Thermal characterization of laser sintering of nylon-12

Precise thermal control of laser sintering is desirable for improving geometric accuracy, mechanical properties, and surface finish of polyamide (nylon) parts. A modeling and measurement system was set up to monitor thermal aspects of laser sintering of nylon-12 processing with a view to develop thermal control strategies to improve these characteristics. A critical component of understanding the thermal processes in laser sintering is to know the thermal properties of the materials being processed. Measurements were made of the thermal conductivity and heat capacity of nylon-12 powder using a transient plane-source method with HotDisk (TM) equipment. Thermal properties are reported over the range 30 degrees C-170 degrees C in a dry N-2 environment similar to the build chamber of a laser sintering machine. The powder was packed in the sample holder at a tap density of 0.547 g/cc (54.2% relative density). Thermal conductivity was found to vary with temperature in the range 0.1-0.114 W/m-K. This data was used in a computational model to understand the powder warmup process with respect to the thermal transport processes between the part, the part bed, and the build chamber. This research was funded by the Air Force Research Laboratory under Grant Number GRT00015778.