1. Comparative analysis of a 3D printed polymer bonded magnet composed of a TPU-PA12 matrix and Nd-Fe-B atomised powder and melt spun flakes respectivelyGranit Hajra, Mihael Brunčko, Leo Gusel, Ivan Anžel, 2025, original scientific article Abstract: The present study reports the development of new polymer bonded magnet containing a Thermoplastic Polyurethane (TPU) – Nylon (PA12) blend as the matrix material and Nd-Fe-B magnetic particles. Two composite materials were explored: one using Nd-Fe-B atomised spherical powder (ASP) and another incorporating Nd-Fe-B melt-spun flakes (MSF). The filaments were formulated by blending TPU, PA12, and one of selected type of Nd-Fe-B particles using a mixing device. The ASP and the MSF were integrated into the matrix via a precise compounding process and 3D printing was used to produce the testing specimens. The preliminary findings indicate that both formulations exhibited promising magnetic properties while maintaining the mechanical characteristics of TPU and PA12. The atomised spherical powder formulation demonstrated worse magnetic behaviour compared to the melt-spun flake formulation. ASP particles enable better fluidity of the composite material during 3D printing. However, the close-packed arrangement of these particles is the cause of much higher porosity and consequently the poorer mechanical and magnetic properties. Optimization of the processing parameters showed significant influence on the final magnetic performance and structural integrity of the printed specimens. Keywords: bonded magnets, Nd-Fe-B melt spun flakes, Nd-Fe-B atomised powders, material extrusion, additive manufacturing, fused specimen fabrication Published in DKUM: 08.01.2025; Views: 0; Downloads: 6
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2. A holistic approach to cooling system selection and injection molding process optimization based on non-dominated sortingJanez Gotlih, Miran Brezočnik, Snehashis Pal, Igor Drstvenšek, Timi Karner, Tomaž Brajlih, 2022, original scientific article Abstract: This study applied a holistic approach to the problem of controlling the temperature of critical areas of tools using conformal cooling. The entire injection molding process is evaluated at the tool design stage using four criteria, one from each stage of the process cycle, to produce a tool with effective cooling that enables short cycle times and ensures good product quality. Tool manufacturing time and cost, as well as tool life, are considered in the optimization by introducing a novel tool-efficiency index. The multi-objective optimization is based on numerical simulations. The simulation results show that conformal cooling effectively cools the critical area of the tool and provides the shortest cycle times and the lowest warpage, but this comes with a trade-off in the tool-efficiency index. By using the tool-efficiency index with non-dominated sorting, the number of relevant simulation cases could be reduced to six, which greatly simplifies the decision regarding the choice of cooling system and process parameters. Based on the study, a tool with conformal cooling channels was made, and a coolant inlet temperature of 20 °C and a flow rate of 5 L/min for conformal and 7.5–9.5 L/min for conventional cooling channels were selected for production. The simulation results were validated by experimental measurements. Keywords: conformal cooling, injection molding, tooling, additive manufacturing, numerical simulation, non-dominated sorting Published in DKUM: 05.12.2024; Views: 0; Downloads: 3
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3. A study on the compressive behavior of additively manufactured AlSi10Mg lattice structuresDavid Liović, Sanjin Krščanski, Marina Franulović, Dražan Kozak, Goran Turkalj, Emanuele Vaglio, Marco Sortino, Giovanni Totis, Federico Scalzo, Nenad Gubeljak, 2024, original scientific article Abstract: The mechanical behavior of the metallic components fabricated by additive manufacturing (AM) technologies can be influenced by adjustments in their microstructure or by using specially engineered geometries. Manipulating the topological features of the component, such as incorporating unit cells, enables the production of lighter metamaterials, such as lattice structures. This study investigates the mechanical behavior of lattice structures created from AlSi10Mg, which were produced using the laser beam powder bed fusion (LB-PBF) process. Specifically, their behavior under pure compressive loading has been numerically and experimentally investigated using ten different configurations. Experimental methods and finite element analysis (FEA) were used to investigate the behavior of body-centered cubic (BCC) lattice structures, specifically examining the effects of tapering the struts by varying their diameters at the endpoints (�end ) and midpoints (�mid ), as well as altering the height of the joint nodes (h). The unit cells were designed with varying parameters in such a way that �end is changed at three levels, while �mid and h are changed at two levels. Significant differences in Young’s modulus, yield strength, and ultimate compressive strength between the various specimen configurations were observed both experimentally and numerically. The FEA underestimated the Young’s modulus corresponding to the configurations with thinner struts in comparison to the higher values found experimentally. Conversely, the FEA overestimated the Young’s modulus of those configurations with larger strut diameters with respect to the experimentally determined values. Additionally, the proposed FE method consistently underestimated the yield strength relative to the experimental values, with notable discrepancies in specific configurations. Keywords: lattice structure, BCC, compressive behavior, additive manufacturing, AlSi10Mg Published in DKUM: 25.11.2024; Views: 0; Downloads: 2
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4. The influence of the ratio of circumference to cross-sectional area of tensile bars on the fatigue life of additive manufactured AISI 316L steelLuka Ferlič, Filip Jerenec, Mario Šercer, Igor Drstvenšek, Nenad Gubeljak, 2024, original scientific article Abstract: The static and dynamic loading capacities of components depend on the stress level to which the material is exposed. The fatigue behavior of materials manufactured using additive technology is accompanied by a pronounced scatter between the number of cycles at the same stress level, which is significantly greater than the scatter from a material with the same chemical composition, e.g., AISI 316L, but produced by rolling or forging. An important reason lies in the fact that fatigue cracks are initiated almost always below the material surface of the loaded specimen. Thus, in the article, assuming that a crack will always initiate below the surface, we analyzed the fatigue behavior of specimens with the same bearing cross section but with a different number of bearing rods. With a larger number of rods, the circumference around the supporting part of the rods was 1.73 times larger. Thus, experimental fatigue of specimens with different sizes showed that the dynamic loading capacity of components with a smaller number of bars is significantly greater and can be monitored by individual stress levels. Although there are no significant differences in loading capacity under static and low-cycle loading of materials manufactured with additive technologies, in high-cycle fatigue it has been shown that the ratio between the circumference and the loading cross section of tensile-loaded rods plays an important role in the lifetime. This finding is important for setting a strategy for manufacturing components with additive technologies. It shows that a better dynamic loading capacity can be obtained with a larger loading cross section. Keywords: AISI 316L stainless steel, additive manufacturing, FEM, high-cycle fatigue, fractography analysis Published in DKUM: 25.11.2024; Views: 0; Downloads: 13
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5. Metallurgical and geometric properties controlling of additively manufactured products using artificial intelligenceSnehashis Pal, Igor Drstvenšek, 2021, original scientific article Abstract: This article has presented a technical concept for producing precisely desired Additive
Manufactured (AM) metallic products using Artificial Intelligence (AI). Due to the stochastic
nature of the metallic AM process, which causes a greater variance in product properties
compared to traditional manufacturing processes, significant inaccuracies in metallurgical
properties, as well as geometry, occur. The physics behind these phenomena are related to
the melting process, bonding, cooling rate, shrinkage, support condition, part orientation.
However, by controlling these phenomena, a wide range of product features can be achieved
using the fabricating parameters. A variety of fabricating parameters are involved in the
metal AM process, but an appropriate combination of these parameters for a given material
is required to obtain an accurate and desired product. Zero defect product can be achieved
by controlling these parameters by implementing Knowledge-Based System (KBS). A suitable
combination of manufacturing parameters can be determined using mathematical tools with
AI, considering the manufacturing time and cost. The knowledge required to integrate AM
manufacturing characteristics and constraints into the design and fabricating process is beyond
the capabilities of any single engineer. Concurrent Engineering enables the integration of design
and manufacturing to enable trades based not only on product performance, but also on other
criteria that are not easily evaluated, such as production capability and support. A decision
support system or KBS that can guide manufacturing issues during the preliminary design
process would be an invaluable tool for system designers. The main objective of this paper is to
clearly describe the metal AM manufacturing process problem and show how to develop a KBS
for manufacturing process determination. Keywords: metallurgical properties, geometry, additive manufacturing, artificial intelligence, knowledge-based system Published in DKUM: 25.09.2024; Views: 0; Downloads: 9
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6. Bioinspired design of 3D-printed cellular metamaterial prosthetic liners for enhanced comfort and stabilityVasja Plesec, Gregor Harih, 2024, original scientific article Abstract: Traditional prosthetic liners are often limited in customization due to constraints in manufacturing processes and materials. Typically made from non-compressible elastomers, these liners
can cause discomfort through uneven contact pressures and inadequate adaptation to the complex
shape of the residual limb. This study explores the development of bioinspired cellular metamaterial
prosthetic liners, designed using additive manufacturing techniques to improve comfort by reducing
contact pressure and redistributing deformation at the limb–prosthesis interface. The gyroid unit
cell was selected due to its favorable isotropic properties, ease of manufacturing, and ability to
distribute loads efficiently. Following the initial unit cell identification analysis, the results from the
uniaxial compression test on the metamaterial cellular samples were used to develop a multilinear
material model, approximating the response of the metamaterial structure. Finite Element Analysis
(FEA) using a previously developed generic limb–liner–socket model was employed to simulate
and compare the biomechanical behavior of these novel liners against conventional silicone liners,
focusing on key parameters such as peak contact pressure and liner deformation during donning,
heel strike, and the push-off phase of the gait cycle. The results showed that while silicone liners
provide good overall contact pressure reduction, cellular liners offer superior customization and
performance optimization. The soft cellular liner significantly reduced peak contact pressure during
donning compared to silicone liners but exhibited higher deformation, making it more suitable for
sedentary individuals. In contrast, medium and hard cellular liners outperformed silicone liners for
active individuals by reducing both contact pressure and deformation during dynamic gait phases,
thereby enhancing stability. Specifically, a medium-density liner (10% infill) balanced contact pressure
reduction with low deformation, offering a balance of comfort and stability. The hard cellular liner,
ideal for high-impact activities, provided superior shape retention and support with lower liner
deformation and comparable contact pressures to silicone liners. The results show that customizable
stiffness in cellular metamaterial liners enables personalized design to address individual needs,
whether focusing on comfort, stability, or both. These findings suggest that 3D-printed metamaterial
liners could be a promising alternative to traditional prosthetic materials, warranting further research
and clinical validation Keywords: bioinspired design, metamaterial model, cellular structure, additive manufacturing, lower-limb prosthetic, 3D printing, finite element method Published in DKUM: 19.09.2024; Views: 0; Downloads: 3
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8. The consolidation of emulsion templating and thiol-ene click chemistry as a route to degradable polyhipes for biomedical applications : doktorska disertacijaViola Hobiger, 2022, doctoral dissertation Abstract: Thiol-ene click chemistry has been on the rise for the past two decades. In the past years, it has also found its way into the synthesis of porous polymers from emulsion templating (polyHIPEs) due to its versatility and convenience. It is an especially attractive pathway for scaffolds intended for biomedical purposes since the resulting materials are often biocompatible and degradable due to hydrolyzable ester bonds introduced via the thiol monomers.
The overall aim of this dissertation was to bring thiol-ene click chemistry with a focus on photopolymerization to the forefront of polyHIPE research, highlighting the great potential in combining the preparation technique of emulsion templating together with thiol-ene click chemistry. A study to understand the mechanisms of emulsion stability with a focus on already established thiol-ene formulations was conducted. It was possible to study and synthesize materials with a bicontinuous pore morphology within this project. Compared to the typical cellular pore morphology of a polyHIPE, a bicontinuous structure could be especially useful for separation applications. Furthermore, it was possible to induce a phase inversion, leading to small polymer particles.
One part of the dissertation focused on synthesizing hydrophilic polyHIPEs from poly(ethylene glycol) monomers and a hydrophilic thiol through an oil-in-water high internal phase emulsion. The resulting materials exhibited high porosity and small average pore diameters of 2.2 µm. Water uptake and degradation studies were performed. The potential of the material for drug release was demonstrated with the chosen model drug salicylic acid.
Furthermore, a HIPE formulation based on the acrylate 1,6-hexanediol diacrylate and thiol tris[(3-mercaptopropionyloxy)-ethyl]-isocyanurate was developed. For the developed poly(acrylate-co-thiol) polyHIPEs, the effect of oxidation thioethers present in the polymer network on the material properties was explored. This investigation was performed firstly to tune material properties, e.g. increase the glass transition temperature and tensile strength, and secondly, to highlight the oxidation properties of thioether-containing polymer networks. The oxidation responsiveness should be considered when a biomedical application is envisioned since inflammatory processes lead to oxidative stress in an organism. The formulation was also investigated for its additive manufacturing potential. The emulsion composition had to be adjusted to obtain a printable emulsion. Furthermore, it was possible to exclude harmful solvents, making the overall printing process more environmentally friendly and less hazardous for operators.
A polyHIPE from the biobased vinyl ester O,O‘-(hexahydrofuro[3,2-b]furan-3,6-diyl) divinyl diadipate (GDVA), which was especially promising as a biocompatible and biodegradable scaffold for tissue engineering, was prepared together with different thiol chain-transfer agents. The synthesis of cellular interconnected polyHIPEs from these starting materials proved challenging. However, the first synthesis of a biobased vinyl ester polyHIPE could be reported.
A final project was conducted in collaboration with Lithoz GmbH. In collaboration, it was possible to establish the first 3D printed ceramics from high internal phase emulsion precursors. For this purpose, trimethylolpropantriacrylte and the thiol trimethylolpropane tris(3-mercaptopropionate) were employed as monomers together with alumina particles to form a composite polyHIPE which would then be submitted to sintering, resulting in an intrinsically porous printed ceramic, allowing for high customization and complex porous morphologies. Keywords: polyHIPE, thiol-ene, photopolymerization, additive manufacturing Published in DKUM: 07.10.2022; Views: 741; Downloads: 112
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9. Influence of Heat Treatments on Microstructure of Electron Beam Additive Manufactured Ti-6Al-4V Alloy : magistrsko deloDamir Skuhala, 2020, master's thesis Abstract: Additive manufacturing of metallic parts is increasing in popularity and starting to emerge as a new competitive manufacturing process. Printed structures from Ti-6Al-4V titanium alloy, produced by electron beam additive manufacturing (EBAM), possess columnar prior β grains and layer bands, alongside an ultrafine lamellar microstructure, which is prone to low ductility and thus requiring thermal post-processing. Several heat treatments were performed in α + β and β field, in one or multiple stages. The results showed that bi-lamellar microstructure can be obtained, and that selection of annealing temperature and cooling rate determines the morphology, thickness, and distribution of both primary and secondary α features. Mechanical properties were evaluated on three selected heat treatments. Annealing of the As-built condition was performed at 710°C (HT1) and 870°C (HT2), resulting in lamellar microstructure with basketweave morphology. In two-stage heat treatment (HT3), the temperature in the first stage has exceeded β transus, while in the second, annealing was performed again at 870°C. The microstructure was characterized as a mixture of lamellar and bi-lamellar with large α colonies inside the rearranged prior β grains. Air cooling was performed in all HT from the final annealing stage. Strength and hardness have decreased with increasingly coarser microstructural features, while fracture toughness was improved, except in HT1, where the decrease in the fracture toughness was mainly attributed to reduced intrinsic toughening. As-built and HT1 conditions were effected by microstructural texture, causing inconsistent fracture morphology, reduced crack roughness and scattering in results. The influence of texture was decreased by coarser microstructure in HT2, while crack tortuosity was increased. Very unpredictable fracture behaviour was observed in HT3 due to large α colonies, as their orientation determines the areas of ductile or cleavage crack propagation. Keywords: Titanium alloys, Ti-6Al-4V, additive manufacturing, EBAM, heat treatments, microstructural optimization, mechanical properties, fracture toughness Published in DKUM: 11.05.2020; Views: 1834; Downloads: 285
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