Date of Award
Doctor of Philosophy
Palaniappa A. Molian
Hot machining has been applied to the turning of extremely hard metals. Ceramics materials have been traditionally formed to near net shape and fired. If finer tolerances are required, then the fired part is ground. The cost of the grinding operation is expensive, up to 90% of a parts total costs are grinding costs. Previous attempts to use lasers for hot machining of ceramics by carbon dioxide lasers have resulted in severe degradation of material properties. Carbon dioxide and Nd:YAG laser assisted machining of ceramics were evaluated based on the physics, materials, and mechanics of the process to determine the feasibility of the process. These factors were also evaluated to determine the limitations of carbon dioxide and Nd:YAG laser assisted machining and candidate materials. Nd:YAG laser assisted machining of silicon nitride experimentally produces a surface finish of 0.3 micrometers. The structure of hot isostatic pressed silicon nitride is grains of beta silicon nitride separated by intergranular silica SiO2, TiO2 and other rare earth oxides. These oxides are transparent to Nd:YAG laser wavelength of 1064 nanometer but the beta structure is highly absorbing. The beta structure is thermal shock resistant where the oxides are not thermal shock resistant. Consequently, Nd:YAG laser assistance of the turning results in softening of the tougher grain by irradiation with softening of the intergranular oxides only by conduction of heat from the grain. Carbon dioxide laser wavelength of 10600 nanometer is absorbed readily by the oxide glasses but not as readily as the beta Si3N4 and would result in the fracture of the intergranular oxides without softening of the grains.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Bruce Clyde Janvrin
Janvrin, Bruce Clyde, "Nd:YAG laser-assisted turning of difficult-to-machine silicon nitride " (1996). Retrospective Theses and Dissertations. 11536.