136
4 Simulation of Transient Keyhole and Weld Pool
Fig. 4.39 Comparison of keyhole shape and velocity distribution of weld pool longitudinal section
at 25 ms with different welding speeds
significantly weakened. More notably, the vortex flow near the trailing edge of the
bottom of the keyhole gradually decreases as the welding speed increases. Over-sized
penetration depth and strong vortex flow at the bottom of the weld pool go against
bubble floating, thus increasing the welding speed may contribute to an increase in
the probability of bubbles overflowing from the weld pool.
The above simulation results can be concluded as follows. ➀ welding speed has
a significant effect on the depth dimension and variation of depth dimension of the
keyhole, the size of the weld pool, the velocity of the weld pool and the temperature gradient inside the workpiece; ➁ under certain conditions, as welding speed
increases, the amplitude of the keyhole depth oscillation significantly decreases, but
the influence on the oscillation period of the keyhole depth is not obvious; ➂ under
certain conditions, as welding speed increases, the penetration depth and the flow
speed of the weld pool decrease, and the vortex flow in near the trailing edge of the
bottom of the keyhole decreases.
4.3.3.2 Influence of Laser Power on Coupling Between Keyhole
and Moving Weld Pool
In the numerical simulation, the laser power was 1.3, 1.5 and 2.0 kW and the welding
speed was 3 m/min. Other parameters are the same as those in Sect. 4.2.2
Figure 4.40 illustrates the variation of the keyhole depth with the welding time
under different laser powers. According to the figure, the higher the laser power, the
earlier the keyhole forms. And the growth rate of the keyhole depth also increases with
the increase of laser power in the forming stage. In addition, when the keyhole depth
reaches a relatively stable average value, the oscillation of the hole depth increases
with the increase of laser power, but the change of the oscillation period is not
obvious. It mainly lies in that under the same condition, the larger the laser power,
the deeper the average keyhole depth, thus the greater the oscillation of keyhole
depth. As can be seen from Sect. 4.3.1, the oscillation period of keyhole depth is
4 Simulation of Transient Keyhole and Weld Pool
Fig. 4.39 Comparison of keyhole shape and velocity distribution of weld pool longitudinal section
at 25 ms with different welding speeds
significantly weakened. More notably, the vortex flow near the trailing edge of the
bottom of the keyhole gradually decreases as the welding speed increases. Over-sized
penetration depth and strong vortex flow at the bottom of the weld pool go against
bubble floating, thus increasing the welding speed may contribute to an increase in
the probability of bubbles overflowing from the weld pool.
The above simulation results can be concluded as follows. ➀ welding speed has
a significant effect on the depth dimension and variation of depth dimension of the
keyhole, the size of the weld pool, the velocity of the weld pool and the temperature gradient inside the workpiece; ➁ under certain conditions, as welding speed
increases, the amplitude of the keyhole depth oscillation significantly decreases, but
the influence on the oscillation period of the keyhole depth is not obvious; ➂ under
certain conditions, as welding speed increases, the penetration depth and the flow
speed of the weld pool decrease, and the vortex flow in near the trailing edge of the
bottom of the keyhole decreases.
4.3.3.2 Influence of Laser Power on Coupling Between Keyhole
and Moving Weld Pool
In the numerical simulation, the laser power was 1.3, 1.5 and 2.0 kW and the welding
speed was 3 m/min. Other parameters are the same as those in Sect. 4.2.2
Figure 4.40 illustrates the variation of the keyhole depth with the welding time
under different laser powers. According to the figure, the higher the laser power, the
earlier the keyhole forms. And the growth rate of the keyhole depth also increases with
the increase of laser power in the forming stage. In addition, when the keyhole depth
reaches a relatively stable average value, the oscillation of the hole depth increases
with the increase of laser power, but the change of the oscillation period is not
obvious. It mainly lies in that under the same condition, the larger the laser power,
the deeper the average keyhole depth, thus the greater the oscillation of keyhole
depth. As can be seen from Sect. 4.3.1, the oscillation period of keyhole depth is