Study of improvement of gap tolerance in laser MIG arc hybrid welding of aluminium alloy

Abstract

Hybrid welding combining YAG laser or fibre laser with MIG arc was carried out on aluminium alloy, and the effects of set-up conditions of a laser beam and a wire, and the laser beam parameters on wire melting phenomena and gap tolerance in butt joint were investigated. It was found that, in order to obtain a deeper penetration, the laser beam should be separated from the wire with a distance at which there was no direct interaction between a laser beam and a droplet during its transfer. On the contrary, in order to get a wider gap tolerance for a butt joint, for example, it was better for the laser beam to be set to cross with a wire over 2 mm so that the laser beam could directly irradiate on the wire surface to melt it. As a result, the arc current could be decreased so efficiently that the molten pool size formed by MIG is decreased and the gap tolerance increased. In the case of the utilization of a fibre laser, it was found that the wire melting phenomena were affected by the laser beam parameters such as the beam diameter and the defocused conditions when welding was not done at a focal position. It was clarified that even at the same laser beam diameter on the work surface, the wire melting phenomena could be different under the different defocused conditions. In the defocused conditions where the focal position was over the work surface, the molten droplet on the wire tip evaporated more easily than the case where the focal position was within the work surface. From the viewpoint of laser absorption by the wire or the molten droplet, according to an arc phenomenon approach, it was found that about 10% of laser energy was absorbed during hybrid welding when the laser beam was directly irradiated on the wire surface.