Analysis of the correlation between plasma plume and keyhole behavior in laser metal welding for the modeling of the keyhole geometry

• The dynamics of keyhole and plume are well correlated, especially for high laser power and feed rate.
• The trend of keyhole and plume behavior changes when reaching a threshold laser power.
• Keyhole stability for medium laser power is predominantly determined by evaporation processes.
• With high feed rate and high laser power the determining factor of keyhole stability is the melt pool.

The process of laser metal welding is widely used in industry. Nevertheless, there is still a lack of complete process understanding and control. For analyzing the process we used two high-speed cameras. Therefore, we could image the plasma plume (which is directly accessible by a camera) and the keyhole (where most of the process instabilities occur) during laser welding isochronously. Applying different image processing steps we were able to find a correlation between those two process characteristics. Additionally we imaged the plasma plume from two directions and were able to calculate a volume with respect to the vaporized material the plasma plume carries. Due to these correlations we are able to conclude the keyhole stability from imaging the plasma plume and vice versa. We used the found correlation between the keyhole behavior and the plasma plume to explain the effect of changing laser power and feed rate on the keyhole geometry. Furthermore, we tried to outline the phenomena which have the biggest effect on the keyhole geometry during changes of feed rate and laser power.