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A key characteristic of powder bed fusion for polymers is that also the non-processed powder in the powder bed is exposed to elevated temperatures. This alters the properties of the remaining powder, which is compensated by refreshing the used powder with new powder. Nonetheless, it is discarded after a certain number of process iterations, which is economically and ecologically highly disadvantageous. Research works intensively to analyse and reduce the concurring effects responsible for powder ageing. This study aims to give a comprehensive overview of the cumulative changes in the powder and the printed parts when conducting several subsequent build cycles.

New polyamide powder (PA12) was used in a total of nine subsequent build cycles with constant sintering parameters and without powder refreshing. After each iteration, the powder and parts were tested for their morphological, thermal and rheological properties.

The results are related to three main changes in the powder during the build cycles: decreasing bulk density (through agglomeration), increasing melt viscosity (through polyamide post-condensation) and increasing melting peak and onset temperatures (through thermal annealing of the powder).

Even though the ageing of PA12 powder in powder bed fusion is well-known, it is not yet fully understood. Studies are not complete and due to different ageing conditions only partially comparable. The detailed study aims to help understand the related effects of powder ageing for process-relevant properties and to show which factors require control to limit the powder ageing.

The overall aim of this research work was the improvement of the failure behavior of printed circuit boards (PCBs). In order to describe the mechanical behavior of PCBs under cyclic thermal loads, thin copper layers were characterized. The mechanical properties of these copper layers were determined in cyclic four-point bend tests and in cyclic tensile-compression tests, as their behavior under changing tensile and compression loads needed to be evaluated.

Specimens for the four-point bend tests were manufactured by bonding 18-μm-thick copper layers on both sides of 10-mm-thick silicone plates. The silicone was characterized in tensile, shear and blow-up tests to provide input data for a hyperelastic material model. Specimens for the cyclic tensile-compression tests were produced in a compression molding process. Four layers of glass fiber-reinforced epoxy resin (thickness 90 μm) and five layers of copper (thickness 60 μm) were applied.

The results showed that, due to the hyperelastic material behavior of silicone, the four-point bend tests were applicable only for small strains, while the cyclic tensile-compression tests could successfully be applied to characterize thin copper foils in tensile and compression up to 1 percent strain.

Thin copper layers (foils) could be characterized successfully under cyclic tensile and compression loads.