## 4 Conclusions  
This paper focuses on the effect of material type, workpiece thickness, cutting speed and assistant gas pressure on cut quality in laser beam cutting of different engineering materials, namely AlMg3 aluminum alloy, St37-2 low-carbon steel and AISI 304 stainless steel using a 5000 W CO\({}_{2}\) industrial laser. The evaluation of cut quality was based on kerf geometry (kerf width and taper angle), surface roughness and cut edge quality. The main results can be summarized as follows.  
The quality assessment of cut sections (in accordance with the standard ISO 17658:2015) confirmed a good overall quality and limited presence of laser cut imperfections since no solidified droplets, irregularity of face profile and burning of surface were observed. The overall top kerf width, bottom kerf width and taper angle were in the ranges of \(599.90\pm 106.85\) um, \(562.06\pm 280.01\) um and \(0.83\pm 2.48\) degrees, respectively.  
Concerning kerf geometry, the top kerf width was mainly affected by the workpiece thickness. Conversely, the bottom kerf width was strongly influenced by the material type, thickness and gas pressure. The decrease in the cutting speed increased the kerf width as a result of the higher energy provided. The latter was less visible in the case of the stainless steel cutting. It is proposed that, in the range of values selected for laser cutting of AISI 304, the increase of cutting speed, where possible, enhanced the irradiation of the cut front, thus increasing its temperature toward the bottom. The taper angle was mostly affected by the material type.  
As for the side kerf roughness, it was found that laser cutting of AlMg3, which exhibited the worst absorption of CO\({}_{2}\) laser radiation, resulted in the highest value of Ra, whereas laser cutting of AISI 304 exhibited the lowest. Furthermore, the arithmetic surface roughness of both AlMg3 and St37-2 increased along the laser beam direction, whereas, in contrast, that of AISI 304 remained practically unchanged. The ANOVA results showed that the arithmetic surface roughness was mainly affected by the interaction between material and cutting speed. In addition, RSm increased when increasing cutting speed, especially in laser cutting of AISI 304. Conversely, in laser cutting of St37-2, RSm increased as the cutting speed decreased; furthermore, it was found that RSm decreased with thickness, demonstrating that the presence of alloy elements leads to a less predictable behavior. The interaction between thickness and gas pressure was found to be significant, showing that the spacing parameter decreased at lower gas pressure in laser cutting of thin sections.  
Optimal cutting conditions, satisfying the straight requirements of the quality standard, were identified for each material: in nitrogen-assisted fusion cutting of AlMg3, the conditions Cs = 50% and P = 100% are preferred; oxygen-assisted cutting of St37-2 with Cs = 100% and P = 100% guarantees the best performance in cutting of sections up to 5 mm in thickness. For thicker sections, the condition Cs = 100% and P = 50% were found most suitable; in nitrogen-assisted cutting of AISI 304, the best cut quality was achieved for Cs = 100% and P = 50%. The best performance, in absolute terms, was obtained in oxygen cutting of 2.5 mm thick St37-2 with Cs = 50% and P = 100%, whereas the worst  
Figure 24: Depth of flow separation in 6 mm thick AlMg3 cut with Cs = 100% and P = 50%.  
was given by nitrogen-assisted fusion cutting of 6 mm thick AlMg3 with Cs = 100% and P = 100%. These results also show that it is possible to apply industrial-relevant high cutting speeds.  
All the authors contributed equally to the various aspect of this work. Conceptualization, V.T. and S.G.; methodology, G.R. and S.G; resources, V.T.; data curation, G.R. and E.M.; writing-original draft preparation, E.M. and G.R.; supervision, V.T. and S.G. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.