Visual Detection of AM Surface Defects Based on Laser Ultrasound Technology

Selective Laser Melting (SLM) process is a kind of Additive Manufacturing (AM) method, which can process parts with arbitrary complex geometry. However, macro-defects will destroy the mechanical properties of metal materials manufactured by SLM. Laser ultrasound can excite broadband surface waves and realize non-contact nondestructive testing of surface defects. In this paper, 316L stainless steel samples are prepared by SLM process are used for laser ultrasonic detection. According to the diffraction phenomenon of surface wave at the defect, a laser ultrasonic B-scan detection platform is built. The B-scan images of different length defects on the sample surface are obtained, and the quantitative detection of surface defects is realized quickly. In order to further improve the signal-to-noise ratio and the accuracy of imaging detection, EEMD (Ensemble Empirical Mode Decomposition) denoising is applied to the collected ultrasonic signal, which improves the accuracy of imaging, makes the signal more stable and realizes the visual detection of surface length defects clearly and intuitively.