Quality Evaluation of Additive Manufacturing Components Based on Zero-Group-Velocity Lamb Waves

Abstract

In the production process of additive manufacturing (AM) components, the occurrence of holes, microcracks, and other defects can seriously affect the physical and mechanical properties of AM components. This paper presents an effective method for quality evaluation of AM components utilizing zero-group-velocity (ZGV) Lamb waves. The displacement distribution and propagation characteristics of the S1-ZGV mode in the AM component are analyzed in detail by the finite element (FE) method, and the changes in the S1-ZGV mode under different quality levels (characterized by different Young’s moduli) are investigated. The results indicate that the S1-ZGV mode in the AM component is distributed in the form of standing waves, whose time-domain waveform persists throughout the entire time-domain. As the level of quality deteriorates, a corresponding reduction is observed in both the frequency and spectral amplitude (SA) of the S1-ZGV mode, and notably, the SA at the initial S1-ZGV frequency (in good material condition) significantly decreases. This observation provides a reliable method for conducting effective quality evaluation of AM components. Subsequently, the S1-ZGV mode is experimentally and successfully excited in the AM component using the pitch-catch technique with air-coupled ultrasonic transducers, and the SA at different detected positions is quantitatively observed to validate the effectiveness of the method. The experimental results reveal that compared to the traditional linear ultrasonic technique based on wave velocity measurement, the SA at the initial S1-ZGV frequency can more effectively evaluate the quality level of the AM component, which are verified by the optical microscope images. These results validate the effectiveness of the SA based on ZGV modes in accurately evaluating the quality level of the AM components.