OBRABOTKAMETALLOV technology Vol. 24 No. 4 2022 shows a better removal of the molten metal from the cut cavity. Significant heterogeneity of the cut surface, including macroscopic size, is characteristic for the specimens obtained according to non-optimal modes (mode No. 9, Fig. 4, a). The specimens obtained using more optimal modes are characterized by a more uniform structure of the cut surface (mode No. 7, Fig. 4, b). The size of peaks above the cutting surface is 200–470 μm in the upper part and 230–600 μm in the lower part. During plasma cutting of C1220 copper specimens, the formation of the largest amounts of flowed metal are observed in the lower part of the cutting (Fig. 5). This is due to the high thermal conductivity of copper and indicates that the molten metal, blown by the gas jet from the cut cavity, solidified at a fairly high rate. In many areas of the cut, the amounts of flowed metal are almost missing, but by adjusting the parameters of the cutting mode it was not possible to achieve its complete absence. The size of irregularities on the cut surface is 25–80 µm at the top and 65–200 µm at the bottom of the cut. The lowest values of irregularities heights are characteristic for the specimens obtained by the mode No. 5. Studies of the structure of Ti-1.5Al-1.0Mn alloy samples with a thickness of 5 mm in cross-section to the cutting plane showed that in the specimens there is quite a significant distortion of the macrogeometry of the cut, especially in the upper part of the specimen (Fig. 6, a, b). Also the size of a heat-affected zone differs significantly (Fig. 6, b, c), having 415–520 µm in the upper part of the cut and 800–1,820 µm in the lower part. Smaller sizes are characteristic for the mode No. 2. At the bottom of the cutting zone amounts of flowed metal with dendritic structure are clearly distinguished (Fig. 6, c). This is caused by displacement of molten metal from the cut zone, its flowing down to the lower part of the cut and solidification as a flowed metal. Studies of regularities of structure organization at higher magnification show that structural changes during cutting under different modes are typical for this type of alloys. In the bulk metal zone (Fig. 6, d) a typical structure with grains elongated in the direction of rolling is characteristic. Fig. 3. Cut faces appearance of specimens of aluminum alloy with a thickness of 12 mm: a – specimen after cutting in non-optimal mode; b – specimen after cutting in optimal mode; 1 – bottom of the cut face; 2 – top of the cut face Fig. 4. Cut faces appearance of specimens of aluminum alloy with a thickness of 40 mm: а – specimen after cutting in non-optimal mode; b – specimen after cutting in optimal mode; 1 – bottom of the cut face; 2 – top of the cut face; 3 – macrodefects of the cut face; 4, 5 – defects in the initial part of the cut face
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