Real-Time Monitoring of AM Processes

Additive manufacturing (AM) refers to a group of disruptive manufacturing technologies, which build complex parts in a layer-by-layer fashion. Laser-based metal AM techniques have extensive applications in many industries. Although laser AM exhibits many advantages over conventional approaches and promises to revolutionize manufacturing, lack of repeatability and stability remains as a key barrier, preventing its widespread adoption by the highly-regulated sectors, such as aerospace and medicine. Overcoming this barrier can be achieved by developing robust in-process closed-loop control systems, in which the effective real-time monitoring of the printing process is essential. This chapter summarizes different real-time monitoring techniques for laser AM. Some of these techniques also apply to AM processes using electron beam or electric arc as the heating source, given their similar mechanisms of heat and mass transfer as laser melting. The chapter starts with a brief introduction of the laser powder bed fusion and directed energy deposition techniques, which is followed by the review of different process sensing techniques, including visible-light and thermal sensing, integrated sphere radiometry, acoustic detection, Schlieren imaging, and operando synchrotron X-ray imaging and diffraction. The strength, limitations, and unique applications of these techniques are elaborated, and the future perspectives on process monitoring and control for metal AM are outlined in the end.