Engineering News 7676

DN Staff

March 4, 1996

25 Min Read
Engineering News

Las Vegas, NV--Amid the neon, celebrities, and myriad "Wow!"-inducing gadgets, the undisputed star of the recent Winter Consumer Electronics Show was DVD--Digital Video Disc--technology. You won't be able to buy a DVD player until at least the fall, but industry analysts agree that DVD will soon be the medium of choice for movies, music, multimedia, and games.

"DVD players should match the VCR in establishing a huge and dynamic industry," says Joseph Clayton, executive VP of Thomson Consumer Electronics and of the Consumer Electronics Manufacturing Association (CEMA). CEMA's numbers put factory sales of DVD players in the U.S. for the first three years at 4 to 5 million units. By 1998, the group believes more than half of all computer disk drives will be DVD drives, and Toshiba officials say we will see recordable DVDs by the end of 1997. Other major play-ers include electronics giants Sony, Philips, Pioneer, and Thomson Consumer Electronics.

Why all the optimism? After all, DVDs look just like CDs, and such new technologies as minidiscs, digital compact cassettes, and digital audio tape haven't exactly had consumers lining up to shell out their hard-earned cash.

Capacity. CD-ROMs hold 0.67 gigabytes--enough space to store encyclopedias. DVD disks can pack up to 17 gigabytes--more than 25 times the capacity of a CD-ROM or CD. Thus, DVDs can store enough data to play back movies with the highest quality video and audio you're likely to see this side of a studio's original print. This capacity is already testing the mettle of software writers, who will be able to create multimedia titles and interactive games an order of magnitude richer than with CD-ROMs.

To achieve multiple-gigabyte capacities, Toshiba engineers created a bonded disk. A 1.2-mm-thick DVD disk is composed of two separate 0.6-mm-thick disks bonded back to back. Thus, on the data-reading side of a single-sided disk, the light from the laser pickup travels through just half the substrate thickness of a regular 1.2-mm CD. The resulting DVD is more resistant to errors caused by slight tilting relative to the laser pickup. This lets manufacturers master DVDs with significantly finer high-density data tracks than CDs, and lets players read the disks with great precision by a shorter wavelength (650 nm) red laser.

Another reason consumers are likely to hop on the DVD bandwagon is standards. Manufacturers--after consulting with the motion-picture, computer, and software industries--agreed last December on one global standard, thus averting a VHS-vs-Beta type of war.

Yet another smart move: backward compatibility. Consumers won't have to forsake their CD collections when they buy a DVD player. Today's audio CDs can play in DVD video players--in fact, at least one manufacturer plans to sell a DVD player that can play DVDs, CDs, and laserdisc movies. Similarly, current CD-ROMs can play in DVD-ROM drives. And by the time the players arrive, 200 to 300 movies will be available on DVD--thanks to including the movie industry in the loop. Prices are expected to be $20 to $30 per title.

Not only are the disks in-expensive, DVD players won't break the bank either. Of the companies that have announced prices, Toshiba is the most aggressive with a planned $499 price tag. Others have mentioned prices of $599 to $799, but so far no one wants to break the $1,000 mark.

That's entertainment! Buyers will be getting maximum bang for the buck. A dual-layer, single-sided DVD can store up to four hours of MPEG-2 video with picture quality that approaches the original D-1 studio master and exceeds that of laserdiscs. A single-layer DVD can hold a 133-minute program with room to spare for Dolby(R) AC-3(TM) stereo or multichannel digital sound along with a choice of three language soundtracks and four different sets of subtitles.

Higher-capacity disks can present subtitles in 32 languages; soundtracks in eight different languages; 9 camera angles for sporting events; 3 display formats (full screen, wide screen, and letterbox); and G, PG, PG-13, R, and NR-17 rated versions of the same movie on one disk.

It's tough to imagine the next quantum leap in storage technology--whether for consumer applications or computers. But the companies and engineers involved would do well to study how DVD pioneers learned from past mistakes and worked together to realize a new technology that's almost certain to succeed.

Plastic fuel tanks

Ashtabula, OH--Complex metal fuel-tank assemblies with joints, seals, solders, welds, and threads can cause hazardous leaks and spills. To eliminate this threat, the Meese Orbitron Dunne (MOD) Co. turned to a rotomolded one-piece, plastic fuel tank.

By replacing multiple components and fasteners with a single plastic unit, the MOD fuel tanks also got rid of several steps in product design, assembly, and production. As a result, the tanks require less labor, time, and materials to produce.

Rotomolded from Phillips Chemical's Marlex(R) cross-linked polyethylene, the corrosion-resistant tanks remain impervious to attack from acids, oils, solvents, salts, alkalis, and other substances that corrode stamped steel and sheet metal. The tanks also resist temperature extremes by minimizing heat exchange to maintain internal fuel temperature in severe outdoor conditions. And the design won't distort or rupture in high temperatures, or catch fire. In fact, tank integrity is assured in temperatures ranging from 30 up to 200F, says MOD's Jeff Dunne.

MOD's in-house engineering staff will custom design the tanks. "We can make them conform to nearly any shape or specification," Dunne reports.

'Green' process creates new foams

Newton, MA--A new environmentally friendly foam process exceeds Clean Air Act requirements by eliminating emissions such as CFCs and volatile organic blowing agents.

Along with the environmental benefits, VPF(TM) technology produces foams with a variety of densities and physical properties, including previously unavailable low-density, ultra-soft products. It was recently developed by Foamex International, in partnership with Recticel Corp. and Beamech Group Ltd.

"Ultra-soft foam can replace polyester fibers because the foam takes on the same feel properties but doesn't mat down," says Vinnie Bonaddio, Manager Applications Development, Foamex International.

The process differs from traditional methods that pour foam at ambient pressure. In the new method, VPF is poured in an air-lock chamber nearly 200 feet in length. It's produced on a continuous basis in the left portion of the chamber and then moved through to the right side where, through air locks, the foam can be brought back to ambient temperature and moved out--without stopping or slowing the foam- creation process.

In the two Foamex facilities already using VPF, it provides direct control of environmental characteristics such as air pressure, temperature, and humidity. These factors can be regulated to change the density of the foam. And, all gases produced throughout the VPF process are absorbed in charcoal filters, creating a clean atmosphere.

Foamex currently uses VPF to produce cushioning foams for furniture and bedding, but future applications under development are foams for automotive trim and accessories, carpet cushion and other carpet products, health care, and industrial and consumer technical foams.

Fluoropolymer regulators, valves fight impurities

Anaheim, CA--Fluid regulators and valves for semiconductor manufacturing and other demanding operations must meet high-purity specifications. That's why Furon Co.'s Fluid Handling Div. turned to fluoropolymer resins to produce these specially engineered components.

All wetted parts of the UltraPure(R) valves and regulators consist of high-purity Teflon(R) PFA or PTFE fluoropolymer resins from the DuPont Co., Wilmington, DE. "They provide a high level of protection against contamination and chemical attack," says Kenji Kingsford, research and engineering manager for Furon.

Body components are injection molded from Teflon PFA 440 HP fluoropolymer resin. Internal flow passes are radiused and fully swept to guard against particulate buildup.

The units' diaphragms consist of Teflon PTFE. A patented design prolongs diaphragm life by allowing free movement without significant stress, according to Kingsford. In conjunction with pressure-balanced poppets, the diaphragm design also permits increased pressure ratings, he adds. The diaphragms have a tongue-and-groove seal to help prevent trapping of fluid.

The regulator's body and bottom cap are made of Teflon PFA. The pneumatic regulator has four internal parts of Teflon PTFE: the poppet, the bottom retainer for the poppet, and two diaphragms. The manual regulator has one diaphragm.

Three external parts, a positioning ring and two flare nuts, are injection molded from DuPont's Tefzel(R) ETFE fluoropolymer resin. "We use Tefzel for critical external components," Kingsford reports. "It offers strength and stiffness, and resists chemicals."

Other regulator components include metal springs coated with Teflon-P PFA powder coating, and an O-ring of DuPont's Viton(R) fluoroelastomer that seals the actuating mechanism.

Ultrapure valves are similar in design to the regulators. However, valves, poppets, and diaphragms of Teflon PTFE are made in one piece, and top and bottom caps are made from Tefzel. Both pneumatic and manual versions are available.

Special PVC solves gasket degradation problem

Upland, CA--When one of Cannon Gasket, Inc.'s key customers had difficulty with plumbing gaskets degrading in aqueous environments, Cannon searched for a material that would combine chemical resistance with just the right mix of physical properties needed to ensure optimal part performance.

The search led Cannon to Teknor Apex Co., Pawtucket, RI. "Cannon's customer required a dynamic material in this critical application where the gasket comes in contact with chlorine-based disinfectants," says Phil Morin, product man-ager for general-purpose compounds at Teknor Apex. Chlorine aggressively de-grades rubber and standard flexible PVC compounds.

The solution: Flexalloy(R) PVC. Unlike most standard flexible PVC compounds that exhibit a sharp drop in physical properties and performance be-low 60 Shore A, high-molecular-weight Flexalloy can be formulated in low durometers (down to 35 Shore A), while maintaining needed physical properties.

"Compared to conventional PVCs, thermoset rubber, and thermoplastic elastomers, Flexalloy high-molecular-weight PVC compounds offer superior physical properties, while possessing rubber-like qualities," says Morin. "A significant advantage of high-molecular-weight PVC compounds centers on their ability to maintain tensile strength, tear strength, and other physical properties over a wide hardness range."

In formulating the product for Cannon, Teknor Apex produced a 60-durometer grade of Flexalloy that met the necessary chemical-resistance requirement. In addition, the material had a tensile strength of 2,100 psi, and a tear strength of 200.

"Making the Flexalloy material available for die-cutting, as with the Cannon die-cut gasket, opens new opportunities for processors who require a tough, chemical-resistant material in hardness levels that can meet their precise needs," Morin predicts. To date, the Flexalloy materials have replaced thermoset rubber in a number of automotive and medical-equipment applications. They have also found expanded use for hand and tool grips, hose and tubing, footwear, and weatherstripping.

Multiple servers offer super-computer-class performance

Maynard, MA--Digital Corp. says it can offer affordable supercomputer-class performance by linking together several of its Alpha servers to act as a single system. By combining new technology with "commodity" components, DEC officials say they can offer 57.6 GFLOPS of performance for $4.5 million. Industry analyst Gary Smaby of the Smaby Group calls the Digital AlphaServer 8400 array "a preview of the next generation in enterprise supercomputing."

"Digital is making high-performance computing afford- able for more applications than ever before," adds Michael Levine, scientific director of the Pittsburgh Supercomputing Center. "This approach is elegantly simple, very powerful, and cost effective."

At a recent supercomputing conference in San Diego, DEC showcased an array of eight AlphaServers with a total of 96 64-bit Alpha processors--each offering 600 MFLOPS.

DEC engineers use a standards-based PCI-bus Memory Channel interconnect, offering 100Mbytes/sec, to link the servers. A High Performance Fortran compiler and other tools allow the arrayed system to be programmed as easily as a single system, DEC officials say.

Very Large Memory technology is key to boosting system performance, by increasing the amount of information that can be stored in memory, DEC engineers explain. Because Alpha is a true 64-bit architecture, it can handle up to 14 Gbytes of data in memory, compared with 2 Gbytes for 32-bit systems. Putting more information in memory speeds performance by eliminating the need to call data from slower, electro-mechanical disk drives.

AlphaServer arrays begin at $70,000 for a model 2000 with two processors, 256M memory, and 4G disk space.

Desktop prototyping offers design flexibility

Mossville, IL--Desktop rapid prototyping will help Caterpillar engineers spot problems earlier than ever before, as well as consider more options at the beginning of a design cycle, according to engineering supervisor Fred Brotherson.

Caterpillar was the first company to receive a beta version of 3D Systems' new Multi-Jet Modeling (MJM) device. So far, users are impressed. "It's a tremendous technology. It's what we have been looking for," Brotherson says. "This is truly an office machine."

The goal is to make the system work just like a plotter for the engineer at a CAD station: choose one option to print out a paper plot, and another to request the actual physical proto-type. "We're almost there," he adds.

MJM uses a 96-jet "print head" to create models out of thermopolymer. The head moves back and forth on the X-axis like a printer, layer by layer, to create a prototype.

This system is a concept modeler, so accuracy isn't a big concern. "We haven't even measured parts," he notes. Instead, speed and convenience are the major issues. For accurate models that can be used for serious testing, Caterpillar will continue using conventional prototyping, such as 3D Systems' stereolithography.

Caterpillar engineers have already made changes in designs based on the early concept models, he says. The concept models are useful to quickly see if there are problems, such as an unsupported wall, incorrect radii, or sharp corners.

"It gives us time back in our design cycle," Brotherson explains.

Caterpillar would like to speed up the process--models can now take several hours to produce--as well as make it a little easier for engineers to use at their desks. And, users must be careful with the models, because they break easily if dropped. But overall, Brotherson says, "The engineers really like it. There's a lot of interest in this at Caterpillar. Another plant is constantly contacting me, with check in hand saying, 'I want one. Who do I pay to get it?'"

High-G camera documents crash tests

Southfield, MI--How do you document impacts of up to 100Gs? Not many electronic products would survive such abuse. But that's just what engineers at Lear Seating Corp. are inflicting on new high-speed electronic cameras from Eastman Kodak Co., San Diego.

Lear engineers are using the cameras to document crash-test simulations for automotive seating designs. The cameras are part of Lear's "HYGE" Sled, a crash simulator at the company's new Advanced Technology and Test Center.

"With on-board digital-image capture, the HYGE Sled gives us an important advantage: The ability to test a seating system and review high-resolution color results within minutes," says Art Vartanian, vice president of advanced engineering at Lear.

The Kodak EktaPro RO (record only) imager captures 512- x 384-pixel color images at speeds up to 1,000 frames per second. It withstands 100Gs at 10 milliseconds in any axis, and up to 50Gs at 100 milliseconds.

The imager's charge-coupled sensor meets U.S. Department of Transportation guidelines for analysis-quality images. Previously, this could only be accomplished with film cameras, says Vartanian. The new cameras are mounted on the sled and a body buck via outriggers. Instead of a test subject passing through the camera's frame, the imagers ride along with the subject. This allows close-up views of seat components and restraint systems during the critical high-impact phase of testing, Vartanian says.

When its memory is full, the camera automatically downloads images to a memory module, or waits until programmed to do so. Images are transferred to a removable PCMCIA hard drive or solid-state flash-memory module, where they can be read by a desktop PC for review and analysis.

An electronic shutter speed of 100 microseconds provides blur-free images, Kodak claims. The current RO camera captures up to 500 images in dynamic RAM; Kodak engineers plan to increase that capacity to 2,000 frames later this year.

Self-clinching nuts bolster handlebar design

Woonsocket, RI--The fasteners that hold a bicycle's handlebars must be corrosion- and vibration-resistant and provide good holding power. That's why engineers at Girvin Inc., a manufacturer of full-suspension mountain bikes and components, chose self-clinching nuts for their new Pro-Flex 656 full-suspension bike.

Pro-Flex's fork suspension takes a unique design approach by using two PEM(R) nuts from Penn Engineering and Mfg. Corp., Danboro, PA, to clamp on the handlebar stem. The Girvin "flex stem," which also uses a PEM nut on the spring assembly, allows for an inch of play in the handlebars.

In joining this assembly, Girvin engineers ruled out welding or attempting to install threads in aluminum in favor of self-clinching stainless-steel nuts. Permanently installed, each nut provides the required threads and makes assembly and disassembly easier. The fasteners also resist corrosion.

The nuts provide desired threads in a location where there is little space for conventional fastening hardware, says Girvin CAD Designer Ken Warren.

Engineers chose PEM stainless-steel nuts for previous Girvin mountain-bike designs to hold rear struts to spring assemblies. Type CLS nuts with a thread size of M6 x 1 can be quickly and accurately installed into aluminum using a standard press, say Girvin engineers. The press delivers the necessary force to squeeze the fasteners into 8.75-mm pre-drilled holes.

The installation force completely embeds each nut's clinching ring and knurled collar into the 0.090-inch-thick aluminum. The displaced metal flows into a back-tapered shank, thus locking the fastener permanently into place. The embedded knurled ring also provides high torque-out resistance, say Penn engineers. Since all clinching takes place on the fastener side of the aluminum, the front side remains flush and smooth.

PEM nuts provide the necessary load-bearing threads for easy insertion of screws from the front to complete the assembly, says Warren. In the flex stem assembly, the springs are removable. Disassembly is accomplished in one step by taking out the screw, without any worry that the nut will loosen or fall out, he adds.

Plastic reduces parts, improves maintenance

Summit, NJ--When designing the Metris(R) residential gas-measurement system, engineers at Schlumberger Industries selected Celcon(R) acetal copolymer for several integrated components. The resin's key benefit: It allowed effective parts consolidation and enabled the meter's measurement chamber to be separated from the die-cast housing. This enables efficient long-term modular replacement of the chamber.

In the past, the center body, two side covers (which form the measurment chamber), and the top were all made of aluminum. Now, the center body and side covers are made of Celcon, reducing the total number of aluminum castings from four to two.

"Because Celcon has both inherent lubricity and excellent dimensional stability, it allowed us to mold the bearings and measurement chamber into one integral unit," explains Dave Adams, new products manager for Schlumberger. Lubricity is important not only for low wear of the bearing surface, but also to decrease friction between moving pieces, which can cause reductions in the accuracy of the meter.

Celcon's resistance and impermeability to gases and hydrocarbons contributed to the Metris system's operating reliability and precision. Also, the resin's low moisture absorption resulted in high shape retention. "Celcon acetal provided us another distinct advantage, resistance to extreme temperatures," Adams says. "The Metris can handle temperature ranges of -20 to 120F."

In addition to the center body, Celcon is used for 11 other components in the Metris, including the side covers, diaphragm flags, links, valve links, cam crank, valve cover guides, diaphragm plates, link block, gear shaft, retaining clip, and bushings.

Dow reaps automotive interior/exterior awards

Detroit--What do the window encapsulation system on the 1996 Chrysler minivans and the blow-molded knee bolster system on the 1996 Chevrolet Astro and GMC Safari vans have in common? Both picked up awards for the year's most innovative use of plastics from the Society of Plastics Engineers. However, the big winner in each case was The Dow Chemical Co., which supplied materials for the winners.

The one-piece knee bolster, which garnered the body interior award, is said to be the first blow-molded part used in an interior structural application. The components reduced cost by $4 per vehicle and weight by 40% vs a two-piece, steel-reinforced, welded plastic knee bolster. Development time also was reduced considerably. The material used: Dow's Pulse(TM) 880BG PC/ABS blend.

"The blow-molding process was a real star for us on this project," says GM Design Engineer John Moll. "We were able to make engineering changes more quickly and easily."

The window encapsulation system, winner of the exterior award, gives the appearance of one glass panel running the entire length of the vehicle. Because there is no exposed hardware, wind noise is minimized and the vehicle is easier to clean. Attachment studs are molded into the single-side encapsulation. The material used: Dow's Pellethane(TM) 2103-87A thermoplastic poly-urethane resin.

Exterior appearance created the greatest challenge for the development team, according to Raymond Dill, lead engineer for Donnelly Corp., the encapsulation system's manufacturer. "Vehicle styling demanded a flush glass look with no visible hardware to complement the clean, aerodynamic lines of the design," Dill adds.

Window seals on the minivans perform very effectively with the single-side encapsulation design, says Dill. The system has 7% mold surface area, said to be the least mold surface area in the industry. Also, the thermoplastic urethane offered shorter cycle times than RIM--a major consideration for the high-volume program.

Concept truck showcases 'green' technologies

--Walter Wingo, Washington Editor

Washington, DC--It turns heads as it tours American cities. Its sleek, contoured body of aluminum sheeting and low-slung cab remind many onlookers of a dolphin on wheels.

Making an eye-catching vehicle, however, was not the main aim of Volvo Truck Corp. in creating its 15-ton Environmental Concept Truck (ECT). Volvo ordered its engineers to design a delivery truck that would serve as a rolling testbed for new, earth-friendly technologies. The truck would have to wend its way through cramped city streets, giving off little noise and no emissions.

Volvo formed an ECT team of 15 full-timers and 15 part-timers. They had free rein to combine conventional components with many that are highly experimental. Management gave them only 18 months to complete the project.

"The result," boasts design engineer Hans Hallung, "is probably the most advanced truck ever built."

ECT's series-coupled driveline offers two choices: hybrid power or battery power. It consists of a gas turbine, running on ethanol, with an integrated high-speed generator and batteries. That system powers an electric motor attached to the rear axle. With no valves, pistons, gearbox, or propeller shaft, ECT hums like a large golf cart.

Under hybrid power, the generator, which--like the turbine--runs at 70,000 rpm, produces 110 kW. It can recharge the nickel-metal-hydride batteries from 20% to 80% in 20 minutes. Also, the driveline's electric motor serves as a vehicle retarder. Instead of escaping as surplus heat, braking energy helps charge the batteries.

Unfortunately, the batteries and various rectifiers weigh nearly two tons. Hallung expects that to change as researchers develop lighter, more efficient batteries.

ECT has independent front suspension with twin links. Position and power sensors detect minute changes in the road surface. A computer regulates the wheels' hydraulic cylinders so the truck stays horizontal.

Volvo demonstrated ECT's all-wheel steering system in a small loading area outside a Washington, DC, hotel. With its rear wheels swivelling in the opposite direction from the front wheels, the 32.8-ft-long truck turned a circle of less than 56 ft. Then, showing how it can get into small parking spots, ECT "crabwalked" from side to side.

Among other ECT features: video cameras instead of mirrors, sensors that warn of close objects, and windshield wipers that adjust according to how hard it is raining.

Volvo poured more than $13 million into the project. Despite all that cost and work, ECT will never make it to a dealership. The truck would be far too expensive to buy and run commercially.

Volvo officials, however, contend that many ECT parts and systems--including the hybrid powerplant--will find their way into future trucks, making them cleaner, safer, and more efficient than those on highways and streets today.

Patented ink first to imprint Kraton

--Mark A. Gottschalk, Western Technical Editor

Santa Ana, CA--A new patented ink formulation marks what no other ink could before: Shell Chemical's Kraton(R) elastomer. Under development for 16 months by engineers at Talaurian Technologies, the ink imprints during conventional hot-stamping, or it can be incorporated into the molding process with pre-inked labels placed in the cavity.

"The magic is in the ink," says John Jacobson, Talaurian's chairman and CEO. "It chemically bonds with the substrate and, with sufficient heat and pressure, becomes part of the substrate, not just a layer of ink." He claims that such adhesion makes the ink usable for critical applications such as keycap labels for medical products or control-panel buttons in automobiles.

Actually based on Kraton itself, the ink is available as labels only in a variety of colors and sizes from a few millimeters square to two square feet.

Jacobson notes that processing in-mold adds five to seconds to the part's cycle time. But the ink requires no pretreatment of the material with adhesion promoters or post treatment curing. Though developed for marking Kraton, the ink will also permanently im-print Telcar(R), Sarlink(R), Exylar(R), and Dynaflex(R).

"The Kraton world has been waiting for this for years," says Jacobson. "We've shocked a lot of people who said this couldn't be done."

Custom circuit breaker prevents accidents

Whittany, NJ--When an AT&T customer demanded circuit breakers protected from accidental actuation, company engineers turned to Carling-switch, Plainville, CT.

AT&T's cellular wireless transceivers for base stations include multiple rocker circuit breakers. The breakers prevent equipment damage due to power surges or glitches. However, someone leaning against the rocker switch could accidentally turn off the system, leaving customers without cellular phone service.

"We originally used Carlingswitch's standard A Series rocker circuit breaker," says Behzad Mottahed, member of AT&T's technical staff. "But a Japanese customer wanted protection against accidental turn-off."

First, AT&T proposed a rocker guard--a piece of plastic on either side of the switch to prevent accidents. But the customer noted that somebody could still use a finger to activate the breaker. AT&T engineers consulted Carlingswitch again. The company came up with a design consisting of a shroud over the rocker. The only way you can turn the switch off is by pushing a pencil or similar object through the shroud's hole.

Mottahed re-ports that Carlingswitch turned around prototype breakers in two weeks. And David Berryman, Carlingswitch market development manager, says that the custom product proved so popular that Carlingswitch now offers the shrouded circuit breaker as a standard product.

Composite lightens jet engine

Wallingford, CT--A fan exit case made entirely from composites promises to make jet engines lighter and less expensive to manufacture. The part was developed by Dow-United Technologies and Pratt & Whitney for a commercial aircraft engine.

The fan exit case uses the same resin-transfer molding (RTM) process applied to the F22 fighter-jet engine. The case, which holds the turbine-engine core to the fan case, is a critical part and the first ever built from composites. "The loads that the engine must withstand, including extreme out-of-balance caused by a broken fan blade, are very high. And all of those loads get transmitted through this part," says David Maass, business development manager at Dow-UT Composite Products.

RTM can create more complex parts than pre-preg processes where resin and fibers are combined into a sticky sheet and then formed into the part geometry. "In order to get a good-quality part, you have to apply simultaneous heat and pressure to cure the epoxy," says Maass. "It's difficult to apply pressure to the part when it's a very complicated configuration. Fibers compress and wrinkle, or it may be physically impossible to apply pressure in the desired direction."

By contrast, the RTM process in- jects resin at low to moderate pressure to provide the necessary cure pressure. The mold defines all surfaces of the part. "We put the fiber into the mold straight and dry, and we don't have to apply pressure to those fibers in do- ing so," explains Maass. "With the fan exit case, there was no practical way to do that, with the quality we need, using conventional processes."

The resin used varies with the part's temperature requirement. For the fan exit case, engineers chose an epoxy. Dow-UT is also developing higher-temperature applications using a BMI resin capable of operating temperatures of 350-400F, says Maass.

RTM's ability to produce complex geometries cuts cost, Maass says. "If we can mold fewer complicated parts, that reduces the number of inspections and secondary assembly operations. We can make more complicated parts and integrate many parts into one."

Dow-UT teamed with Pratt & Whitney and several other companies as part of a Defense Department project called Affordable Composites for Propulsion.

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