Effects of Welding Polarity on Weld Appearance of Pulsed GMAW in Hyperbaric Environment

The hyperbaric environment can cause contractive welding arc and unstable welding process. Since pulsed gas metal arc welding (GMAW-P) has the characteristics of controllable heat input and good arc stiffness, it is a useful attempt to apply GMAW-P under the hyperbaric environment. Experiments of underwater dry GMAW-P with different polarities are carried out at ambient pressures of 0.1-1.0 MPa, and the variation tendency of the current and voltage waveforms along with the increase of the ambient pressure is analyzed, thus the change regulations of the welding process stability for GMAW-P with different polarities are determined along with the increasing ambient pressure. Based on this, the variation regulations of the welding spatters and the weld appearances of GMAW-P with different polarities are analyzed comparatively with the increasing ambient pressure. Along with the increase of the ambient pressure, the periodicities of the current and voltage waveforms are gradually weakened, and the welding process tends to be unstable, the spatters are gradually increased, and the weld appearance becomes worse for GMAW-P with electrode positive polarity(DCEP). While GMAW-P with electrode negative polarity(DCEN) is applied, the periodicities of the current and voltage waveforms under high pressure are less stable than that at one atmosphere, but compared with GMAW-P with DCEP at the same pressure, the periodic regularity is enhanced, the welding process is relatively stable, and spatters produced during the welding process are less and smaller. In addition, the weld widths of GMAW-P with DCEP and DCEN are reduced and the reinforcements are increased with pressure. The arc shape and corresponding arc force of GMAW-P with different polarities under the hyperbaric environment are discussed, and the reasons for the above phenomenon are confirmed, which provide effective theoretical basis for the improvement of welding process under the hyperbaric environment.