The method most commonly used for cutting thick [1.90 cm (0.75 in.)] steel where edge quality is of no concern is flame cutting by oxyacetylene torch. This method provides the energy to heat the steel beyond its melting point, and gas pressure forces the molten material (dross) through the thickness of the material. Cutting torches typically remove a kerf of approximately 0.63 to 1.27 cm (0.25 to 0.5 in.). Gas cutting is noisy, generates large quantities of smoke into the environment and forms large pieces of dross which can travel up to 3.04 m (10 ft) and cause fires. Typically, when flame cutting shipboard, a fire watch is required. Also, if any type of flammable material exists on the opposite side of the cut, it must be removed for several inches on both sides of the cut line to preclude backside combustion. A search for a better method of cutting thick steel sections, including those with coating materials attached, centered around a high-powered CO2 laser. The CO2 laser had successfully demonstrated its ability to weld heavy sections of steel with 100% penetration from one side and create a very narrow heat-affected zone. It was decided to expand this welding process to cutting by introducing high-pressure assist gases. The gas would force the molten puddle created by the focused laser beam through the steel material, thereby creating a cut through the material as opposed to allowing the molten material to fuse back together without the assist gases (creating a welded joint). It was decided to take advantage of the laser's high-powered density to cut/vaporize non-metallic material attached to the steel plate. Also, there was interest in the effects of a laser beam on asbestos material.
