The most widely used high power industrial lasers are the Nd:YAG and CO2 lasers. The chemical oxygen iodine laser (COIL), whose wavelength (1.315 μm) is between that of the Nd:YAG (1.06 μm) and CO2 (10.6 μm) lasers, is another high power laser for industrial applications. The cutting capability of these lasers is investigated in this paper. The cut depth strongly depends on the absorptivity of the cut material, kerf width and cutting speed. The absorptivity is an unknown parameter for which experimental data at high temperatures are currently unavailable. Theoretical values of the absorptivities of various metals are obtained using the Hagen-Ruben relationship. It is found that the absorptivity of a metal is linearly proportional to the square root of its resistivity and also inversely proportional to the square root of the wavelength. The absorptivities of the COIL and Nd:YAG lasers are 2.84 and 3.16 times larger than that of the CO2 laser, respectively. Based on these theoretical values of the absorptivity, the cut depths for several metals are analyzed at various laser powers and cutting speeds for these lasers. For identical cutting parameters, the cut depths for stainless steel and titanium are deeper than those of most other metals. Due to the wavelength dependence of the absorptivity, the cut depths for COIL and Nd:YAG lasers are expected to be 2.84 and 3.16 times deeper than that for the CO2 laser.

Almost all laser-assisted materials processing involves melting, vaporization and plasma formation which affect the utilization of laser energy for materials processing. To account for the effect of these phases, an effective absorptivity is defined, and a simple mathematical model is developed for the cutting of thick-section stainless steel using a high power chemical oxygen—iodine laser (COIL). The model is based on an overall energy balance, and it relates the cutting depth with various process parameters that can be used to predictively scale the laser materials processing performance to very thick sections. The effects of various process parameters such as laser power, spot size, cutting speed and cutting gas velocity on the cutting depth are discussed. The results of the mathematical model are compared with experimental data. Such a comparison provides a means of determining the effective absorptivity during laser materials processing.

A chemical oxygen-iodine laser (COIL) was used for cutting aluminum and carbon steel. Cut depths of 20 mm were obtained in aluminum and 41 mm in carbon steel using an N 2 gas assist and 5-6 kW of power on target. The same laser at the same power level produced a cut depth of 65 mm in carbon steel with an O 2 gas assist; a low quality cut to a depth of nearly 100 mm in carbon steel was demonstrated. These data are compared with existing COIL and CO 2 laser cutting data. COIL cuts carbon steel and stainless steel at approximately the same rate. For a given cut depth, power and spot size, COIL cuts steel approximately three times faster than a CO 2 laser using an inert gas assist. COIL cutting speeds in carbon steel are improved by approximately a factor of three when an O 2 assist is used in lieu of an N 2 gas assist. With an N 2 gas assist, COIL cuts aluminum at approximately the same rate as CO 2 cuts steel. To improve the agreement between data and an existing theoretical cutting model, an empirical correction factor was added to the model; this modification provides excellent agreement with data.

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