Experimental study on the warpage and tensile strength of additively manufactured semi-crystalline polyamide 6

Semi-crystalline polymers offer great mechanical propertiesand are ubiquitously found in everyday life. Despite of this, theyare not yet widespread among additive manufacturing processes,due to their high tendency to warp. This leads to unstable buildprocesses and dimensionally inaccurate parts, which greatlyreduces their usability. This paper describes the findings of anexperimental study designed to identify relevant parameters thataffect the warpage and investigate the influence of themanufacturing method on the mechanical properties of semicrystalline PA6.The first experiment investigates the effect of waterabsorption over time, measuring weight and curling of 64specimens over three weeks. The second part of this study focuseson the changes in geometry caused by the warpage by evaluatinga basic model for simple part geometries. At last, a tension testwas conducted and the results were compared to injectionmolded parts of the same material.The results indicate, that while the absorption of water playsan important role in the warpage of hydrophilic polymers likePA6, other environmental factors also have a significantinfluence. The model evaluation showed, that the warpagegeometry of the tested parts can be approximated with only threeparameters for very simple parts, if there are no irregularities inthe manufacturing process. The tensile tests revealed, that theadditively manufactured specimens reach up to 85.9 % of thestrength of the injection molded reference parts, most likely dueto imperfect filling and reduced density.Overall, this study provides an insight into the challenges ofadditively manufacturing semi-crystalline polymers and thepotential of PA6 as a tougher alternative to the commonmaterials.