Experimental setup for in situ visualization studies of laser sintering of polymer particles

Products manufactured by Selective Laser Sintering suffer from low mechanical stability and reproducibility [1]. This is mainly caused by an incomplete sintering of the polymer particles, resulting in significant remaining porosity after sintering, as well as limited interlayer adhesion. Hence, more insight in the effects of the different processing conditions and material characteristics on the final product morphology is required. Therefore it is important to understand the sintering of the particles during the process and to utilize this knowledge in material processing. The sintering of two polymer particles has been studied in literature by hot stage microscopy [2], but this technique does not simulate the conditions in an SLS machine. Therefore a dedicated experimental setup, which incorporates the main features of a 3D SLS printing device and at the same time allows in-situ visualization of the sintering dynamics by means of optical microscopy and/or X-rays is developed. A visible light laser is used to achieve good spatial resolution and control over the supplied energy. Energy absorption of the polymers containing colored dye was quantified by means of UV-VIS spectroscopy. Initial thermal characterization by DSC and TGA enabled us to define the stable sintering region for the particles. Subsequently, experiments were conducted using pairs of polymer particles inside a temperature controlled chamber. The polymer particles were subjected to a known amount of laser energy with the ultimate objective to study the sintering dynamics, which is a crucial stage in SLS. The dynamics of the growth of the neck between both particles is compared to available models for sintering kinetics of molten polymers. References: [1] Zarringhalam, Hadi, et al. Materials Science and Engineering: A 435 (2006): 172-180. [2] Berretta et al. Journal of Material Science: 51.10 (2016): 4778 - 4794. S19-23