Shear viscosity measurements on Polyamide-12 polymers for laser sintering
journal contributionposted on 30.04.2015 by Barry Haworth, Neil Hopkinson, David J. Hitt, Xiaotao Zhong
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Purpose – Laser sintering kinetics and part reliability are critically dependent on the melt viscosity of materials, including polyamide 12 (PA-12). The purpose of this paper is to characterise the viscosity of PA-12 powders using alternative scientific methods: constrained boundary flows (capillary rheometry) and rotational rheometry. Design/methodology/approach – Various PA-12 powders were selected and characterised by both techniques. Measurement of molecular weight was also carried out to interpret the viscosity data. Findings – Results demonstrate conventional pseudoplastic flow in all PA-12 materials. Zero-shear viscosity has been quantified by rotational rheometry; a notable observation is the striking difference between virgin/used PA-12. This is interpreted in terms of molecular weight and chain structure modifications, arising from polycondensation of PA-12 held at the bed temperature during laser sintering. Research limitations/implications – Accurate zero-shear viscosity data provide scope for use in predictive computational models for laser sintering processes. Careful sample preparation and equipment operation are critical prerequisites for accurate rheological characterisation of PA-12 powders. Practical implications – Differences in flow behaviour and molecular structure allow prediction and deeper understanding of process-property relationships in laser sintering, giving potential for further optimisation of material specification and in-process machine parameter control. Originality/value – This is believed to be the first time that techniques other than melt flow rate (MFR) have been reported to measure the viscosity of PA-12 in a laser sintering context, noting the effects of pre-drying and molecular weight, then predicting differences between virgin/used powders in practical sintering behaviour.
The authors would like to acknowledge the research funding from the Engineering and Physical Sciences Research Council (EPSRC) of Great Britain, via the Innovative Manufacturing and Construction Research Centre (IMCRC) at Loughborough University. Other contributions, notably those from the research partners/industrial sponsors (EOS Gmbh, Burton Snowboards), Anurag Pandey at Loughborough University (rotational rheometry) and Smithers-Rapra (GPC analysis) are also acknowledged with thanks.
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