Acoustic emission monitoring reveals keyhole formation and evolution

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.