Numerical analysis of magnetic fluid dynamics behaviors during resistance spot welding

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. (c) 2007 American Institute of Physics.