2.7 Numerical Simulation of Fluid Flow in Weld Pool …
55
reduced. Therefore, the rate of increase in the size of weld pool decreases as the laser
power increases.
Figure 2.26 shows the velocity vector diagram of weld pool fluid flow in XOZ
plane when laser power is 3000 W and welding speed is 0.06 m/s. The weld pool
has an asymmetric horseshoe shape. As can be seen in Fig. 2.26, there is an obvious
eddy on the upper surface of the weld pool and at a little distance from the keyhole.
The weld pool is horseshoe-shaped, and there is an obvious eddy on the shoulder of
the weld pool. The maximum speed of the weld pool surface reaches 1.4 m/s. The
velocity of fluid flow in weld pool is small, but the direction of flow is obviously
affected by the fluid flow on the surface of weld pool. Careful observation shows that
the flow velocity on the surface layer of the weld pool is significantly higher than
that on the subsurface layer.
From the point of view of Newtonian fluid, the velocity difference between surface
fluid and subsurface fluid is caused by the shear stress of the fluid. Newton shear
stress is calculated using the following formula:
τ = η
dw
dz
(2.55)
Substitute η of material viscosity and the obtained velocity in the equation. The
viscous shear stress between the surface and subsurface is about 61.2 Pa. The results
show that the flow direction of Z = 0.0023 m plane fluid is opposite to that of surface
Fig. 2.26 Velocity vector distribution of weld pool in XOZ plane in deep penetration laser welding
55
reduced. Therefore, the rate of increase in the size of weld pool decreases as the laser
power increases.
Figure 2.26 shows the velocity vector diagram of weld pool fluid flow in XOZ
plane when laser power is 3000 W and welding speed is 0.06 m/s. The weld pool
has an asymmetric horseshoe shape. As can be seen in Fig. 2.26, there is an obvious
eddy on the upper surface of the weld pool and at a little distance from the keyhole.
The weld pool is horseshoe-shaped, and there is an obvious eddy on the shoulder of
the weld pool. The maximum speed of the weld pool surface reaches 1.4 m/s. The
velocity of fluid flow in weld pool is small, but the direction of flow is obviously
affected by the fluid flow on the surface of weld pool. Careful observation shows that
the flow velocity on the surface layer of the weld pool is significantly higher than
that on the subsurface layer.
From the point of view of Newtonian fluid, the velocity difference between surface
fluid and subsurface fluid is caused by the shear stress of the fluid. Newton shear
stress is calculated using the following formula:
τ = η
dw
dz
(2.55)
Substitute η of material viscosity and the obtained velocity in the equation. The
viscous shear stress between the surface and subsurface is about 61.2 Pa. The results
show that the flow direction of Z = 0.0023 m plane fluid is opposite to that of surface
Fig. 2.26 Velocity vector distribution of weld pool in XOZ plane in deep penetration laser welding