142
5 Dynamic Behaviors of Metal Vapor/Plasma Plume …
keyhole is compared under different welding process conditions. At the same time,
the spouting velocity and oscillating degree of the metal vapor at the opening are
studied under both steady and unsteady welding conditions. The results are helpful
to guide the design and optimization of laser welding process.
5.2 Dynamic Model of Metal Vapor/Plasma in Transient
Keyhole
Because the process of deep penetration laser welding is very complicated, in this
model, the main influencing factors in deep penetration laser welding process are
considered, the secondary factors are ignored, and the model is simplified on the
premise of accurately and reasonably describing the welding process. In order to
improve the efficiency of simulation calculation. The following specific assumptions
are made:
(1) The molten metal liquid is considered incompressible and the mixed phase
model is used for the solid–liquid interface treatment.
(2) The metal vapor produced during welding is an ideal compressible gas, the
density of which varies with time and position, with the effect of viscosity
ignored.
(3) At the gas–liquid interface of the keyhole, the effect of the Knudsen layer is
not considered for the gas phase boundary, while the refraction, reflection and
absorption of metal vapor to the laser are taken into account for the laser energy
distribution in the keyhole.
(4) It is assumed that the main driving force of metal vapor is the surface pressure
of coupling ambient pressure and recoil pressure.
(5) The effect of the protective gas added in the actual welding process on the
whole laser welding process is ignored in the study.
5.2.1 Governing Equations
(1) Governing equations of transient keyhole and moving weld pool behaviors
Accurate dynamic keyhole profiles and surface temperature distributions serve as the
basis for modeling the metal vapor dynamics during laser welding. These physical
characteristics can be determined by free surface heat transfer and fluid flow calculations of weld pool. The equations of mass conservation and momentum conservation
depicting the heat transfer and fluid flow of the liquid metal in the study are as
follows:
∇ ·
− →
U l = 0
(5.1)
5 Dynamic Behaviors of Metal Vapor/Plasma Plume …
keyhole is compared under different welding process conditions. At the same time,
the spouting velocity and oscillating degree of the metal vapor at the opening are
studied under both steady and unsteady welding conditions. The results are helpful
to guide the design and optimization of laser welding process.
5.2 Dynamic Model of Metal Vapor/Plasma in Transient
Keyhole
Because the process of deep penetration laser welding is very complicated, in this
model, the main influencing factors in deep penetration laser welding process are
considered, the secondary factors are ignored, and the model is simplified on the
premise of accurately and reasonably describing the welding process. In order to
improve the efficiency of simulation calculation. The following specific assumptions
are made:
(1) The molten metal liquid is considered incompressible and the mixed phase
model is used for the solid–liquid interface treatment.
(2) The metal vapor produced during welding is an ideal compressible gas, the
density of which varies with time and position, with the effect of viscosity
ignored.
(3) At the gas–liquid interface of the keyhole, the effect of the Knudsen layer is
not considered for the gas phase boundary, while the refraction, reflection and
absorption of metal vapor to the laser are taken into account for the laser energy
distribution in the keyhole.
(4) It is assumed that the main driving force of metal vapor is the surface pressure
of coupling ambient pressure and recoil pressure.
(5) The effect of the protective gas added in the actual welding process on the
whole laser welding process is ignored in the study.
5.2.1 Governing Equations
(1) Governing equations of transient keyhole and moving weld pool behaviors
Accurate dynamic keyhole profiles and surface temperature distributions serve as the
basis for modeling the metal vapor dynamics during laser welding. These physical
characteristics can be determined by free surface heat transfer and fluid flow calculations of weld pool. The equations of mass conservation and momentum conservation
depicting the heat transfer and fluid flow of the liquid metal in the study are as
follows:
∇ ·
− →
U l = 0
(5.1)