In brief

Uncertainty analysis reveals the quality of porosity measurements for additive manufacturing.

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Solid approaches to fault finding

29 Sep 2023

New equations and methodology enable the uncertainty of porosity measurements to be evaluated in additively manufactured metals for safer, high-quality components.

Sometimes the empty spaces in a material are just as important as the material itself. Take the porous network inside human bones, for example. These pockets decrease the overall weight of bones while keeping them strong and resilient to impact.

Similarly, the porosity of metal components made using additive manufacturing (AM) influences their overall physical properties. The AM process can sometimes introduce unwanted defects such as tiny cavities hidden inside the metal, termed porosity.

“These imperfections can compromise the structural integrity of AM components, leading to failure,” said Joseph John Lifton, Technical Lead in the Intelligent Product Verification Group at A*STAR’s Advanced Remanufacturing and Technology Centre (ARTC).

Yet, accurately gauging porosity in metals fabricated using AM remains a challenge in industry. A technique like optical microscopy, while providing high-resolution images, only offers limited information because test samples have to be ground and polished layer-by-layer, which can cause important defects to be missed entirely. Furthermore, because optical microscopy is destructive, the approach cannot be used for final product verification.

“X-ray computed tomography provides non-destructive, 3D insights into the porosity of a component, but struggles with scanning large AM components made from dense metals,” said Lifton, adding that with further R&D effort, the technique can become the new gold standard for ensuring that AM components are safe and defect-free.

Lifton and his team used the Archimedes’ principle, a method widely used in industry to calculate a component’s density by first weighing it in air and then in a liquid. Comparing these values to the density of the bulk material allows manufacturers to accurately detect the presence of any porosity.

The team developed equations to calculate the uncertainty of the porosity measurements, where measurement uncertainty is the doubt associated with a measurement result. No measurement result is complete unless accompanied by a statement of uncertainty. The work enables AM researchers and manufacturers to understand the quality of their porosity measurements, and thus make informed engineering decisions on the safety and performance of AM components.

Lifton and his team have been awarded funding by the National Additive Manufacturing Innovation Cluster to advance their work on standardising porosity measurement using X-ray computed tomography. In addition to their work on porosity measurement “We are also developing methods to measure and characterise the internal surface roughness of AM samples, with a particular focus on internal channels and lattice structures,” concluded Lifton.

The A*STAR-affiliated researchers contributing to this research are from the Advanced Remanufacturing and Technology Centre (ARTC).

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Lifton, J.J., Tan, Z.J., Goh, B. and Mutiargo, B. On the uncertainty of porosity measurements of additively manufactured metal parts. Measurement 188, 110616 (2022).│article

About the Researcher

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Joseph John Lifton

Technical Lead, Intelligent Product Verification Group

Advanced Remanufacturing and Technology Centre (ARTC)
Joseph John Lifton is a Technical Lead in the Intelligent Product Verification Group at the Advanced Remanufacturing and Technology Centre (ARTC), focusing on advanced metrology for manufacturing. Lifton’s doctoral research from the University of Southampton centred on X-ray computed tomography (XCT) for dimensional metrology. He lectured on the topic at the University of Southampton and secured funding to advance XCT research through the AdvanCT project funded by EURAMET. As a Research Fellow at the Singapore Institute of Manufacturing Technology from 2017 to 2019, Lifton worked on XCT-based porosity measurements for aerospace ceramics. Since 2019, Lifton has led ARTC's XCT quality assurance work for metal additive manufacturing, funded by Singapore's Industry Alignment Fund, and has been awarded funding from the National Additive Manufacturing Innovation Cluster for standardising XCT-based porosity measurement in metal additive manufacturing in collaboration with ASTM.

This article was made for A*STAR Research by Wildtype Media Group