Grooved bearings boost scanner performance

Swindon, England --To function at the extreme speeds(>10,000 rpm) necessary for high-performance optical scanning, top-of-the-line scanners employ self-acting aerodynamic bearings. Such bearings incorporate herringbone (journal bearings) or spiral (thrust bearings) grooves to improve distribution of air or a fluid film. Better lubricant distribution, in turn, may be used to increase load-carrying capacity, stiffness, or stability.

Schematic Arrangement of EMM System
Electrolyte filtering and temperature control ensure there is no conductivity drift, which can alter the current level in successive machining operations.

H.K. Productions Ltd., London, wanted to improve the stiffness and stability of the optical scanners used in the company's digital enlargers. Unfortunately, conventional processes available for grooving of air bearings present problems: chemical etching is slow and difficult to control; milling can leave burrs; coining or rolling plastically deforms the component, compromising dimensional precision; and laser-beam etching is expensive.

Solution? Implementation of a patented electrochemical micromachining process. Developed by Loadpoint Ltd., EMM comprises a stationary workpiece, a stationary conforming electrode, an electrolyte, and power supply. A control system sequences the machining cycle and monitors key process parameters.

During operation, the electrolyte pumps through the gap between the electrode and workpiece. Current passing between the electrode and workpiece removes workpiece material. Groove depth is directly proportional to the product of current and time.

"The use of pulsed current in place of DC current," explains Loadpoint Technical Director Frank Wardle, "distinguishes EMM from traditional electrochemical machining (ECM) processes used to achieve high material removal rates." As a result, Wardle says EMM equipment design is more easily tailored to a wide range of engineering components. Other electrochemical micromachining characteristics include:

High speed. Typically it takes only a few seconds to machine a complete set of grooves on a bearing.

• No tool wear. Since the tool is an electrode, it gives repeatable groove forms over long periods of operation.

• Negligible distortion. There are no cutting forces to deform the workpiece surface, so grooving can be a final machining operation.

• Precision. EMM is capable of meeting a tolerance of ±15% on groove depth.

Limitations? Electrochemical micromachining can only be used on electrically conductive materials, and a hot water rinse is necessary to remove electrolyte from the workpiece surface.

Other Applications

Computer disc drives

• Surface texturing and patterning

• Machining fragile components

• Deburring

Additional details, England…Contact Frank Wardle, Loadpoint Ltd., Chelworth Industrial Estate, Cricklade, Swindon, Wiltshire SN6 6HE, England , Tel: +44 1793-751160, Fax: +44 1793-750155.

Additional details, U.S.…Contact Gerald Marshall, 1808 Pinecone Court, Morgan Hill, CA 95037-7049, Tel: (408) 779-4828, Fax: (408) 779-4705.