Investigation of humping defect in high speed gas tungsten arc welding by numerical modelling

Abstract

Humping defect which commonly occurs in high current and high speed welding seriously deteriorates weld property. The periodical humping formation in high speed GTAW is investigated by a transient three-dimensional numerical model. A double-ellipse arc shear stress model is proposed. The arc heat flux and arc pressure distributions are modelled varying with molten pool surface evolution self-adaptively. The temperature, liquid metal velocity and resultant weld bead formation are simulated. The molten pool behaviors and their effects on humping formation are discussed. The numerical results show that the deformation of molten pool surface and the elongation of gouging region are two initial requirements for humping formation. The instant solidification, inertia force, surface tension, Marangoni shear stress and gravity also have significant effects on fluid flow in lateral peripheries of molten pool, which influences the humping formation correspondingly. This model gives a preliminary explanation to the tendency of humping in high current and high speed welding condition and the susceptibility of humping to workpiece thickness, active element concentration and workpiece inclination. The simulated weld bead profile, molten pool flow pattern and temperature history are validated with experimental weld appearance, high speed CCD images and temperature measurement, respectively, and good agreements are obtained.