Laser opto-ultrasonic dual detection for simultaneous compositional, structural, and stress analyses for wire + arc additive manufacturing

The complex, nonequilibrium physical, chemical, and metallurgical nature of additive manufacturing (AM) tends to lead to uncontrollable and unpredictable material and structural properties. Therefore, real-time monitoring of AM is of great significance. However, current AM relies on separate postprocess analyses, which are usually destructive, costly, and time-consuming. In this study, we investigated a laser opto-ultrasonic dual (LOUD) detection approach for simultaneous and real-time detection of elemental compositions, structural defects, and residual stress in aluminium (Al) alloy components during wire + arc additive manufacturing (WAAM) processes. In this approach, a pulsed-laser beam was used to excite the surfaces of Al alloy samples to generate ultrasound and optical spectra. As a result, the compositional information can be obtained from the optical spectra, while the structural defects and residual stress distributions can be extracted from the ultrasonic signals. The silicon (Si) and copper (Cu) compositions obtained from optical spectral analyses are consistent with those obtained from the electron-probe microanalyses (EPMA). The 1 mm blowhole and the residual stress distribution of the sample were detected by the ultrasonic signals in the LOUD detection, which shows consistency with the conventional ultrasonic testing (UT). Both results indicate that the LOUD detection holds the promising of becoming an effective testing method for AM processes to ensure quality control and process feedback.