OBRABOTKAMETALLOV Vol. 25 No. 4 2023 technology Ta b l e 1 Automatic submerged arc welding modes Specimen Welding arc current, A Arc voltage, B Welding speed, cm/min 1 600 37 54 2 600 37 3 500 37 4 400 37 5 450 37 6 450 27 7 500 27 8 500 27 foil tape longitudinally at the interface between the ceramic backing and the workpiece surface in other specimens. Therefore, specimens 1 and 2 in table 1 have the same parameters. Welds were visually inspected as described in STO 9701105632-003-2021 with magnifying glass LI-10, caliper, and welder’s gauge UShS-3. Welds were radiographically inspected as required by GOST ISO 17636-1-2017 by using a radiation source, X-ray system PION-2M, X-ray film Agfa D4, a source-to-film distance of 350 mm, exposure time of 10 sec., and radiographic technique 1. Strain behavior of welded specimens was measured based on its digital twins obtained by MCAx laser scanning and 3D model processing with the Focus 10 Inspection software. We used the Microsoft Excel analysis package for statistical modeling. Relationship between input parameters (welding current X1 and arc voltage X2) and output parameters (weld cap height and weld root bead height and weld cap width and root bead width) was found. Basic value of the variables was determined by experiment assuming the arc process stability at welding a full-size weld. Results and discussion Welding of the specimens with the tested flux produced a gentle, silent arcing, no fumes, and easy postweld removal of the hardened slag layer. The appearance of the resulting welded specimens is shown in fig. 2. Visual inspection showed the following: all specimens had a properly formed weld bead with no surface defects at the weld’s face. On the reverse side in Sample 1, discontinuities are observed with a width of 1.5–2.0 mm, a depth of 1.0–1.5 mm and an average length of 10 mm, located mainly at the start and central part of the weld. Weld root was formed against the surface of the ceramic backing with a vigorous interaction with its material, and therefore the bead surface does not replicate the smooth surface shape of the backing. The root bead in Specimen 2 also has discontinuities at the start of the weld with a depth of 0.2–0.5 mm, a width of 1.5–2.0 mm, and an average length of 5 mm. Specimen 3 does not have any surface defects in the root bead that are common to Specimen 1 and 2, but its surface was shaped in the same way. The welding parameters used for Specimen 4 were inadequate to achieve the required root bead size at the start of the weld. Penetration stabilized in the center of the weld, but the root bead was welded unsupported, failing to contact the surface of the ceramic backing. The surface of Specimen 5 is similar to that of Specimen 3. Specimens 6 to 8 have a clear pattern of ceramic backing segments with a smooth surface at the root bead and are perfectly sized to match the configuration of the backing’s supporting part. Therefore, to weld 5 mm thick mild steel sheets with the tested flux, the welding parameters of 400 A/37 V are inadequate for forming the root bead, and 600–500 A/37 V are excessive in energy and cause melting of the backing material and vigorous interaction with the molten weld pool, gas emission, and the occurrence of defects such as discontinuities. The best welding parameters are 450–500 A/27 V.
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