In laser beam welding processes, a serious challenge is to overcome limitations in processing speed set by the humping effect. This effect, which starts if a certain welding speed is exceeded for a given configuration of material and processing parameters, is characterized by melt pool instabilities leading to periodic droplet formation on the seam surface. Experimental results showed that in welding with single-mode fiber lasers at higher laser powers the welding speed from which humping will occur decreases with increasing power.
Using a single-mode fiber laser with a beam power of 1 kW and a beam quality of M2 < 1.05, an experimental study of the humping effect was conducted for bead-on-plate welding of mild steel, free-cutting steel and stainless steel. To improve the understanding of this phenomenon, welds showing uniform periodical humping have been evaluated in view of their geometrical characteristics such as humping distance, width of the humps and humping frequency, including an evaluation of their statistical spread.
The detailed evaluation of the welds showed that the geometrical characteristics of the humping beads are closely associated with process parameters like laser power, welding speed, focal length, focal position and inclination angle of the beam and the resulting weld geometry. These observations are evaluated in view of the potential effect of the individual parameters for shifting the humping limit to higher welding speeds.