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In an attempt to expand the range of engineering polymers used for laser sintering, this paper examines the morphology, flowability and interparticle interactions of two commercially available poly (ether ether) ketone (PEEK) powders, not yet optimised for the LS process, by comparison with the LS optimised Polyamide (PA) and Polyetherketone (PEK) powdered polymers . The effect of incorporating fillers and additives on the flow behaviour is also analysed. The Particle Size Distribution (PSD) results alone do not allow ranking the powder materials in relation to the flow behaviour. The particle morphology has a stronger influence on the flow characteristics for materials with similar PSDs. The work also provides additional characterization parameters to be considered when analysing LS powders. Graphical abstract

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Powders used in additive manufacturing (AM) are spread into a compact layer of particles for sintering and this process is repeated layer by layer to form the final products. Spreading of rod-shaped particles in realistic AM settings is simulated using the discrete element method (DEM) to investigate the effects of particle shape and operating conditions on the bed quality, characterised by its surface roughness and solid volume fraction. It is discovered that larger particle aspect ratios, Ar, or higher spreader translational velocities result in a lower bed quality, i.e. a larger surface roughness and a smaller volume fraction. The surface roughness increases monotonically with Ar. However, the volume fraction exhibits a maximum at Ar = 1.5 for randomly packed powder beds that are formed by the roller type spreaders moving at low translational velocities. It is also found that a roller outperforms a blade spreader in terms of the quality of the prepared bed at the same operating conditions. The micro-structural analysis of the beds also shows particle alignment in response to the induced flow, which is qualitatively confirmed by a set of purposely-designed experiments. In addition, a shape segregation is documented for powders with mixed aspect ratios (Ar) such that particles with larger Ar tend to accumulate on the upper layers of the bed

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Currently, the HT-LS sector is predominantly based around one commercial poly ether ketone (PEK) polymer. Although the combination of polymer and process works well, a lower melting temperature polymeric material, part of the same Poly Aryl Ether Ketone (PAEK) family would be preferable in certain applications. This study presents the optimisation and characterisation of Poly Ether Ether Ketone (PEEK), a polymer which is part of the PAEK family with a 30 ˚C lower melting temperature than PEK. The systematic characterisation of laser sintered samples of PEEK revealed a very good overall performance in comparison with the HP3 PEK material, with no change in storage modulus and only 25 % drop in tensile strength. The possibility of variable building configurations available within the HT-LS system, i.e. reduced, half and full chamber building modes, is examined in relation to the mechanical performances of the components. The effect of the post sintering time, an additional heating phase supplied to the powder bed at every layer, found only in the HT-LS system EOSINT P 800, is also examined.

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This paper presents a systematic study of the helical auxetic yarn (HAY) via careful in-house fabrication and characterisation of a wide range of polymeric fibres and yarns. It provides a better understanding of the auxetic behavior of the HAY in order to tailor their properties for specific applications. The study focused on three parameters: component moduli, the core/wrap diameter ratio and the initial wrap angle. The results show that a larger difference in component moduli, a higher core/wrap diameter ratio and a lower initial wrap angle can produce a larger maximum negative Poisson's ratio value and thereby a better auxetic performance for HAYs. All three parameters could be carefully utilised when in combination to achieve the required auxetic behaviour of HAYs. Moreover, the instantaneous true Poisson's ratio analysis accurately presents the instantaneous behaviour of highly strain dependent HAYs.