Optimization of X-Ray CT Measurement Accuracy for Metal AM Components

This NASA innovation is a method for quantifying and improving accuracy of X-Ray CT-based metal AM part inspection by comparing X-Ray CT data with a high-fidelity 2D surface imaging technique such as surface profilometry. Using surface profilometry that has a NIST-traceable calibration, the technique guarantees a specific level of high fidelity, allowing surface profilometry data to serve as a ground truth reference with which to judge X-Ray CT accuracy and detectability. To deploy the method, both 3D X-Ray CT data and 2D high-fidelity surface images are acquired on the same metal AM part. 3D X-Ray CT data is then segmented and reoriented to extract a 2D X-Ray CT surface image. Measurements of features (e.g., surface-breaking porosity) are then made in both datasets, followed by a comparison of various metrics. This comparison serves two purposes: (a) quantifying the accuracy of the X-Ray CT inspection performed, and (b) providing an objective function which can be minimized to optimize X-Ray CT inspection. The objective function allows engineers to tune X-Ray CT parameters to minimize the function. These optimized parameters can then be implemented to achieve higher accuracy and defect detection reliability in X-Ray CT imaging. Once an X-Ray CT process is optimized for a specific metal AM component, analysis and certification can be accelerated. This technology helps develop X-Ray CT-based metal AM part inspection processes with high accuracy and reliable detectability. Industries for which metal AM parts are desirable and safety, reliability, and fatigue life is of concern (e.g., aerospace, commercial space, automotive, medical) could benefit from the invention. Companies including X-Ray CT inspection system manufacturers using optical sensors and software, NDE data analysis software providers, and end-users in the industries may be interested in licensing this NASA invention. In aerospace and other industries, metal additive manufacturing (AM) technologies are poised to enable the rapid production of complex, custom components that provides a host of advantages. However, metal AM exhibits high complexity compared to conventionally manufactured parts (e.g., point-by-point deviations in grain structure, material properties, and defect conditions). These complexities make it difficult to ensure accuracy and detectability of critical defects via nondestructive evaluation (NDE). As a result, despite their promise, few metal AM parts have made their way into commercial use for safety-critical applications (aerospace, medical, etc.). X-Ray Computed Tomography (X-Ray CT) has become the gold standard for volumetric characterization of metal AM components. However, X-Ray CT can have defect detection measurement uncertainty, particularly for porosity (the most prominent safety-critical defect in metal AM). A recent study of different labs performing X-Ray CT-based inspection of metal AM parts found that, across 10 different facilities, maximum pore size measured varied by a factor of 4.5 and bulk porosity estimated varied by over a factor of 7! Clearly, a new highly accurate and reliable technique is required that can help develop and can improve the accuracy and reliability of part-specific X-ray CT NDE to speed up certification, enabling industry to realize the advantages of metal AM components for safety-critical applications.