1. Mechanisms of defect formation in Ti-6Al-4V product during re-melting of layers in selective laser meltingSnehashis Pal, Matjaž Finšgar, Radovan Hudak, Viktoria Rajtukova, Tomaž Brajlih, Nenad Gubeljak, Igor Drstvenšek, 2023, izvirni znanstveni članek Opis: Knowledge of defect formation mechanisms in the manufacturing process helps improve product quality. In this study, defect formation due to re-melting of each layer in selective laser melting of Ti-6Al-4V demonstrated the physical behavior in the manufacture of metallic parts. The re-melting strategy was based on scanning with low energy density (ED) and increased ED with various combinations of laser processing parameters. The increased EDs and their parameters, namely laser power, scanning speed, and hatch distance, were selected based on the previous research experience by the authors. The concept of selecting a low ED followed by a high ED was to reduce the spattering of the powder material during the process. The low ED caused partial sintering of the powder, while the high ED caused the melting of the material, resulting in different metallurgical properties of the manufactured parts. Densities, pore properties, porosity in the initial layers, surface morphologies, and microstructures in the defective areas of the samples were studied to determine the effects of re-melting. Advantages and disadvantages were found with respect to the range of applications of the products
Ključne besede: re-melting, pore properties, defect, surface morphology, Ti-6Al-4V, selective laser melting
Objavljeno v DKUM: 14.03.2025; Ogledov: 0; Prenosov: 2
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2. Combined effect of build orientation and energy density on density and mechanical properties of selectively laser melted Co-Cr-W-SiSnehashis Pal, Igor Drstvenšek, 2022, izvirni znanstveni članek Opis: The selective laser melting (SLM) process for manufacturing metals continues to be
challenging in terms of achieving the maximum metallurgical properties that the process can
provide. There are a variety of manufacturing parameters in the process that have individual
characteristics, and when combined with other variables, the characteristics can be varied.
However, in this study, the two most important manufacturing parameters, namely build direction
and laser power, were considered to investigate their effects on density and tensile properties.
Previously, the best scanning speed, hatch spacing, and layer thickness were determined, which
directly affect the volumetric energy density in the SLM process. In this study, three different
orientations and three different laser powers were selected, namely the X, Y, and Z directions and
55 W, 75 W, and 95 W laser power, respectively. Significant differences in product density were
observed for the samples fabricated in the different orientations and with the different laser
powers. The specimens fabricated in the Z direction always exhibit higher strength and ductility,
which are significantly different from the specimens fabricated in the X and Y directions, while
the laser power was 75 W and 95 W, respectively
Ključne besede: cobalt-chromium alloy, orientation, density, tensile strength, ductility, selective laser melting
Objavljeno v DKUM: 25.09.2024; Ogledov: 0; Prenosov: 9
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3. Investigation of the best manufacturing orientation of Co-Cr-W-Si dental prosthetic elements in the selective laser melting processSnehashis Pal, Janez Gotlih, Igor Drstvenšek, 2022, izvirni znanstveni članek Opis: It is well known that Selective Laser Melting (SLM) does not provide the same mechanical
properties in all directions of the part. This is due to the microstructural grain orientation and
pore shape in SLM products. Therefore, depending on the direction of the pressure applied to the
SLM product, a different manufacturing orientation is required to achieve the best mechanical
properties. Changing the microstructural grain orientation is difficult through SLM, but a process
to reduce the size and number of the pores can be discovered through different combinations
of manufacturing parameters. In prosthodontics, pressure is usually applied in the vertical
direction, which leads to compression and bending of crowns with bridges. The compressive
load can be easily absorbed in the crowns, but the bending force has a significant effect here.
Therefore, a product with high tensile strength and high ductility is needed to survive longer.
Considering these requirements, this study determined the best parameters for laser processing
by SLM method to reduce porosity and improve mechanical strength and ductility of Co-CrW-Si alloy products. The result is a relative product density of 100% for cubic specimens and a
yield strength, ultimate tensile strength, and elongation at break of the tensile specimens of 900
MPa, 1200 MPa, and 15%, respectively, obtained in specimen build-up in the Z direction with a
laser power of 60 W and a scanning speed of 450 mm/s. Eventually, the best orientation for the
production of dental prosthetic elements using the SLM process was determined.
Ključne besede: cobalt-chromium alloy, dental implant, density, tensile strength, ductility, selective laser melting
Objavljeno v DKUM: 03.07.2024; Ogledov: 78; Prenosov: 14
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4. Dimensional deviations in Ti-6Al-4V discs produced with different process parameters during selective laser meltingSnehashis Pal, Marijana Milković, Riad Ramadani, Janez Gotlih, Nenad Gubeljak, Radovan Hudak, Igor Drstvenšek, Matjaž Finšgar, Tomaž Brajlih, 2023, izvirni znanstveni članek Opis: When manufacturing complicated products where both material and design play a role, especially thin and curved components, it is difcult to maintain accurate dimensions in Selective Laser Melting. Considering these difculties, this article presents the dimensional errors in the fabrication of Ti-6Al-4V discs and their thermomechanics during manufacturing. Various combinations of laser processing parameters were used to fabricate the 2.00 mm thick discs with a diameter of 5.70 mm. It was found that the thickness shortened and the round shape changed to an oval shape for most of the discs. The thickness decreased along the build-up direction from the bottom to the top and formed a taper that increased with increasing energy density (ED). The horizontal diameter of the discs changed slightly, while the vertical diameters changed remarkably with increasing ED. On the other hand, reducing the laser power resulted in a reduction of the roundness error, while it caused a reduction of the thickness. The hatch spacing signifcantly afected the volume of the melt pool and caused a change in the vertical diameter. The central part of the curved surface of the discs became concave and the concavity increased due to the increasing ED.
Ključne besede: dimension, Ti-6Al-4V, lase power, scanning speed, hatch spacing, selective laser melting
Objavljeno v DKUM: 29.03.2024; Ogledov: 219; Prenosov: 9
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5. Fine martensite and beta-grain variational effects on mechanical properties of Ti–6Al–4V while laser parameters change in laser powder bed fusionSnehashis Pal, Tonica Bončina, Gorazd Lojen, Tomaž Brajlih, Erika Švara Fabjan, Nenad Gubeljak, Matjaž Finšgar, Igor Drstvenšek, 2024, izvirni znanstveni članek Ključne besede: martensite, Ti-6Al-4V, microstructure, tensile strenght, selective laser melting
Objavljeno v DKUM: 26.01.2024; Ogledov: 285; Prenosov: 23
Celotno besedilo (17,10 MB) |
6. The use of selective laser melting in mandibular retrognathia correctionAndrej Čretnik, Anita Fekonja, 2022, izvirni znanstveni članek Opis: Digitalization and additive manufacturing offer new possibilities in the manufacturing of individualized medical and dental products. In the paper we present the results of the first 30 consecutive growing patients (15 males and 15 females), with a mean age of 13.69 years (SD = 1.26), who were treated for mandibular retrognathia (skeletal Class II malocclusion), using fixed sagittal guidance (FSG) appliance, individually manufactured by selective laser melting (SLM). Lateral cephalometric radiographs were taken before (T0) and after (T1) treatment and a detailed cephalometric analysis was performed. with a special focus on a time period for malocclusion correction. The analyzed data were compared with the control group (CG; treated with intermaxillary Class II elastics) that was matched for pretreatment age and pretreatment cephalometric measurements. Both methods were effective in the correction of Class II malocclusion, but the time period of correction was significantly shorter (16.03 ± 1.09 months vs. 20.65 ± 4.12 months) with the FSG appliance. After treatment visual skeletal and dentoalveolar effects were achieved, with statistically significant differences measured in mandibular incisors inclination (0.45° in FSG and 2.84° in CG) and distance (−0.61 mm in FSG and 0.13 mm in CG), in mandibular first molar inclination (−1.07° in FSG and 1.18° in CG) and overbite (−3.82 mm in FSG and −2.46 mm in CG), all in favor of FSG appliance. After the final mean treatment time of 16.03 ± 1.09 months, visual skeletal and dentoalveolar effects were achieved, with significant differences in sagittal (SNB angle, SNPg angle, mandibular length (CoGn) and consequently decrease in ANB angle) as well as in vertical (lower anterior facial height (LAFH) and gonial angle) measurements noted, with no reported complications. As the time needed for malocclusion correction was comparable with the reports in the traditional use of the functional appliance and as all the cosmetical and functional changes in all the treated patients remained stable after a 2-year observational period, growing patients with Class II malocclusion could benefit with this type of treatment. As all the cosmetical and functional changes in all the treated patients remained stable after a 2-year observational period, growing patients with Class II malocclusion could benefit from the treatment with FSG appliance.
Ključne besede: selective laser melting, individualized manufacturing technology, mandibular retrognathia
Objavljeno v DKUM: 18.09.2023; Ogledov: 513; Prenosov: 32
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7. Vpliv izdelovalnih parametrov na lastnosti izdelkov iz Ti-6Al-4V, narejenih s selektivnim laserskim taljenjem in plastenje površine z bioaktivnim polimeromSnehashis Pal, 2019, doktorska disertacija Opis: Technological parameters included in energy density (ED) are the more powerful tools in selective laser melting (SLM) technology which can be used in the time of fabrication to regulate chemical, metallurgical, and mechanical properties of a product. The volumetric Energy Density (ED) depends on the energy input employed by the laser power, scanning speed, hatch spacing, and the layer thickness. Density, microstructure, surface morphology, dimension accuracy, strength and porosity including the number of pores, place of the pore, size of a pore shape of a pore, inclusions of pores of an SLM product depends on the processing parameters. As the powder material fusion process is done by track by track and layer by layer, the architecture of the microstructure in a product is oriented as the direction of building up too. The research has emphasized on metallurgical properties, tensile properties, and producing the non-porous products from Ti-6Al-4V alloy powder and surface modification using bioactive polymer for orthopedic application. The research has followed four steps to study the metallurgical properties and finding out the combinations of technological parameters in producing non-porous products. The purpose of the first step of the study was to examine the effects of ED on the product properties and to obtain an optimum ED as well as the optimal range of scanning speed. The second step of the study has focused on the influences of laser power. The third step of the study has investigated the effect of amounts of track overlapping and hatch spacing. Almost a zero-porosity product has been able to produce by following these three steps of the ongoing research. The fourth step has studied the metallurgical properties emphasizing on re-melting of every layer. High-density products have been found in the fourth step where a small amount of very small sized pores are present as a result of keyhole effect and gaseous bubble entrapment mainly. Four buildup orientations have been selected for each ED in the first step of the study to examine the tensile properties of the products. The best buildup orientation has been seen in longitudinally vertical tensile specimens considering tensile properties. The tensile properties have also been studied in the second and third step of the study with best build up orientation of the tensile specimens. The alterations of metallurgical and tensile properties have also been investigated after heat-treatment of the specific samples. Dimensional accuracies were also invigilated on the cubic, and tensile specimens over the studies and consequently, inaccuracies have been noticed. The fifth step of the study has observed the pore properties, adhesion properties, the compressive strength of gelatin coating manufactured using unidirectional freezing and the freeze-drying process of three different gelatin concentrations on four different surfaced Ti-6Al-4V alloy substrates. The results indicate that the coating properties depend on the substrate’s surface texture as well as the concentration of gelatin. Above 80% of porosity, interconnected and well-aligned pores of 75-200 μm have been obtained which is required to stimulate bone ingrowth histologically.
Ključne besede: selective laser melting, unidirectional freezing, fabricating parameters, porosity, microstructure, mechanical strength
Objavljeno v DKUM: 01.04.2019; Ogledov: 1896; Prenosov: 147
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