Reliable qualification of additive manufactured (AM) parts is needed for safety-critical applications where every part must be fully inspected. While melt-pool monitoring can optimize process parameters, it cannot certify that no critical defects remain in the finished part. Defect characterization is usually performed post-process by x-ray computed tomography (CT) inspection. If any critical defects are found, they are usually unrepairable at that point. Hence, there is a need for reliable in-line, in-situ detection of critical defects during the AM build process, so that corrective action could be taken to repair them, or the part could be scrapped early before completion.





We have demonstrated the feasibility of meeting this need by applying laser ultrasonic testing (LUT), where one laser beam generates pulsed ultrasonic waves and another laser beam detects those waves scattered by subsurface defects. We use a unique adaptive interferometric receiver that enables non-contact LUT measurements to be performed on rough and moving surfaces at elevated temperatures and at process speeds.





We report here advances in LUT that will greatly improve the state of the art in detection sensitivity and reliability, with increased suppression of mechanical and acoustical disturbances, while also enabling the implementation of a simpler and more agile laser beam delivery and measurement probe design. We describe our inspection method, our signal-processing methods, and concepts for integration of our LUT system onto production AM machines as well as machines for use in space.