EFFECT OF PROCESS CONDITIONS ON TEMPERATURE DISTRIBUTION IN THE POWDER BED DURING LASER SINTERING OF POLYAMIDE-12

A sintered part's mechanical properties are often variable dependent on the temperature at which it was sintered. Prior research has investigated how predefined process conditions (such as scan speed and laser power) in the Sinter' software affect built parts (Majewski & Hopkinson, 2011), however, little work focuses on other process conditions that can directly affect the temperature distribution in the bed relative to these parts. These conditions are not always controllable in the Sinter' software. By replacing the scanner at the top of the Sinterstation 2000 with a thermal imaging camera, an insight into the temperature distribution on the part bed was obtained. A temperature variance of up to 7 degrees C was found across the bed, as well as a large temperature drop and recovery period on powder layer recoat. This paper explores the possible causes of this variation in the processing of DuraForm (TM) Polyamide-12 powder by monitoring and assessing build operations, enabled by replacing the front viewing window with a retro-fitted thermal imaging camera. The part bed was observed and various process conditions analyzed including powder recoat, part and feed heaters, and swing gate configuration. On powder recoat, the part bed exhibited a drop in temperature because the fresh layer of powder is at a lower temperature than the powder already present in the part bed. The part bed temperature drop lessens with raised feed bed temperatures however there are limitations. Thermal analysis of the part heater proved that the uneven part bed heat distribution was not linked to the temperature gradient of the part heater. Swing gates were found to minimise hot and cold spots but spend a substantial time oscillating on roller passing.