Chapter 5
Dynamic Behaviors of Metal
Vapor/Plasma Plume Inside Transient
Keyhole
Abstract This chapter introduces the time dependent plasma/plume dynamics
inside the keyhole during laser welding. Mathematical models of the transient highspeed plasma/plume dynamics based on compressible Euler flow assumptions are
given. Characteristics of the time dependent plasma/plume behaviors such as uneven
distribution, multiple flow directions, strong oscillations and local evaporations at
keyhole wall are found and discussed by numerical simulations.
5.1 Introduction
At present, investigation of metal vapor dynamic behaviors in transient keyholes
during deep penetration laser welding is very limited. Due to small size of the keyhole,
and high temperature and drastic changing of metal vapor in the keyhole, it is quite
difficult to detect the physical state of metal vapor inside the keyhole during welding
process by experimental method. Numerical simulation of metal vapor in the keyhole
may provide an effective method for better understanding the welding process. Based
on the physical process and experimental results of laser welding and the keyhole
profile and weld pool flow patterns consistent with the experimental results of Xray, and with compressibility of the metal vapor and effect of recoil pressure and
ambient pressure taken into account, a mathematical model is established to describe
the dynamical behaviors of metal vapor inside a keyhole during deep penetration
laser welding, and corresponding boundary conditions for compressible gas–liquid
interface in line with the physical reality are derived.
During laser welding, the moving weld pool, transient keyhole and compressible
metal vapor are closely related. The dynamic behaviors of metal vapor in the transient
keyhole exert an effect on the variation of the weld pool and the evolution of the
keyhole, thus affecting the quality of the whole welding process. The moving state of
metal vapor in the keyhole is a link between the shape of the vapor outside the keyhole
and the morphology of the keyhole and the welding quality, and its kinetic study is
helpful to realize on-line monitoring by high-speed video recording. The simulation
study on the properties of metal vapor in the keyhole and the experimental study can
guide and draw lessons from each other. The dynamic state of metal vapor in the
© 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_5
141
Dynamic Behaviors of Metal
Vapor/Plasma Plume Inside Transient
Keyhole
Abstract This chapter introduces the time dependent plasma/plume dynamics
inside the keyhole during laser welding. Mathematical models of the transient highspeed plasma/plume dynamics based on compressible Euler flow assumptions are
given. Characteristics of the time dependent plasma/plume behaviors such as uneven
distribution, multiple flow directions, strong oscillations and local evaporations at
keyhole wall are found and discussed by numerical simulations.
5.1 Introduction
At present, investigation of metal vapor dynamic behaviors in transient keyholes
during deep penetration laser welding is very limited. Due to small size of the keyhole,
and high temperature and drastic changing of metal vapor in the keyhole, it is quite
difficult to detect the physical state of metal vapor inside the keyhole during welding
process by experimental method. Numerical simulation of metal vapor in the keyhole
may provide an effective method for better understanding the welding process. Based
on the physical process and experimental results of laser welding and the keyhole
profile and weld pool flow patterns consistent with the experimental results of Xray, and with compressibility of the metal vapor and effect of recoil pressure and
ambient pressure taken into account, a mathematical model is established to describe
the dynamical behaviors of metal vapor inside a keyhole during deep penetration
laser welding, and corresponding boundary conditions for compressible gas–liquid
interface in line with the physical reality are derived.
During laser welding, the moving weld pool, transient keyhole and compressible
metal vapor are closely related. The dynamic behaviors of metal vapor in the transient
keyhole exert an effect on the variation of the weld pool and the evolution of the
keyhole, thus affecting the quality of the whole welding process. The moving state of
metal vapor in the keyhole is a link between the shape of the vapor outside the keyhole
and the morphology of the keyhole and the welding quality, and its kinetic study is
helpful to realize on-line monitoring by high-speed video recording. The simulation
study on the properties of metal vapor in the keyhole and the experimental study can
guide and draw lessons from each other. The dynamic state of metal vapor in the
© 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_5
141