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12/05/91

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'ICE SCULPTURE' - NEW WAY TO MAKE BETTER RACKET

STANFORD -- By moving from "baking bread" to creating "ice sculpture," a Stanford University researcher has developed a way to automate an exotic technique for molding objects as diverse as graphite tennis rackets, fiberglass car bodies and artificial limbs.

George Springer, chair of the department of aeronautics and astronautics, works with composite materials, fusing plastics or resins with fibers such as graphite. The parallel orientation of the fiber sheets give composites ant-like strengths for their light weight, low density and moldability.

"These are the materials of the future," Springer said. As a consultant to industry and government, he has worked on the composites used to create the fiberglass bodies of Pontiac Fieros, windmill blades at Altamont Pass, Beech's Starship I airplane and at least one type of artificial heart.

Springer and graduate students Hugo Sarrazin and Rick Hosey in the Structures and Composites Laboratory, in conjunction with a team of Stanford scientists from the Aerospace Robotics Laboratory, recently demonstrated how to automate the production of composite materials, from design to finished product. This technique could enable manufacturers to create cheaper, lighter, stronger and more aesthetically pleasing goods.

The project's major sponsors are McDonnell-Douglas and the Stanford Integrated Manufacturing Association (SIMA), an industry- sponsored consortium whose members include Boeing, Lockheed, Ford, General Motors, Alcoa and General Electric.

Composite structures can be manufactured two ways, Springer said.

Currently, manufacturers use the "bread baking" method, which requires "cooking" resinous epoxy and graphite fibers under high pressure for hours, days or even weeks. The combination of heat and pressure causes the materials to harden like the crust on a loaf of bread, Springer said.

The procedure can be costly - requiring an oven big enough to accommodate parts of airplane wings - and tricky - the materials can be under- or over-cooked, ruining the pattern of fibers in the resin.

Springer favors the "ice sculpture" method, used to produce thermoplastic composites, those in which plastic instead of epoxy binds the fibers. Materials are heated to 800 degrees Fahrenheit, then molded around forms and cooled to room temperature, where they set into their permanent shapes.

Springer demonstrated the prototype for automated thermoplastic manufacturing in his laboratory: A robot lays successive plies of plastic-graphite tape over a form. To bond the layers together, the robot blows hot nitrogen gas over the tape while its roller-arm applies 50 to 100 pounds of pressure.

Sensors embedded in the tape layers relay the material's status to a computer, which immediately tells the robot to adjust the temperature, pressure or tape-laying speed. Several robot arms could work on the same structure at once, speeding up production, Springer said.

Composite materials are not as cheap as plastics and do not operate at high temperatures as well as ceramics, Springer said, but they combine the beneficial properties of metals, plastics, fibers, resins and ceramics.

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This release was written by Dawn Levy, a Stanford News Service science-writing intern.

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