Similarity analysis for thermal signature comparison in metal additive manufacturing

Metal additive manufacturing differs from traditional manufacturing processes primarily due to repeated heating and cooling cycles that are inherent to the process. Such cycling leads to different thermal signatures and associated heterogeneities in solidification, solid-state transformation, microstructure, and properties of the printed part. There is, therefore, a need to develop methods to compare thermal signatures in a part with reference to part qualification criteria. In this work, we have developed and demonstrated a similarity analysis procedure to meet this need. Thermal signatures are extracted from in-situ infrared (IR) thermography during a part built using a laser powder bed fusion (L-PBF) machine. Layer-wise variations in thermal signature as a function of part geometry were revealed. Ex-situ microstructure characterization was used to validate the results from similarity analysis. Results and analysis confirmed that our similarity analysis is indeed a useful tool for rapid comparison of thermal signatures, i.e., heterogeneity within the part. Similarity analysis was also useful in identification of anomalous thermal signatures. The analysis method paves the way for deploying in-situ monitoring of AM parts for qualification of AM components.