Effect of pressure gradient driven convection in the molten pool during the deep penetration laser welding

The pressure distribution around the keyhole during the deep penetration laser welding is simulated. The simulation physically corresponds to the process of a focused laser beam irradiating on the surface of a moving workpiece. A calculation of the velocity vectors and absolute pressure near the front wall and dynamic pressure in the laser weld pool shows that the pressure gradients is directly related to the velocity magnitude of the pool fluid flow, and the dynamic pressure gradient against the welding direction at the rear of weld pool is a retarding force. The velocity of fluid flow near the real wall of the keyhole is smaller, and the formation of the shoulder in the weld pool is contributed by a combination of the movement of the keyhole relative to the workpiece which forms a force that is called expellant force and the friction force of the metal vapor escaping from the keyhole and buoyancy. (c) 2006 Elsevier B.V. All rights reserved.