December 5, 2025Open Access

Acoustic emission monitoring reveals keyhole formation and evolution

FBFabien BriffodNational Institute for Materials Science MWMakoto WatanabeNational Institute for Materials Science TSTakayuki ShiraiwaThe University of Tokyo

Key Points

Keyhole formation evidenced by distinct acoustic signatures, impacting melt pool dynamics and porosity.
Acoustic emission monitoring tracked frequency variations related to melt pool depth and laser parameters.
Investigated various materials including Inconel625 under different laser settings to assess AE signal characteristics.
Results suggest that effective monitoring can improve process reliability and efficiency in additive manufacturing.

Abstract

We present results from airborne acoustic emission (AE) monitoring during the Laser Powder Bed Fusion (LPBF) process. A distinct acoustic signature was consistently observed alongside keyhole formation and plume instability, with its frequency inversely proportional to the depth of the melt pool. The effects of laser scanning speed, laser power, material (Ti-6Al-4V, S316L, Inconel625), and laser spot size on AE signals were systematically investigated. A resurgence of high-frequency components for deep melt pools was found to coincide with the onset of keyhole-induced porosity. This acoustic signature is attributed to fluctuations at the liquid-vapor interface, which drive oscillations in the vaporization plume. Multi-track experiments further demonstrated the potential of AE monitoring for real-time fault detection and closed-loop process control in LPBF.

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Briffod et al. (Fri,) studied this question.

synapsesocial.com/papers/694022492d562116f28fbca6 https://doi.org/https://doi.org/10.1038/s41598-025-27232-1

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