Effects of Oscillation Width on Arc Characteristics and Droplet Transfer in Vertical Oscillation Arc Narrow-Gap P-GMAW of X80 Steel

Abstract

In fields, such as oil and gas pipelines and nuclear power, narrow-gap welding has often been used for the connection of thick and medium-thick plates. During the welding process, a lack of fusion was prone to occur due to groove size limitations, seriously affecting the service safety of large structures. The vertical oscillation arc pulsed gas metal arc welding (P-GMAW) method was adopted for narrow-gap welding in this study. The influence of the oscillation width on arc morphology, droplet transfer behavior and weld formation during narrow-gap welding was studied. Oscillation widths from 0 to 4 mm were used to weld narrow-gap grooves with a bottom width of 6 mm. The results show that, in non-oscillation arc welding, the arc always presented a bell cover shape, and the droplet transfer was in the form of one droplet per pulse, while the sidewall penetration of the weld was relatively small, making it prone to a lack of fusion. With an increase in the oscillation width, the arc gradually shifted to the sidewall. The droplet transfer mode was a mixed transfer of large and small droplets, and the sidewall penetration continued to increase, which was conducive to the fusion of the sidewall. However, when the oscillation width was wider than 3 mm, it led to the phenomenon of the arc climbing to the sidewall, and the weld was prone to porosity, undercutting and other welding defects. The oscillation width has a major impact on the stability of the welding process in vertical oscillation arc narrow-gap welding.

Effect of Increasing Oscillation Width on the Arc Characteristics and Droplet Transfer Behavior of X80 Steel in the Overhead Welding Position of Narrow Gap P-GMAW

“…After the previous droplet transfer is completed, a pointed tip remains at the center of the wire end, as shown at 0.8 ms. The tip rapidly melts during the droplet growth stage of the next cycle, which is different from when the droplet gradually moves away from the welding wire tip during flat welding [51]. At the overhead welding position, due to the opposite direction of gravity and droplet transition, the droplet continuously falls with the increasing molten metal mass during its growth period, enveloping the wire end in the middle and forming a mushroom-shaped head, as shown at 2.2 ms in Figure 3.…”

Implementation of a two-stage algorithm for NG-GMAW seam tracking and oscillation width adaptation in pipeline welding

“…It is a common practice to use arc sensors for seam tracking [27–30]. However, in the process of narrow gap welding, too small oscillation width will lead to insufficient heat input to the sidewall and cause the fusion defect, while too large oscillation width will cause the phenomenon of arc wall jumping [31–33], which will greatly affect the working accuracy of the arc sensor. Advanced welding power sources [26,34] and strict groove processing and pipe alignment [35] can alleviate this problem to some extent, but it will greatly increase production costs.…”

“…Based on the achievements of previous research work [32,33], the main objective of the present study was to integrate welding seam tracking using arc sensors for root, filler and cap layers welding, and oscillation width adaptation throughout the entire oscillation period for NG-GMAW pipeline welding. In order to track the weld bead of interior and exterior grooves, a two-stage algorithm is designed.…”