Abstract
The modelling of weld pool oscillation is carried out in order to make clear the natural frequency and the oscillation mode of the pool in the fully penetrated welding of thin plate. The oscillations of the elliptical pool are discussed because the molten pool in the traveling arc welding takes the oval shape. In the case of the elliptical pool with a finite depth having both a top surface and a bottom surface, the dispersion relation between the natural frequencies, the pool shape, the surface tension and the density of the melted metal is derived.