Semi-crystalline polymers offer great mechanical properties and are ubiquitously found in everyday life. Despite of this, they are not yet widespread among additive manufacturing processes, due to their high tendency to warp. This leads to unstable build processes and dimensionally inaccurate parts, which greatly reduces their usability. This paper describes the findings of an experimental study designed to identify relevant parameters that affect the warpage and investigate the influence of the manufacturing method on the mechanical properties of semi-crystalline PA6.
The first experiment investigates the effect of water absorption over time, measuring weight and curling of 64 specimens over three weeks. The second part of this study focuses on the changes in geometry caused by the warpage by evaluating a basic model for simple part geometries. At last, a tension test was conducted and the results were compared to injection molded parts of the same material.
The results indicate, that while the absorption of water plays an important role in the warpage of hydrophilic polymers like PA6, other environmental factors also have a significant influence. The model evaluation showed, that the warpage geometry of the tested parts can be approximated with only three parameters for very simple parts, if there are no irregularities in the manufacturing process. The tensile tests revealed, that the additively manufactured specimens reach up to 85.9% of the strength of the injection molded reference parts, most likely due to imperfect filling and reduced density.
Overall, this study provides an insight into the challenges of additively manufacturing semi-crystalline polymers and the potential of PA6 as a tougher alternative to the common materials.