A numerical analysis of heat and fluid flow with a deformable curved free surface in a laser melting process

In this study, a numerical investigation was performed to examine the effects of curved surface shapes, laser power intensity, and the thermophysical properties of a material such as Reynolds and Capillary numbers on the shape, size, and surface topography of the melt pool. This investigation was completed via two-dimensional axisymmetric thermocapillary convection analyses during laser melting processes with deformable free surfaces. In general, a bump has a deep crater at the center and a low peripheral rim, a bowl-like shape. This is caused by the surface temperature gradient-induced thermocapillary flow driving the molten material towards the cooler region, which has higher surface tension. For flat and parabolic free surfaces, surface deformations such as crater depth and rim height increase gradually with decreasing Re and increasing Ca, Bf, and especially the curvature of the free surface. In particular, it is noted that the curvature of the free surface has significantly little effect on the crater depth and rim height for a higher Re and lower Bf with fixed Ca. Its effect is considerably strengthened at a lower Re and higher Bf, indicating stronger convection. In the case of a sinusoidal wavy surface, it is noted that the crater depth and rim height increase monotonically with increasing Ca at fixed Re and Bf, while they decrease with increasing Re and Bf at fixed Ca due to the inward transfer of relatively large amounts of molten material compared to the surface tension gradient driving force, which causes the recovery of the crater center. Hence, the slope of the crater decreases significantly.