SUMMARY

Blown powder, laser based directed energy deposition (DED) systems are recognized as a promising manufacturing method for their ability to shorten production cycles and create complex part geometries. An impediment to large scale use of DED lies in poor powder catchment efficiency, the condition in which a portion of injected powder escapes the melt pool resulting in a decreased ratio of printed material mass to mass of supplied feedstock. The wear state of a coaxial nozzle on a DED system within a hybrid manufacturing machine tool has been observed to cause a decrease in catchment efficiency over time. In this coaxial blown powder DED system, a correlation between catchment efficiency and powder stream diameter has been identified, that causes a 15-20% loss in efficiency sustained over incremental nozzle tip reduction up to -1 mm. The proposed research will further address the wear effects and implement process improvement measures to compensate this loss in powder catchment with the following research objectives: (1) to understand the dependent relationships between catchment efficiency as a dynamic variable and the resulting economic impact on deposition volume, material cost, and powder disposal; (2) to analyze the impacts of decreasing powder catchment efficiency on deposition quality (such as geometry, defect structure, and grain structure); and (3) to develop and validate a diagnostic model that can infer nozzle deterioration from deposition imaging and make appropriate machine maintenance recommendations. The fundamental knowledge and monitoring solutions generated will provide first steps in mitigating this quality control issue and lay a foundation for further study of wear effects and process improvement measures for powder fed DED systems.