Numerical Simulation Of Weld Pool Flow In Laser Welding With Powder Feed

Laser welding with powder feed has advantages of larger gap tolerance, higher energy efficiency and lower threshold of laser deep penetration over traditional laser welding. Compared with laser welding with wire feed, powder components adjustment and flexible transmission are more accessible. Thus, the research and application of laser welding with powder feed gain continuous attention. Most papers focus on welding crafts of laser welding with powder feed while few report the weld flow and the interaction between powder and pool. This research focus on driven force of weld pool, temperature and flow flied, alloy elements distribution via numerical simulation.A 3D transient model was developed based on laser welding with powder feed. VOF method was applied to trace the liquid-air interface, the change of liquid surface was took into consideration. Driven forces such as recoil force, surface tension, powder impact, gravity and buoyancy were took into account in this model. Research showed recoil pressure was the key force of keyhole formation and promote the frequent fluctuation of keyhole depth and weld flow velocity. Surface tension hindered the formation of keyhole, but it promoted liquid metal flowing from keyhole to the edge of pool. The impact of powder caused big deformation of pool surface and increased flow velocity there. Gravity and buoyancy contributed little to weld pool flow.Gray value method and high speed camera were applied to obtain the velocity and quantity distribution of powder. Then the effect of powder state on temperature and flow felid were analysed. The results indicated that powder temperature caused local higher or lower temperature zones and velocity of powder caused vortex beneath weld pool surface. Pits formed due to the impact of powder and the depth of pit grew as the velocity of powder increased.In non-penetration condition,vortex turned stronger as laser power increased. In full penetration condition, vortex existed in upper and down part of the pool. The impact of droplet on weld pool was more intense in laser welding with wire feed than with powder feed, which led to instability during welding.Alloy element distribution under different process parameters was analysed. The increase of laser power and velocity of powder contributed to the homogenization of alloy element while increase of powder feed enlarged the inhomogeneity in non-penetration conditions. In full penetration condition, alloy element mostly distributed in the upper part. Simulation results showed that the adaption of high laser power, high velocity of powder combined with high powder feed the alloy element distribution tended to be homogeneous relatively. Laser welding with wire feed was better than laser welding with powder feed in the homogenization of alloy element distribution.