Product Code: ICAL07_806

The Effect of Laser and Welding Parameters on Keyhole and Melt Pool Behavior during Fiber Laser Welding
Authors:
Antti Salminen, Lappeenranta University of Technology; Lappeenranta Finland
Anna Fellman, Lappeenranta University of Technology; Lappeenranta Finland
Presented at ICALEO 2007

The keyhole laser welding is the most important laser welding process for metal industry. This process utilizes the high energy density of laser beam to vaporize and melt material thus producing a keyhole to material via which the energy is brought to the material. There are various mathematical models created to explain the shape and behavior of keyhole and melt pool during welding. However, the validation of actual keyhole shape, size and behavior against the models is lacking due to the difficulties in performing the measurements. The commonly accepted assumptions are that the size of keyhole is according to focal spot size and that the stability of the keyhole plays a major role when considering the ability of the laser welding process to produce high quality welds. This study utilizes a photography system and concentrates on the visual evaluation of the keyhole size, behavior, stability and effects of wavelength, beam quality and welding parameters on them. The material used was common 3 mm thick austenitic stainless steels grade 1.4301. The effects of laser wavelength, width of an airgap, welding speed, laser beam power and alignment were tested and their effects on keyhole behavior were observed and measured by visually examination of the pictures made by the photography system. The welds were evaluated by visual and metallographic examination. The effect of wavelength and focal point size can be seen from the results. Also it was possible to see the effect and cause of different weld flaws from the keyhole and meltpool behavior. It was also possible to see the equivalent flaws from the cross sectional macrographs. The system tested was also proven to give pictures with acceptable quality for quality assessment from the area.