The laser cutting of the low-carbon and stainless steel with fiber and CO 2 lasers was compared by a similar technique. The dependence of the cut surface roughness on cutting parameters was analyzed for stainless steel sheets of 3 and 5 mm and mild steel sheets of 5, 10, 16 mm. The speed at which the roughness is minimal was found. For the cutting of stainless steel with nitrogen, the minimal achieved roughness is approximately similar for two types of lasers, whereas the speed correlating with the minimal roughness was higher in the fiber-laser case. When cutting the mild steel with oxygen, the СО 2 laser enables to reach lower roughness at higher cutting speed. For the oxygen-assisted laser cutting, the empirical relations were found which connect the cutting speed and laser power associated with the minimal roughness, with the cut sheet thickness, for the cutting processes by the fiber and СО 2 -laser.

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