Optimal choice of the technology of thick steel sheets laser cutting

Laser cutting of steel when oxygen is used as a process gas can be done by two methods. The first one is the laser-oxygen cutting, which presents the forced combustion of iron in oxygen. In this case, the laser radiation and exothermic reaction of oxidation make roughly equal contribution in the energy balance. The second method is the oxy-laser cutting when the laser beam just initiates the combustion reaction, which provides almost all energy needed for the cutting. This method is used for thick sheets. As of today, there are no scientifically proven criteria of the choice of the cutting method for a certain sheet thickness providing the qualitative cut with the low roughness. Above all it results from the insufficient information about the mechanisms of the cut surface shape formation. Available theoretical models of the laser cutting cannot be a reliable tool to choose the optimal cutting method regarding the sheet thickness. In this paper, the problem is solved experimentally. Generalization of a large body of experimental data enables to have the empirical dependence of the optimal cutting speed Vq, at which the roughness is minimal, on the cut sheet thickness: QUOTE . The criterion is proposed, the maximal sheet thickness tm is found; above it, the high-quality laser-oxygen cutting is impossible. The value tm is found from the condition Vq = Vc, where the critical speed Vc, at which the uncontrolled side burning begins, the cutting roughness increases, and the high-quality cutting is impossible. The measured value Vc is equal to 0.4…0.5 m/min, which correlates to tm = 40…50 mm. The oxygen-assisted laser cutting of low-carbon and low-alloyed steels is advisable starting from the thickness of 30…40 mm. The tests of the laser-oxygen cutting of sheets of 18…50 mm showed that at the thickness of 30 and 40 mm, the oxygen-assisted laser cutting provides the cut quality not worse than the laser-oxygen cutting if the process parameters are optimal.

laser cutting, oxygen cutting, surface roughness, sheet thickness