Product Code: ICAL08_703

The Effect of Welding Parameters on Keyhole and Melt Pool Behavior during Laser Welding with High Power Fiber Laser
Authors:
Antti Salminen, Lappeenranta University of Technology; Lappeenranta Finland
Janne Lehtinen, Cavitar Ltd; Tampere Finland
Petri Harkko, Cavitar Ltd; Tampere Finland
Presented at ICALEO 2008

Laser welding has ever growing role in manufacturing technology. Keyhole laser welding is the most important laser welding process for metal industry. This process utilizes efficiently 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. The welding becomes ever more efficient with new generation of lasers having excellent beam quality and good abortion. There are various mathematical models explaining 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 of the actual dimensions. 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. Previous studies have shown that the welding process produces good quality in case the focal point in is below the surface of the workpiece. The keyhole size resulting high quality weld is typically 85% of the focal point size. This study utilizes an advanced 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 and 6 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. It was possible to see the effect and cause of different weld flaws from the keyhole and meltpool behavior revealed with the photographic system. The system tested was also proven to give pictures with acceptable quality for quality assessment from the area.
The new photographic system gives a deeper sight into the behaviour of the keyhole and plasma formation and shape as function of other welding parameters. It also shows the spattering and weld bead formation quite accurately.