Post processing for nylon 12 laser sintered components

Abstract

This research investigates the effect of post-processing on the mechanical characteristics and behaviour of laser sintered components produced by selective laser sintering (SLS). It aims to understand the material’s behaviour and to develop postprocessing methods that can be used to improve and maintain consistency in the mechanical properties of the layer manufactured material. Duraform Polyamide (Nylon 12) and a Sinterstation VanguardTM SLS machine were used to produce test specimens. The behaviour of the layer material characteristics was established using different fabrication orientations and tensile, compression, shear and flexure tests as benchmarking investigations. The results show that there are significant variations in mechanical properties, as well as divergences from previous results. In addition, section thickness in closed and open hollow structures was investigated in order to establish its effect on mechanical properties. The larger a sintered area, the greater the tensile properties gained when there is an increase of section thickness and when solid specimens are used. Moreover, when fill and outline scanning strategies were implemented in producing the specimens, the improvements were obtained in the tensile properties of nylon 12 laser-sintered material with no impact on geometry. To further improve the mechanical properties, a new post processing method that included heat treatment in air and vacuum environments was investigated. Experiments were conducted in air from room temperature to 140oC with a treatment time of 120 minutes and vacuum heat treatment was conducted from room temperature to 180oC with 16 hours and 100 hours treatment time. The material properties in both conditions were then analysed in terms of tensile properties, thermal characterisations, microstructure and geometrical changes. Heat treatment in air showed no significant improvement in mechanical properties. However, Nylon 12 SLS material heat-treated in a vacuum showed considerable improvement in crystallinity and peak melting point. Heat treatment for a longer period to approach the melting point, especially on material with the different section thicknesses and solid specimens and particularly in a vacuum, has a greater impact on mechanical properties, but this may not be sufficient to justify the cost and time involved.