Thermal Calibration of Ratiometric, On-Axis Melt Pool Monitoring Photodetector System Using Tungsten Strip Lamp

Abstract

In situ melt pool monitoring is a set of technologies widely deployed on industrial, metals-based laser powder bed fusion (LPBF) additive manufacturing (AM) systems. This study investigates the use of a calibrated tungsten ribbon lamp as a reference standard to calibrate a photodetector based, on-axis melt pool monitoring system. Calibration demonstrates two functions: (a) enable a reference for measuring and ensuring system repeatability, and (b) enable reference to physical temperature values based on the measured photodetector signals. The second function is explored in this paper. A regression-based model is derived based on bichromatic Planck thermometry theory. The calibrated tungsten lamp is then placed within a LPBF system, and resulting photodetector signals are measured at different lamp temperature set points to calibrate the model. Finally, several additional characterization tests and their results are presented verifying the temporal response of the lamp, measurement noise as a function of sampling time, and spectroscopic measurements of the LPBF optics and their potential effect on temperature calibration. A framework is also developed to normalize temperature readings across the build plate to remove location-dependent optical artifacts.