Selective Laser Sintering of PA6: Effect of Powder Recoating on Fibre Orientation

• Published in: Journal of composites science Vol. 4; no. 3; p. 108
• Main Authors: Heckner, Tobias, Seitz, Michael, Raisch, Sven Robert, Huelder, Gerrit, Middendorf, Peter
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 2020
• Subjects: Alignment; Anisotropy; Carbon; Computed tomography; Design of experiments; Energy; Factorial design; Fiber lasers; Fiber orientation; fibres; Flux density; glass; Investigations; Laser sintering; Literature reviews; Mathematical analysis; Mechanical properties; Mechanical tests; Modulus of elasticity; PA6; polyamide; Polymers; Process parameters; Rapid prototyping; recoating; selective laser sintering; Shear stress; Stiffness; Tensile strength; Tensors; Thickness
• ISSN: 2504-477X; 2504-477X
• DOI: 10.3390/jcs4030108

In Selective Laser Sintering, fibres are strongly orientated during the powder recoating process. This effect leads to an additional increase of anisotropy in the final printed parts. This study investigates the influence of process parameter variation on the mechanical properties and the fibre orientation. A full factorial design of experiment was created to evaluate the processing parameters of recoating speed, layer thickness and laser power on the part’s modulus of elasticity. Based on the mechanical testing, computed tomography was applied to selected samples to investigate the process-induced fibre microstructure, and calculate the fibre orientation tensors. The results show increasing part stiffness in the deposition direction, with decreasing layer thickness and increasing laser power, while the recoating speed only shows little effect on the mechanical performance. This complies with computed tomography imaging results, which show an increase in fibre orientation with smaller layer thickness. With thinner layers, and hence smaller shear gaps, shear stresses induced by the roller during recoating increase significantly, leading to excessive fibre reorientation and alignment. The high level of fibre alignment implies an increase of strength and stiffness in the recoating direction. In addition, thinner layer thickness under constant laser energy density results in improved melting behaviour, and thus improved fibre consolidation, consequently further increasing the mechanical properties. Meanwhile, the parameters of recoating speed and laser power do not have a significant impact on fibre orientation within their applicable process windows.