A longitudinal study of Ti-6Al-4V ELI powder reuse for laser powder bed fusion in a certified medical device manufacturing facility

Powder feedstock is the primary input to metal additive manufacturing processes such as laser powder bed fusion. Its characteristics are crucial for producing high-quality components. Realization of the waste reduction and cost benefits that this technology offers requires reclaiming, processing, and reusing powder feedstock. While these benefits can be significant, there are challenges related to the industrial implementation of powder reuse, including the variability in powder quality that can propagate through to the produced material. This variability can be both negative and positive, but ultimately leads to uncertainty for both users and regulators. This means material and process qualifications are difficult to achieve when powder feedstock is being repeatedly reused. This study reports the effects of 175 Ti-6Al-4V ELI powder reuse cycles, characterized at 23, 104, and 175 reuses, in a certified medical device production facility, whereby powder was topped up with virgin powder from the same production lot after each build cycle. To the best of our knowledge, this is the longest reuse campaign reported in the literature. During this campaign, flowability improved with Hall flow rate decreasing by 5.4% and apparent density increasing by 0.8%. The particle size distribution remained stable, with net changes of no more than 2.1%. Particle elongation decreased by 2.9%, and the form factor distribution narrowed around its unchanged mean. Oxygen concentration progressively increased in both the powder (8.2%) and the produced material (25.1%). The average microhardness increased by 3.7% at all measured indentation depths, which is attributed to this oxygen pickup. All property means remained within the material specification limits for both powder and produced material throughout the reuse campaign. The findings of this study suggest that such extensive reuse campaigns can be implemented while fulfilling the requirements of industry powder material specifications, although such reuse processes do induce variability in the properties of both the powder and produced material. The degree of this variability is specific to the type of powder reuse approach implemented and the specific characteristics of the associated powder processing environments.