Chapter 2
Model of Quasi-Steady Weld Pool
Dynamics and Numerical Simulation
2.1 Introduction
Laser welding is a joining process in which a focused laser beam is coupled to the
surface of a material to be welded to generate heat and melt the material. The welding
process can be optimized in three aspects: determining a set of process parameters
which make the welding process basically stable and are reproducible; monitoring
the changes of various parameters in the welding process to ensure the quality of the
joint; real-time control of the parameters of the laser welding process.
The instability of laser welding is its intrinsic characteristic. The instability is
caused by fluctuation of parameters in four aspects during the laser welding process,
including the fluctuation of laser output parameters, the effect of changing plasma
flow at the exit of the keyhole on the incident laser beam, the dynamic instability of the
weld pool motion, and the instability of the vapor flow in the keyhole. The interaction
of these parameters makes the laser welding process extremely complicated. Hence,
the basic point of departure is to simplify some complex parameters, ignoring the
influence of some minor factors, to study the influence of the laser welding parameters
on the temperature field and velocity field of the weld pool in quasi-steady state by
numerical simulation.
The steady state refers to a state in which the weld pool does not change with time
under certain conditions. The quasi-steady state means that the temperature field and
velocity field of the laser welding pool do not change with time, but the instantaneous
quantities are changing at all times. The “Quasi” means that although the degree is
not completely enough, it can still be regarded as a certain kind of thing, that is, it is
close to a stable state but still unstable.
In any welding process, the main factor closely related to the quality of the weld
joint is the stable existence of a weld pool, and for the deep penetration laser welding
process, the main manifestation is the stable existence of the keyhole in the weld
pool. Experiments and researches on the deep penetration laser welding process
have shown that, in the deep penetration laser welding process, many parameters
such as laser welding power, focus position, welding speed, assembly gap, etc. in
© 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_2
19
Model of Quasi-Steady Weld Pool
Dynamics and Numerical Simulation
2.1 Introduction
Laser welding is a joining process in which a focused laser beam is coupled to the
surface of a material to be welded to generate heat and melt the material. The welding
process can be optimized in three aspects: determining a set of process parameters
which make the welding process basically stable and are reproducible; monitoring
the changes of various parameters in the welding process to ensure the quality of the
joint; real-time control of the parameters of the laser welding process.
The instability of laser welding is its intrinsic characteristic. The instability is
caused by fluctuation of parameters in four aspects during the laser welding process,
including the fluctuation of laser output parameters, the effect of changing plasma
flow at the exit of the keyhole on the incident laser beam, the dynamic instability of the
weld pool motion, and the instability of the vapor flow in the keyhole. The interaction
of these parameters makes the laser welding process extremely complicated. Hence,
the basic point of departure is to simplify some complex parameters, ignoring the
influence of some minor factors, to study the influence of the laser welding parameters
on the temperature field and velocity field of the weld pool in quasi-steady state by
numerical simulation.
The steady state refers to a state in which the weld pool does not change with time
under certain conditions. The quasi-steady state means that the temperature field and
velocity field of the laser welding pool do not change with time, but the instantaneous
quantities are changing at all times. The “Quasi” means that although the degree is
not completely enough, it can still be regarded as a certain kind of thing, that is, it is
close to a stable state but still unstable.
In any welding process, the main factor closely related to the quality of the weld
joint is the stable existence of a weld pool, and for the deep penetration laser welding
process, the main manifestation is the stable existence of the keyhole in the weld
pool. Experiments and researches on the deep penetration laser welding process
have shown that, in the deep penetration laser welding process, many parameters
such as laser welding power, focus position, welding speed, assembly gap, etc. in
© 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_2
19