OBRABOTKAMETALLOV technology Vol. 24 No. 4 2022 using visual and dimensional control. Methodologically, the work was structured so that during the tests an optimal cutting speed, required for the fastest obtaining of a high-quality cutting with the smallest distortions of macrogeometry, the zone of thermal influence and the most uniform cutting surface were determined. For this purpose, different parameters of current and cutting speed were initially used. Then, if the cutting quality was acceptable, the cutting speed was increased. If the cutting quality was unsatisfactory, the cutting speed was reduced. Additionally, the parameters of piercing time and height, cutting height, etc. were determined. After carrying out the experiments on plasma cutting, analysis of specimens’ cut surface by means of visual measuring control with taking a picture of a surface by camera Pentax K-3 with focal distance of objective 100 mm was made. An optical microscope Altami MET 1C was used for metallographic examination of specimens. Microhardness was determined using a Duramin 5 microhardness tester. Measurements of microhardness were carried out on metallographic thin sections starting from a distance of 10 µm from the cutting surfaces. A depth, to which changes in microhardness were determined, was chosen from the size of a heat-affected zone. Cutting out samples for research was carried out by the method of electrical discharge on wire cut EDM machine DK7750 transverse to a plane of the cut. In addition, using a confocal microscope Olympus LEXT 4100 the cut surfaces were evaluated by determining the height of roughness above the cut surface. General conclusions about the quality of the cutting were formulated based on the evaluation of all the main factors and depended on the total depth of microroughness from the cut surface, macrogeometry disturbance and the heat-affected zone. Additionally, a location of these defects was taken into account; since the macrogeometric disturbances of the cut surface and the heat-affected zone are partially overlap. Results and discussion During the process of plasma cutting of specimens of metals and alloys a specific relief with different structure for different alloys is formed on the cut surface. For example, the cut surface of titanium alloy for most samples is characterized by the presence of a regular relief that differs in the upper and lower parts (1, 2 in Fig. 2, a). Moreover, the appearance of the sample surface in the upper and lower parts of the cut differs clearly enough, which may be related to different features of blowing of molten metal by the gas jet from the cutting zone. Fig. 2. Appearance of the cut face of the titanium alloy samples: a – the plate is 5 mm thick; b – two plates are 5 mm thick; 1 – bottom of the cut face; 2 – top of the cut face; 3 – bottom of the cut face of upper plate; 4 – top of the cut face of upper plate; 5 – top of the cut face of lower plate; 6 – bottom of the cut face of lower plate
RkJQdWJsaXNoZXIy MTk0ODM1