Прегледај по Аутор "Košarac, Aleksandar"

Сада се приказује 1 - 20 од 39
  • Сличица
    Ставка
    ANALITIČKO ODREĐIVANJE SOPSTVENIH FREKVENCIJA POGONSKOG VRATILA
    (Univerzitet u Istočnom Sarajevu, Mašinski fakultet Istočno Sarajevo, 2016-12) Vučetić, Nikola; Košarac, Aleksandar; Blagojević, Mirko; Antunović, Ranko; Marković, Biljana; Antunović, Ranko
    Modalna analiza je dinamička analiza linearnih sistema sa N stepeni slobode koja se zasniva na metodi razvijanja po vlastitim oblicima ili tonovima. Kroz ovaj rad je prikazano analitičko određivanje sopstvenih frekvencija oscilovanja pogonskog vratila mjenjačkog prenosnika snage DMB 6.80.235 primjenom Ojler-Bernulijeve teorije greda. Dobijeni rezultati su poređeni sa rezultatima sopstvenih frekvencija baziranim na ranijim istraživanjima, a dobijenim na osnovu eksperimentalne postavke, kao i numeričkim putem uz upotrebu software-a Ansys Workbench 12.1. Konačan cilj rada je dobijanje pouzdanog matematičkog modela sprezanjem parcijanih prenosnih funkcija.
  • Сличица
    Ставка
    ANALIZA NAPONSKOG STANJA KUKE KORIŠĆENJEM MKE
    (Mašinski fakultet, Univerzitet Istočno Sarajevo, 2011) Trifković, Spasoje; Radić, Nebojša; Šehovac, Savo; Košarac, Aleksandar; Milutinović, Miroslav
    Kuka je dio koji se najviše koristi za vješanje tereta kod dizalica. Težina kuke je teret koji dizalica mora uvijek dizati, čime se smanjuje nosivost i povećava potrebna snaga dizanja. Zbog toga, dimenzije kuke treba da imaju najmanje potrebne vrijednosti, pri propisanom stepenu sigurnosti. U ovom radu je izvršena analiza naponskog stanja kuke na uobičajeni način i uz pomoć računara, koristeći metodu konačnih elemenata (MKE). Uobičajeni način proračuna kuke se sastoji u provjeri napona u vlaknima materijala u pojedinim presjecima. Krivi dio kuke je proračunat na dva načina, približnom i tačnom metodom. U prvom slučaju je kuka posmatrana kao pravi stap ekscentrično opterećen, a u drugom kao krivi štap.
  • Сличица
    Ставка
    ANALIZA OSJETLJIVOSTI SNABDIJEVAČKIH LANACA DRVNIM PELETOM ZA REALNE USLOVE KOJI ODGOVARAJU BOSNI I HERCEGOVINI
    (Mašinski fakultet Istočno Sarajevo, Univerzitet u Istočnom Sarajevu, 2018) Vasković, Srđan; Radović, Zoran; Batinić, Krsto; Halilović, Velid; Gvero, Petar; Gajić, Anto; Mrkić, Maja Bosančić; Golubović, Dušan; Košarac, Aleksandar; Jeremić, Dejan
    Biomasa predstavlja značajan obnovljivi resurs. Posebno ako se njenom korišćenju prilazi sistematski i uz dobro planiranje. Drvna biomasa je najznačajniji predstavnik biomase koji se već uveliko koristi u proizvodnji peleta. S obzirom da je veliki broj mašina, postrojenja, ljudi i opreme uključen u proizvodni lanac peleta, potrebno je ustanoviti koji to faktori i koliko utiču na ovaj proces. Prije svega misli se na konačno formiranje cijene drvnog peleta i njegove zavisnosti od drugih energenata, cijena sirove biomase, transportnih distanci, cijene električne energije i slično. Ovaj rad je spojio proizvodni lanac peleta sa postrojenjem i distribucijom toplote u objekat preko odgovarajućeg matematičkog modela. Upravo smo u prošle dvije godine bili svjedoci nedostataka drvnog peleta i naglog porasta njegove cijene na tržištu. To svakako dodatno promoviše ovu problematiku i daje joj smisao za istraživanje. Postavlja se pitanje šta su realni uslovi pri kojima treba da dođe do povećanja cijena peleta na tržištu i za koliko? Odgovore na to daje ovaj rad.
  • Сличица
    Ставка
    Calibration of a Hybrid Machine Tool from the Point of View of Positioning Accuracy
    (MDPI, 2024-06-18) Tabaković, Slobodan; Zeljković, Milan; Živanović, Saša; Budimir, Alexander; Dimić, Zoran; Košarac, Aleksandar
    The 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.
  • Сличица
    Ставка
    Comparison of different mathematical models for prediction of self-excited vibrations occurance in milling process
    (University of East Sarajevo,Faculty of Electrical Engineering, 2019) Košarac, Aleksandar; Mlađenović, Cvijetin; Zeljković, Milan; Šikuljak, Lana; Maksimović, Mirjana; Mijić, Danijel
    In modern production, despite the existence of other production methods, metal cutting still plays an important role. The performance of machine tools has a decisive role in terms of productivity and quality of production increase. Undoubtedly, productivity and quality of production are two mail requirements which are key elements to stay on top in a competitive market. One of the most influencing factor that affect the machine tools are vibrations. The most unwanted vibrations that can appear during metal cutting process are self-excited vibrations, which are one of the three kinds of mechanical vibration, free vibration, forced vibration, and self-excited vibration. When it comes to improving the performance of machine tools, the analysis of the appearance of self-excited vibrations and their isolation occupy a significant place. The aim of this paper derives from trends and limitations exists in metal production. The way to isolate the self-excited vibrations is to predict their occurrence by defining the stability lobe diagram. The paper presents two popular analytical methods for identifying stability lobe diagrams in milling, which shows the boundary between stable and unstable zone of machining operations, depending on the number of revolutions of the spindle and cutting depth. First considered method is Fourier series approach and second one id average tooth angle approach. Lather, both stability lobe diagrams were compared with results obtained experimentally.
  • Сличица
    Ставка
    CREATE SISO STATE SPACE MODEL OF MAIN SPINDLE FROM ANSYS MODEL
    (Faculty of Technical Sciences, Department for Production Engineering, 2015) Košarac, Aleksandar; Zeljković, Milan; Mlađenović, Cvijetin; Živković, Aleksandar; Kovač, Pavel
    This paper shows identification of dynamic characteristics of working unit module main spindle, based on application of APDL ANSYS and MATLAB software. Single Input Single Output (SISO) state space MATLAB model will be developed from an APDL ANSYS main spindle model. The first step in defining the state space model is to define the eigenvector elements for all modes for only the input and output degrees of freedom. The next step is analysing the each mode contribution and sort them from the largest to smallest. One of the modal reduction technique is then applied, and modes with smallest contribution are simply truncated.
  • Сличица
    Ставка
    CUTTING PARAMETERS INFLUENCE ON SURFACE ROUGHNESS IN AL 7075 MILLING
    (Faculty of Electrical Engineering, University of East Sarajevo, 2020) Košarac, Aleksandar; Šikuljak, Lana; Obradović, Čedomir; Mlađenović, Cvijetin; Zeljković, Milan
    Aluminum and its alloys are nowadays a very commonly used material in the aerospace and automotive industries. Due to its good mechanical properties, low density, high hardness, good thermal properties, and good machinability, Al7075 is one of the most commonly used aluminum alloys. This work investigates the effect of cutting parameters on surface roughness in finish milling of Al7075 aluminum alloy. Considering the negative effects of conventional cutting fluids (coolants and lubricants), oils or water emulsions on the environment and health, and the negative economic effects resulting from the foregoing, this study also analyzes the possibilities the use of different coolant-lubricant types on cutting. In this connection, the subject of research is also the influence of the cooling method on surface roughness in end milling.
  • Сличица
    Ставка
    DEFINISANJE KARTE STABILNOSTI OBRADNOG SISTEMA PRIMENOM FREKVENTNE ANALIZE SIGNALA VIBRACIJA
    (Mašinski fakultet, Univerzitet u Beogradu, 2020) Mlađenović, Cvijetin; Zeljković, Milan; Košarac, Aleksandar
    Samopobudne vibracije predstavljaju jednu od najnepovoljnijih pojava u procesu rezanja, koje kao posledicu mogu imati ubrzano habanje ili lom alata, naglo pogoršanje kvaliteta obrađene površine, povećanje bučnosti, povećanje potrošnje energije, itd. U cilju izbegavanja navedenih negativnih uticaja, pri definisanju režima rezanja se primenjuju dijagrami koji, u zavisnosti od broja obrtaja glavnog vretena i dubine rezanja, prikazuju granicu između stabilnog i nestabilnog područja rada mašine alatke sa stanovišta samopobudnih vibracija. Ovi dijagrami, nazvani - karte stabilnosti mogu biti definisani primenom matematičkih modela (analitičkih, numeričkih, ...) ili eksperimentalnim ispitivanjima (metod tangenti, zvučno mapiranje,...). U radu je prikazano definisanje karte stabilnosti obradnog sistema eksperimentalnom identifikacijom samopobudnih vibracija. Granične dubine rezanja, potrebne za definisanje karte stabilnosti, određene su metodom dekomponovanja vremenskog signala samopobudnih vibracija. Predložena metoda je primenjena za određivanje graničnih dubina rezanja pri obradi glodanjem aluminijuma Al7075 na obradnom centru EMCO ConceptMill 450. Dobijeni rezultati su verifikovani poređenjem karata stabilnosti određenih primenom navedene i više matematičkih i eksperimentalnih metoda.
  • Сличица
    Ставка
    DETERMINATION OF THE PARASITIC FORCES THAT OCCUR AS A CONSEQUENCE OF THE MOVEMENT OF THE ROLLER OVER THE MINIATURE PROFILED GUIDE
    (University of Novi Sad, Faculty of Technical Sciences, 2019) Kočović, Vladimir; Kostić, Sonja; Vasiljević, Saša; Santoši, Željko; Košarac, Aleksandar; Kuzmanović, Siniša; Rackov, Milan
    In order to achieve a greater efficiency degree of electrical, mechanical or other assemblies that work by consuming any form of energy, the frictional force that occurs between all moving elements of the system should be minimized. Nowadays, a lot of standard sliding and rolling pairs have been developed, which provide linear movement. Since manufacturers of these elements do not prescribe coefficient of friction when moving movable rollers on a fixed rail, it is often necessary to know the resistance to motion of these elements due to the correct selection of the drive system, and therefore it is necessary to determine them. In this paper, the resistance to motion of roller through the miniature profile guide 15 mm in width and 10 mm in height was tested.
  • Сличица
    Ставка
    Eksperimentalno - analitički metod za definisanje karte stabilnosti pri obradi struganjem
    (Elektrotehnički fakultet Univerzitet u Istočnom Sarajevu, 2014) Košarac, Aleksandar; Mlađenović, Cvijetin; Živković, Aleksandar
    Vibracije mašina alatki je pojava koja uzrokuje ne mali broj problema pri procesu obrade, kao što su habanje ili lom alata, loš kvalitet obrađene površine, povećanje potrošnje energije, povećanje bučnosti mašine, itd. Najnepovoljniji oblik vibracija predstavljaju samopobudne vibracije, koje mogu dovesti do nestabilnog rada mašine alatke, tzv. podrhtavanja (eng. Chatter). Da bi se izbjegle posljedice samopobudnih vibracija, pri radu mašine alatke potrebno je odrediti (izolovati) one režime rezanja pri kojima dolazi do pojave podrhtavanja. U tu svrhu, potrebno je formirati karte stabilnosti koje prikazuju granicu između stabilnog i nestabilnog rada mašina u zavisnosti od broja obrtaja i dubine rezanja za sve kombinacije brzine pomoćnog kretanja. Prethodno podrazumjeva čitav niz eksperimenata, što iziskuje veliko vrijeme i ne male troškove za ispitivanje. Iako je eksperimentalna metoda najpouzdanija, u posljednje vrijeme se sve više ulažu napori da se definisanje karte stabilnosti za pojedine mašine alatke izvrši analitičkim ili eksperimentalno-analitičkim metodama. U radu je prikazan eksperimentalno - analitički metod definisanja karte stabilnosti. Metod je ilustrovan na procesu obrade struganjem. Na osnovu eksperimentalno određenih modalnih parametara karakterističnih podsistema mašine alatke, analitičkim putem definisana je karta stabilnosti na kojoj je moguće jasno uočiti kritične dubine rezanja pri određenim brojevima obrtaja.
  • Сличица
    Ставка
    EXPERIMENTAL METHOD FOR DEFINING THE STABILITY LOBE DIAGRAM IN MILLING Č4732 (42CrMo4) STEEL
    (University POLITEHNICA Timisoara, Faculty of Engineering Hunedoara, 2019) Košarac, Aleksandar; Mlađenović, Cvijetin; Zeljković, Milan; Šikuljak, Lana; Imre, Kiss
    Self-exciting vibration (chatter) is an unwanted phenomenon that can occur in metal cutting. Self-exciting vibration is a phenomenon that has a negative effect on productivity, leads to accelerated wear or breakage of the tool, and in some cases can lead to breakage of elements of jigs and fixtures or elements of the machine tools. In order to predict and control the process of creating self-excited vibration, different methods have been developed. One way of predicting self-excited vibration is defining stability lobe Diagram, which shows the boundary between stable, conditionally stable and unstable cutting process, whereby combinations of cutting depth, cutting speed, i.e. spindle speed and feed rate are observed. Methods for defining the stability lobe diagram can be analytical, and experimental. This paper shows the experimental method of defining the stability lobe diagram, on machining steel Č4732 (42CrMo4). Metal cutting is carried out on a vertical machining center. The methodology for defining the stability lobe diagram implies that a series of experiments were done, were workpiece surface to be milled is made with a slope of 3°. In this way, when moving the tool, the cutting depth gradually increases until the moment of self-excited vibration occurs. The occurrence of the vibration is registered by measuring the acceleration, where the accelerometer was being mounted on the main spindle carrier, as close as possible to the tool. After the self-excited vibration occurred, which is manifested by a sudden jump of acceleration amplitude, and by the change in the sound, the cutting process is stopped and then the axial depth of the cut at which the vibration occurs determined by the tangent method in Matlab. The obtained stability lobe diagram has two dimensions, which means that all measurements were performed for one, a constant value of feed rate per tooth.
  • Сличица
    Ставка
    EXPERIMENTAL VERIFICATION OF NUMERICAL GEARBOX DRIVE SHAFT MODAL ANALYSIS RESULTS
    (University of Novi Sad, Faculty of Technical Sciences, 2016) Vučetić, Nikola; Blagojević, Mirko; Košarac, Aleksandar; Antunović, Ranko
    This paper shows the experimental determination of drive shaft DMB. 6.80.325 natural frequencies using available equipment for data acquisition and processing on the Faculty of Mechanical Engineering in East Sarajevo. The results were compared with the values of natural frequencies determined numerically in software Ansys Workbench 12.1 in which the mentioned shaft was modeled previously. Experimental results were processed in software packages MatLab and OriginPro.
  • Сличица
    Ставка
    Identifikacija samoizavanih vibracija pri obradi struganjem primenom savremene dijagnostičke opreme
    (Institut IMK "14. oktobar", Kruševac, 2013) Košarac, Aleksandar; Zeljković, Milan; Mlađenović, Cvijetin; Živković, Aleksandar; Gašić, Milomir
    Pojava samoizazvanih vibracija pri obradi rezanjem je odavno uočena, ali i danas predstavlja vrlo aktuelno polje istraživanja kako sa stanovišta matematičkog modeliranja i predikcije, tako i sa stanovišta eksperimentalnog ispitivanja i upravljanja obradnim procesom. Razvojem NU mašina alatki i sve većom primenom visokobrzinske obrade, pomenuti problemi su postali još izraženiji, pa su detekcija i prevencija nastanka samoizazvanih vibracija postale suštinski važne za eksploataciju ovih obradnih sistema. U radu je prikazan način utvrđivanja trenutka nastanka samoizazvanih vibracija pri obradi struganjem, kao jednog od indikatora dinamičke nestabilnosti obradnog sistema, primenom savremene dijagnostičke opreme National Instruments i LabView i Matlab softvera. Takođe, na osnovu eksperimentalno dobijenih rezultata, primenom metode tangenti, određene su granične vrednosti dubine rezanja pri kojima dolazi do nastanka samoizazvanih vibracija, kao osnove za definisanje karte stabilnosti obradnog sistema, i identifikaciju najosetljivijeg elementa sa stanovišta dinamičkog ponašanja mehaničke strukture mašine alatke.
  • Сличица
    Ставка
    Industry 4.0 and Multi-tasking machining
    (SCIENTIFIC TECHNICAL UNION OF MECHANICAL ENGINEERING “INDUSTRY 4.0”, 2023) Sekulić, Milenko; Savković, Borislav; Aleksić, Anđelko; Košarac, Aleksandar; Moljević, Slaviša; Anić, Jelica; Popov, Georgi
    A clear trend of Industry 4.0 and smart manufacturing is to promote the increased use of multi-tasking machine tools. These machines are easily integrated into digital production systems and enable real-time data acquisition, remote monitoring and adaptive cutting processing. The integration of multi-tasking machine tools and digital manufacturing systems will improve the implementation of predictive maintenance, process optimization and production efficiency. Moreover, the development of robotics and AI along with the adoption of Industry 4.0 will increase the market share of these machine tools. The market demand is expected to increase further due to the rise of Industry 4.0. The paper analyzes the main advantages of multi-tasking machining, focusing on the advanced features of multi-tasking machine tools, as well as the latest trend of integrating additive manufacturing processes with CNC machining.
  • Сличица
    Ставка
    INFLUENCES OF THE MILLING DIRECTION ON SURFACE QUALITY ON MILLING X155CrVMo12-1 STEEL
    (International Engineering and Technology Institute, 2022) Babić, Igor; Košarac, Aleksandar; Gao, Rui; Zunjic, Aleksandar
    Surface quality is one of the main characteristics of a product and manufacturing process. In milling, there are two possible ways a tool moves relative to the movement of the workpiece – up and down milling. This paper investigates the effect of milling direction on surface quality and shows that the effect is independent of quality in terms of the arithmetic average of the roughness profile – Ra.
  • Сличица
    Ставка
    INTEGRITY ASSESSMENT OF AN AIRCRAFT CYLINDER ASSEMBLY WITH A CRACK
    (Associated Publishers, 2022) Vučetić, Nikola; Jovičić, Gordana; Antunović, Ranko; Sovilj-Nikić, Sandra; Košarac, Aleksandar; Jeremić, Dejan
    The repeatability of the air-cooled piston engine cylinder assembly failure due to a crack in the cylinder head, as well as its severity from the aspect of crew and passenger safety were the main motives for our research. In this paper an integrity assessment of a cylinder assembly with a crack was performed. By modeling cracks of different lengths in the cylinder head and considering the values of stress intensity factors and J-integral values at a given crack length on the one hand and determining the critical values of these fracture mechanics parameters on the other hand, the stability of the crack was examined. As part of the research, the dependence of the crack length on the stress intensity factor was established. The methodology proposed in this paper can be adapted to assess the integrity of other similar structural elements
  • Сличица
    Ставка
    Loop-the-Loop as a Real Tribomechanical System Applicable in Engineering Education
    (Faculty of Engineering, University of Kragujevac, Serbia, 2021) Miljojkovic, Jasmina; Kočović, Vladimir; Košarac, Aleksandar; Šimunović, Katica
    Using a "loop-the-loop" system, the authors developed a double-track apparatus and based their experimental research on theoretical foundations related to the motion on an inclined plane laid by Leonhard Euler. The method enabled the quantification of very small "energy losses". The paper presents the results of experimental research and the analysis of the changes in friction force and other causes of energy dissipation. In engineering education, the method contributes to a deep understanding of the concept of energy transformation – the appearance of "energy losses" in real tribomechanical systems.
  • Сличица
    Ставка
    Machining Simulation and Verification of Tool Path for CNC Machine Tools with Serial and Hybrid Kinematics
    (Faculty of mechanical and civil engineering Kraljevo, University of Kragujevac, 2017) Zivanović, Saša; Tabaković, Slobodan; Zeljković, Milan; Mlađenović, Cvijetin; Košarac, Aleksandar; Gašić, Milomir
    Development of modern machine tools basically is directed on improvement of kinematic structures and exploitation characteristics. As a result of this in last two decades industry more and more uses machine tools based on parallel and hybrid kinematics with significant increasing of speed of main and movement and feederate. In order to provide more efficient exploitations of these machines, reduce of the preparation time of production, increase of the safety of users and machines is necessary application of software for simulation and verification programs. This paper presents the concept of modern technological preparing of manufacturing in the case of the definition of virtual machine tools based on conventional - serial and hybrid kinematics, simulation of machining and verification of programs for machining of characteristic workpiece.
  • Сличица
    Ставка
    Neural-Network-Based Approaches for Optimization of Machining Parameters Using Small Dataset
    (MDPI, 2022) Košarac, Aleksandar; Mlađenovic, Cvijetin; Zeljković, Milan; Tabaković, Slobodan; Knežev, Miloš
    Surface quality is one of the most important indicators of the quality of machined parts. The analytical method of defining the arithmetic mean roughness is not applied in practice due to its complexity and empirical models are applied only for certain values of machining parameters. This paper presents the design and development of artificial neural networks (ANNs) for the prediction of the arithmetic mean roughness, which is one of the most common surface roughness parameters. The dataset used for ANN development were obtained experimentally by machining AA7075 aluminum alloy under various machining conditions. With four factors, each having three levels, the full factorial design considers a total of 81 experiments that have to be carried out. Using input factor-level settings and adopting the Taguchi method, the experiments were reduced from 81 runs to 27 runs through an orthogonal design. In this study we aimed to check how reliable the results of artificial neural networks were when obtained based on a small input-output dataset, as in the case of applying the Taguchi methodology of planning a four-factor and three-level experiment, in which 27 trials were conducted. Furthermore, this paper considers the optimization of machining parameters for minimizing surface roughness in machining AA7075 aluminum alloy. The results show that ANNs can be successfully trained with small data and used to predict the arithmetic mean roughness. The best results were achieved by backpropagation multilayer feedforward neural networks using the BR algorithm for training
  • Сличица
    Ставка
    Next-Gen Manufacturing: Machine Learning for Surface Roughness Prediction in Ti-6Al-4V Biocompatible Alloy Machining
    (MDPI, 2023-11-15) Košarac, Aleksandar; Tabaković, Slobodan; Mlađenović, Cvijetin; Zeljković, Milan; Orašanin, Goran; Liang, Steven Y.
    Mechanical 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.