The stress and motion state of droplet in MIG welding with alternating longitudinal magnetic field were analyzed, and the impact of alternating longitudinal magnetic field on the droplet transfer were studied by high-speed video camera. The results show that the droplet is spherical approximately and transfer to molten pool along the welding wire axis without external longitudinal magnetic field. When alternating longitudinal magnetic field was introduced into welding process, the droplet rotate around the welding wire clockwise and counter-clockwise alternately. Shape of droplet became flat and direction of transfer deviated from the welding wire axis under the action of magnetic field. As the exciting current increased, extent of deviation from the wire axis increases. When the exciting current is too large (I >20A), extent of deviation is too large and droplet are disintegrated into several small droplet during the transition. So droplet can not transfer into molten pool successfully and the bead can’t be formed.

In order to optimize the MIG welding procedure of aluminum alloy with longitudinal magnetic field and improve the mechanical property, effect of longitudinal magnetic field frequency on microstructure and properties of surfacing layer were investigated. The results show that when the additional longitudinal magnetic field was introduced into welding process, grain was refined, the wear resistance and tensile strength of the surfacing layer were improved as longitudinal magnetic field frequency increased. When frequency of magnetic field is 20 Hz and exciting current is 15 A, effect of grain refining is the best and the mechanical property is the highest. But when exciting current continue to increase, grain became coarse and the mechanical property decreased. So it is concluded that grain was refined and the mechanical property of the surfacing layer were improved under longitudinal magnetic field. But magnetic field frequency has an optimal value; otherwise grain refining and the mechanical property can’t achieve the best effect.

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In the study three dimensions finite element mathematical model of MIG welding with longitudinal magnetic field was established. By ANSYS FEA software the temperature and other physical characteristics of the arc were obtained including the distributions of current density and arc pressure on the anode surface. The simulated results show that when the additional longitudinal magnetic field was introduced into welding process, the temperature of arc decreased remarkably and peak value of temperature changed from 16 950K to 13 700K at a welding current of 120A. Under the action of longitudinal magnetic field, on the one hand, heat flux density and current density at the anode surface decrease in the arc core and rise at the edge of arc, on the other hand, arc pressure decrease and arc potential increase. Keywords: Numerical simulation; MIG welding arc; magnetic field

Welding arc deposition is a high efficient rapid forming technology which can be used to rapidly form metal functional parts directly. While, Traditional slicing methods in the rapid forming process always produce ‘staircase’ or additional support structure which reduce deposition accuracy and efficiency, bring about the dissipation of materials. Even that it cannot exploit the advantages of welding arc deposition method. This paper proposes a slicing strategy which is suitable for rapid forming based on welding arc deposition. During slicing stage, the CAD model is decomposed into different pieces based on its geometrical feature to make each piece can be deposited in one direction without support structure, and layer thickness is determined according to the height of each sub volume and welding parameter database. A typical part is built with this method. It shows that this method is feasible and high efficient.