Development of Ultra-Smooth Diamond Tooling for Machining Lightweight Mirrors

DMI has produced functionally-graded diamond-TiC-Ti cutters for machining lightweight mirror optics, particularly those made of SiC, with high precision and with minimal wear of the cutting edge. The improved wear (relative to commercial diamond tools) is achieved by orienting diamond crystals on the tips of specially designed cutter inserts, so as to exploit the anisotropy in diamond hardness. The reduction in tip wear enhances the precision of machining in uninterrupted cuts. The advantage is most clearly seen when hard ceramics, such as SiC, are machined, but the new cutter technology also provides benefits in machining certain metallic systems. Another innovation is the fabrication of a set of spherically-shaped Diamonite? smoothers, which improve the quality of the finishing operation; thus, for the first time, giving an ultra-smooth surface finish. The combined innovations should enable the optics industry to enhance the performance of large telescopes and interferometers. In Phase I, we designed a special diamond cutting tool for SiC, manufactured samples of cutters and smoothers, conducted research on machining and smoothing of mirror materials, and proved the validity of the concept. In Phase II, we propose to develop ultra-smooth diamond tooling and diamond tool fabrication techniques. The deliverables are diamond-TiC-Ti cutters to achieve higher precision of turning and Diamonite? smoothers to realize better surface finish. In addition, procedures for the reproducible fabrication of mirror optics will be defined. In Phase III, we will implement our developed tools and techniques with end-user companies, and produce machined parts to NASA specifications. This new class of tools should also have wide applications in the machining of structural and functional ceramics.