Investigation on direct measurement method of particle velocity in the plume for intelligent laser welding-oriented

Abstract

The dynamic plume behavior is one of the key features that allows one to obtain the required information for monitoring the process quality of the intelligent laser welding. This paper proposed a method of directly measuring particle velocities in plume induced in fiber laser keyhole welding based on the self-mixing interferometry (SMI) effect. This method was verified by measuring tiny metal objects with known sizes and velocities. The particle velocities can be calculated according to the number of SMI fringes induced by the particles, and the temporal data. To measure the diameters of particles, it is expedient to use a detection laser with a spot diameter larger than that of particles. A smaller diameter of the detection laser spot will result in more accurately measured values of particle velocities. A direct measurement was conducted to assess the particle velocities in the plume induced in fiber laser keyhole welding. These particles in plume had a velocity of 1.9–90 m/s, and more than 45% of these particles had a velocity of 10–60 m/s. Particles with larger diameters were more likely to have higher velocities.