8.3 Keyhole and Weld Pool Dynamics in Welding with Filler Wires
221
1.0 and 2.0 m/s. When the maximum speed of the weld pool fluctuates violently, the
flow stability is relatively poor, meaning poor flow stability of the weld pool.
It can be concluded from the foregoing simulation analysis and comparison that
in the process of laser welding with filler wires, when the wire enters the weld pool
in contact transition mode, the increase of wire diameter under given conditions will
result in the increase of the maximum speed absolute value fluctuation of the weld
pool, thus weakening the stability of the weld pool.
8.3.7 Comparison of Transient Keyhole and Weld Pool
Behaviors in Free Transition with Those in Contact
Transition
The transient keyhole and moving weld pool behaviors in the process of laser welding
with filler wires and the process of single-beam laser welding are compared and
analyzed in this section. The main technical conditions used during the comparison
and analysis are consistent, as shown in Tables 8.1 and 8.4. The same is true for the
material of the parent metal and the parameters used in numerical calculation. In the
process of laser welding with filler wires, the contact transition and free transition
are simulated respectively.
Figure 8.19 shows the comparison of simulation results of non-metal-droplet
transition (single-beam laser welding), free transition and contact transition at the
same moment under the same conditions. At the same moment, the single-beam laser
welding has a greater penetration depth and a smaller weld pool in the keyhole front
and back edge, as shown in the figure. The analysis reveals that in the process of
welding with filler wire, the addition of wire absorbs some laser energy, which leads
to a decrease in the penetration depth.
Figure 8.20 shows the comparison of the maximum speed of the weld pool in nonmetal-droplet transition, free transition and contact transition. Where, the red line
represents the maximum speed variation curve of the weld pool with time in contact
transition, the black line represents the maximum speed variation curve of the weld
pool with time in free transition, and the blue line represents the maximum speed
variation curve of the weld pool with time in non-metal-droplet transition. According
to the variation trend of the three curves, the weld pool in non-metal-droplet transition
(blue line) has a significantly greater fluctuation frequency of maximum speed than
that in contact transition and free transition, which indicates that the flow stability of
the weld pool in non-metal-droplet transition is lower than that in free transition and
contact transition. However, the maximum speed variation fluctuation of the weld
pool with time in free transition is slightly larger than that in contact transition. In
the initial stage, because of the influence of transition droplets, the maximum speed
of the weld pool in free transition increases from 0 to 2.2 m/s, and then fluctuates
around 1.75 m/s, with the maximum value of 3.0 m/s and the minimum value of
1.5 m/s. However, the fluctuation in contact transition is gentle. It fluctuates around
221
1.0 and 2.0 m/s. When the maximum speed of the weld pool fluctuates violently, the
flow stability is relatively poor, meaning poor flow stability of the weld pool.
It can be concluded from the foregoing simulation analysis and comparison that
in the process of laser welding with filler wires, when the wire enters the weld pool
in contact transition mode, the increase of wire diameter under given conditions will
result in the increase of the maximum speed absolute value fluctuation of the weld
pool, thus weakening the stability of the weld pool.
8.3.7 Comparison of Transient Keyhole and Weld Pool
Behaviors in Free Transition with Those in Contact
Transition
The transient keyhole and moving weld pool behaviors in the process of laser welding
with filler wires and the process of single-beam laser welding are compared and
analyzed in this section. The main technical conditions used during the comparison
and analysis are consistent, as shown in Tables 8.1 and 8.4. The same is true for the
material of the parent metal and the parameters used in numerical calculation. In the
process of laser welding with filler wires, the contact transition and free transition
are simulated respectively.
Figure 8.19 shows the comparison of simulation results of non-metal-droplet
transition (single-beam laser welding), free transition and contact transition at the
same moment under the same conditions. At the same moment, the single-beam laser
welding has a greater penetration depth and a smaller weld pool in the keyhole front
and back edge, as shown in the figure. The analysis reveals that in the process of
welding with filler wire, the addition of wire absorbs some laser energy, which leads
to a decrease in the penetration depth.
Figure 8.20 shows the comparison of the maximum speed of the weld pool in nonmetal-droplet transition, free transition and contact transition. Where, the red line
represents the maximum speed variation curve of the weld pool with time in contact
transition, the black line represents the maximum speed variation curve of the weld
pool with time in free transition, and the blue line represents the maximum speed
variation curve of the weld pool with time in non-metal-droplet transition. According
to the variation trend of the three curves, the weld pool in non-metal-droplet transition
(blue line) has a significantly greater fluctuation frequency of maximum speed than
that in contact transition and free transition, which indicates that the flow stability of
the weld pool in non-metal-droplet transition is lower than that in free transition and
contact transition. However, the maximum speed variation fluctuation of the weld
pool with time in free transition is slightly larger than that in contact transition. In
the initial stage, because of the influence of transition droplets, the maximum speed
of the weld pool in free transition increases from 0 to 2.2 m/s, and then fluctuates
around 1.75 m/s, with the maximum value of 3.0 m/s and the minimum value of
1.5 m/s. However, the fluctuation in contact transition is gentle. It fluctuates around