Optimum sintering region for laser sintered nylon-12

Abstract

It is well known that the mechanical properties of laser sintered Nylon-12 improve with increased applied energy. However properties can reach a maximum after which, the application of additional energy can a lead to a decline in part properties. It is thought that the reason for this decline is that the additional energy causes polymer chain degradation or other changes in molecular structure. This paper aims to use thermogravimetric analysis (TGA) to investigate the thermal degradation of nylon-12 and explain the deterioration of mechanical properties when high energy density conditions are applied during processing. The key findings are the application of modelling methods to predict the temperatures achieved during laser sintering of nylon-12. It is shown that temperatures in the laser sintering machine can achieve levels above 300°C. At these temperatures, TGA data show that mass loss occurs and could cause mechanical property breakdown. This practical work coupled differential scanning calorimetry and TGA as a means of identifying thermal transitions in the material. The term ‘stable sintering region’ is proposed as a novel concept for the laser sintering community, and can have implications for better understanding of how process parameters can affect parts built in the machine. In addition, the concept could be used in the material selection process when screening potential new polymers for the process. One limitation of laser sintering, compared to other polymer processes such as injection moulding, is the limited understanding of the connection between machine parameters and part properties. This work aims to improve that understanding by discussing the pattern of thermal behaviour, including degradation, seen in polyamide exposed to high laser parameters.