Increasing density and mechanical performance of binder jetting processing through bimodal particle size distribution 

Abstract

Binder jetting is an additive manufacturing (AM) technology that has gained popularity and attention in recent years for production applications in tooling, biomedical, energy, and defense sectors. When compared to other powder bed fusion-based AM methods, binder jetting processes powder feedstock without the need of an energy source during printing. This avoids defects associated with melting, residual stresses, and rapid solidification within the parts. However, one of the challenges of this process is the relatively lower densities which impacts part density, and subsequently, sintering and mechanical properties. In this study, we investigated the influence of bimodal powder size distributions (a mixture of coarse to fine particles) as a method for increasing part density and mechanical strength, and used stainless steel (SS) 316L bimodal mixtures in this case. Four unimodal and two bimodal groups were evaluated under similar AM processing conditions for sintered density measurements and flexural strengths. Our results demonstrated that bimodal size distributions showed a statistically significant increase in density by 20% and ultimate flexural strength by 170% when compared to the highest performing unimodal group. In addition to experimental findings, reactive molecular dynamics simulations showed that the presence of finer powders along with coarser particles in the bimodal particle mixture contribute to additional bonds that are stronger across the particle interfaces. Findings from this study can be used to design bimodal particle size distributions to achieve higher density and better mechanical properties in binder jetting AM process.

3D/4D printed bio-piezoelectric smart scaffolds for next-generation bone tissue engineering

“…Therefore, BJ technology has demonstrated significant advantages in forming bio-piezoelectric scaffolds, especially for ceramic materials. Recently, Clares et al [107] proposed a bimodal particle size distribution strategy that can significantly enhance the density and mechanical properties of BJ-printed objects, providing an effective solution for creating highperformance bio-piezoelectric scaffolds using the BJ technique. However, there are still several restrictions on piezoelectric scaffold manufacturing by BJ: (i) the post-treatment (sintering or infiltration) is typically required to improve densification, (ii) the printed objects show a high surface roughness and low printing resolution.…”