Simulation of molten bridge in copper electrical contacts for relay

The formation process of the molten bridge of relay copper contacts is studied in this paper based on a hydrodynamics model. A series of mathematics models are applied to this study, including mass continuous equation, momentum conservation equation, energy conservation equation and electric field equations. And the melt physics mechanism of molten bridge resulted by joule heats is also considered in this model. According to above considerations, the deformation occurs in the area where molten bridge and electrodes combine each other is calculated with the help of moving mesh and automatic re-mesh method in COMSOL Multiphysics code. A simplified symmetric 2D molten bridge model is established with a 4um gap, 4um initial diameter and 20 A∼50 A current. The variation of some key characteristic parameters, such as geometrics of molten bridge in different periods, temperature distribution in cross sections and current density distribution, are analyzed. And the melt down duration of molten bridge under different current is also calculated in this simulation. The results indicate that the hottest area of molten bridge occurs in the central position which is the thinnest part in the whole bridge, and the thermal expansion stress and the surface tension are the most important factors contribute to the deformation. It is also illustrated that the melt down duration reduces rapidly due to current increment.