The velocity of powder particles in Laser Material Deposition (LMD) is one the key factors that influence the amount of energy that particles absorb on their individual trajectories through the laser beam on the way between the powder nozzle and the substrate. The amount of energy that is absorbed or reflected by the powder particles above the melt pool determines the temperature on the substrate surface, and hence influences the formation of the melt pool and the deposition of the powder material.

Knowledge about the particle velocity is therefore essential for any effort of modeling the LMD process – not only for physical simulation where a particle’s energy input can be integrated along its trajectory, but also in an experimental environment of process parameter studies, where an understanding of the interdependencies between the process parameters is crucial.

In this study, a measurement setup using a high-speed camera and an illumination laser is used to measure the velocity of powder particles in the powder gas jet of coaxial powder nozzles from Fraunhofer ILT Aachen. The process laser is not used during the measurements. Several parameters that are known to influence the particle velocity are varied: Feed gas rate, shielding gas rate, nozzle geometry (width of annular gap), and powder mass flow rate. Four different powder types are compared.

The influence of these process parameters on the particle velocity is measured. Four different evaluation methods for tracking individual particles and calculating the velocity distribution within the powder gas jet are used and compared: Manual frame-by-frame particle tracking and manual evaluation from multiple exposures in single frames, as well as particle tracking velocimetry and particle image velocimetry, which incorporates region-of-interest boxes into the algorithm.