Adaptive powder nozzle setup for enhanced efficiency in laser metal deposition

Abstract

Laser metal deposition (LMD) is a blown powder process used for the additive manufacturing of large and/or complex parts. The laser spot size is determined by the fiber optic cable and the imaging ratio of the process optics. Spot sizes typically used in LMD can range from 200 μm to several millimeters, whereby zoom optics can be employed to change the laser spot focus within seconds during the process. However, industrial powder nozzles are still static in terms of powder spot size. Changing the powder spot size in line with the laser spot size could ensure the favorable dual outcome of time savings when printing large volumes while also generating fine near-net-shape features. To help overcome the current limitations in the LMD process, this work examines an adaptive powder nozzle setup. In this discrete coaxial layout of three single lateral powder injectors, the individual powder injectors can be adjusted closer to or further from the process to, respectively, dilate or shrink the powder stream focus. Different inner diameters of powder injectors are hereby examined. The resulting powder propagation behavior is characterized for different setups of the single powder nozzles. Single beads are welded with different nozzle setups for fine and coarse powder spots, while the laser spot size is changed accordingly using zoom optics. The laser power is a closed-loop controlled by a two-color pyrometer to achieve comparative process temperatures. The single beads are evaluated with regard to their geometry. High-speed imaging provides supplementary information on weld bead generation.