Lessons learned in the design of reference fiducials for layer-wise analysis of test coupons made by laser powder bed fusion

The ability to align ex-situ inspection data of an additively manufactured (AM) part to its build geometry can be helpful, for example, to correlate observed in-situ monitoring events or features to measured discontinuities, such as pores and cracks, in ex-situ inspection. In some cases, the original part design does not lend itself to such an alignment due to the absence of datum surfaces. In this study, the concept of incorporating inclined, cylindrical protrusions as reference fiducials in the design of cylindrical AM test coupons is investigated. Six coupons with proposed fiducials were built and inspected using X-ray computed tomography (CT). Dimensional measurements performed on the fiducials expose shortcomings in the proposed fiducial design—mainly a result of limited dimensional fidelity of small features by AM—and allow us to make suggestions on how the design can be improved. Nevertheless, an alignment scheme based on the reference fiducials is compared with an approach based on inherent coupon surfaces on layer-wise porosity measurements by X-ray CT on one of the test coupons.