Theoretical Research Of Metal Melt Ejection Induced By Long Pulsed Laser

In this thesis, a physical model has been established to simulate the melt ejection induced by millisecond pulsed laser on Aluminum slab. The formation of the keyhole that is influenced by the laser parameters has also been investigated in such numerical way by using finite element method (FEM).In the first part, the long pulsed laser induced melt ejection has been researched in both experimental and numerical way. A two dimensional model has been developed to simulate the melt ejection induced by millisecond pulsed laser on Aluminum slab. In order to verify the feasibility of such model, the numerical results and experimental data have been compared in terms of the aspect ratio of keyhole, the morphology of the keyhole and the trajectory angel of the melt ejecta. All the results match well.In the second part, the impacts that the laser peak energy and pulse duration have on target center temperature, drilling depth, the radius of the keyhole, drilling velocity, the velocity and the mode of expulsion and the quality of keyhole have been investigated by using the developed model. The results of simulation indicates that under the circumstance where the laser pulses have the same spot radius and pulse duration, but an increment of laser energy, the temperature at the center of Al target increases and evaporation happens after the surface temperature reaches boiling point and later the target sustains in the status of equilibrium vaporization; keyhole depth and drilling velocity are linearly increased with the increase of laser energy, respectively; the growth of the keyhole radius is in the trend to be gentle; the velocity of melt ejecta increases rapidly with the increased laser energy as well as the transition of expulsion mode; the quality of keyhole is good. Under the circumstance where the laser pulses have the same spot radius and laser energy, but an increment of pulse duration, the temperature at the center of target decreases; the keyhole depth firstly decreases and then increases; the radius of the keyhole increases dramatically; the drop of drilling velocity has the tendency to be gentle; the quality of the keyhole gets worse and worse and some tiny little eddies are founded in the layer of liquid metal where the peak and valley happens.This research may provide the theoretical references to the understanding of the interaction between millisecond pulsed laser and the materials, as well as be beneficial to the application of the laser materials processing and military.