Recycling of polyamide 12 based powders in the laser sintering process

Purpose - The purpose of this paper is to investigate the polyamide 12 (PA12) powder properties deterioration in the laser sintering (LS) process and propose a methodology for more efficient powder recycling. The main goals are: to recommend a level of input PA2200 powder properties which could guarantee acceptable part quality in the LS process; and selection of the refresh rate in order to minimise the consumption of fresh material. Design/methodology/approach - The paper analyses the LS processing conditions and current recycling practices in relation to the deterioration or ageing of the PA12-based powders. Samples of new and recycled grades of PA2200 powder were artificially aged in a temperature-control led oven and then tested using melt flow rate (MFR) indexer. Also, un-sintered powder samples collected from different locations within various builds, and different LS machines (EOSINT P700 and Sinterstation (R) 2500 HiQ) were tested. Findings - The powder exposed at higher temperature and longer time experiences a much higher deterioration rate. The temperature and the time at which the un-sintered material was exposed are the most influential parameters for the powder aging. It was confirmed that the MFR index is a very sensitive indicator of the changes in the powder properties and provides a relatively fast and inexpensive method of measuring the rate of the powder degradation because of the LS process. The powder located in the periphery and the top of a build has a higher MFR and therefore is less deteriorated. In contrast, powder located in the centre, or in the bottom of a long build has much lower MFR and therefore is less usable. Practical implications - Based on the findings, a methodology for powder recycling is proposed. It allows a better control of the input material properties, a consistent quality of the fabricated parts, and more efficient use of the LS material. Originality/value - The paper provides some useful information for the properties deterioration of PA12-based powders (PA2200) in relation to the temperature and time at which the material is exposed in the LS.