Correlating Dimensionless Enthalpy, Pyrometry, and Melt Pool Geometry Within the Laser Powder Bed Fusion Energetic Regime

A Path to In-Situ Melt Pool Control Demonstrated on Tungsten.

Abstract

In the realm of laser powder bed fusion (LPBF), controlling the melt pool in situ represents a critical challenge, as numerous defects are associated with its dynamics. This research demonstrates the utility of pyrometric signals in gaining insights into the depth of vapor capillaries during LPBF processes. By establishing a correlation between a semi-empirical enthalpy model and pyrometric data, gathered on a powder-free substrate, a pathway towards the in-situ control of melt pool geometry is unveiled. The study introduces a dimensionless enthalpy model designed for predicting the aspect ratio of melt pools in LPBF. A linear relationship between the depth of melt pools, pyrometric signals, and dimensionless enthalpy is established through correlation with this model and measurements from metallographic cross sections. Histographic analysis of pyrometric data reveals unique signatures that correlate with conduction and keyhole mode melting, suggesting that these distinct histogram forms are indicative of keyhole stability. The findings confirm that the relationships defined in this study are applicable across varying spot sizes and hatch distances, allowing for the inference of optimal parameters directly from pyrometric signals. This research lays the groundwork for real-time control of melt pool geometry, marking a significant advancement towards enhancing the quality and consistency of LPBF and holds potential applications to laser welding processes.