Multi-sensor monitoring of powder melting states via melt pool optical emission signals during laser-based powder bed fusion

Abstract

The instability of the powder melting states is a common problem in laser-based powder bed fusion of metals (PBF-LB/M). Optical signal monitoring based on melt pool emissions has great potential to solve this problem, but there is a lack of research on the inherent correlations between the optical emissions and powder melting states. In this paper, a synchronous monitoring method of multi-sensor signals based on automatic trigger by numerical control programming was proposed. Then the relationships between the characteristic changes in melt pool signals and the powder melting state variations were carefully examined based on the statistical method. The results showed that the data collection method achieved synchronous monitoring of multi-sensor signals in the target process. The combination of the melt pool light intensity and melt pool area can effectively capture powder melting state variations owing to the changes of powder thickness. Among them, the melt pool light intensity can accurately monitor powder melting state variations caused by the powder thickness of 30 μm to 210 μm. While the melt pool area is susceptible to powder melting state variations caused by the powder thickness of 210 μm to 300 μm. Meanwhile, two emission characteristics (mean intensity and standard deviation) of the optical emissions were closely related to the melting states and stability of the powder.