Numerical analysis of magnetic fluid dynamics behaviors during resistance spot welding

Abstract

Magnetic fluid dynamic behaviors during resistance spot welding have important influences on weld nugget formation. In this paper, a coupled multiphysics finite element model, which realizes the coupling of mass conservation, momentum conservation, energy conservation, and the Maxwell system of equations, is proposed to systematically investigate the fluid flow and heat transfer behaviors in a spot weld nugget. It is found that the flow field in the spot weld nugget evolves through five consecutive stages: incubation, fluctuation, rapid growth, rapid attenuation, and termination. Molten metal in the nugget makes regular rotational flow in four symmetrical loops, which changes the temperature gradient in weld nugget during heating and holding, and also yields significant effects on the shape and thickness of weld nugget.

Magnetohydrodynamic behaviors in a resistance spot weld nugget under different welding currents

“…The overall iterative solution procedure built in the earlier study [9] is used to perform parametric analyses under three different levels of welding currents: 7800, 8000 and 8200 A. A single-phase AC welding machine (Medar200s) is used for this research, therefore, the alternating welding current is used as the current source input of the model to improve the analysis precision.…”

“…The material is 1.5 mm thick mild steel sheets, electrode force 3580 N, welding time and holding time both 10 cycles. All the material properties needed for electric, thermal, flow and magnetic analyses are the same as in the earlier research [9] . MHD analyses are first performed for welding process to investigate the fluid flow and heat transfer under the induced magnetic field, and then fluid dynamics analyses are performed for subsequent holding process to investigate the flow and heat transfer under the inertial force.…”

“…(3) and (4) In this research, f s is assumed to vary linearly with temperature [9][10][11] . The source term S h describes the heat generation density, which can be given by…”

“…A hybrid multiphysics coupled finite element (FE) model has been developed and the MHD behaviors in a nugget were systematically investigated under a specific current (8200A). The validated model has shown great advantages over the traditional coupled electrical-thermal-mechanical model [7][8][9] .…”

Visualization of Fluid Flow and Heat Transfer in Resistance Spot Weld Nugget

“…ANSYS/Multiphysics was used to realize the coupling of the electric, magnetic, thermal and flow fields. The material models used the published data 8) . Figure 3 showed the flow field at the end of welding cycles.…”