Fusion zone during focused electron-beam welding

The effects of electron beam focusing characteristics on fusion zone are analytically investigated in this paper. The size and shape of fusion zone are important factors determining the weld quality during electron beam welding and depend on beam power, welding velocity, and focusing parameters. In this analysis, assuming the beam profile to be Gaussian distribution and considering the momentum balance at the cavity base and effective convection heat transfer, an analytical model for a focused electron beam irradiating into a paraboloid of revolution-shaped cavity on a workpiece is developed. The influences of the focal spot size, focal location relative to workpiece surface and beam-convergence angle on fusion zone are presented. Results reveal that a focused beam with small focal spot size and beam-convergence angle can induced a deep and narrow fusion zone and the deepest penetration occurs when the focal spot is located at the position between the workpiece surface and the bottom of fusion zone. The shapes of deep and shallow fusion zone approximate a cone with a spherical cap and a paraboloid revolution, respectively.