Experimental observation of keyhole shapes in the laser welding of aluminum blanks

A camera-based in situ monitoring system for the Nd:yttrium–aluminum–garnet laser keyhole welding process of aluminium has been developed. The use of an external illumination source for image formation decouples the performance of this system from many process parameters. A prototype of the monitoring system was used to investigate two different welding modes, which have been observed during the laser welding process of AA5182 alloy sheets. One welding mode results in a circular keyhole shape, while the second mode has a more elliptical shape. Welds resulting from both welding modes also have a different surface structure at the top and bottom weld surface. Mechanical tests showed a marginal difference in mechanical properties of both welding types. However, the welding mode with an elliptical keyhole shape is more susceptible to holes in the weld seam. Experiments showed that this welding process can be visualized well with the developed monitoring system and that both welding modes can be distinguished clearly.