Effect of the Blowing Angle of Shielding Gas on Weld Morphology in Laser Application

Author    |    Nancy Chu    |    March 7, 2020

Why shielding gas needed?

Continuous laser welding technique uses a high-power laser beam as a heat source to irradiate the surface of the workpiece, so that melting and connecting occurs, then, a beautiful weld joint formed. In such process, the laser beam is irradiated on the material’s surface to melt the workpiece. However, the vaporization of metals melted will also occur, thus forming metal vapor plasma. That vapor has an effect on absorption, refraction and reflection for laser, resulting in the energy actually reaching the surface of workpiece reduced, to affect the stability of the molten pool.

Therefore, during the welding process, blowing shielding gas with a higher ionization energy is required to suppress the generation of plasma. At the same time, such shielding gas also has an effect on isolating the air to prevent the molten pool from oxidized and reducing the welding spatter for a smooth, uniform welding surface.

Effect of shielding gas on weld morphology

In addition to selecting appropriate shielding gas according to welding materials, it is very necessary to study the effect of parameters such as blowing angle, direction and flow rate of the gas on weld morphology. Now, let’s study the effect of different blowing angles on under the same welding condition.

Influence of Parameters on Weld morphology

In the test, controlling other variables of blowing at the same condition, the effect on weld morphology at different flow rate is the same, however, the larger the flow rate, the more obvious effect on the weld penetration, meantime, and the effect on the surface and lower weld width are small. Therefore, only change blowing angle while shielding gas flow is 5L/ min and other variables controlled. The results are shown in Figure 1. The weld cross-section metallography image is shown in Figure 2.

Figure1. Weld penetration and width at different blowing angle

Figure2. Weld Morphology at Different Blowing Angles

It can be seen from the experimental data that the weld penetration first increases and then decreases with the increase of blowing angle. When the blowing angle is 0° or greater than 45°, the penetration decreases rapidly. When the blowing angle is 30°, the welding penetration reaches the maximum.

The weld width of welds is determined by the attenuation of plasma on laser and the effect of gas flow on molten pool. When the blowing angle is 0°, the weld width is the smallest. The melting width increases with increasing blowing angle, and when the angle is greater than 45°, the width changes little.

Result Analysis

The effect of shielding gas on weld morphology is mainly controlling by plasma size which determines the power density of laser that reaches the surface of the workpiece. Observing the weld cross-section metallography image, it can be seen that the morphology tends to
thermal conductivity welding model at 0 ° or 75 °, and it shows obvious deep penetration at 30 ° and 45 °.

In conclusion, under the same welding process parameters, the blowing angle of shielding gas should be recommended to be 30 ° to increase the penetration, and If wider width required, it is recommended to be 45 ° for surface width or 0 ° or 75 ° for wider width of the lower part.

Content source: JPT laser. Translated by Nancy Chu.