Abstract
Thermal tomography is a computational method for heat diffusion-based imaging of solids, which provides 3D visualization of data from flash thermography measurements. We investigate thermal tomography imaging and nondestructive evaluation of stainless steel and nickel super alloy metallic structures produced with the laser powder bed fusion (LPBF) additive manufacturing (AM) process. Metallic structures produced with LPBF contain defects, and there are limited capabilities to evaluate these structures non-destructively. Thermal tomography reconstruction of 3D apparent spatial effusivity provides information about AM structure geometry and internal material flaws. We study performance of thermal tomography in imaging of metallic structures through COMSOL computer simulations of transient heat transfer and through reconstruction of data obtained from experimental measurements. Thermal tomography reconstructions of structure shape and dimensions are shown for the Inconel 718 AM structure which has variations in the horizontal plane but is uniform along the depth dimension. Reconstruction of internal defects is investigated using a stainless steel 316L specimen with flat bottom hole (FBH) indentations, and the Inconel 718 plate is produced with the LPBF method, which contains imprinted hemispherical shape low density regions containing non-sintered metallic powder. The FBHs have the same sizes as the imprinted defects in the LPBF specimens but offer better imaging contrast. Thermal tomography reconstructions provide visualizations of internal defects and allow for estimation of their sizes and locations. Results of this study demonstrate that thermal tomography can be used for visualization and quality control in AM.
Highlights
Thermal tomography is a computational method for heat diffusion-based imaging of solids, which provides 3D visualization of imaging data from flash thermography measurements
We investigate thermal tomography imaging and nondestructive evaluation of stainless steel and nickel super alloy metallic structures produced with the laser powder bed fusion (LPBF) additive manufacturing (AM) process
We have investigated 3D imaging of AM metallic structures using the thermal tomography method
Summary
Scitation.org/journal/adv this study is development of a 3D imaging method for nondestructive evaluation (NDE) of additively manufactured (AM) metallic structures and validation of structure shape. Thermal tomography imaging potentially provides a number of advantages for NDE of AM structures in real-time and post-manufacturing because the method is non-contact, one sided, and scalable to arbitrary size structures.. Thermal tomography imaging potentially provides a number of advantages for NDE of AM structures in real-time and post-manufacturing because the method is non-contact, one sided, and scalable to arbitrary size structures.. In postmanufacturing NDE, x-ray computed tomography can be used for high-resolution imaging of small coupons shaped in a body-ofrevolution symmetry form (spheres or cylinders).. In postmanufacturing NDE, x-ray computed tomography can be used for high-resolution imaging of small coupons shaped in a body-ofrevolution symmetry form (spheres or cylinders).21 This provides sampled information about the quality of the AM process but not about the actual structure. Thermal tomography 3D reconstructions are obtained for flash thermography experimental data for an AM IN718 structure, which has variations in the horizontal x-y plane but is constant along the vertical z-axis. A similar approach can be used for real-time monitoring of the AM process
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