Spatial powder flow measurement and efficiency prediction for laser direct metal deposition

Powder deposition is a critical element for coating and additive processes such as laser direct metal deposition. The flow rate and distribution of the powder affect the size of the deposited tracks and the total efficiency of the process. Therefore, knowledge of the three-dimensional shape of the powder flow and its relative position to the melt pool is crucial for any process modeling and enables an assessment of the nozzle design. Herein, a robust, industry-oriented method is proposed to measure and evaluate the 3D powder flow density from a nozzle, considering the effect of the base material. A setup was developed to measure the flow with high spatial and temporal resolution and to determine the position of the stream focus, laser beam, and tool axis. An algorithm correlates time-dependent measurement data with the spatial position of the stream, derives a volumetric distribution plot and predicts the catchment efficiency of the process considering any misalignment. The analysis of two nozzle designs reveals the influence of the powder distribution on the process capability to perform multi-layer additive manufacturing. A comparison between the predicted and actual powder catchment efficiency shows good correlation for varying standoff distances and melt pool sizes. The prediction was applied successfully by building a multi-layer structure with high geometric accuracy.