Deviations of the SLM Produced Lattice Structures and Their Influence on Mechanical Properties

Abstract

Selective laser melting (SLM) is an additive manufacturing technology suitable for producing cellular lattice structures using fine metal powder and a laser beam. However, the shape and dimensional deviations occur on the thin struts during manufacturing, influencing the mechanical properties of the structure. There are attempts in the literature to describe the actual shape of the struts’ geometry, however, on a smaller data sample only, and there is a lack of a universal FEA material model applicable to a wider range of lattice structure diameters. To describe the actual dimensions of the struts, a set of lattice structures, with diameters ranging from 0.6 to 3.0 mm, were manufactured using SLM. These samples were digitized using micro-computed tomography (μCT) and fully analyzed for shape and dimensions. The results show large deviations in diameters of inscribed and circumscribed cylinders, indicating an elliptical shape of the struts. With increasing lattice structure diameter, the deviations decreased. In terms of the effect of the shape and dimensions on the mechanical properties, the Gaussian cylinder was found to describe struts in the diameter range of 1.5 to 3.0 mm sufficiently well. For smaller diameters, it is appropriate to represent the actual cross-section by an ellipse. The use of substitute ellipses, in combination with the compression test results, has resulted in FEA material model that can be used for the 0.6 to 3.0 mm struts’ diameter range. The model has fixed Young’s and tangential modules for these diameters and is controlled only by the yield strength parameter (YST).

Towards Realistic Numerical Modelling of Thin Strut-Based 3d-Printed Structures

“…One of the probable reasons is the elliptical cross sections of the printed struts caused by the layering effect. This assumption is consistent with the research findings by Vrana et al (2022) and Dallago et al (2018).…”

“…However, given the significance of a realistic numerical model, the focus has been recently shifting towards incorporating experimental data from the printed structures, for example, geometrical deviations and material properties into the numerical models (Gorguluarslan et al, 2015;Tkac et al, 2020). Vrana et al (2022) have experimentally investigated and numerically incorporated the shape and dimensional differences in lattices manufactured in an aluminium alloy using selective laser melting (SLM). They aimed at predicting their stress-strain response.…”

Influence of Process Energy on the Formation of Imperfections in Body-Centered Cubic Cells with Struts in the Vertical Orientation Produced by Laser Powder Bed Fusion from the Magnesium Alloy WE43

“…The diameter deviations of the produced struts from the nominal diameters are listed in Figure 13, based on the maximum inscribed and minimum circumscribed cylinders. The maximum inscribed cylinder, which represents the load-bearing cross-section of the strut [39], reaches a larger diameter than required for both vertical (Figure 13a) and inclined (Figure 13b) struts. The deviation from the diameter increases with the linear energy and strut diameter.…”

Compression and Tensile Testing of L-PBF Ti-6Al-4V Lattice Structures with Biomimetic Porosities and Strut Geometries for Orthopedic Implants

“…However, while surface roughness is often an undesirable byproduct of the laser powder bed fusion process, it is advantageous in the design of orthopedic implants, providing additional surface area for the osseointegration of bone cells [51]. The differences between the relative density for CAD and as-produced lattices are considerable and may be attributed to the surface roughness (despite HIP) and the process parameters chosen for this study, such as the layer thickness (40 microns) or laser power [50]. However, while surface roughness is often an undesirable byproduct of the laser powder bed fusion process, it is advantageous in the design of orthopedic implants, providing additional surface area for the osseointegration of bone cells [51].…”