Electron Beam Welding: Heat Flow Model including Peclet Number
Electron beam welding is recognized as a low heat input for obtaining thinnest bead width and longest weld penetration among the technologies to provide low distortion. The challenge is to keep the electron beam focused without distractions to surroundings which is obtained by performing the process in a vacuum chamber. EBW modeling is similar to laser weld in terms of heat flux flow with a surface heat on bead area in the form a Gaussian distribution. When the beam forms a keyhole, the heat is conducted to the base metal by a frustum distribution. As there is no blind end at the bottom, a portion of the heat would leave out to ambience through the lower end of the bead. The heat flow mechanism is calculated using Peclet number from where the empirical formulae power distribution is determined. Peclet number variation is calculated as a function of radial distance, penetration depth and distance from wall. A method for incorporating weld velocity and gas flow in simulation and modeling is also discussed. Finite element analysis is done and temperature graphs were obtained for welding using Ansys software. Weld material used is SS304 and temperature dependent thermal and structural properties are considered. The output obtained is the thermal isotherms around the weld to estimate the fusion, bead and heat effected zones.
Electron beam welding, Laser weld, Gaussian distribution, Frustum distribution, Peclet number.