Influencing factors on humping effect in laser welding with small aspect ratios

In the present work, the humping phenomenon is investigated regarding various influencing factors such as volume flow rate, power level, focal diameter, welding situation, material thickness, and thermophysical material properties by means of three-dimensional microscopy inspection, high-speed imaging, and micro-cross sections. Due to applied small focal diameters and shallow weld depths, the results are in particular suitable to welding with small aspect ratios and a predominant horizontal melt flow field. Differences in welding situations caused by two-dimensional and three-dimensional heat conduction are clarified using various material thicknesses. Additionally, influences on onset of humping effect in welds with root fusion and incomplete penetration are compared. Stainless steel, nickel, and titanium are used as specimens in order to point out the influence of thermophysical material properties. Using the example of stainless steel, a functional description of the humping threshold feed rate is introduced based on the volume flow rate and compared qualitatively to the other materials. Finally, the influence of power level, focal diameter, and material thickness on onset of humping is clarified.