Машински факултет [Научни радови] / Faculty of Mechanical Engineering [Scientific papers]
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- СтавкаNext-Gen Manufacturing: Machine Learning for Surface Roughness Prediction in Ti-6Al-4V Biocompatible Alloy Machining(MDPI, 2023) Kosarac, Aleksandar; Tabakovic, Slobodan; Mladjenovic, Cvijetin; Zeljkovic, Milan; Orasanin, GoranMechanical engineering plays an important role in the design and manufacture of medical devices, implants, prostheses, and other medical equipment, where the machining of bio-compatible materials have a special place. There are a lot of different conventional and non-conventional types of machining of biocompatible materials. One of the most frequently used methods is milling. The first part of this research explores the machining parameters optimization minimizing surface roughness in milling titanium alloy Ti-6Al-4V. A full factorial design involving four factors (cutting speed, feed rate, depth of cut, and the cooling/lubricating method), each having three levels, implies the 81 experimental runs. Using the Taguchi method, the number of experimental runs was reduced from 81 to 27 through an orthogonal design. According to the analysis of variance (ANOVA), the most significant parameter for surface roughness is feed rate. The second part explores the possibilities of using different ML techniques to create a predictive model for average surface roughness using the previously created small datasets. The paper presents a comparative analysis of several commonly used techniques for handling small datasets and regression problems. The best results indicate that the widely used machine learning algorithm Random Forest excels in handling regression problems and small datasets.
- СтавкаAnalysis of Power Losses in Constrained Cycloid Drive(Strojarski Facultet, Sveucilist Joseph Jurj Strossmayer in Osijeka, 2023) MAČKIĆ, Tihomir; MARJANOVIĆ, Nenad; TICA, Milan; TROHA, Sanjin; MILUTINOVIĆ, Miroslav; RAŠOVIĆ, NebojšaThe aim of this paper is to present a theoretical model for efficiency evaluation of a simple cycloid drive train with one degree of freedom (DOF) or constrained cycloid drive. In order to evaluate the efficiency, it is necessary to find the losses generated in the simple cycloid drive, where only losses depending on the load were considered. Expressions for determining speed ratios, efficiency, velocities and forces acting inside the cycloid drive are presented. These expressions are implemented in the theoretical model, where the places where the losses occur are defined. A computer program was created to facilitate analysis and obtain loss values based on different input data. Only load-dependent losses were considered in the theoretical model and computer program. In order to verify the theoretical model, experimental measurements were performed. A physical model of the simple cycloid drive train was created and analyzed on the test bench. The results for "S1" operating mode, i.e. when shaft 2 is stopped, show a mean value of the efficiency of 63.49%, for experimental measurements, while the mean value for theoretical analysis is 65.25%. For the operating mode "S2", i.e. with shaft 1 stopped, the mean value of the experimental measurements of the efficiency is 60.9%, while the theoretical mean value is 62.82%.
- СтавкаInfluence of Surface Preparation of Aluminum Alloy AW-5754 and Stainless Steel X5CRNI18-10 on the Properties of Bonded Joints(MDPI, 2024) Zdravković, Nataša; Klobčar, Damjan; Milčić, Dragan; Zupančić, Matevž; Žužek, Borut; Milčić, Miodrag; Ðurić, AleksijaAdhesive bonding has proven to be a reliable method of joining materials, and the development of new adhesives has made it possible to use bonding in a variety of applications. This article addresses the challenges of bonding metals such as the aluminum alloy EN AW-5754 and the stainless steel X5CrNi18-10. In this study, the effects of laser cleaning and texturing on the surface properties and strength of two bonded joints were investigated and compared with mechanical preparation (hand sanding with Scotch-Brite and P180 sandpaper). The bonded joints were tested with three different epoxy adhesives. During the tests, the adhesion properties of the bonded surface were determined by measuring the contact angle and assessing the wettability, the surface roughness parameters for the different surface preparations, and the mechanical properties (tensile lap-shear strength). Based on the strength test results, it was found that bonded joints made of stainless steel had 16% to 40% higher strength than aluminum alloys when using the same adhesive and surface preparation. Laser cleaning resulted in maximum shear strength of the aluminum alloy bond, while the most suitable surface preparation for both materials was preparation with P180 sandpaper for all adhesives.
- СтавкаCalibration of a Hybrid Machine Tool from the Point of View of Positioning Accuracy(MDPI, 2024) Tabakovic, Slobodan; Zeljkovic, Milan; Zivanovic, Sasa; Budimir, Alexander; Dimic, Zoran; Kosarac, AleksandarThe development of machine tools in the last twenty years includes, among other things, the application of mechanisms with a non-linear kinematic structure as the mechanical basis of machines. This results in significant improvements in kinematic characteristics and problems related to non-linear dependencies of the accuracy of the drive elements and the realization of movement in the machine’s external coordinates. The paper presents an approach to machine tool calibration based on the original O-X glide mechanism based on the ISO 230-4 standard with the mono- and bi-directional compensation of systematic errors and adaptation to the specifics of the mechanism’s kinematics. A machine tool prototype was designed and built for the research presented in the paper. The obtained results indicate the possibility of applying the existing recommendations and standards for testing the accuracy of machine tools with the need to correct the methodology by using linear and non-linear kinematic structures in machine tools.
- СтавкаComparison between Mechanical Properties and Joint Performance of AA 2024-T351 Aluminum AlloyWelded by Friction Stir Welding, Metal Inert Gas and Tungsten Inert Gas Processes(MDPI, 2024) Milčić, Miodrag; Klobčar, Damjan; Milčić, Dragan; Zdravković, Nataša; Ðurić, Aleksija; Vuherer, TomažThe aim of this work is to study joining Al 2024-T3 alloy plates with different welding procedures. Aluminum alloy AA 2024-T351 is especially used in the aerospace industry. Aluminum plates are welded by the TIG and MIG fusion welding process, as well as by the solid-state welding process, friction stir welding (FSW), which has recently become very important in aluminum and alloy welding. For welding AA2024-T35 with MIG and TIG fusion processes, the filler material ER 4043—AlSi5 was chosen because of reduced cracking. Different methods were used to evaluate the quality of the produced joints, including macro- and microstructure evaluation, in addition to hardness and tensile tests. The ultimate tensile strength (UTS) of the FSW sample was found to be 80% higher than that of MIG and TIG samples. The average hardness value of the weld zone of metal for the MIG- and TIG-produced AA2024-T3511 butt joints showed a significant decrease compared to the hardness of the base metal AA2024-T351 by 50%, while for FSW joints, in the nugget zone, the hardness is about 10% lower relative to the base metal AA2024-T3511.