Chapter 6
Behaviors of Keyhole and Weld Pool
Under the Effect of Side-Blown Gas
Abstract This chapter introduces the behaviors of keyhole and weld pool under the
effect of side-blown gas. Flow patterns of the side-blown gas in laser welding of
a Titanium alloy are presented. The influences of side-blown gas on the weld pool
profiles and the transient keyhole and weld pool dynamics at the present of keyhole
plume are discussed. Moreover, stable mechanisms of side-blown gas on keyhole
and welding oscillations are presented.
6.1 Introduction
In deep penetration laser welding, the heat source exerts an effect on the laser beam,
plasma, keyhole, weld pool, and other several sub-systems, and these subsystems
influence each other during welding. Figure 6.1 illustrates the dynamic coupling
of sub-systems in deep penetration laser welding. As can be seen in the figure,
(1) The plasma can produce refraction and inverse bremsstrahlung absorption to
incident beams, and the fluctuation of the plasma makes power-density distribution
on workpiece surface fluctuate. (2) The laser beam provides energy required for
producing and maintaining plasma, and the fluctuation of laser power density can
result in the fluctuation of plasma. (3) The keyhole and the weld pool offer mass
sources for plasma and define the boundary of plasma flow fields. Therefore, the
fluctuation of keyhole and weld pool undulates plasma. (4) Fluctuation of velocity
and pressure fields in plasma in the keyhole can cause the fluctuation of keyhole and
weld pool. (5) The fluctuation of power-density distribution of laser beams changes
surface ablation pressures in keyhole and undulates the keyhole and the weld pool. (6)
The variation of keyhole shape changes path for multiple reflections of the laser beam
in the keyhole, thus resulting in surface laser power-density distribution fluctuating
in the keyhole. In addition, the laser welding process is generally protected by using
auxiliary gas flow which can directly affect the plasma, keyhole and weld pool,
so the introduction and parameters of auxiliary gas flow play an important role in
maintaining the stability of welding process.
At present, there are many researches on the influence laws and mechanisms of
side-blown gas on laser-induced plasmas and reports on influence laws of side-blown
© China Aviation Publishing & Media Co., Ltd. 2021
S. Gong et al., Weld Pool Dynamics in Deep Penetration Laser Welding,
https://doi.org/10.1007/978-981-16-0788-2_6
165
Behaviors of Keyhole and Weld Pool
Under the Effect of Side-Blown Gas
Abstract This chapter introduces the behaviors of keyhole and weld pool under the
effect of side-blown gas. Flow patterns of the side-blown gas in laser welding of
a Titanium alloy are presented. The influences of side-blown gas on the weld pool
profiles and the transient keyhole and weld pool dynamics at the present of keyhole
plume are discussed. Moreover, stable mechanisms of side-blown gas on keyhole
and welding oscillations are presented.
6.1 Introduction
In deep penetration laser welding, the heat source exerts an effect on the laser beam,
plasma, keyhole, weld pool, and other several sub-systems, and these subsystems
influence each other during welding. Figure 6.1 illustrates the dynamic coupling
of sub-systems in deep penetration laser welding. As can be seen in the figure,
(1) The plasma can produce refraction and inverse bremsstrahlung absorption to
incident beams, and the fluctuation of the plasma makes power-density distribution
on workpiece surface fluctuate. (2) The laser beam provides energy required for
producing and maintaining plasma, and the fluctuation of laser power density can
result in the fluctuation of plasma. (3) The keyhole and the weld pool offer mass
sources for plasma and define the boundary of plasma flow fields. Therefore, the
fluctuation of keyhole and weld pool undulates plasma. (4) Fluctuation of velocity
and pressure fields in plasma in the keyhole can cause the fluctuation of keyhole and
weld pool. (5) The fluctuation of power-density distribution of laser beams changes
surface ablation pressures in keyhole and undulates the keyhole and the weld pool. (6)
The variation of keyhole shape changes path for multiple reflections of the laser beam
in the keyhole, thus resulting in surface laser power-density distribution fluctuating
in the keyhole. In addition, the laser welding process is generally protected by using
auxiliary gas flow which can directly affect the plasma, keyhole and weld pool,
so the introduction and parameters of auxiliary gas flow play an important role in
maintaining the stability of welding process.
At present, there are many researches on the influence laws and mechanisms of
side-blown gas on laser-induced plasmas and reports on influence laws of side-blown
© China Aviation Publishing & Media Co., Ltd. 2021
S. Gong et al., Weld Pool Dynamics in Deep Penetration Laser Welding,
https://doi.org/10.1007/978-981-16-0788-2_6
165