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Deviations of the SLM produced Lattice Structures and Their Influence on Mechanical properties
(MDPI, 2022-04-26) Vrána, Radek; Koutecký, Tomáš; Červinek, Ondřej; Zikmund, Tomáš; Pantělejev, Libor; Kaiser, Jozef; Koutný, Daniel
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 (CT) 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).
Microstructure of Selective Laser Melted Titanium Lattices and In Vitro Cell Behaviour
(Tanger, 2021-09-15) Hernandez Tapia, Laura Guadalupe; Carranza-Trejo, Azalia Mariel; Kashimbetova, Adelia; Tkachenko, Serhii; Koledová, Zuzana; Koutný, Daniel; Malý, Martin; Čelko, Ladislav; Montufar Jimenez, Edgar Benjamin
Selective laser melting (SLM) is a metal additive manufacturing technology that allows the fabrication of complex near-net-shape titanium parts. Among possible applications, titanium is important for the biomedical sector, in particular for orthopaedics due to its low elastic modulus, biocompatibility, high mechanical strength and corrosion resistance. Several studies show the structural properties and mechanical behaviour of titanium lattices that in parallel exhibited the porosity, mechanical strength and elastic modulus of trabecular bone. However, less attention has been devoted to study the biological response to titanium parts fabricated by SLM. Therefore, this work aimed to fabricate commercially pure titanium lattices by SLM and study the behaviour of bone-forming cells cultured on the lattices. The results show that Saos-2 osteoblast-like cells proliferated and covered the entire available surface of the titanium lattices becoming confluent and quiescent. The activity of alkaline phosphatase and the production of extracellular calcium deposits confirmed the growth of viable and mature osteoblasts. The cytocompatibility of the titanium lattices is an additional advantage that adds to the possibility to mimic the porosity and mechanical properties of bone by computer-aided design and subsequently implement the lattice fabrication by SLM, fitting the requirements of individual patients and, consequently, offering a broad range of new bone repair alternatives in orthopaedics. Keywords: selective laser melting, titanium, microstructure, osteoblast, cytocompatibility.
Computational Approaches of Quasi-Static Compression Loading of SS316L Lattice Structures Made by Selective Laser Melting
(MDPI, 2021-05-10) Červinek, Ondřej; Werner, Benjamin; Koutný, Daniel; Vaverka, Ondřej; Pantělejev, Libor; Paloušek, David
Additive manufacturing methods (AM) allow the production of complex-shaped lattice structures from a wide range of materials with enhanced mechanical properties, e.g., high strength to relative density ratio. These structures can be modified for various applications considering a transfer of a specific load or to absorb a precise amount of energy with the required deformation pattern. However, the structure design requires knowledge of the relationship between nonlinear material properties and lattice structure geometrical imperfections affected by manufacturing process parameters. A detailed analytical and numerical computational investigation must be done to better understand the behavior of lattice structures under mechanical loading. Different computational methods lead to different levels of result accuracy and reveal various deformational features. Therefore, this study focuses on a comparison of computational approaches using a quasi-static compression experiment of body-centered cubic (BCC) lattice structure manufactured of stainless steel 316L by selective laser melting technology. Models of geometry in numerical simulations are supplemented with geometrical imperfections that occur on the lattice structure’s surface during the manufacturing process. They are related to the change of lattice struts cross-section size and actual shape. Results of the models supplemented with geometrical imperfections improved the accuracy of the calculations compared to the nominal geometry.
Wear of grinding rotors with thermally-sprayed coatings in a high-speed mill
(Elsevier, 2018-10-15) Tkachenko, Serhii; Dvořák, Karel; Jech, David; Slámečka, Karel; Klakurková, Lenka; Paloušek, David; Čelko, Ladislav
In this paper, the erosion behavior of three types of protective thermally-sprayed coatings and non-coated substrate steel was investigated under semi-industrial test conditions using a laboratory high-speed pin mill DESI-11. The grinding in the mill was performed by two counter rotors, on which protective coatings were deposited either by atmospheric plasma spraying (APS) (Cr3C2-NiCr and NiCrBSi coatings) or by high velocity oxy-fuel (HVOF) process (WC-CoCr coating). The grinding rotors with deposited coatings were used for milling of the Portland cement, and rotors' weight loss was monitored after milling of 1, 3, 5, 10, and 15 kg of this material. The lowest weight loss in the mixed impact erosion conditions was exhibited by WC-CoCr coating, which was followed by Cr3C2-NiCr and NiCrBSi coatings. The greatest material removal on the anterior and the right lateral faces of rotor pins was a result of erosion damage at high impact angles through surface fatigue wear and the following failure of protective coatings down to the substrate. In contrast, the top and the left lateral faces of the pins were subjected mostly to the ploughing and microcutting at oblique impact angles that resulted in significant erosive damage only if hardness of the pin was lower than that of the Portland cement (Cr3C2-NiCrcoated and non-coated steel pins). The study also found a significant disproportion between the volumetric wear losses of various rows of pins of grinding rotors. The central part of the grinding tool consisting of two counter rotors (both rows of 2-row rotor and a middle row of 3-row rotor) suffered more intensive erosion wear than the external part (outer rows of 3-row rotor). The design of the mill and the resulting variability in parameters of milled powder particles at different sites of the grinding tool (such as particle size, particle flux and particle velocity) were considered as main reasons of this phenomena.
Use of micro computed-tomography and 3D printing for reverse engineering of mouse embryo nasal capsule
(IOP Publishing, 2016-03-02) Tesařová, Markéta; Zikmund, Tomáš; Kaucká, Markéta; Adameyko, Igor; Jaroš, Josef; Paloušek, David; Škaroupka, David; Kaiser, Jozef
Imaging of increasingly complex cartilage in vertebrate embryos is one of the key tasks of developmental biology. This is especially important to study shape-organizing processes during initial skeletal formation and growth. Advanced imaging techniques that are reflecting biological needs give a powerful impulse to push the boundaries of biological visualization. Recently, techniques for contrasting tissues and organs have improved considerably, extending traditional 2D imaging approaches to 3D. X-ray micro computed tomography (uCT), which allows 3D imaging of biological objects including their internal structures with a resolution in the micrometer range, in combination with contrasting techniques seems to be the most suitable approach for non-destructive imaging of embryonic developing cartilage. Despite there are many software-based ways for visualization of 3D data sets, having a real solid model of the studied object might give novel opportunities to fully understand the shape-organizing processes in the developing body. In this feasibility study we demonstrated the full procedure of creating a real 3D object of mouse embryo nasal capsule, i.e. the staining, the CT scanning combined by the advanced data processing and the 3D printing.

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