Effects of processing on microstructure and properties of SLS Nylon 12

There currently exists the requirement to improve reproducibility and mechanical properties of SLS Nylon parts for Rapid Manufacturing (RM). In order to achieve this, further fundamental research is needed and this paper addresses this need by investigating effects of potential sources of the lack of reproducibility (i.e. build procedure/parameters and powder blend) and reports effects in relation to crystal structure, microstructure, chemical structure (molecular weight) and mechanical properties. Different γ crystal forms were identified and related to the un-molten particle cores and the molten/crystallised regions of the microstructure. The melt point of the γ form varied depending on processing conditions. Observable differences were also present when comparing the microstructure of the parts. Molecular weight of parts was significantly higher than virgin powder but used powder (powder already held at elevated temperature) also showed an increase in molecular weight. This was related to improved elongation at break of parts built from the used powder, consistent with previous studies. Tensile strength showed some increase with parameters selected for improved strength but Young’s modulus values were broadly similar.