Thermal Calibration of Commercial Melt Pool Monitoring Sensors on a Laser Powder Bed Fusion System

Publication Title: Thermal Calibration of Commercial Melt Pool Monitoring Sensors on a Laser Powder Bed Fusion System

Subject: Additive manufacturing
Temperature measuring instruments--Calibration
Laser powder bed fusion
Process monitoring

Government Author: Commerce Department, National Institute of Standards and Technology (NIST) .

Abstract: Co-axial melt pool monitoring in laser powder bed fusion (LPBF) additive manufacturing (AM) often utilizes various photodetectors to acquire signals relatable to the dynamic thermal melt pool phenomena. In turn, it is expected that these thermal signatures are relatable to the quality of the fabrication and can therefore the final AM part. To relate these signal values to real, physical temperatures, a thermal calibration must be done. However, the relatively high temperatures and small size of typical LPBF melt pools cannot be easily replicated by most thermal calibration sources. This paper describes a potential method for thermal calibration, which uses a lower temperature, commercial off-the-shelf calibration blackbody. The method calculates an 'effective' temperature for a hypothetical small source of any diameter, which would have the same radiance temperature of the larger, lower temperature blackbody. The paper details the theoretical rationale, provides a proof-of-concept calculation, then demonstrates the procedures conducted on a commercial LPBF melt pool monitoring system. Finally, while this method itself does not provide an absolute calibration nor ability to ascribe real melt pool temperatures to the melt pool monitoring sensor signals, discussion is provided that details the practical utility, details why the measured calibration values are realistic, and describes future improvements to the methodology.