Laser Sintering (LS) is an additive manufacturing technology that is progressively used to manufacture functional products for end-use applications. However, LS technology provides limited ability to produce thin-walled structures that feature high material quality. A key parameter determining the quality of LS polymeric parts is porosity. This article presents a new approach towards clarifying the porosity characteristics of thin-walled structures produced by LS. Therefore, thin sheets of different thickness built in different orientations within the building chamber are examined by means of X-ray micro tomography. The porosity analysis includes the overall porosity, pore number density, pore size distribution and porosity distribution along the thickness of the thin sheets. The results show that the porosity characteristics strongly depend on the thickness and the build orientation of the thin sheets. This investigation helps to estimate the quality of three dimensional hollow bodies produced by LS and moreover, contributes to a better understanding of the pore formation in LS processes.

No abstract

Purpose This study aims to investigate the effect of the material thickness and build orientation on the mass transfer of low molecular weight substances through polyamide 12 (PA12) structures produced by laser sintering (LS). Design/methodology/approach Disc-shaped PA12 sheets having a nominal thickness ranging from 700 to 2,000 µm were built in horizontal, vertical and diagonal orientations and their permeation properties to oxygen and water vapor were measured. The structural properties of the sheets were examined by X-ray micro-computed tomography, differential scanning calorimetry and polarized light microscopy. Findings All the LS sheets that were investigated had water vapor and oxygen permeation coefficients that are in the range of those of PA12 produced by traditional manufacturing technologies. Despite significant differences in the porosity characteristics, the permeation properties of sheets built in different orientations were similar. The pores seem to have no measurable effect on the mass transfer rates in the sheets, and the transport processes seem to predominantly follow the rules of a regular solution-diffusion mechanism. The results showed a non-significant trend toward thickness-dependent permeation coefficients, which agrees with the observed differences in the crystal structures of the sheets. Practical implications The results are an important basis for the qualification of LS technology for direct manufacturing in applications requiring special barrier performance. Originality/value This study provides new information on mechanisms of mass transport through LS PA12 and the effect of the material thickness and build orientation. Furthermore, the results enhance understanding of the structural properties of thin polymeric sheets produced by LS.