基于Level-Set方法的小孔及熔池动态形成数值模拟

Numerical simulation of deep-penetration laser welding based on level-set method

构建了激光深熔焊接三维混合态连续模型,模拟了固液界面过渡层的固、液态共存和熔池高于焊接表面的特征,并采用Level-Set方法追踪了气液界面的移动,计算得到了小孔和熔池的动态形成过程.结果表明,熔池在小孔前沿薄后沿厚,温度梯度在小孔前沿大后沿小,小孔及熔池前沿和后沿存在明显的非对称性;孔壁上蒸发的金属蒸气由孔壁流向小孔中轴线,且向孔外喷射;孔底吸收的激光功率密度最大,最高温度3 700 K位于孔底,高于汽化温度567 K;小孔形成的初期阶段孔深的变化较快,但随着小孔深度的增加,孔深变化速率逐渐下降.

A three-dimensional continuous mixed-state model was established.The feature that molten pool is higher than the welding surface during laser welding was obtained by using level set method in the model,as well as the simulation of the mixed state of solid-liquid in the solid-liquid zone and the tracking the movement of the vapor-liquid interface.The results demonstrated that,the wall of the keyhole and the layer of the molten pool with asymmetry were thin on the front wall of the keyhole and was thick on the rear wall.Also,the temperature gradient was large on the front wall of the keyhole and was small on the rear wall.The metal vapor evaporating from the keyhole wall flowed to the axis of the keyhole,and then was ejected outside the keyhole.The maximum absorption of the laser intensity occurred on the bottom of the keyhole.The maximum temperature of 3 700 K on the keyhole wall was higher than the vaporization temperature over 567 K.The depth of the keyhole increased quickly during the initial stage of the formation.However,the changing rate of the keyhole depth gradually decreased with the increase of the depth of the keyhole.