Fracture Characteristics of an Aluminum Oxide Ceramic during Continuous Wave Carbon Dioxide Laser Cutting

A series of experiments was conducted to determine the influence of workpiece thickness, cutting speed, and beam power on the onset of fracture in aluminum oxide (Al2O3) during continuous wave CO2 laser cutting. Samples of Coors AD-96 substrate of thickness 0.040, 0.050, and 0.080 in. thick, respectively, were cut at combinations of feedrates and power levels to determine the conditions at which fracture of this ceramic occurs with respect to these two parameters. Plots of the lowest value of feedrate producing a fracture-free cut at a given power were constructed for each material thickness. To explain the results qualitatively, a simplified thermal analysis of the problem was conducted. The two-dimensional temperature field resulting from a moving line source was calculated analytically to determine the maximum temperature gradient expected in the workpiece as a function of power and feedrate. A similar numerical computation was carried out for a moving distributed cylindrical source, to simulate a laser spot, accounting in addition for the variation of thermal conductivity of the workpiece with temperature. Both models successfully predicted the trends observed in the experimental study where increasing feed-rates at a given power and workpiece thickness resulted in increasing temperature gradients while decreasing power at a given feedrate and workpiece thickness resulted in increasing temperature gradients.