Sensing defects during directed-energy additive manufacturing of metal parts using optical emissions spectroscopy

Critical components produced via additive manufacturing must be free of unwanted defects. While defects may be detectable after deposition using nondestructive testing techniques, detecting defects during the deposition process offers many benefits: it may enable users to interrupt deposition to repair the part, or to abort deposition to minimize further loss of time and material. Here, we present a method for real-time defect detection during directed-energy additive manufacturing of metals. The method utilized optical emission spectroscopy and a custom-built data acquisition and control infrastructure. It was implemented on a LENS MR-7 machine, and employed during manufacturing of Ti-6Al-4V components in which defects were intentionally introduced. Emission spectra were correlated with defect locations, determined via computed tomography and metallographic cross-sectioning. Preliminary results indicated that defect formation was correlated with atomic titanium (Ti I) and Vanadium (V I) emissions and that measurement of the line-to-continuum ratio for line emissions could be used for defect detection. Based on these findings, sensing strategies for defect detection and, potentially, in-situ-defect repair may be realizable.