Crystallization behavior under process conditions in Powder Bed Fusion of polymers

Abstract

With respect to materials, the powder bed fusion process is largely accompanied by semi-crystalline thermoplastics, with polyamide 12 most predominately used. Not yet experimented is the influence of the newly applied powder - capable of up to 40 K lower temperatures than the building bed - on the melt pool, and its effect on crystallization. Crystallization-induced stresses directly after powder application leads to the break-off criterion curling or later warpage; furthermore, mechanical limitations are expected due to rapid crystallization. The influence of the applied powder and the repeated exposure of overlying layers on the crystallization kinetics is simulated by flash DSC measurements, demonstrating that the undercooling has a significant influence on crystallization time. However, if the exposure of the overlying layers, and therefore increased temperature is considered, an enhanced crystallization time is observed. These results contribute to the understanding of crystallization behavior in the process, and verify published heat simulation.