In-situ measurement methods for microscale surface impurities in powder bed fusion: a review

Abstract

Despite ongoing improvements and optimisation efforts, the powder bed fusion (PBF) process continues to face challenges related to repeatability, robustness, and stability. These challenges can lead to the formation of microscale surface impurities on each layer, such as balling, spatter and surface pores, which can adversely affect the overall quality of the final part. The layer-by-layer fabrication approach in PBF offers an opportunity to assess fabrication quality in real-time by detecting these impurities at each layer during the manufacturing process through in-situ sensing methods. With advancements in sensing and computing technologies, there has been a significant increase in studies focused on developing in-situ methods for the real-time detection of surface impurities and feedback mechanisms. However, it is necessary to understand the effectiveness and capability of these in-situ methods in detecting microscale surface impurities, as well as to evaluate their potential advantages, drawbacks, and the existing gaps in the literature. This study first summarises the common microscale surface impurities and their potential impacts on part quality, including mechanical properties and surface finish. It then reviews the existing in-situ methods capable of detecting these microscale impurities, providing insights into the strengths and limitations of current techniques, and identifying gaps in the literature while suggesting directions for future research.