## 1 Introduction
The reasons of this behavior have not yet been fully understood. Possible explanations are concerned with material removal, recoil pressure, cut front absorptivity, primary losses and multiple reflections [6]. As a consequence of the intense laser-material energy transfer, these effects may reduce the effective laser beam intensity at the cut front surface. Indeed, the capacity of the material to absorb the laser radiation is dependent on the coupling between the laser beam and the cut front. The absorptivity of CO\({}_{2}\) laser radiation is optimal when the incident angle is close to 90\({}^{\circ}\), while the maximum absorptivity of solid-state laser radiation is achieved for smaller angles. In thick section cutting, the cut front inclination usually is close to 90\({}^{\circ}\), and it depends on the cutting speed [7]. In laser cutting of medium and thick sheets, the absorptivity of ferrous alloys to 1 \(\upmu\)m radiation on the surface of the cut front can be lower than its theoretical optimum; this issue can be addressed to the inclination angle of the cut front. As consequence, in these applications, the absorptivity of the CO\({}_{2}\) laser beam can be even higher than that of the solid-state laser beam. In addition, the distribution of the coefficient of absorptivity on the cut front is more uniform in CO\({}_{2}\) laser cutting, whereas it shows a large drop in the middle of the workpiece thickness in fiber laser cutting [8]. The minimum roughness is related to the absorbed laser energy per unit volume of the removed metal for both laser types regardless of thickness [9]. In the present work, a CO\({}_{2}\) laser was adopted because it outperforms solid state laser in cutting of thick sheets due to the higher effective laser beam intensity. Moreover, in CO\({}_{2}\) laser cutting of thick sections, the higher kerf width of CO\({}_{2}\) lasers exerts a major role in facilitating the melt removal. LCB is strongly influenced by process parameters; therefore, proper selection of process parameters is required to minimize the amount of energy transferred to the material during machining in order to reduce the thermal damage. To date, a large number of experimental and theoretical investigations have been performed on the LBC of metals. [PERSON] et al. [10] used regression analysis to describe the combined effects of laser power and cutting speed on kerf width, surface roughness, size of HAZ and drag line of 4130 steel. It was reported that low feed rate results in smooth surface and low drag line frequency. [PERSON] et al. [11] developed ANN models for predicting cut quality of CO\({}_{2}\) nitrogen cutting of AISI 304 stainless steel and proposed operating diagrams in support of the parameter selection. The melt removal rate in laser cutting of thick-section stainless steel was characterized by [PERSON] et al. [12]. It was demonstrated that the efficiency of the melt removal from the cut kerf is affected by assisting gas pressure, nozzle diameter and focal point position. The effect of oxygen in laser cutting of low-carbon and medium-carbon steel was investigated by [PERSON] [13]. It was established that the use of oxygen as an auxiliary gas allows the reduction of power and the increase in cutting speed. A mathematical model to predict the drag line width and drag line frequency on stainless steel was developed by [PERSON] [14]. It was shown that mechanisms such as molten solidification, gas dynamics and fluctuation of power are associated with the formation of drag lines. [PERSON] et al. [15] investigated the effects of process parameters on cutting region temperature and cut edge quality in Nd:YAG laser cutting of AL6061T6 alloy. It was concluded that the laser power density, which in turn depends on the nozzle standoff distance, has a major effect on the cutting region temperature and cut edge quality when the sheet thickness increases.