大功率激光作用下小孔形成数值模拟

Modelling of the Keyhole Formation under High Intensity Laser Power

激光深熔焊以小孔效应为特征,小孔使得激光束流与被焊接材料之间的耦合效率大大提高。小孔内的逆轫致吸收使得激光能量逐步衰减。另一方面,小孔内等离子体向熔池传热,起到焊接内热源的作用。因此,利用建立组合体热源模型,选择旋转高斯热源和双椭球形体热源模拟激光能量的分布,结合SIMPLE算法,求解不可压缩流体的质量守恒、动量守恒和能量守恒方程,得到了大Péclet数下的小孔形态。模拟结果显示,控制容积法中的体热源传热方式不同于有限元法的表面热流密度分布方式。最后,将模拟结果和钛合金激光焊接的焊缝形状和尺寸进行了对比,说明所选择的体热源模型在激光深熔焊模拟中具有较好的适应性。

Keyhole effect is one of the characteristics during deep penetration laser welding. Laser keyhole results in obvious improvement of the coupling efficiency of laser power in the metal sheet. The laser energy attenuation along the thickness of the sheet occurs due to the inverse bremsstrahlung absorption inside the keyhole. On the other hand, the keyhole plasma plays welding heat source role in transferring laser energy to melt pool. As a result, a combination of a rotary volumetric heat source with a double ellipsoid volumetric heat source was proposed, and the governing equations consisting of mass conservation, momentum conservation and energy conservation for the incompressible fluid flow and heat transfer are solved using SIMPLE algorithm based on control volume method. Influence of weld process parameters on the keyhole dimensions was simulated. In addition, validation experiments were carried out in order to compare weld shape and its size.