Laser-Ultrasound and Acoustic In-Line Monitoring of 3D Metal Printing

The use of 3D printing to manufacture finished metal parts is poised to revolutionize the manufacturing industry.  However, in-line monitoring during fabrication is critical as parts fabricated under identical conditions can have varying numbers and severity of defects.  Two promising techniques for in-line monitoring during additive manufacturing are acoustic emissions and laser-based ultrasound.   Acoustic emission (AE) systems are relatively low cost and will not increase the build times for 3D printing as they are passive systems.  AE has also demonstrated potential for detecting changes in laser power and powder feed rate for a LENS Optomec Directed Energy Deposition System.  However, AE may lack the sensitivity and specificity to detect smaller defects during the build.  Laser-Based ultrasound (LUS) has the advantage of identifying individual defects ~100 µm provided they are relatively close to the surface, and it may be possible to detect smaller defects as well as quantify variations in the elastic moduli and residual stress of the materials.  However, LUS may increase the build times.  Therefore, both potential techniques need to be explored, and perhaps combined, in the future to achieve optimal in-line monitoring.