Effect of welding heat input conditions on the dynamic behavior of pulse laser beam welding molten pool for Ti6Al4V thin plate with clearance

Abstract

Abstract For a practical pulse laser beam welding (PLBW) process of metal sheets assembled in butt joint configuration, the precise control of the assembling clearance has been a challenge. The existence of machining burrs and assembly errors will lead to forming severe defects, such as misalignment, welding leakage, and penetrating. In this paper, a pair of Ti6Al4V plates with a 0.2 mm air gap was tested by an improved PLBW process. A three-dimensional multi-phase and multi-physical field coupling model of Ti6Al4V alloy plate with a reserved air gap was established according to the weld profile, and the dynamic behavior of the keyhole and molten pool was simulated. Transient temperature field, velocity field, keyhole size, and liquid bridge connection were calculated by using different welding heat input parameters. The results showed that the weld profile simulated by the CFD model is in good agreement with the experimental results, and the deviation is between 0.68% and 7.95%. After the laser power reaches the peak value, the metal steam eruption weakens and the obvious Marangoni vortex appears in the molten pool. The simulated keyhole is always in three stages, that is, the keyhole appears, and then gradually forms the through-hole. The through hole keeps oscillating, and finally, the keyhole shrinks and disappears when the laser power drops to zero. With the increase of laser peak power, the keyhole shape becomes more curved, indicating that the keyhole oscillation is enhanced. With the increase in welding speed, the stability of the molten pool is improved, and the area of the liquid bridge rises more regularly.