ULTRA-PRECISION DIAMOND MACHINING OF ADVANCED TECHNOLOGY COMPONENTS

The design, development, and application of ultra-precision CNC machines for

the single point diamond turning of non-conventional metal optical components (Al, Ge, etc. )

the diamond grinding of ferrite and, other ceramic components for magnetic disc flying heads, etc.

is described. In both cases, tolerances on workpieces in the order of ± 0·1 μm were specified and achieved, together with the overriding need to minimize degenerated surface layers, i.e. surface damage.

The effects of chip formation at low depths of cut are discussed. The factors affecting the depths of “damaged layers” formed in turning and grinding are mentioned. Typical advanced technology components for which ultra-precision diamond turning or grinding are widely used are:

Convex mirrors for high output C0₂ laser resonators

X-ray mirrors

infrared lenses in germanium for thermal imaging systems

scanners for laser printers. and drums for copiers

elliptical mirrors for YAG laser beam collectors

spherical bearing surfaces in beryllium, copper, and other materials

ceramics for magnetic read/write heads for computer memory discs

ceramics for cams, cam followers, valve seat inserts, cylinder liners, bearings, cylinder heads, turbo impell ers, etc.

Both single point and diamond grinding for ultraprecision low stress surfaces demand high precision machines that provide

high stiffness of structures and high band-width servo drives;

low rumble, high averaging bearings such as hydrostatic air or oil;

high internal damping of stuctures and drive systems;

multi closed loop control of many parameters, including temperature of coolant and temperature gradients across structures and sub-systems;

coolant delivery to the abrasive/workpiece interface is of critical importance for controlling high surface finish and minimizing surface tresses.

The paper gives examples of how these problems are satisfied in today's state of the art ultra-precision CNC machine tools.