An improved simulation of temperature field in Laser–low current

Abstract

This study aimed to achieve efficient and precise connection of thin steel sheets for vehicles by analyzing the thermal process of Laser-MAG hybrid high-speed welding lap of thin galvanized steel sheets. A high-speed camera combined with an NI AD data acquisition system were used, and the transition behavior and electrical signals of low-current MAG and Laser-MAG hybrid welding were examined. The thin sheet MAG welding droplet transition method mainly comprised short-circuit transfer. During the short-circuit phase, the voltage decreased and the current increased sharply, forming a short-circuit liquid column. When current increased to a certain level, the liquid bridge burst, the droplets carried heat and kinetic energy to the weld pool, the arc voltage returned to a no-load state, and the arc was re-ignited. In the arcing phase, the current first decreased steeply and then slowly, while the voltage decreased slowly and smoothly. According to the different heat source characteristics of the arc combustion and short-circuit stages during short-circuit transition, a new MAG heat source for low-current short-circuit transition was developed. This study employed a double-ellipse heat source with different powers for the arc combustion stage as well as a uniform body heat source that considered the thermal and kinetic energies of the melt droplets for the short-circuit stage. The thermal input of low current MAG welding was described by double-ellipse and uniform body heat source periodic loading. Moreover, the laser exerted an attraction and compression influence over the arc during the hybrid welding, which promoted the droplet transfer. Therefore, based on the novel MAG heat source, a hybrid Laser-MAG heat source in the short-circuit transition mode was developed. The laser beam heat source was described using a three-dimensional column heat source, the arc attraction and compression by the laser were considered indirectly through distribution parameter tuning for the double-ellipse model, and the laser-promoted transition effects of the droplets were described through the cycle frequency alterations of a double ellipsoid and homogeneous heat source. this heat source model was used to determine the MAG welding and hybrid welding temperature fields. Using hybrid Laser-MAG welding, a weld with a high depth-to-width ratio and complete penetration was obtained. The weld geometry and weld pool length were determined through welding tests, and the test results coincided with the fusion line trend and shape of the weld obtained by simulation, proving the rationality of the developed heat source model.