Investigation on plume formation during fiber laser keyhole welding based on in-situ measurement of particles in plume

Abstract

In this study, the particles in plume were in-situ measured based on the self-mixing effect of the semiconductor laser for revealing the plume formation during fiber laser keyhole welding. The plume consisted of two parts: the oscillating part at the bottom, and the slender part shaped like focused laser beam and with a decreasing ascending velocity. The diameters of particles in plume mainly distributed in the range of 0.3 μm∼0.65 μm (accounting for about 70 %). Along the laser beam direction, both the diameter and density of particles in plume decreased with the increase of the height. In the same horizontal measurement plane, the particle diameter distributed uniformly, and particle density decreased sharply when the monitoring plane further from the laser beam center. There are a great quantity of particles in the oscillating plume caused by eruption of the laser-induced vapor on the front keyhole wall, and that formation of the slender plume is related to the fact that when the oscillating plume is erupting along the laser beam direction, particles in it can enter the laser beam to move in the laser beam direction and to give out light after being heated by the laser beam.