require ISO certification next year.

HOECHST NOT ALONE

Use of robots for testing large volumes of resin samples is a labor-saving technique being exploited by a number of other resin producers (see following story). At least one other major German resin producer has installed high-tech automated molding cells in order to provide gap-free documentation of all processing operations from pellets to final testing protocol. The Application Technology Dept. of Bayer AG in Leverkusen, West Germany, has a bank of 14 injection machines that produce 12,000-14,000 test specimens per day without human intervention.

A central computer monitors processing conditions on each machine--including sufficient data to graph each injection cycle--for statistical process-control (SPC) purposes. Part are demolded by robots and placed in special magazines. For each type of test sample, Bayer has separate, interchangeable cavity inserts that fit into a standardized mold base. Preheated cavity inserts are loaded automatically into the mold base, and setup conditions for that mold are downloaded from the central computer to the machine. Automated testing systems can perform 6500 notched Izod tests and 250-400 tests of other types daily. Test data are also stored in the central computer.

Dow Chemical Co., Midland, Mich., has a different innovative quality program, in which identical injection machines and molds are being installed at its resin plants and central research lab to be used as rheometers to monitor flow consistency of Dow's resins (see PT, July '89, p. 111).

AUTOMATED CELL IN SUMMIT

At the center of the Hoechst Celanese automated cell configuration is a Mannesmann Demag D100-182, 110-ton injection molder from the Plastics Machinery Div. of Mannesmann Demag Corp., Torrington, Conn. The unit is operated by a Demag NCIII computer control system, which also serves as the controller for the entire cell.

Integrated with the Demag molder is a three-axis, top-entry, gantry-style W150 robot from Wittman Robot and Automation Systems Inc., Torrington, Conn. The robot removes test bars from the molder and places them on a Mettler GM54 weighing system. If the test bar conforms to the proper weight, the robot will stack the part on a designated contained; if rejected, the robot will deposit the part on a conveyor for regrinding. Test bars also can be automatically rejected by the system it there is a deviation in the established injection-pressure curve during the mold cycle.

Resin is automatically supplied to the molder via a material feed/drying/conveying system from Motan Plastics Industry Equipment & Systems Inc., Kalamazoo, Mich. The Motan system includes 12 50-lb drying and storage hoppers, which are monitored by a Siemens S15 programmable logic controller. The cell also includes a Mokon mold-temperature controller.

By year-end there will be two more identical test bar production cells installed at Summit. A quality-control vision system eventually will be added to the three cells. The three automated production cells will form the front end of an automated testing sytem to be installed and integrated by early 1992.

The fully automated test cell, now being developed by Hoechst in Germany, will accept samples from the three molding cells and conduct tests of tensile strength, flexural modulus and notched Izod impact.

Another vital piece of the system is a proprietary software package developed for Hoechst by Mannesmann to link an IBM host computer in Summit with the test operations of company production and compounding facilities in Bishop, Texas; Shelby, N.C.; Auburn Hills, Mich.; Florence, Ky.; and Winona, Minn. A total of nine additional specimen molding systems--identical to the one in Summit--will be installed at those sites during the next 18 months. These systems will be linked to Summit via computer modem so that the same molding parameters will be used at each facility.