Energy balance in high-quality cutting of steel by fiber and СО$_2$ lasers

The energy balance of laser cutting of low-carbon and stainless steel sheets with the minimum roughness of the cut surface is experimentally studied. Experimental data obtained in wide ranges of cutting parameters are generalized with the use of dimensionless parameters (Peclet number and absorbed laser energy). It is discovered for the first time that the minimum roughness is ensured at a certain value of energy per unit volume of the melt (approximately 26 J/mm$^3$), regardless of the gas type (oxygen or nitrogen) and laser type (fiber laser with a wavelength of 1.07 $\mu$m or СО$_2$ laser with a wavelength of 10.6 $\mu$m).