Arc Contraction Behavior of GMA Welding Process Based on Change of Arc Length at Hyperbaric Air Condition

Abstract

The underwater hyperbaric dry GMA welding method is one of the best emergency maintenance methods for underwater structures. With the increase of ambient pressure, GMA welding quality decreases. The main reason is that GMA welding arc shrinks under high pressure, which leads to the instability of welding process. In order to find out the main factors that affect the contraction of GMA welding arc, theoretical analysis, numerical simulation and experimental verification are used to study the contraction behavior of GMAW arc under high pressure. Based on the governing equation of high-pressure GMA welding arc, the numerical simulations of GMA welding arc under the two conditions of constant arc length and arc length adjustment were carried out by FLUENT software under the environmental pressure of 0.1 MPa, 0.3 MPa, 0.5 MPa and 0.7 MPa, respectively. The contraction of the arc under the two arc length conditions was compared. Through the underwater high-pressure GMA welding test platform, the welding experiments under 0.1, 0.3, 0.5 and 0.7 MPa ambient pressures were carried out. A high-speed camera was used to obtain the arc morphology under different ambient pressures. It was verified the accordance between the experiment results and the simulation data. The results show that the axial and radial dimensions of hyperbaric GMA welding arc decrease with the increase of ambient pressure, showing the phenomenon of arc contraction, especially the arc length decreases significantly, which increases the frequency of short-circuit drop transfer and affects the stability of welding process.