Microphone signal specialities in laser powder bed fusion: single-track scan and multi-track scan

Acoustic emission is a promising candidate among online process monitoring methods in laser powder bed fusion. Although previous studies have demonstrated the feasibility for acoustic-based monitoring, an underlying understanding of the acoustic specialities related to laser–powder interactions in the enclosed chamber is scarce. This research employed a microphone to collect the acoustic emission signal during laser printing processes. Two contents are contained in the raw data: static pressure variation and acoustic signal. The features of each content are investigated and it follows several significant findings. First, more violent fluctuations of ambient gas static pressure in the chamber are due to the high temperature gradient of ambient gas and recoil pressure over the laser-material interaction zone, which typically occurs in a very low frequency band (10 kHz). For powder bed additive manufacturing, these results offer a guidance for signal processing and machine learning to dig out the signal signatures of a specific defect in terms of acoustic monitoring.