Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707103
Title: Assessment of TPUs for use in the laser sintering process
Author: Geca, Piotr
ISNI:       0000 0004 6060 6901
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2016
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Abstract:
Additive Manufacturing (AM) technologies and especially the Laser Sintering (LS) systems have made an enormous impact on the manufacturing market in the last decade and their adoption continues to grow. Currently, the market of sinterable polymer powders is heavily dominated by polyamides (PAs), which fail to address all the possible LS application niches. Thermoplastic Elastomers (TPEs) and more specifically Thermoplastic Polyurethanes (TPUs) have the potential of broadening LS applications, by offering alternative, rubber-like properties to manufactured parts. Laser Sintering is a highly demanding process in regards to materials' thermal properties, as well as bulk properties of its powder form. In the first part of project we assessed TPU powder's compatibility with the Formiga P100 LS system. We found that the greatest obstacle to powder's safe use was its poor ability to flow and the resulting incompatibility with the powder deposition system. Improvement of flow properties was attempted by use of annealing process as well as addition of flow agent (FA). We found neither solution to produce satisfactory bulk properties, but we note that higher levels of FA are likely to increase the additive's effectiveness. In the second part of the project we assessed the performance of twelve diverse batches of TPU, to form a better understanding of factors influencing the mechanical performance of sintered parts. Based on a new paradigm, the sintering process was split into issues of particle coalescence and densification. We found that the particle size and melt viscosity had a strong effect on the strength of interparticle bonds formed in a limited sintering time. When long sintering time was simulated by oven-sintering, we found that parts' density was chiefly determined by powders' ability to cross over into closed-pore densification stage. Powders with Specific Surface Area of 90m²/kg and less were unable to densify and formed a stable open-pore structure instead. Avoiding this threshold condition is the first priority in designing future powder batches.
Supervisor: Majewski, Candice ; Frederik, Claeyssens Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.707103  DOI: Not available
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