OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 1 2024 shape defl ection (sometimes more than 10 mm), as well as the non-uniform structure of the material of the resulting products, which negatively aff ects physical and mechanical properties of materials and, as a consequence, fi nished products performance characteristics [1–7]. One of the directions of research in this area is the implementation of the surfacing process when an electric arc is additionally exposed to an external magnetic fi eld, which can be traditionally divided into longitudinal [8–18] and transverse [19–29] ones, which has found its application in improving the quality of the processes of various types of electric arc welding and surfacing. In many studies, it was found that under the infl uence of a magnetic fi eld, the rate of wire melting increases, the microstructure improves, the depth and area of the fusion zone decreases, which has a positive eff ect on the quality of welded joints [8–29]. It was also noted in [8, 12, 14, 16, 18] that a longitudinal magnetic fi eld causes an arc column to rotate around its axis and to contract, reducing the cross-section of the arc column; the arc becomes harsher, and heating is more concentrated, which improves the technological properties of the arc and improves the quality of welding process and welds. However, despite the positive eff ect of a longitudinal magnetic fi eld on the quality of welding, the analysis of papers in the area under consideration has shown that the process of additive shaping by an electric arc with axial feeding of steel fi ller wire in a shielding gas environment, in particular, with additional infl uence of the longitudinal magnetic fi eld on the electric arc has been studied insuffi ciently [30–35]. In particular, the issue of changes in the geometry of single surfaced layers and specimens formed in this way using a wire made of structural steels has not been suffi ciently studied. Therefore, the purpose of this work is to study experimentally the infl uence of a longitudinal magnetic fi eld during additive shaping by an electric arc with axial feeding of a fi ller wire made of structural steel in shielding gas environment on changes in the geometry of the surfaced layers, namely, changes in the dimensions of single surfaced layers, changes in the overall sizes of the specimens, consisting of several layers, changes in the defl ection from straightness in vertical direction for the side walls of the specimens and changes in the defl ection in the width of the specimen walls. Research methods To conduct this study, the Department of Mechanical Engineering Technologies and Equipment of Southwest State University, developed a machine based on a CNC machine equipped for implementing GMAW technology or the technology of additive shaping of products by an electric arc with axial feeding of a fi ller wire in a shielding gas environment (Fig. 1). The developed machine consists of a sequential kinematic chain, which includes an aluminum base (frame) (1), with linear guides (2) fi xed on it, along which, by means of a ball screw and stepper motors (3) a CNC machine table (4) with a rotary table (5) located on it are driven along the X axis (X coordinate), Z axis module (6) is driven along the Y axis (Y coordinate), and a feeding mechanism (7) is driven along the Z axis (Z coordinate). The rotary table provides rotation of a workpiece about the Y axis (angular coordinate B) and rotation of a workpiece about the Z axis (angular coordinate C). The machine is controlled using a control unit (8), which includes an Arduino Mega 2560 control board with the Ramps 1.6 add-on (grblMega-5X fi rmware), six TB 6600 stepper motor drivers, a 12 V 30 A power supply. GrblGru_v5.1.0 opensource software is used to implement control programs. The developed installation provides simultaneous 5-axis surfacing (5-axis continuous processing). The feeding mechanism (7) consists of a stepper motor, a clamp and steel rollers that feed the welding (surfacing) wire from the coil (9) through the steel tube to the welding head into the welding (surfacing) zone. An electromagnet (10) is attached to the welding head. The semi-automatic KEDR MIG-160GDM welding machine was used as a power source. The study of the infl uence of a longitudinal magnetic fi eld on changes in the geometry of the surfaced layers was carried out by surfacing a wire of 1.2 mm in diameter made of Sv-08G2S (0.08 % C; 2 % Mn; 1 % Si). In accordance with the methodology described in [26], for this wire the surfacing conditions were as follows: 17.5 V (voltage); 55 A (current); 2,267 mm/min (wire feeding speed); an approximate roller diameter was 3.0 mm; the length of a roller was 50 mm; wire length per roller was 312.5 mm; electrode extension was 10 mm; CO2-Ar welding mixture was used as a shielding gas; gas pressure (fl ow) was 0.15 MPa.
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