Deterioration of polyamide powder properties in the laser sintering process

Polyamide 12 (PA12)-based powders are the most used materials in the laser sintering (LS) process for rapid manufacturing of functional parts. An average of 80-90 per cent of the powdered material in the LS building chamber is not sintered and could be reused. However, the properties of the recycled powder vary, which ultimately affects the quality of produced parts. These differences are due to the process conditions such as temperature and time, the LS machine design, and properties of the powder used for parts fabrication. This paper analyses the LS processing conditions and current recycling practices in relation with the deterioration or ageing of the PA12-based powders. Samples of new and recycled grades of PA2200 powder were artificially aged in a temperature-controlled oven and then tested using differential scanning calorimetry, melt flowrate indexer, and gel permeation chromatography. It has been found that the temperature and the time at which the unsintered powder was exposed are the most influential factors for the deterioration of LS powder properties.