SCALING LAWS FOR THE REACTIVE-GAS LASER CUTTING OF THICK STEEL SHEETS

摘要

In spite of many investigations, modern theoretical models do not allow to predict the optimum modes of the laser cutting from the viewpoint of the minimum roughness. This is particularly important for thick sheets. In the present paper, for the case of low-carbon steel of 5...25 mm thick, we defined experimentally the parameter range at which the cutting quality is maximum. The quality criterion was the cutting surface roughness, which must be minimum. The cutting was performed with a CO_2 laser, and oxygen was used as an assistant gas. The paper also studies the possibility to describe the cutting process by the similarity method. It has been assumed that thermal processes are the governing ones for the qualitative cutting. As dimensionless parameters, we chose the normalized power W/k_mt (T_m - T_0) and normalized speed vb/a (Peclet number), which involve the laser power W, cutting speed v, cutting width b, and also substance constants. It has been established that the minimal surface roughness is reached within the whole thickness range if the laser energy value per a unit volume of the removed material, and the power per a sheet thickness unit are held constant. The results are formulated as ratios which enable to determine the optimum values of the laser power and cutting speed for the given sheet thickness. Within the range of big thicknesses, the conditions of cutting with minimal roughness are written as ratios between dimensionless variables. The results also enable to evaluate the limit thickness of the sheet, above which the qualitative cutting becomes impossible.