Experimental measurement of the powder flow velocity in a three-port coaxial laser metal deposition nozzle by high-speed imaging

Additive manufacturing has been successfully used as a new technology to produce complex components with improved properties compared with the traditional manufacturing process. However, the powder used as feedstock requires a homogeneous powder mass flow. Velocity and amount of powders fed into the molten pool are crucial to obtain reproducible deposits (tracks). Therefore, monitoring of key parameters in the laser metal deposition (LMD) process is of high importance to obtain repeatability during either repair or printing components. In order to evaluate LMD relevant parameters, a new particle velocity measurement algorithm is proposed. The experimental tests were digitized with a high-speed camera at 8 kHz. Spherical powder of maraging steel with a close size distribution of 90-150 mu m has been used as powder feedstock. The algorithm is composed of three modules: the preprocessing of the images, the calculation of the displacement vectors, and the validation and adjustment of the speeds. The sensitivity of the algorithm was validated using synthetic images, showing good performance at noise rates close to 40 dbW. The uncertainty obtained is 0:62m/s, which was calculated by comparing the results obtained against numerical simulations. The proposed method is specific to additive manufacturing processes using metallic powders as feedstock.