Journal
RAPID PROTOTYPING JOURNAL
Volume 19, Issue 1, Pages 28-36Publisher
EMERALD GROUP PUBLISHING LIMITED
DOI: 10.1108/13552541311292709
Keywords
Viscosity; Sintering; Polymers; Laser sintering; Nylon-12; Rheology; Polycondensation; Molecular weight
Funding
- Engineering and Physical Sciences Research Council (EPSRC) of Great Britain, via the Innovative Manufacturing and Construction Research Centre (IMCRC) at Loughborough University
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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.
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