Green light for automated performing?

An automated preforming process developed by Owens-Corning Fiberglas Corp. of Toledo, Ohio, is moving closer to commercial status in the U.S. and Europe (see PT, Mar. '92, p. 42; May '93, p. 21). The "P-4" (Programmable Powdered Preform Process) technology is a robotized system conceived to overcome drawbacks of conventional preforming methods. These problems include slow cycles, inconsistent placement of reinforcements, and waste of raw materials, says Glenn Sandgren, leader of the Long-Fiber Group at the Owens-Corning Science and Technology Center in Granville, Ohio. The P-4 process also is said to allow greater design freedom by controlling the orientation, positioning, and length of fibers.

As yet, there are no commercial installations of the P-4 system. However, Owens-Corning is actively negotiating two automotive projects in the U.S. One is a semi-commercial project with the Automotive Composites Consortium, Troy, Mich., for making a pick-up track bed. If the deal is consummated, ACC envisions placing the system at the Textron Automotive plant in Americus, Ga., where it would be available to consortium members Ford Motor Co., General Motors Corp., and Chrysler Corp. (Sandgren wouldn't reveal details of the pending projects at press time.)

In addition, Peugeot of France is using the prototype P-4 system at Owens-Corning's Technical Support Center in Battice, Belgium, to make components for an experimental all-composite electric car.

HOW IT WORKS

The P-4 system at the Battice lab - the only system installed to date - consists of a jointed-arm robot with three glass-delivery systems, a heating and cooling system, and a mold carrier with preform screens. The first glass-delivery system deposits a surface veil of low-tex roving; the second chops and orients fiber lengths from 1 to 5 in. and combines them with powdered binder; and the third places continuous fibers in random loops or straight oriented strands. The mold carrier system is a low-pressure press with a sliding table and preforming screens. Two parallel closed-loop ducts circulate hot (up to 572 F) and cold air.

With the mold-carrier table in the outer position, cold air is sucked through the lower screen while a thin layer of surface veil is applied without binder. Next, glass filaments, cut to 0.5-in. length, are dispersed over the preform screen and randomly oriented. Either chopped or continuous fibers are then delivered to the screen in an oriented fashion, and thermoplastic powder binder is applied at the same time.

After spray-up, the table is moved into the press, which closes and circulates hot air through the preform, melting the binder. After the binder is melted, cold air is circulated to cool the preform to about 160 F, and cooling continues until the table returns to the spray-up position. Demolding (which, along with loading, is the only step not currently automated) is facilitated by the surface veil.

FASTER CYCLES

Cycle time for a large part is about 3 min, says Sandgren. Total waste is only about 2%, versus 12-50% for thermoforming of glass mat. The process also uses less binder because little of it escapes from the preform. Because powder binder requires less energy than wet binders to cure, energy consumption is one-third to one-tenth that of the wet process, says Sandgren.

The glass delivery system can dispense over 13 lb/min - 25 lb/min if a second chopper is added to the robot. Glass can be delivered in any direction by dropping a baffle in front of the orifice, and fiber length can be varied from 0.25 in. to 3 in. on the fly, which is critical for fine details, says Sandgren.

The process is suitable for parts as large as track beds and as small as 5 sq ft. Cost of the system depends on its size and speed, but may range from $500,000 to $1.5 million.