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Automated system speeds preforming.

A new automated net-shape fiber preforming system for RTM and SRIM can produce preforms with selectively varied fiber orientation and wall thickness in about a minute. In development for more than two years, the CompForm system is now commercially available and was demonstrated recently at the CompForm lab in Chesapeake, Va.

The equipment system was developed by C.A. Lawton Co., DePere, Wis., to use special binder resins from Freeman Chemical Co., Port Washington, Wis. It was first unveiled at the 1990 SPI Composites Institute conference (see PT, Jan. '90, p. 15; April '90, p. 35). At that time, Lawton and Freeman had just applied for patents for this sophisticated, robotic preforming operation. Those patents reportedly are now on the verge of being granted.

A temporary hitch in commercialization of the system occurred when Freeman was acquired by Cook Composites and Polymers of Kansas City, Mo., in April 1990. After that sale, Lawton licensed CompForm's process technology to American GFM of Chesapeake, Va., which continued the system's development and has since established a CompForm division for the exclusive manufacturing of the preforming system.

HOW IT WORKS

CompForm transcends previous efforts to automate preform fabrication, its developers say, in that a preform can be engineered with nonuniform wall sections containing various types, thicknesses, and configurations of reinforcements with precise location of specific reinforcement in high-stress points. The system also allows the addition of ribs, closed sections, cores, and encapsulation of metal, foam, wood, or other materials.

A key element of the system is Cook's polyacrylate- and epoxy-based binder resins tailored to be compatible with the composite matrix resin. These binder resins have three times faster cure rates than they had two years ago when CompForm was first introduced, spokesmen say. After the fiber broad-goods reinforcement (usually mat) is cut to predetermined patterns, it is permeated with the binder by spraying, calendering, or rolling.

Next, single or multiple plies of reinforcement are placed on one half of an epoxy mold mounted in a vertical press, and a transparent film is placed over the layup. Manual ply layup was used during the recent demonstrations, but CompForm plans to install robots to show how it can be done automatically.

The forming press closes and 15-20 psi vacuum is applied to mold the details of the preform shape. When the mold opens again, the half with the preform shuttles into a uv-curing tunnel for about 15 sec. Cook's newest binder resins are especially susceptible to the uv radiation, and the short time in the tunnel ensures there is minimal heating of the reinforcement or mold surface. CompForm sources say it is possible to use transparent acrylic molds so that uv energy can be directed into the preform from both sides, speeding cure of the binder even more.

After this initial preforming operation, additional sections of reinforcement can be attached to sections of the original preform by robotic application of "energetic stitching," using the same directed uv energy as before.

Originally, C.A. Lawton was considering microwave energy as an optional alternative to uv curing of the resin binder. Lawton opted to concentrate mainly on uv since microwave would be desirable mainly for curing opaque (i.e., carbon-fiber) composites, and most of those applications are in the now-stagnant defense industry.

Once the preform is cured, it can be transferred to an American GFM cutting table equipped with ultrasonic knives for 3-D net-shape trimming to final dimensions. The result is that when the final part is molded from the preform, only fiber-free resin flash will need to be trimmed.
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Title Annotation:C.A. Lawton Co.'s CompForm system
Author:Monks, Richard
Publication:Plastics Technology
Date:Aug 1, 1992
Words:592
Previous Article:User-friendly features.
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