126
4 Simulation of Transient Keyhole and Weld Pool
(a) Coefficient of -0.1 N/(m•K)
(b) Coefficient of -0.5 N/(m•K)
Fig. 4.23 Transient surface speed field comparison of weld pool at 15 ms of welding with different
surface tension temperature coefficients
therefore, the thermal capillary force is not the decisive factor for the formation and
growth of the weld pool, mainly due to the important effect of recoil pressure and
other factors on the formation of the weld pool.
Figure 4.24 and Fig. 4.25 show the variation curves of the keyhole depth and
the penetration depth with welding time under two kinds of thermal capillary force
conditions respectively. The smaller the absolute value of the surface tension temperature coefficient, the larger the amplitude of the keyhole depth oscillation, as shown
in Fig. 4.24. The analysis suggests that it is mainly because the maximum depth
of the keyhole is relatively large at this moment. In spite of little difference in the
growth rate of the penetration depth under two different conditions, a smaller absolute value of the surface tension temperature coefficient leads to weaker convection
on the surface of the weld pool, further resulting in greater penetration depth, as
shown in the Fig. 4.25.
It can be concluded based on the foregoing results that: ➀ The thermal capillary
force exerts an important influence on the surface velocity of the weld pool. The
Fig. 4.24 Variation curves
of the keyhole depth with
time under different thermal
capillary force conditions
Time/ms
Surface tension temperature coefficient = -0.1 N/(m•K)
Surface tension temperature coefficient = -0.5 N/(m•K)
Keyhole depth/mm)
4 Simulation of Transient Keyhole and Weld Pool
(a) Coefficient of -0.1 N/(m•K)
(b) Coefficient of -0.5 N/(m•K)
Fig. 4.23 Transient surface speed field comparison of weld pool at 15 ms of welding with different
surface tension temperature coefficients
therefore, the thermal capillary force is not the decisive factor for the formation and
growth of the weld pool, mainly due to the important effect of recoil pressure and
other factors on the formation of the weld pool.
Figure 4.24 and Fig. 4.25 show the variation curves of the keyhole depth and
the penetration depth with welding time under two kinds of thermal capillary force
conditions respectively. The smaller the absolute value of the surface tension temperature coefficient, the larger the amplitude of the keyhole depth oscillation, as shown
in Fig. 4.24. The analysis suggests that it is mainly because the maximum depth
of the keyhole is relatively large at this moment. In spite of little difference in the
growth rate of the penetration depth under two different conditions, a smaller absolute value of the surface tension temperature coefficient leads to weaker convection
on the surface of the weld pool, further resulting in greater penetration depth, as
shown in the Fig. 4.25.
It can be concluded based on the foregoing results that: ➀ The thermal capillary
force exerts an important influence on the surface velocity of the weld pool. The
Fig. 4.24 Variation curves
of the keyhole depth with
time under different thermal
capillary force conditions
Time/ms
Surface tension temperature coefficient = -0.1 N/(m•K)
Surface tension temperature coefficient = -0.5 N/(m•K)
Keyhole depth/mm)