Online multi-physics field measurement of melt pool temperature and flow fields during metal additive manufacturing

Metal additive manufacturing is crucial in modern industries, with the melt pool serving as the fundamental building block. The melt pool behavioral characteristics are fundamental to the structural integrity of the final product. In additive manufacturing, the melt-pool dynamics and thermodynamics measurements are required to better understand and control the microstructure. Based on the trajectory tracking of unmelted powders, a melt-pool flow field reconstruction method was proposed in this study. Specifically, the conditions for collecting unmelted powder were derived theoretically. Boundary extraction and center localization methods specifically tailored to the characteristics of the powders were developed. A particle-tracking technique based on grayscale correlation was introduced, which incorporated a matching probability approach to achieve particle matching and trajectory tracking between adjacent frames. By analyzing the powder melting characteristics, a reassessment of the unmelted powder on the melt-pool surface was conducted, and the accuracy of the flow field reconstruction was enhanced by utilizing the trajectory interpolation algorithm that was developed along with the boundary constraints. Furthermore, by integrating the principle of colorimetric temperature measurement, simultaneous measurements of the temperature and flow fields were achieved using the same measurement optical path. In addition, a high-speed online multi-physics field detection system for the melt pool was developed. This integrated monitoring system enables synchronous online measurements and evolutionary behavior analysis of the multi-physics field data during additive manufacturing, offering pivotal technical support for a deeper comprehension of dynamics and thermodynamics of the melt pool.