1. Predictive modelling of weld bead geometry in wire arc additive manufacturingKristijan Šket, Miran Brezočnik, Timi Karner, Rok Belšak, Mirko Ficko, Tomaž Vuherer, Janez Gotlih, 2025, izvirni znanstveni članek Opis: This study investigates the predictive modelling of weld bead geometry in wire arc additive manufacturing (WAAM) through advanced machine learning methods. While WAAM is valued for its ability to produce large, complex metal parts with high deposition rates, precise control of the weld bead remains a critical challenge due to its influence on mechanical properties and dimensional accuracy. To address this problem, this study utilized machine learning approaches—Ridge regression, Lasso regression and Bayesian ridge regression, Random Forest and XGBoost—to predict the key weld bead characteristics, namely height, width and cross-sectional area. A Design of experiments (DOE) was used to systematically vary the welding current and travelling speed, with 3D weld bead geometries captured by laser scanning. Robust data pre-processing, including outlier detection and feature engineering, improved modelling accuracy. Among the models tested, XGBoost provided the highest prediction accuracy, emphasizing its potential for real-time control of WAAM processes. Overall, this study presents a comprehensive framework for predictive modelling and provides valuable insights for process optimization and the further development of intelligent manufacturing systems.
Ključne besede: wire arc additive manufacturing, WA AM, predictive modelling, machine learning, weld bead geometry, XGBoost
Objavljeno v DKUM: 13.03.2025; Ogledov: 0; Prenosov: 7
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2. Morphological, mechanical, and in-vitro bioactivity of gelatine/collagen/hydroxyapatite based scaffolds prepared by unidirectional freeze-castingYasir Beeran Potta Thara, Tomaž Vuherer, Uroš Maver, Vanja Kokol, 2021, izvirni znanstveni članek Opis: The fabrication of biomaterials to be used in segmental bone defects, mimicking the bone's organic-inorganic architecture and mechanical properties to induce osteogenesis, persists as a key challenge. The purpose of this study was to elucidate the effect of a lightweight, morphologically graded, and multiphase self-standing scaffold structure prepared from a combination of gelatine (Gel), collagen type 1 (Col) and/or hydroxyapatite (HAP) nanoparticles by a unidirectional freeze-casting process at different temperatures (−20, −40, −60 °C), followed by carbodiimide induced cross-linking, on their in-vitro mechanical stability and bioactive properties. In addition, the rheological study of differently formulated Gel solutions has been performed to determine the effect of Col and HAP content on their microstructural arrangement, which, together with the freezing kinetic, affects Gel/Col orientation and cross-linking, and, thus, the scaffold's mechanical strength and stability. A bone-like anisotropic, interconnected, and graded porosity (from 120 to a few μm) scaffold structure with up to 30% total porosity and ~61 μm average pores' diameter is obtained by using a higher Col content (Col: Gel = 2:5) and freezing temperature (−20 °C) while forming a few μm thick close-to-parallel lamellae, separated with a 10–100 μm space when prepared at −60 °C. Such a structure influenced in-vitro stability strongly (lower swelling without weight loss), being accompanied with a ~76% increase of compression strength (to 37 kPa) and ~67% decrease of elastic modulus (to 17 kPa) when prepared with HAP and incubated in HBSS for 7 days. On the other hand, a significant reduction of both strength (~78%, to 15 kPa) and elasticity (~95%, to 5 kPa) was noted for a scaffold prepared with HAP at −60 °C, being related to faster degradation and the formation of a highly opened structure on the bottom, required to stimulate the bone ingrowth, while a more closed network structure on the top to adhere with the surrounding soft tissue. None of the scaffolds induced cytotoxicity to human bone-derived osteoblasts, even after 19 days of incubation, but rather improved their viability while promoting cells' adhesions, proliferation, and differentiation, being supported with an increased alkaline phosphatase activity and rod-like CaP formation.
Ključne besede: biomimetic scaffolds, rheology, unidirectional freeze-casting, morphology, compression properties, bioactivity
Objavljeno v DKUM: 10.03.2025; Ogledov: 0; Prenosov: 3
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3. Varivost novejših toplotno odpornih materialov in njihova uporaba v termoenergetskih objektih : diplomsko deloLuka Ferlež, 2024, diplomsko delo Opis: V diplomski nalogi smo analizirali vplive parametrov varjenja na kakovost zvara, pri varjenju temperaturno odpornega jekla X10CrVMoNb9-1 (P91).Izvedli smo mobilne in laboratorijske meritve trdote (po Vickersu) v osnovnem materialu in v varu, izvedeli smo tudi natezni preizkus preko vara. Meritve smo izvedeli na štirih vzorcih, ki so bili iz proizvodnje izločeni, zaradi neustreznih trdot in pomanjkljivega nadzora nad samim varjenjem. Pridobljene rezultate smo primerjali s tistimi zapisanimi v pristojnih standardih. V diplomski nalogi pa smo tudi analizirali vplive temperature in časa na odpornost jekla P91 proti lezenju, ter vpliv toplotne obdelave pred in po varjenju.
Ključne besede: jeklo X10CrVMoNb9-1, parametri varjenja, trdota, natezni preizkus, odpornost proti lezenju, TVP, toplotna obdelava
Objavljeno v DKUM: 06.03.2025; Ogledov: 0; Prenosov: 18
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4. Simulation and mechanical properties of fine-grained heat-affected zone microstructure in 18CrNiMo7-6 steelTomaž Vuherer, Fidan Smaili, Edvard Bjelajac, Mirza Manjgo, Gorazd Lojen, 2022, izvirni znanstveni članek Opis: Heat-affected zones (HAZs) in real welds are usually quite narrow, and consequently most standard mechanical tests are difficult or even impossible. Therefore, simulated microstructures are often used for mechanical tests. However, the most often used weld thermal cycle simulator produces only a few millimeters wide area of simulated microstructure in the middle of specimens. Consequently, these kind of simulated specimen are not suitable for standard tensile tests, and even for Charpy impact tests, the simulated area can be too narrow. Therefore, to investigate the mechanical properties of a fine-grain heat-affected zone in 18CrNiMo7-6 steel, two methods were used for simulation of as-welded microstructures: (a) a weld thermal cycle simulator, and (b) as an alternative, though not yet verified option, austenitizing in a laboratory furnace + water quenching. The microstructures were compared and mechanical properties investigated. The grain sizes of the simulated specimens were 10.9 μm (water-quenched) and 12.6 μm (simulator), whereby the deviations from the real weld were less than 10%. Both types of simulated specimen were used for hardness measurement, Charpy impact tests, and fatigue tests. Water-quenched specimens were large enough to enable standard tensile testing. A hardness of 425 HV, yield strength Rp02 = 1121 MPa, tensile strength Rm = 1475 MPa, impact energy KV = 73.11 J, and crack propagation threshold ΔKthR = 4.33 MPa m0.5 were obtained with the water quenched specimens, and 419 HV, KV = 101.49 J, and ΔKthR = 3.4 MPa m0.5 with the specimens prepared with the simulator. Comparison of the results confirmed that the annealed and quenched specimens were suitable for mechanical tests of FG HAZs, even for standard tensile tests. Due to the use of simulated test specimens, the mechanical properties determined can be linked to the FG HAZ microstructure in 18CrNiMo7-6 steel.
Ključne besede: weld joint, fine-grained HAZ, simulation of microstructure, hardness, impact toughness, tensile properties, fatigue crack growth, 18CrNiMo7-6 steel
Objavljeno v DKUM: 05.12.2024; Ogledov: 0; Prenosov: 8
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5. The influence of the rolling direction on the mechanical properties of the Al-Alloy EN AW-5454-DMatjaž Balant, Tomaž Vuherer, Peter Majerič, Rebeka Rudolf, 2024, izvirni znanstveni članek Opis: A complementary characterisation of the Al-alloy EN AW-5454 was carried out, intended for obtaining the laser hybrid welding parameters of subassemblies in the automotive industry. The investigation included a microstructural examination and the determination of the alloy’s properties using several analytical methods (HV5 hardness measurement, tensile test, Charpy impact toughness, fracture mechanics analysis). Samples were prepared in the longitudinal and transverse directions of a cold-rolled sheet of EN AW-5454 with thicknesses of 3.5 mm and 4 mm. The measured hardness on the thinner sheet was 5% higher than on the thicker sheet. The tensile and yield strength were nominal, while the elongations were smaller by 2.2–3.2% for the longitudinal samples and by 2.7–13.7% for the transverse samples. The smaller deviations from the nominal values are for the thinner sheet metal. A precise topographical analysis showed the brittle fractures of the samples. The Charpy impact toughness results on the thicker plate showed a 20% greater work needed to break it in the longitudinal direction than in the transverse direction. With the thinner sheet metal, 40% greater work was needed. SEM (scanning electron microscope) analysis has shown that the intermetallic Al6(Mn,Fe) particles in the longitudinal samples were mostly intact, with evidence of tough areas on the upper part of the fracture, indicating a better toughness than the specimens in the transverse direction. More crushed intermetallic particles were observed at the fractures of the transverse samples, and their distribution appeared to be more oriented in the direction of rolling. Fracture mechanics SENB (single edge notch bending) tests and their analysis showed that the resistance of the material to crack propagation in the longitudinal sample was about 50% greater than that in the transverse sample. SEM analysis of the fractures showed that the state of the intermetallic particles in the fracture mechanics testing and the fracture mechanism differed from the one in the Charpy fractures.
Ključne besede: Al-alloy EN AW-5454, characterisation, microstructure, properties
Objavljeno v DKUM: 02.12.2024; Ogledov: 0; Prenosov: 6
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6. Izdelava in analiza navarov varjenih z rutilno oplaščeno elektrodo pravokotnega prereza : doktorska disertacijaEdvard Bjelajac, 2024, doktorska disertacija Opis: Navarjanje z obločnimi postopki so v praksi pogosto uporabljene metode za površinsko zaščito novih ali degradiranih mehanskih delov, ki so med življenjsko dobo izpostavljeni različnim mehanizmom obrabe. Med njimi ima pomembno mesto navarjanje z oplaščeno elektrodo, ki se zaradi enostavnosti opreme in neobčutljivosti na vremenske razmere, pogosto uporablja pri trdem navarjanju na terenu.
Predstavljen je razvoj in izdelava nove pravokotne oplaščene elektrode. Vse do sedaj razvite oplaščene elektrode za ročno obločno varjenje so okrogle oblike, s polnim ali cevastim kovinskim jedrom. Razvita in izdelana je bila oplaščena elektroda pravokotnega preseka. Izdelana je bila v dveh oplaščenjih, z rutilnim, nelegiranim po standardu EN ISO 2560-A, E 42 0 RR 12, Rutilen 2000 S in z rutilnim legiranim po standardu EN 14700 E Fe, E DUR 60 R. Obe oznaki sta komercialna imena slovenskega proizvajalca dodajnih materialov za varjenje SIJ Elektrode Jesenice d.o.o., ki je bil pri izdelavi omenjene elektrode partner.
Vzporedno z navarjanjem s pravokotno oplaščeno elektrodo je potekalo primerjano navarjanje z okroglo oplaščeno elektrodo z enakim oplaščenjem in presekom kovinskega jedra. Navari so bili metalografsko pregledani z optičnim in SEM mikroskopom, na njih so bili izvedeni mehanski in lomno mehanski testi in testi obrabne obstojnosti.
Rezultati raziskav so pokazali, da je zaradi potovanja obloka vzdolž kovinskega jedra mogoče izdelati navare z znatno manj razmešanja kot pri okrogli oplaščeni elektrodi, nov produkt odpira veliko možnosti za dodatne raziskave v prihodnosti.
Ključne besede: ročno obločno varjenje, oplaščena elektrode pravokotnega preseka, trdo navarjanje, stopnja razmešanja
Objavljeno v DKUM: 15.10.2024; Ogledov: 0; Prenosov: 18
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7. Comparison of the mechanical properties of hardfacings made by standard coated stick electrodes and a newly developed rectangular stick electrodeEdvard Bjelajac, Andrej Skumavc, Gorazd Lojen, Mirza Manjgo, Tomaž Vuherer, 2024, izvirni znanstveni članek Opis: Cladding with a stick electrode is one of the oldest arc processes for adding a deposit on a base material. The process is suitable for outdoor working, but the disadvantages are low productivity and large dilution rates. In this work, a simple solution is proposed, which would enable cladding of a larger area with one pass and decrease the dilution rate at the same time—a new type of electrode was developed, exhibiting a rectangular cross-section instead of a round one. Hardfacings, welded with E Fe8 electrodes according to EN 14 700 Standard were welded on mild steel S355 J2 base material with three different coated stick electrodes. The first one was a commercially available, standard, round hardfacing electrode, the second was the same, but with a thinner coating, and the third one was a newly developed rectangular electrode. All three types had equal cross-sections of the metallic core and the same type of coating. Manufacturing of the rectangular electrodes in the laboratory is explained briefly. One- and multi-layer deposits were welded with all three types. Differences were observed in the arc behavior between the round and rectangular electrodes. With the rectangular electrode, the microstructure of the deposit was finer, penetration was shallower, and dilution rates were lower, while the hardness was higher, residual stresses predominantly compressive, and the results of instrumented Charpy impact tests and fracture mechanics tests were better.
Ključne besede: hardfacing, dilution rate, hardness, Charpy impact toughness, residual stress, fracture toughness
Objavljeno v DKUM: 14.05.2024; Ogledov: 298; Prenosov: 26
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8. Uporaba različnih postopkov navarjanja za izboljšanje obrabne obstojnosti : magistrsko deloDavid Novak, 2024, magistrsko delo Opis: Navarjanje je pomemben postopek povečevanja obrabne obstojnosti strojnih delov. V magistrski nalogi sta predstavljena postopka navarjanja z MAG tehnologijo in s PTA tehnologijo. Izvedli smo navarjanje z dodajnimi materiali, ki so trenutno v uporabi v podjetju Farmtech d. o. o., in jih primerjali z novima za uporabo s PTA in MAG tehnologijo. Za primerjavo smo izvedli test obstojnosti proti obrabi, meritev trdot v prerezu talonov in meritev površin namešanja. To smo nadgradili tudi s stroškovno in časovno analizo. Rezultati bodo služili kot smernice za odločitev k implementiranju PTA tehnologije v obstoječo proizvodnjo.
Ključne besede: navarjanje, obrabna obstojnost, obrabni preskus, PTA tehnologija navarjanja, MAG tehnologija navarjanja
Objavljeno v DKUM: 06.05.2024; Ogledov: 214; Prenosov: 0
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9. Advance analysis of the obtained recycled materials from used disposable surgical masksAlen Erjavec, Julija Volmajer Valh, Silvo Hribernik, Tjaša Kraševac Glaser, Lidija Fras Zemljič, Tomaž Vuherer, Branko Neral, Mihael Brunčko, 2024, izvirni znanstveni članek Opis: The production of personal protective equipment (PPE) has increased dramatically in recent years, not only because of the pandemic, but also because of stricter legislation in the field of Employee Protection. The increasing use of PPE, including disposable surgical masks (DSMs), is putting additional pressure on waste collectors. For this reason, it is necessary to find high-quality solutions for this type of waste. Mechanical recycling is still the most common type of recycling, but the recyclates are often classified as low-grade materials. For this reason, a detailed analysis of the recyclates is necessary. These data will help us to improve the properties and find the right end application that will increase the value of the materials. This work represents an extended analysis of the recyclates obtained from DSMs, manufactured from different polymers. Using surface and morphology tests, we have gained insights into the distribution of different polymers in polymer blends and their effects on mechanical and surface properties. It was found that the addition of ear loop material to the PP melt makes the material tougher. In the polymer blends obtained, PP and PA 6 form the surface (affects surface properties), while PU and PET are distributed mainly inside the injection-molded samples.
Ključne besede: mechanical recycling, disposable surgical mask, morphology, surface properties, mechanical properties, nonwoven materials, PPE
Objavljeno v DKUM: 09.04.2024; Ogledov: 232; Prenosov: 22
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10. Determination of shear bond strength between PEEK composites and veneering composites for the production of dental restorationsAnamarija Kuchler, Klementina Pušnik Črešnar, Iztok Švab, Tomaž Vuherer, Majda Žigon, Mihael Brunčko, 2023, izvirni znanstveni članek Opis: We studied the shear bond strength (SBS) of two PEEK composites (BioHPP, BioHPP plus) with three veneering composites: Visio.lign, SR Nexco and VITA VM LC, depending on the surface treatment: untreated, sandblasted with 110 μm Al2O3, sandblasted and cleaned ultrasonically in 80% ethanol, with or without adhesive Visio.link, with applied Visio.link and MKZ primer. For the BioHPP plus, differential scanning calorimetry (DSC) revealed a slightly lower glass transition temperature (Tg 150.4 ± 0.4 °C) and higher melting temperature (Tm 339.4 ± 0.6 °C) than those of BioHPP (Tg 151.3 ± 1.3 °C, Tm 338.7 ± 0.2 °C). The dynamical mechanical analysis (DMA) revealed a slightly higher storage modulus of BioHPP (E’ 4.258 ± 0.093 GPa) than of BioHPP plus (E′ 4.193 ± 0.09 GPa). The roughness was the highest for the untreated BioHPP plus, and the lowest for the polished BioHPP. The highest hydrophobicity was achieved on the sandblasted BioHPP plus, whereas the highest hydrophilicity was found on the untreated BioHPP. The highest SBSs were determined for BioHPP and Visio.lign, adhesive Visio.link (26.31 ± 4.17 MPa) or MKZ primer (25.59 ± 3.17 MPa), with VITA VM LC, MKZ primer and Visio.link (25.51 ± 1.94 MPa), and ultrasonically cleaned, with Visio.link (26.28 ± 2.94 MPa). For BioHPP plus, the highest SBS was determined for a sandblasted surface, cleaned ultrasonically, with the SR Nexco and Visio.link (23.39 ± 2.80 MPa).
Ključne besede: BioHPP, CAD/CAM milling, BioHPP plus, pressing, veneering composites, roughness, wettability, shear bond strength
Objavljeno v DKUM: 05.04.2024; Ogledov: 213; Prenosov: 21
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