Non-destructive analysis (NDA) of external and internal structures in 3DP

Purpose Three-dimensional printing (3DP) is an increasingly popular additive manufacturing (AM) process. The structure produced in 3DP comprises of two main elements: an external "shell" and an inner "core". The variation of this structure and print strategy dictates many factors, such as the final physical properties, the final weight of the part, the total material usage, effects on warpage and the build speed. As such, the accuracy and repeatability of these geometric structures is of importance. The measurement and validation of the actual printed structure is especially challenging due to the nature of the materials system. The purpose of this paper is to present an effective method to analyze the internal structure of a 3DP. Design/methodology/approach - A dedicated video-monitoring system has been developed to capture and characterize the 3DP build structure layer-by-layer. A significant image-processing phase involved image calibration, filtering, thresholding and segmentation. The investigation is composed by three substudies. First, the reliability of the developed system was determined by comparing nominal dimensions of a benchmark part with video and contact measurements. The two studies have focused on the "shell" and "core" characterization, respectively. Findings - A resolution of 508 pixel per inch was determined. From the first studies, benchmark elements of 0.5 mm presented a deviation between 0.29 and 0.44 mm from their normal dimension. The thickness of the external shell was analyzed, in both clear and coloured modes. Dimensions ranged between 1.51 and 1.58 mm for a clear part, and 1.59 and 1.69 mm for the coloured version. A further study resulted in a 3D virtual model of the internal mesh structure, which had been printed at high saturation. Originality/value - The internal structure of a 3D printed part has been successfully analyzed by in-process monitoring providing information and data not available through conventional analysis of the final part. This system provides a solution for real-time non-destructive analysis, which is currently absent in various forms of AM.