Tomosynthesis for large additive manufacturing parts

Abstract

X-ray computed tomography (XCT) is up to now the golden method for non-destructive quality inspection of additively manufacturing (AM) parts. Indeed, the method gets rid of the complexity of shape and high surface roughness typical of AM parts. However, when one side of the part is too thick, which happens frequently with parts manufactured with a direct energy deposition (DED) process implementing a metallic wire and an arc (DEDArc), XCT reaches its limits. Moreover, XCT is a high cost and time-consuming method, thus alternative quality assurance methods are required. Tomosynthesis appears to be an interesting alternative solution while the method does not require the X-rays to cross the thicker section of the part to be inspected. In tomosynthesis, the projections are not acquired over 360°, but over less than 180°, so it is possible to ensure that the X-ray source remains on the thinner side of the part to acquire the projections. Then, instead of proceeding to the reconstruction of a three-dimensional (3D) image, the projections are assembled and registered by a deblurring algorithm to provide a stack of 2D images on which a software enables to adjust the focus on each 2D image to analyse the part 2D image by 2D image in depth. In this paper, a comparison of X-ray radiography (RT), XCT and tomosynthesis images reveals the potential of tomosynthesis on a steel DED-Arc flat wall-shaped specimen. The comparison validates the tomosynthesis images on a part whose thickness still enables XCT to be performed, to demonstrate the potential of tomosynthesis when XCT reaches its limits.