| Welding seam back chipping is a necessary technological operation to meet the demands of complete penetration or other welding requirements during the welding process of metal containers with large size and thick wall, such as spherical tank, storage tank and pressure vessel. The quality of back chipping is not only in relation to the quality of final welding seam, but also the schedule and cost of the whole project. The research of back chipping can be basis of processes planning and technology parameters optimization. Meanwhile, it will be a theory foundation for the subsequent welding.Therefore, the law of welding seam back chipping was studied based on the newly developed automatic back chipping machine with a disk-type non-consumable electrode. According to the principle and structure of the disk-type electrode, a new corresponding heat source model was derived using the traditional volume heat source model for reference. Then based on heat transfer theory and heat elastoplasticity theory, the thermal and stress field model were built by ANSYS software, and their weak coupling phenomena was handled by indirect approach. The dynamic evolutions of the thermal field, stress field, and the final residual stress field were analyzed. At the same time, the effects of current and speed on thermal field were discussed.Results show that transient large energy input, quicker speed make the metal melt instantaneously and heat conduct in short time. Furthermore, the molten metals are blown away in a moment which leads to dramatical change of thermal field. Great temperature gradient occur in thermal field, the T8/5 cooling time in heat affected zone is only 0.8 s in simulation. With the decrease of speed or increase of current, the region of thermal distribution is widened, the peak temperature rises in thermal cycle, dwell time at high temperature extends, and cooling rate slows down. In addition, the groove sectional area decreases as back chipping speed increases. The valid sectional area of groove is 17.96 mm2, 14.00 mm2, 11.08 mm2 respectively with the parameters of voltage for 22 V, current for 600 A, speed for 10 mm/s, 15 mm/s, 20 mm/s separately; However, the groove sectional area increases as current rises. The valid sectional area of groove is 11.84 mm2, 13.12 mm2, 14.00 mm2 respectively with the parameters of voltage for 22 V, speed for 15 mm/s, current for 500 A, 550 A, 600 A separately. The simulation results of stress field show that it is tensile residual stress around the groove, and compressive residual stress with transition to plate edge. The region of high tensile residual stresses is very narrow at both sides of the groove, its maximum value achieves to 227 MPa, the residual stresses are minor and well-distributed away from groove, about 25-50 MPa. Therefore, a sharp distribution state of residual stress is formed. As for the stress distribution in the work piece surface, it is smaller tensile stress close to the groove, and then rapidly increases, then decreases rapidly from peak. At this time, longitudinal stress turns to compressive stress, while transverse residual stress tends to 0 directly. Overall, the value of longitudinal stress is much greater than the transverse stress. There is three dimensional stress concentration at groove bottom viewed from thickness direction.
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