Study On Filler Metal Transfer Behavior Of Laser Welding Aluminum With Pre-melted Liquid Filler

Currently, laser welding with filler wire has been widely used in industrial production, however, the process of wire feeding results a great impact on the welding process stability. On the one hand, the energy of the laser source is divided into two parts, one for the formation of the weld pool, the other part for melting the wire, and the wire for the reflected laser energy will cause laser energy incident on the instability of the weld pool; In addition, the process of laser welding with filler wire, the wire is fed directly to the position of the laser beam, filler wire located above the keyhole would cause greater impact, and may even lead to the collapse of the keyhole in the welding process, resulting in porosity and other defects. Especially during the process of laser welding with filler wire aluminum alloy, laser energy reflectance by wire is much greater, the above problems are particularly serious.In the subject, the laser welding aluminum with pre-melted liquid filler is studied, which uses tiny arc to pre-melt the wire, so that the wire can slowly flows into the front edge of the pool in liquid, in this process, the laser energy is only used for the weld pool. This method can effectively improve the stability of the welding process, for the reason that the energy of laser is much more stable, besides, the filling material can be fed directly to a further location from the keyhole in liquid, so that can avoid the direct impact of the keyhole, so, the stability of the weld pool and the keyhole in the welding process can be promoted.The subject mainly focus on the filler material transfer behavior of laser welding aluminum alloy with liquid filler, during the study, discovered that the process of transition fill material can be divided into liquid droplets and the transition bridge two transition typical of the transition modes, and on the transition modes were studied and analyzed for its main influencing factors.Compared to conventional laser welding with filler wire, the process stability of liquid bridge transition mode of laser welding aluminum alloy with liquid filler has a significant upgrade, within a certain range can stabilize liquid fill material, continuous transition, significantly reduced weld spatter, and weld porosity has dropped significantly; however, during the liquid bridge mode transition process, a more narrow, higher precision range of the process is needed. Out of this range will lead to discontinuity of the process, not even for welding, and liquid bridge transition mode is poor for fluctuation adaptability, easily lead to the interruption liquid bridge, reduce the welding quality.Compared to liquid bridge transition mode, the droplet transition mode has a wider range, and better for welding process adaptability, however, droplet transition mode transition process is not stable, resulting in lower quality welding, needs the promotion by the role of external forces in order to ensure continuous melting drops and stable transition. The transition filling material characteristic of droplet transition mode has been studied, founded that the control of droplet transfer direction and the size of the transition is the key to good welding process, back wire feed makes the droplet directly transferd into the weld pool, the size of the droplet and the transition period is relatively small, the weld has improved; the subject also simulated Surface Evolver software-based analysis, to explore the feasibility of vibration assisted droplet transition tests.Finally, aluminum radial vibration assisted droplet transition mode physical simulation test is studied, statistical analyses the droplet transfer characteristics in the radial vibration conditions, the stability of the filling material of the transition process was observed and analyzed, and, ultimately, get forming good, low porosity welds.