Temperature induced ageing of PA12 powder during selective laser sintering process

Abstract

The selective laser sintering process has the potential to permanently overcome the boundary between model construction and functional components. The basic prerequisite for this is that components with reproducible quality can be manufactured. For this purpose, the virgin material must already be of the same quality. During the process, the laser sintered powder is heated to temperatures just below the melting temperature and held until the end of the building process. This results in thermal aging of the powder. Powder, which is not sintered, gets refreshed after the production process with new powder and can be reused. Due to the repeated refreshing process of the aged powder, a mixture is produced whose quality is difficult to define. By means of rheometry and differential scanning calorimetry (DSC), both new powder and powder, which was taken from a laser sintering process, are characterized. At the same time, the thermal aging is simulated by means of an oven heat. The rheological investigations show that the storage results in an increase of the viscosity, both in the process and in the oven. The reason is a post-condensation and thus the extension of the molecular chains. In addition, extended molecular chains lead to a faster reaching of the sol-gel transition and thus to a change from viscous to elastic material behavior. The post-condensation also leads to an increase in the melting temperature, which can be detected by means of DSC. The aging of the laser sinter powder can be reproduced by means of the oven storage and permits further investigations to ensure the quality of the virgin material.