Optical coherence tomography as NDE method for quality control in additive manufacturing

Additive Manufacturing (AM) needs non-destructive tools for in-line quality control. Optical imaging methods are common solutions, as they allow for fast evaluation of most common geometry defects. However, one needs a tomography method to see buried defects, such as Optical Coherence Tomography (OCT). The method uses short coherent light in the near infrared spectrum. Materials that are at least partially transparent at wavelengths ranging from 800 nm to 1300 nm can be inspected with commercially available instruments at depths ranging from a few hundreds of microns to a few millimeters. This limited penetration depth is not a drawback if the structure is built layer wise, which is typical for AM. The ability to see even through a single layer is an advantage. This report contains a collection of OCT data obtained on structures 3D printed from polymers, biomaterials, ceramics and metals. Information on structure geometry and surface quality can be extracted from most of the materials with resolution specified by the optics of the system and used for quality evaluation on par with optical methods. In the case of materials transparent to the light used, one can detect subsurface defects, inhomogeneities and delamination. The results presented in this study were obtained on samples after the printing process was completed as well as during the manufacturing process. The ability of the OCT to acquire relevant data in real time proves the potential of the method for future applications as a quality control tool in additive manufacturing.