Can high-speed machining compete with metal casting? It might seem unlikely, but when it comes to complex aluminum impellers, Turbocam Inc. of Dover, N.H., has found a way to make it work.

The impellers are used in truck and bus turbochargers to improve engine efficiency. This, in turn, makes it easier for vehicles to meet mileage and emission standards. Machining improves impeller tolerances over casting.

But machined precision does not come cheap. "When we first entered the market, our 4-to-5-inch impellers cost $600 to $800," said Turbocam's vice president of manufacturing engineering, Rob Bujeaud. "To compete with castings, we had to get down to $60 to $80."

Advances in high-speed machining speeds enable companies to compete with metal castings in complex parts.

Turbocam did just that by building a new facility in Barrington, N.H., which combines high-speed machining with automated 24/7 operation. Where Turbocam typically machines lots of a few hundred parts, its new Turbocam Automated Production Systems facility is designed for runs of 10,000 or 20,000 pieces.

High-speed machining is at the heart of the operation. During the past few years, the technology has changed significantly. The industry has developed linear motors that enable tools to quickly accelerate, decelerate, and reach full torque along each of their five axes.

Computerized controllers have also grown faster. They must position each tool on a five-axis machine by converting complex curves into millions of points in three-dimensional space. Only in the past few years have processors grown fast enough to push linear motors to their limits.

TAPS already ran high-speed machines made by two leading European firms, Switzerland's Mikron Agie Charmilles AG and Germany's Chiron Werke GmbH & Co. For its new line of turbocharger impellers, however, it turned to Moore Tool Co. Inc. in Bridgeport, Conn.

"We wanted to buy an American-made machine if we could," Bujeaud explained. "Moore was located within a half-day's driving distance from us. Because we were their first customer for a high-speed machine, they were willing to modify it to fit our needs."

Bujeaud said his four Moore FSP 300x five-axis CNC machining centers are as fast and accurate as their European competitors, though not yet as reliable. The machines run all day, every day, making impellers ranging from 2 to 6 inches in diameter. They can shave half the material off a 19-pound aluminum forging to produce a 10-inch impeller in just under three hours. Volumetric accuracy over the entire part holds to 0.001 inch. With surface finish quality of 1255, it requires no hand finishing. Feed rates range from 190 to 282 square feet per minute.

Since it was developed for NASA nearly 50 years ago, polybenzimidazole has built an outstanding reputation for retaining its physical properties at temperatures that wilt other polymers and some metals. Unfortunately, PBI developed another reputation as well: It is a bear to process.

Users typically compression-mold pure PBI powders into stock shapes, then machine them into parts. "It's a great product, but it requires a lot of machine time and significant capital," admitted Mike Grunder, vice president of PBI Performance Products Inc. of Charlotte, N.C. This has limited applications to such niches as aircraft connectors, chemical plant valves, and military components.

By blending PEEK with PBI, Victrex plc has developed a resin with outstanding heat resistance and very good processability.

Now that may be about to change. PBI Performance Products, which makes Celazole PBI, has teamed with England's Victrex plc, which makes polyetheretherketone polymer. By blending PBI and PEEK, they have created a new material, Victrex T, whose melt processability could bring PBI heat performance to a broader range of applications.

In many ways, Victrex T is a marriage of equals. PBI gains processability, but gives up some of its physical properties, Grunder said. PEEK, a high-performance polymer in its own right, boosts its strength, hardness, and resistance to wear and creep. The blend's coefficient of thermal expansion approaches that of PBI, among the lowest of all commercial polymers.

Best of all, Victrex T stands up to heat. It retains excellent mechanical properties up to 300°C (about 572°F), about 40°C higher than glass-filled PEEK alone. Unfilled Victrex T has about three times more flexural modulus at 250°C than conventional unfilled PEEK. It does even better when filled with glass or chopped carbon fiber.

Victrex is planning to sell the new blend into markets where PEEK doesn't quite meet temperature targets. "Our markets are molded bearings, bushings—anything that faces mechanical loads and aggressive temperatures and chemicals," said Victrex product manager Andrew Ragan.

"When you think about blending, you imagine getting a product that's middle of the road," he said. "In our case, we get a product with outstanding wear and friction properties that also withstands heat and carries a load."

Watch inline skaters and skateboarders accelerate out of a turn, sky on a ramp, or speed down a sidewalk scored with cracks and crevices. Their polymer wheels stand up to an amazing amount of abuse while keeping a sure grip on the surface and even providing a measure of comfort along the way.

Strong engineering makes such performance possible. Now Mearthane Products Corp. of Cranston, R.I., hopes to use technology developed for high-end skate wheels to smooth travel and dampen vibration on camera dollies, conveyor systems, and portable (and often very sensitive) laboratory and medical instruments.

A soft elastomer interior surrounded by a hard urethane outer shell enables these cast wheels to emulate the gripping power and vibration-free ride of pneumatic tires.

MPC's Mtech wheels use a layered combination of materials to reproduce the performance of air-filled pneumatic tires, according to vice president of operations Mark Schlegel.

Inside is a soft urethane elastomer similar to the material used in superballs. Its high resilience scores up to 90 percent rebound on the Bashore bounce test, even when heated by aggressive skating. The outer layer consists of a long-lasting hard urethane with a high coefficient of friction for good grip. The company can engineer the properties of both layers to suit customers' requirements.

The result is a wheel that acts like a tire. "The soft elastomer acts as a cushion for the hard outer surface, which provides durability," Schlegel said. "The inner layer deforms, flattening on the edges during a turn to get more traction, then bounces back to its original configuration for less rolling resistance."

How does this play out in industrial products? Conventional industrial rubber and foamed rubber wheels attenuate vibration, but wear rapidly. Urethane and other hard plastics last longer, but transmit shocks. MPC's wheels combine durability and cushioned movement.

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