Discrete Phase Modeling of the Powder Flow Dynamics and the Catchment Efficiency in Laser Directed Energy Deposition With Inclined Coaxial Nozzles

Abstract

Laser directed energy deposition (DED) is one of the most promising additive manufacturing processes for restoring high-value components. The damaged components can have complex free-form shapes, which necessitate depositions with an inclined nozzle, where the gravity can adversely affect the powder flow dynamics and the powder catchment efficiency (PCE). PCE is defined as the fraction of the total mass flowrate entering the melt pool, and a low PCE can render the process inviable. In this paper, the effect of nozzle inclination on the powder flow dynamics and resulting PCEs have been studied. It was found that the powder flow dynamics is altered significantly in an inclined nozzle and results in an asymmetric and skewed powder jet. The PCE deteriorates rapidly with an increase in the nozzle inclination due to the progressive defocusing and falls below 20% at 75 deg. A discrete phase model has been developed to understand the powder flow dynamics at different inclinations and process conditions. The mass flow distribution asymmetries on the focal plane at various nozzle inclinations have been analyzed via the model. The model can predict PCEs at different nozzle inclinations with reasonable accuracy ranging from 5.4% at 0-deg inclination to 29.2% at 45-deg inclination. The carrier gas flow, particle size, and laser diameter affect the PCE significantly and can be used to counter the enhanced powder loss at large nozzle inclinations. Process maps have been developed to identify the favorable, acceptable, and low PCE regions to select optimal DED parameters.