## 2 Experimental Research  
Experimental work in this paper was conducted on CNC machine FlameCut 2513 (Arpel Automation, Belgrade, Serbia). Specifications of CNC plasma machine are stated in Table 1. Compressed air was applied as plasma gas. Compressor SCK5 200 PLUS (ALUP Kompresoren Gmbh, Reutlingen, Germany) integrated with air-purifying and drying system served for preparing compressed air. LG 100 IGBT InverterAir Plasma Cutting Machine (Wenzhou Rstar Welding Equipments Manufacture Co., Ltd., Wenzhou, China) was chosen as plasma arc current source. Figure 2a presents CNC plasma cutting machine together with arc current source, compressor, and cutting torch assembly. Aluminum alloy EN AW-5083 was defined as workpiece material. Mechanical composition as well as physical and mechanical properties of this material are presented in Table 2. Due to magnesium presence, this aluminum alloy was characterized by high weldability and corrosion resistance. Due to such properties, it is very widely applied in shipbuilding industry, marine applications, and automotive, transport, and aircraft industry [23]. As is already mentioned, plasma jet manufacturing process of aluminum leaves some concerns regarding its sensitivity to heat input and workpiece heat-affected zone. However, authors conducted investigation regarding influence of variable process parameters of plasma jet cutting process on heat-affected zone and material structure [24]. They found out that because aluminum alloy 5083 is non-heat-treatable alloy, significant structural changes in workpiece heat-affected zone did not appear. Thus, this aluminum alloy is very convenient for plasma jet processing. Workpiece sheet thickness that will be cut through in experimental trials is 3 mm. Experimental plan was defined according to Taguchi L27 orthogonal array with three variable process parameters: cutting speed \(v\) (mm/min), arc current \(I\) (A), and cutting height \(H\) (mm), as presented in Table 3. Process parameters that were kept constant are outlet nozzle diameter, 1.2 mm, and plasma gas (compressed air) pressure, 6 bar. Process parameters levels and ranges were defined according to preliminary experimental trials, manual instructions, and industrial experts' consultations. In each experimental trial, three same circular cuts were produced. Plasma jet circular cutting was performed along a contour with a diameter of 20 mm. Example of top and bottom view of produced circular sample is shown in Figure 2b. Figure 1: Research methodology framework. \begin{table}
\begin{tabular}{l l} \hline
**Producer** & **Arpel Automation** \\ \hline Model & FlameCut 2513 \\ \hline Overall sizes (mm) & 3720 \(\times\) 2500 \(\times\) 1850 \\ \hline Weight (kg) & 1300 \\ \hline Tool travels (X, Y, Z) & 3000 mm \(\times\) 1500 mm \(\times\) 200 mm \\ \hline Maximum tool speed & 20,000 mm/min \\ \hline Supply & 400 V/50 Hz \\ \hline Drive & AC Servo \\ \hline X, Y, Z drive & Ball screw \\ \hline Accuracy & 0.1 mm/m \\ \hline Plasma type & User defined \\ \hline \end{tabular}
\end{table} 
Table 1: Specifications of CNC machine FlameCut 2513. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & & & & & & & & \\ \hline Al & Ti & Cr & Zn & Si & Mg & Cu & Fe & Mn \\ \hline Balance & 0.15 & 0.05–0.25 & 0.25 & 0.40 & 4–4.90 & 0.10 & 0.40 & 0.40–1 \\ \hline \multicolumn{8}{c}{**Physical Properties**} \\ \hline Density & Melting point & Thermal expansion &
\begin{tabular}{c} Modulus of \\ elasticity \\ \end{tabular} & Thermal conductivity & Electrical resistivity \\ \hline
2.65 g/cm\({}^{3}\) & 570 \({}^{\circ}\)C & 25 \(\times\) 10\({}^{-6}\)/K & 72 GPa & 121 W/m-K & 0.058 \(\times\) 10\({}^{-6}\)\(\Omega\)-m \\ \hline \multicolumn{8}{c}{**Mechanical Properties**} \\ \hline Proof stress & Tensile strength & Elongation & Shear strength & Vickers Hardness \\ \hline
145 MPa & 300 MPa & 23\% & 175 MPa & 75 HV \\ \hline \end{tabular}
\end{table} 
Table 2: Properties of aluminum EN AW 5083 alloy.