High Pressure GMAW Arc Shrinkage Analysis And Numerical Simulation

Underwater dry welding is applied to the installation and emergency maintenance of wading equipment.In the actual welding process,the high pressure environment caused by the water depth has a great influence on the welding process and reduces the welding quality.The shrinkage of welding arc in high pressure environment is the direct influence factor of underwater dry welding process and welding quality.However,there are many factors influencing the phenomenon of arc shrinkage,which has not yet been fully clarified.It is of practical significance to study the mechanism of welding arc shrinkage in high pressure environment for improving the welding quality in underwater high pressure environment.The numerical simulation method is used to simulate the welding arc temperature field,magnetic induction intensity,electric field strength and welding arc shape of the Gas Metal Arc Welding(GMAW)under different pressure,and their variation law is explored.Numerical simulation results show that the maximum temperature of GMAW arc temperature field decreases with the increase of ambient pressure,the magnetic induction intensity and electric field strength of the welding arc increase with the increase of environmental pressure.Meanwhile,as the pressure increases,the high temperature region of the GMAW arc center shrinks,and the arc shape changes from a bell to a spindle.For many factors affecting the arc shrinkage of high pressure GMAW,the effects of cathode spot,arc force and particle energy on welding arc are analyzed from the perspective of plasma physics.With the increase of pressure,the number of cathode spots decreases,and the electron emission of cathode spots intensifies when the conductive channels gather in a local region.At the same time,The accumulation of more positive ions near the cathode spot causes a stronger electric field in the cathode region,which promotes the ability to emit electrons at thecathode spot,prolongs the residence time of the cathode spot,and intensifies the aggregation of the conductive region to the cathode spot.Under the high pressure environment,the magnetic pressure at the edge of welding arc increases,and the internal self-shrinking force enhances,causing arc contraction.When the ambient pressure increases,the energy dissipation of welding arc increases.According to the principle of minimum voltage,the current density in the center of arc column increases and the conductive channel in the area of arc column shrinks.The welding test under different pressures is carried out by means of the underwater high-pressure GMAW test platform.The high-speed camera system and the welding pool observation camera were used to observe the welding arc and welding pool behavior under different pressure.The experimental results show that as the ambient pressure increases,the radial dimension of the welding arc decreases,resulting in radial shrinkage,which is basically consistent with the numerical simulation results.During the experiment,it was also found that the axial dimension of the welding arc in the high pressure environment gradually decreased with the increase of the environmental pressure.The axial size compression was further confirmed by analysis and numerical simulation.Observed by the welding pool,the increase of the ambient pressure causes the arc in the cathode region to shrink toward the center.However,limited observation means that the dynamic behavior of the cathode spot was not well observed in the experiment.