56
2 Model of Quasi-Steady Weld Pool Dynamics and Numerical Simulation
and subsurface fluid. That is to say, the flow and heat transfer of metal on the surface
of weld pool is strong, but Marangoni flow mainly affects the surface, but has little
effect on the metal flow under the subsurface layer. The generation of eddy is a strong
proof of convective heat transfer. The fluid on the surface of the weld pool runs so
fast that the heat carried by the fluid is transferred rapidly to the surrounding areas.
However, due to the limited melting area of the weld pool, the rapidly flowing fluid
may show two flow patterns. One pattern is that the hot metal on the surface of the
weld pool center is pushed to the edge of the weld pool to form a protuberance. After
the laser heat source moves away, the temperature of the small laser weld pool drops
rapidly, the viscosity increases rapidly, and finally welds with an extra height are
formed. In calculation, it is assumed that the weld pool is plane, which limits the
deformation of the weld pool surface. The second pattern is that the surface metal
will encounter significant resistance when it flows to the edge of the weld pool. After
the metal collides with the solid metal, the backlash force of the solid wall forces
the flow direction velocity to change, resulting in eddy. From the two cases, it can
be inferred that the actual eddy may not be as significant as those calculated.
Figure 2.27 shows the velocity field of weld pool in the YOZ plane when laser
power is 3000 W and welding speed is 0.03 m/s. It can be seen that there are two
distinct eddies near the surface of the weld pool. The existence of eddy indicates
Fig. 2.27 Velocity vector distribution of laser weld pool in YOZ plane
2 Model of Quasi-Steady Weld Pool Dynamics and Numerical Simulation
and subsurface fluid. That is to say, the flow and heat transfer of metal on the surface
of weld pool is strong, but Marangoni flow mainly affects the surface, but has little
effect on the metal flow under the subsurface layer. The generation of eddy is a strong
proof of convective heat transfer. The fluid on the surface of the weld pool runs so
fast that the heat carried by the fluid is transferred rapidly to the surrounding areas.
However, due to the limited melting area of the weld pool, the rapidly flowing fluid
may show two flow patterns. One pattern is that the hot metal on the surface of the
weld pool center is pushed to the edge of the weld pool to form a protuberance. After
the laser heat source moves away, the temperature of the small laser weld pool drops
rapidly, the viscosity increases rapidly, and finally welds with an extra height are
formed. In calculation, it is assumed that the weld pool is plane, which limits the
deformation of the weld pool surface. The second pattern is that the surface metal
will encounter significant resistance when it flows to the edge of the weld pool. After
the metal collides with the solid metal, the backlash force of the solid wall forces
the flow direction velocity to change, resulting in eddy. From the two cases, it can
be inferred that the actual eddy may not be as significant as those calculated.
Figure 2.27 shows the velocity field of weld pool in the YOZ plane when laser
power is 3000 W and welding speed is 0.03 m/s. It can be seen that there are two
distinct eddies near the surface of the weld pool. The existence of eddy indicates
Fig. 2.27 Velocity vector distribution of laser weld pool in YOZ plane