3D printing of clay paste enhanced by scrap polymer from powder bed processes

Abstract

Purpose Powder bed additive manufacturing processes are widespread due to their many technical and economic advantages. Nevertheless, the disposal of leftover powder poses a problem in terms of process sustainability. The purpose of this paper is to provide an alternative solution to recycle waste PA12 powder from HP multi jet fusion. In particular, the opportunity to use this material as a dispersion in three-dimensional (3D) printed clay is investigated. Design/methodology/approach A commercial fused deposition modelling printer was re-adapted to extrude a viscous paste composed of clay, PA12 and water. Once printed, parts were dried and then put in an oven to melt the polymer fraction. Four compositions with different PA12 concentration were studied. First, the extrudability of the paste was observed by testing different extrusion lengths. Then, the surface porosities were evaluated through microscopical observations of the manufactured parts. Finally, benchmarks with different geometries were digitalised via 3D scanning to analyse the dimensional alterations arising at each stage of the process. Findings Overall, the feasibility of the process is demonstrated. Extrusion tests revealed that the composition of the paste has a minor influence on the volumetric flow rate, exhibiting a better consistency in the case of long extrusions. The percentage of surface cavities was proportional to the polymer fraction contained in the mix. From dimensional analyses, it was possible to conclude that PA12 reduced the degree of shrinkage during the drying phase, while it increased dimensional alterations occurring in the melting phase. The results showed that the dimensional error measured on the z-axis was always higher than that of the XY plane. Practical implications The method proposed in this paper provides an alternative approach to reuse leftover powders from powder bed fusion processes via another additive manufacturing process. This offers an affordable and open-source solution to companies dealing with polymer powder bed fusion, allowing them to reduce their environmental impacts while expanding their production. Originality/value The paper presents an innovative additive manufacturing solution for powder reuse. Unlike the recycling methods in the body of literature, this solution does not require any intermediate transformation process, such as filament fabrication. Also, the cold material deposition enables the adoption of very inexpensive extrusion equipment. This preliminary study demonstrates the feasibility and the benefits of this process, paving the way for numerous future studies.

Dimensional accuracy and impact resistance of 3D printed clay reinforced with scrap polymer powder

“…By looking at the parts after the printing process (Figure 9), a severe slumping can be clearly observed on those with higher PA12 content. This result is consistent with findings by Mele et al , 2021) and supports the idea that most of the dimensional error occurring during printing is due to the collapse of the part under its own weight (Chan et al , 2020). This is more evident when increasing the percentage of PA12 because, being the water content constant, the amount of solid clay decreases.…”

“…The printing processes were carried out using the equipment presented in Mele et al (2021). The frame of a Replicator 2X FFF machine was used.…”

“…After printing, specimens were dried and heat treated as described in Section 2.3 and Mele et al ,(2021).…”

“…This method does not allow for understanding the actual dimensional stability of the deposited line. Also, the authors highlighted the need for further studies on geometrical accuracy when scaling up the benchmarks (Mele et al , 2021). Finally, no information on the mechanical properties of the manufactured parts was given.…”

“…A different method for recycling scrap PA12 powders through clay material extrusion additive manufacturing (MEAM) has been recently proposed (Mele et al , 2021). The AM of clay is an increasingly important area of research due to the appealing properties of these materials (Xing et al , 2021; Wolf et al , 2022).…”