CAMBRIDGE, Mass.--Machine tools, or the machines that shape, cut, drill, grind, or polish solid parts, "are the very heart of a manufacturing economy, because all products are made with these tools," says Alexander Slocum, the Alex and Brit d'Arbeloff Associate Professor of Mechanical Engineering at MIT.
Now Slocum and colleagues have designed a device that can make machine tools faster and more accurate. It's "the next link in the evolutionary chain for machine tools," they say.
Dubbed the HydroGuideT, the device is a ceramic platform supported by a very thin film of pressurized water. The part to be machined is attached to the platform, then the platform moves past the machine tool that gives the part its finished shape.
The HydroGuide, which recently won a 1995 R&D 100 Award, belongs to a family of devices known as linear hydrostatic bearings. Such bearings provide a number of advantages over other kinds of bearings for machine-tool applications. For example, because there is a film of liquid between the bearing platform and the rail it moves over, there is no mechanical contact between the two.
And that means no friction. "Friction introduces inaccuracies in a machined part, because it's not predictable and therefore it doesn't allow [the bearing platform] to move exactly where you command it to move," said Nathan R. Kane, a graduate student in mechanical engineering working with Professor Slocum.
To date, however, hydrostatic bearings have not been extensively used in machine tools. That's because their disadvantages--for one, they are costly--outweigh their benefits. "With the HydroGuide, we've made a hydrostatic linear bearing that's much more practical for use in machine tools," said Mr. Kane.
For example, the HydroGuide is less expensive than conventional hydrostatic bearings because of a unique manufacturing process invented by Professor Slocum and colleagues (the process is patent-pending). Further, because it is modular, or composed of standardized parts, it's much easier for designers to incorporate it into a machine tool. (Other hydrostatic bearings must be custom-designed for specific machine tools.)
The HydroGuide is also the only hydrostatic bearing that uses water, rather than oil, as the liquid between the bearing platform and the rail it moves over. This is environmentally friendly, and saves money (it's much more expensive to dispose of used oil).
Finally, the HydroGuide is faster than other hydrostatic bearings, which have a speed limit of about 3/10 of a meter per second. The HydroGuide can operate at up to 2 meters per second.
The HydroGuide is already proving itself in the workplace. In 1994 Weldon Machine Tool asked Professor Slocum to design the HydroGuide into one of its grinding machines. Nine months later the resulting grinder won a "Best of Show" award at the International Machine Tool Show. "Using the HydroGuide the cylindrical parts [Weldon] grinds were four times straighter," Mr. Kane said.
Work on the HydroGuide is supported by the National Science Foundation and Professor Slocum's Alex and Britt d'Arbeloff chair, as well as the corporate sponsors who were co-winners of the R&D100 award. They are: Aesop, Inc. (Professor Slocum is president); New Way Machine Components; Weldon Machine Tool, Inc.; Wilbanks International, Inc., and K. Jung, Inc.
