Chapter 3
Coupling Model and Numerical
Computation Method of Keyhole
and Weld Pool
Abstract This chapter introduces a self-consistent model of coupled keyhole and
weld pool dynamics and its numerical implementation for keyhole mode laser
welding. A self-consistent heat source model dependent on the transient threedimensional keyhole profiles is presented by using the ray tracing algorithm.
Governing equations for three-dimensional transient heat transfer and fluid flow
of weld pool and keyhole free surface tracking are given in detail. The discontinuous
boundary conditions of thermocapillary force, surface tension and recoil pressure on
the interface between keyhole and weld pool are deduced based on incompressible
viscous flow assumptions. Numerical implementations of this self-consistent model
are also introduced.
3.1 Introduction
In the process of deep penetration laser welding, the laser heat source makes the
material rapidly melted and vaporized to form weld pool, metal vapor/plasma and
dynamic keyhole. With the movement of the heat source, the keyhole and the weld
pool continue to advance, and at the same time, complex free-surface motions occur in
the millimeter-scale weld pool, together with various behaviors such as solid–liquid–
gas conversion, heat transfer and mobility, throughout the entire welding process.
The stability of the deep penetration laser welding process and the joint quality after
welding rely heavily on the coupling of the dynamic keyhole and the moving weld
pool. Therefore, it is necessary to establish a coupling model for the laser welding
keyhole and weld pool and use an accurate and efficient numerical computation
method to provide theoretical tools for the quantitative simulation analysis of the
complex multi-phase coupling dynamics behavior and mechanism of the keyhole
and weld pool in the welding process.
This chapter introduces in detail how to establish a laser welding multi-phase
coupling model. A hybrid model is used to describe the real-time changing solid–
liquid surface, assuming that the molten metal in the weld pool is an incompressible
Newtonian thermal fluid. The heat transfer and flow in the weld pool are expressed
by the conservation of energy equation and the Navier–Stokes equation, respectively.
© 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_3
65
Coupling Model and Numerical
Computation Method of Keyhole
and Weld Pool
Abstract This chapter introduces a self-consistent model of coupled keyhole and
weld pool dynamics and its numerical implementation for keyhole mode laser
welding. A self-consistent heat source model dependent on the transient threedimensional keyhole profiles is presented by using the ray tracing algorithm.
Governing equations for three-dimensional transient heat transfer and fluid flow
of weld pool and keyhole free surface tracking are given in detail. The discontinuous
boundary conditions of thermocapillary force, surface tension and recoil pressure on
the interface between keyhole and weld pool are deduced based on incompressible
viscous flow assumptions. Numerical implementations of this self-consistent model
are also introduced.
3.1 Introduction
In the process of deep penetration laser welding, the laser heat source makes the
material rapidly melted and vaporized to form weld pool, metal vapor/plasma and
dynamic keyhole. With the movement of the heat source, the keyhole and the weld
pool continue to advance, and at the same time, complex free-surface motions occur in
the millimeter-scale weld pool, together with various behaviors such as solid–liquid–
gas conversion, heat transfer and mobility, throughout the entire welding process.
The stability of the deep penetration laser welding process and the joint quality after
welding rely heavily on the coupling of the dynamic keyhole and the moving weld
pool. Therefore, it is necessary to establish a coupling model for the laser welding
keyhole and weld pool and use an accurate and efficient numerical computation
method to provide theoretical tools for the quantitative simulation analysis of the
complex multi-phase coupling dynamics behavior and mechanism of the keyhole
and weld pool in the welding process.
This chapter introduces in detail how to establish a laser welding multi-phase
coupling model. A hybrid model is used to describe the real-time changing solid–
liquid surface, assuming that the molten metal in the weld pool is an incompressible
Newtonian thermal fluid. The heat transfer and flow in the weld pool are expressed
by the conservation of energy equation and the Navier–Stokes equation, respectively.
© 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_3
65