Direct part density inspection in laser powder bed fusion using eddy current testing

Abstract

The direct qualification of additively manufactured (AM) metal components fabricated by laser powder bed fusion (LPBF), or the certification of the corresponding AM processes, remains a challenge due to the many influencing parameters, and process-inherent variability. Hence, components lack consistent quality regarding dimensional accuracy, surface quality, and material integrity, since internal defects such as pores and cracks are typical characteristics of such components. Different sensing technologies such as melt-pool monitoring are considered for in-process material integrity assessment, and for process control. However, although melt-pool monitoring provides process related information on the laser-material interaction such as melt-pool temperature and size, it does only indirectly provide sufficient information on the quality and integrity of the layer-wise generated material. Eddy current testing (ECT) is a well-established NDT technique for part quality inspection in many industries, and specifically suited to detect near-surface material defects such as e.g. cracks. This characteristic makes ECT a promising monitoring technology for the layer-wise monitoring of material quality in AM processes. Its integration into a LPBF-machine allows to generate direct material integrity data while the layer-wise acquisition offers potentials to monitor the individual part quality over a full build process, minimizing thereby post-process quality assessment measures. The basic feasibility of an ECT system to directly measure part density demonstrated, using LPBF processed SS316L samples with different densities.