The Arc Physical Characteristics and Molten Pool Dynamic Behaviors in Conduction Plasma Arc Welding
LI Zihan1, XIN Jianwen1, XIAO Xiao2, WANG Huan3, HUA Xueming1(), WU Dongsheng1
1.Welding and Laser Processing Institute, Shanghai Jiao Tong University, Shanghai 200240, China 2.School of Materials Science and Engineering, Henan University of Science and Technology, Luoyang 471023, China 3.Hudong-Zhonghua Shipbuilding (Group) Co. , Ltd, Shanghai 200129, China
Cite this article:
LI Zihan, XIN Jianwen, XIAO Xiao, WANG Huan, HUA Xueming, WU Dongsheng. The Arc Physical Characteristics and Molten Pool Dynamic Behaviors in Conduction Plasma Arc Welding. Acta Metall Sin, 2021, 57(5): 693-702.
Conduction plasma arc welding is widely used to weld thin stainless-steel plates in a liquefied natural gas carrier, in which high arc energy density can be achieved through the constraint effects of the constricting nozzle. However, the welding current is relatively low, such that a keyhole is not formed inside the molten pool in conduction plasma arc welding, causing significantly different arc physical characteristics and molten pool dynamic behaviors from those of keyhole plasma arc welding. In this study, a one-way coupled electrode-arc-molten pool model was developed, and spectral analysis, infrared thermography, and particle tracing methods were used to investigate the arc physical characteristics and molten pool dynamic behaviors in conduction plasma arc welding. In conduction plasma arc welding, numerical and experimental results show that plasma impinges on the surface and flows toward the edge of the molten pool. Two contrary convective eddies were found inside the molten pool. The counterclockwise eddy at the center of the molten pool is driven by arc pressure, Marangoni forces, and Lorentz forces, and the clockwise eddy at the rear part of the molten pool is driven by plasma shear stress, Marangoni forces, and buoyancy forces. Additionally, the maximum temperature of the molten pool in conduction plasma arc welding is higher than that in keyhole plasma arc welding due to higher arc energy density and weaker convection.
Fig.1 Framework of one-way coupled electrode-arc-molten pool model (q(x, y, z), τ(x, y, z), and p(x, y, z) indicate heat source, arc shear stress vector, and arc pressure in x, y, and z coordinate, respectively)
Fig.2 Directions of arc shear stress before (a) and after (b) the deformation of molten pool (o and n indicate horizontal vector and free surface normal vector, respectively)
Parameter
Unit
Value
Parameter
Unit
Value
Density
kg·m-3
6900
Liquidus temperature
K
1727
Viscosity
kg·m-1·s-1
5.9 × 10-3
Solidus temperature
K
1697
Specific heat (liquid state)
J·kg-1·K-1
720
Boiling temperature
K
3133
Specific heat (solid state)
J·kg-1·K-1
760
Heat transfer coefficient
W·m-2·K-4
20
Latent heat of fusion
J·kg-1
2.47 × 105
Coefficient of thermal expansion
K-1
1.5 × 10-4
Thermal conductivity (liquid state)
W·m-1·K-1
28.4
Surface tension
N·m-1
1.8
Thermal conductivity (solid state)
W·m-1·K-1
33.2
Surface tension gradient
N·m-1·K-1
-4.3 × 10-4
Table 1 Physical properties of SUS304 stainless steel used in this model
Fig.3 Schematic sketch of experimental set-up of plasma arc welding
Fig.4 Distributions of temperature and velocity of plasma arc in local coordinate system y0O0z0
Fig.5 Distributions of temperature and velocity at the plasma arc axis (a) and distributions of arc pressure and arc shear stress on the surface of base metal (b)
Fig.6 Distributions of temperature field, fluid flow field (a1-d1), and three-dimensional velocity field (a2-d2) at y0 = 0 at time t = 0.06 s (a1, a2), t = 0.38 s (b1, b2), t = 1.26 s (c1, c2), and t = 1.80 s (d1, d2)
Fig.7 Spectrum of plasma arc at y0 = 0 mm, z0 = 8.3 mm (a) and comparison of experimental and simulated temperatures of plasma arc (b)
Fig.8 The movement of a SiC particle
Fig.9 Thermography image of molten pool surface in local coordinate system x1O1y1 (a) and comparison of experimental and simulated temperatures of molten pool surface (b)
Fig.10 Comparison of calculated and experimental weld profiles
Fig.11 Schematics of momentum coupling mechanism (a) and energy coupling mechanism in conduction plasma arc welding (b)
Fig.12 Schematic of momentum coupling mechanism in keyhole plasma arc welding
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