SMC and RTM dominate equipment news for composites.

Recent developments in FRP composites processing equipment include new software for SMC mold analysis, auxiliaries for automating pre- and post-molding operations, vacuum-assisted RTM technologies, and new or improved equipment for pultrusion, filament winding, and both manual and automated spray-up. Most of these developments were displayed or discussed at the recent SPI Composites Institute annual show and conference in Cincinnati. (Materials and additives news from the meeting were covered in Part I of our composites news report--see PT, April '94, p. 15).

FLOW ANALYSIS FOR SMC

One of the most intriguing new developments at the SPI show was the arrival of commercial flow-simulation software for predicting SMC mold-filling patterns (see PT, April '94, p. 13). As previously reported, the Madison Group: Polymer Processing Research Corp. in Madison, Wis., released Cadpress 3-D finite-element software for PCs and workstations. It was developed at the University of Wisconsin-Madison with funding from GenCorp Research, Akron, Ohio. The software helps users optimize charge arrangements and eliminate nonfills and undesirable knit lines. Plots of filling patterns, pressure distribution, fiber orientation, and warpage displacement can be displayed.

AUXILIARIES FOR SMC

A number of developments for automating various stages of SMC part manufacturing were exhibited at the SPI meeting by a group of 15 companies that work with system integrator RP/C Machinery Alliance Inc., Brighton, Mich.

* Nemeth Engineering Associates, Crestwood, Ky., recently bought a license from the Budd Co., Troy, Mich., for its technology for radio-frequency (RF) bonding of SMC assemblies. One RF bonder reportedly can equal the productivity of three traditional steam-and-electric units--at 40% lower capital cost. Now Nemeth can supply either hot-air or RF curing units for low- and high-volume requirements, respectively.

* Accu-Router, Inc., Morrison, Tenn., has come up with a less expensive way to achieve five-axis machining/routing capability. The answer is to mount a two-axis head with its own electric servo motor on a standard three-axis frame, providing a total of five axes of motion.

The company has designed a prototype unit with a spindle that can carry two tools. Accu-Router three-axis machines have a reach of 12 or 18 in., as compared with 30 in. for a true five-axis system. But the cost of a three-axis system with five-axis capability is in the range of $150,000-200,000, or less than half that of a true five-axis system. Speed and accuracy of both systems are expected to be equivalent.

* Perceptron, Inc. of Farmington, Hills, Mich., which makes non-contact inspection systems, has a new TriCam sensing system to replace its older DataCam sensing head. It uses a gray-scale electronic camera to measure x-y dimensions and a laser for the z dimension. The head weighs only 25% as much as the older head.

* John T. Hepburn, Ltd., Mississauga, Ont., has built what's said to be a unique 1500-2000 ton hydraulic presses that can mold SMC or stamp metal car-door skins at 15 strokes/min. The controller can switch programs from one process to the other at the push of a button. Unlike standard metal-stamping presses, these have stripping cylinders for SMC molding.

* A new "Space Saver" press-unloading robot is available from ISI Robotics, Inc., Fraser, Mich. It's compact (60-in. diam.) but it has 120-in. reach.

* ISI Automation Products Group (APG), Mt. Clemens, Mich., has a relatively new and inexpensive modular belt-conveyor system. It consists of two or more endless belts coupled with drive shafts. The frames are made of aluminum extrusions and come in several different lengths. Belts move in two directions; they can be tilted, raised, or lowered by turning a bolt on the mounting frame. Drives can be a-c fixed-speed or d-c variable-speed. A 5-ft-long, two-belt module costs in the range of $3000.

ISI APG, which is relatively new to plastics (see PT, June '93, p. 81), specializes in robotic end-of-arm tooling. It supplies manual and automatic quick-change couplings for air and electric connections. It also supplies the "Wrist Watch" automation protection system, which provides the robot's wrist with a degree of compliance in all directions and a sensitivity that can be varied by means of an air-pressure setting. If the wrist deflects to a preset limit, it can actuate an emergency stop.

VACUUM-ASSISTED RTM

Two variants of vacuum-assisted RTM were discussed at the show and conference. Gray Fowler, materials application engineer in the Defense Systems & Electronics Group of Texas Instruments Inc., McKinney, Texas, presented a paper on using vacuum to produce primary structural RTM parts with properties exceeding those of auto-claved prepregs. The twin obstacles to that achievement, he said, are raising the fiber volume from the 50% typical of RTM to the 60-65% common for prepregs, and simultaneously achieving good wetout with very low void content.

TI achieved those goals with a VA-RTM system from Advanced Process Technology (APT) Inc., Middlesex, N.J. The basic metering machine was a pneumatically driven, piston-type pump with variable ratio (1:200 to 200:1). The system is designed to use the same sorts of two-component, heat-curing resins that are used in prepregs--epoxies, bismaleimides and cyanate esters. Such resins are highly viscous or semi-solid at room temperature and must be heated up to 275 F for processing. The key to TI's process is a PLC-controlled vacuum-management system, also built by APT. The vacuum system performs several critical functions:

1) Before processing, the material components are heated in separate tanks and agitated under fairly high vacuum (0.1 psi) to degas them, which usually takes 3-4 hr.

2) The tool itself is also evacuated prior to injection, either by drawing a vacuum directly in the mold or by placing it in a vacuum chamber or autoclave. This removes all air that could be entrapped by the resin and also removes surface moisture from the preform fibers. Because preform moisture content can vary, the closed-loop vacuum-control system is programmed to ensure complete moisture removal under all circumstances. The system continuously evacuates the chamber until it can achieve and hold a preset vacuum level of 0.006 psi for a 6-min "soak" time. This is accepted as evidence that the preform is fully stripped of moisture. Only then does the controller proceed to the next step in the cycle program.

3) In order to prevent resin bubbling, the process vacuum must not be higher than the degassing vacuum. Hence, the PLC controller automatically reduces the vacuum to 0.02 psi before injection. Vacuum is held during injection mainly to minimize voids. The resin mix is injected under positive pressure of 300-400 psi. Fowler notes that vacuum injection eliminates the need to try to predict the tool's filling pattern since there is no danger of air entrapment if the tool does not fill uniformly.

4) Once the tool is filled, the vacuum is automatically released, leaving the part to be cured at a positive pressure of about one atmosphere.

Using this procedure, Fowler says, "a void content much lower than a prepreg system can be achieved with better part-to-part repeatability." As a demonstration, a densely braided preform of 1.5-in. diam. was injected to yield a 66-68% fiber volume and calculated void content of 1.7%, much lower than the 5-7% typical for prepregs.

Tooling design is a key factor in achieving such high fiber volume, says Fowler. The tool should compact the preform from its typical initial state of 55-60% volume fraction to 65-70%. This compaction will help prevent fiber "washing" under pressurized injection. Since uniform compaction is essential, complex shapes may require an automated, multi-piece mold that will provide closure movements perpendicular to all mold faces. Fowler says that such a tool, with hydraulic slides powered by the press, could also form molded-in holes, cutouts, and bosses.

Another variant of VA-RTM is called VRI or "vacuum resin infusion" by Synergistic Composite Systems (SCS), Houston. This approach uses only a single mold and a vacuum bag. The key is the patented transparent PET top film, which allows the part to be cured by uv light at room temperature. This special film is not flat but "crinkled" so as to allow air to escape without need of a breather felt or bleeder on top of the laminate. (The need for such felt has been an obstacle to uv curing.)

SCS is a joint venture of Film Technology Inc., Houston, which supplies the "Quick Draw" PET film, and Sunrez Corp., El Cajon, Calif., which supplies the resin. The resin can be any polyester, vinyl ester, or thermosetting acrylic that has been specially formulated with a photoinitiator from BASF AG in Germany. The result is a one-part resin system with indefinite pot life. Standard shop vacuum is sufficient for impregnation, and either sunlight or uv lamps can be used for curing. This is a completely closed system, minimizing VOCs, and it is not limited by size or by ambient temperature. VRI will be used to line a 200-ft-diam. concrete water tank and also to produce a 200-250 ft long corvette-class ship for the U.S. Navy. In a test for the latter project, VRI was used to make a 12 x 18 ft section of hull plate about 3/8-in. thick. It was filled in 20 min while standing upright at 60 [degrees] from the horizontal.

SCS says existing boat molds can be converted for VRI. The process reportedly can save time, since laminates over 0.75 in. thick that contain 35-70% by weight glass mat can be uv cured at one shot. Properties reportedly are better than with spray-up, owing to reduced voids. SCS says the uv initiator adds about 20-30[cents]/lb to resin cost.

DuPont Advanced Material Systems, Wilmington, Del., is developing a VA-RTM "infusion molding" process that uses "minimal equipment and facilities." DuPont says it's not ready to release details at present, other than to say this "portable," room-temperature process uses only vacuum to fill a lightweight, single-sided tool. It's also said to be a "clean" process with "virtually no open emissions or worker exposure to fumes or volatiles." The development program is aimed at producing foam- or balsa-cored composites for civil-engineering "infrastructure" applications in construction or transportation.

OTHER RTM NEWS

Liquid Control Corp., North Canton, Ohio, introduced at the SPI meeting a compact meter/mix/dispense machine, the Multiflow CMF6. It's half the size of former models and more accurate--to [+ or -]0.5%, the company says. BPO or MEKP catalysts reportedly can be metered accurately down to 0.7% concentration. This air-driven unit is said to handle filler loadings up to 70% by weight. It offers volumetric ratios from 1:1 to 140:1 and flow rates to 1.5 gal or about 16 lb per minute. A 50-lb/min version is also available.

There's also news in clamping systems. Venus-Gusmer, Kent, Wash., is now building hydraulic presses in small to medium sizes for RTM and RIM. One will be shown at NPE in Chicago this month. These presses have "booking" or tilting platens, which can facilitate parts demolding and mold preparation.

And Linden Industries, Inc., Peninsula, Ohio, is now offering hydraulic presses for RTM, RIM, and SRIM from Wemhoner of Germany. Virtually any size or tonnage can be supplied. These can also have tilting platens. For RTM or SRIM, these presses can be used to trim parts in the mold with the aid of special knife-edge tooling.

OTHER PROCESSES

There is some news in pultrusion, filament winding, and spray-up. Composite Process Equipment, Inc. (CPE) in Haslet, Texas, reports that last year it delivered to BP Chemicals in Auburn, Wash., what may be the biggest pultrusion machine ever built. It has 52 x 18 in. working envelope and 100,000 lb of pulling force.

CPE president Lee Green notes that the company has built pultrusion equipment with in-line braiding. Although filament winding has been combined with pultrusion in the past, braiding appears to be a newer twist.

One processor that has used braiding in-line with pultrusion is DFI Pultruded Composites, Inc., Erlanger, Ky. In the last 18 months or so, DFI has braided glass and aramid fibers with pultrusion to improve hoop strength, torsion resistance, and damage tolerance. According to product manager John Doyle, the company has braided up to 32 yarns at once in-line, and he notes that two braiders can be run in tandem to build up thick profiles.

In filament winding, a relatively new supplier is Accurate Machine Tool of Cleveland, which has introduced the Acc-u-wind 2000 computer-controlled winding machine. It boasts simple programming, minimal maintenance, and low cost (under $28,000). It uses a 486 PC controller with menu-driven software and on-line help. A two-axis program reportedly can be set up and ready to run in 30 sec. The control accommodates up to 10 patterns per program. The ball-screw carriage drive reportedly eliminates the stretching and inaccuracy of chain drives. Accuracy and repeatability are said to be 0.002 in. Max. winding length and diameter are 60 in. and 13 in., respectively. Options include third and fourth axes and higher spindle and carriage speeds. Contact Accurate's representative, Mid-America Sales, Brookfield, Wis.

Electroid Co., Springfield, N.J., has upgraded its TCM-2000 filament-winding tension-control modules with a new drive system that provides unlimited takeback. In addition, the company's Tension Control Network software has been enhanced to provide real-time graphic displays and on-line data archiving for SPC. Up to 255 TCM-200 modules can be networked with an NSM-1 central controller to provide digital, closed-loop tension control to [+ or -]3% and payout speeds to 400 ft/min.

In spray-up equipment, Venus-Gusmer has a new four-axis gantry-mounted gel-coat and chopper-gun system for automated spraying of panels up to 30 ft wide for autos, trucks, RVs, boats, construction, and corrosion-resistant applications. The gantry system provides x-y-z axes plus a rotary wrist movement. The system automatically rotates the gun to keep the spray fan at a right angle to the path of travel.

And for manual spraying, Glas-Craft, Inc., Indianapolis, offers the new SSAx Soft Stream Applicator System. This is a simple kit of three parts that converts Glas-Craft external-mix, airless/air-assist (AAC) guns to a "flow coater" type of device. The conversion reportedly takes only 20 sec. Unlike some other flow coaters on the market, this one needs no solvent flush and it has no extended tip to get in the way of glass chopping. Price is $250.

Glas-Craft has also updated its HVLP (high-volume/low-pressure) spray system. Heated resin hoses are now available, which are said to be more efficient and controllable than block heaters. Also new is an all-pneumatic audible alarm for loss of catalyst pressure; it can also automatically shut off the pump's air motor.