In-situ acoustic emission monitoring for porosity detection in directed energy deposition manufacturing

Directed Energy Deposition (DED) is an additive manufacturing process that enables the fabrication of complex metallic components; however, process induced defects such as porosity remain a critical concern. This study investigates Acoustic Emission (AE) as an in-situ, non-destructive testing (NDT) method for correlating real-time process signals with internal porosity in DED-fabricated stainless-steel specimens. AE signals were continuously acquired during fabrication, while post-process X-ray Computed Tomography (CT) was used to quantify pore size, distribution, and volume fraction. The novelty of this work is the spatial correlation of in-situ AE measurements with CT-identified porosity to identify defect-prone regions during fabrication. The results show that stable AE amplitudes above approximately 55 dB, with fewer high-energy transient events, were associated with improved material consolidation and lower porosity, while fluctuations in AE activity corresponded to regions with increased pore formation. These findings demonstrate the potential of AE monitoring for assessing process stability and defect evolution in DED, providing a practical complement to conventional post-process inspection methods.