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Прегледај по Аутор "Zeljković, Milan"

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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.
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.
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.
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.
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.
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.
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.
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.
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
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.
Određivanje frekvencijskih karakteristika sklopa glavnog vretena mašine alatke primjenom Ojler – Bernulijeve teorije greda i pozicionog sprezanja
(Elektrotehnički fakultet Univerzitet u Istočnom Sarajevu, 2016) Košarac, Aleksandar; Zeljković, Milan; Mlađenović, Cvijetin; Živković, Aleksandar; Milojković, Slobodan
U radu je prikazana analitička metoda određivanja prenosne funkcije sklopa glavnog vretena mašine alatke, kao osnova za određivanje karte stabilnosti. Glavno vreteno se modeluje iz segmenata, uključujući i mjesta oslonaca (ležajeve), koristeći pri tome Ojler – Bernulijevu teorija greda. Prenosna funkcija sklopa glavnog vretena se određuje metodom poziciong sprezanja prenosnih funkcija segmenata za određene granične uslove, odnosno krutosti i prigušenja mjesta spoja segmenata, zatim oslonaca (ležajeva) i sl. Verifikacija dobijenih matematičkih modela izvršen je numerički, primjenom metoda konačnih elementata, kao i eksperimentalnim ispitivanjem, tj. eksperimentalnom modalnom alalizom.
POSSIBILITIES FOR INTERACTIVE CONTROL OF MACHINE TOOLS IN THE VIRTUAL REALITY ENVIRONMENT
(UNIVERRSITY POLITEHNICA TIMISOARA, FACULTY OF ENGINEERING HUNEDOARA, 2013) Košarac, Aleksandar; Prodanović, Saša; Zeljković, Milan
The virtual product development is a modern approach in the product development process. Apart from the visualization itself, the virtual product development encompasses the whole range of testing in the virtual reality (VR) environment. Different testing performed in the virtual reality environment before prototype production can increase productivity and decrease development time. As an illustration of possibilities of performing different kind of testing in VR environment, this paper shows simulation in the VR environment of the process controlled by programmable logical controller (PLC) and MATLAB/SIMULINK. As an interface between VR and MATLAB/SIMULINK environment VR Toolbox library is used, and between MATLAB/SIMULINK and PLC controller that is OPC standard.
Prediction of self-excited vibrations occurance during aluminium alloy AL 7075 milling
(Faculty of Electrical Engineering, University of East Sarajevo, 2019) Košarac, Aleksandar; Šikuljak, Lana; Šalipurević, Miloš; Mlađenović, Cvijetin; Zeljković, Milan
Despite the existence of other production methods, metal cutting still plays an important role in modern production. The performance of machine tools has a decisive role in terms of productivity and quality of production increase. When we are talking about improving the performances of machine tools, the analysis of the appearance of self-excited vibrations and their isolation take a significant place. The aim of this paper comes from trends and limitations that are present in metal production. The paper presents analytical and experimental methods for identifying stability lobe diagrams in the aluminum alloy Al 7075 milling. The influence of certain regime on the occurrence of selfexcited vibrations, i.e. the definition of vibrational stable processing regimes, is considered.
PRIMJENA SAVREMENIH TEHNOLOGIJA VIZUELIZACIJE U PROJEKTOVANJU FLEKSIBILNIH TEHNOLOŠKIH STRUKTURA
(Elektrotehnički fakultet, Univerzitet u Istočnom Sarajevu, 2011-03) Košarac, Aleksandar; Zeljković, Milan; Gatalo, Ratko
Predmet istraživanja u ovom radu je razvoj programskog rješenja za automatizovano modularno projektovanje pojedinih tipova mašina alatki za obradu rotacionih dijelova (mašina za obradu krajeva, strugova i brusilica), i njihovo komponovanje u fleksibilne tehnološke strukture višeg nivoa. Za realizaciju programskog rješenja primjenjen je CAD programski sistem univerzalne namjene CATIA, i programski jezik VBA, uz uvažavanje činjenice da se isto moglo realizovati primjenom bilo kog savremenog CAD programskog sistema i njemu odgovarajućeg programskog jezika. Ulazne informacije u programski sistem predstavljaju skup radnih predmeta, odnosno njihove geometrijske karakteristike, a izlaz je koncepciono rješenje fleksibilne tehnološke strukture. U cilju što vjerodostojnijeg prikaza koncepcije projektovanih komponeti i struktura višeg nivoa složenosti razvijena je i aplikacija za simulaciju rada, odnosno kretanja pojedinih komponenti. Upravljanje kretanjem pojedinih komponenti fleksibilne tehnološke strukture je izvedeno u MATLAB/Simulink okruženju, a kao interfejs između MATLAB/Simulink okruženja i virtualne realnosti korišten je VR Toolbox.
STATE SPACE MODELING FROM FEM MODEL USING BALANCED REDUCTION
(Technical faculty "Mihajlo Pupin", Zrenjanin, 2016) Košarac, Aleksandar; Zeljković, Milan; Mlađenović, Cvijetin; Živković, Aleksandar; Prodanović, Saša
This paper shows discretized model of main spindle working unit module obtained byANSYS software. Based on the conducted modal analysis for first ten bending modes within frequency range from 0 to 10 kHz,main shapes and natural frequency (eigenfrequency) have been determined,and modal matrix was formed. Obtained results were afterwards used to determinemodel dynamic behavior in the state space using MATLAB. State space model wasfurther used as reference onefor modal reductionwhereby balanced reduction method was applied. Frequency response of full model (all oscillatory modes) and reduced model for direct FRF and cross FRF are presented through Bode diagram. Reliability of the model is verified by comparing the impulse response offull modeland reduced modelin time domain.
VIRTUALNA REALNOST - NOVI PRILAZ U PROJEKTOVANJU I PROIZVODNJI
(Elektrotehnički fakultet, Univerzitet u Istočnom Sarajevu, 2006-03) Gatalo, Ratko; Navalušić, Slobodan; Zeljković, Milan; Milojević, Zoran; Megađa, Ištvan
U radu je, ukratko, prikazan razvoj tehnologije virtualne realnosti, karakteristike različitih sistema i prisutni trendovi u projektovanju proizvoda korišćenjem virtualne realnosti. Pored toga izloženi su i odrerđeni primeri rezultata, ostvarenih na Institutu za proizvodno mašinstvo, Fakulteta tehničkih nauka u Novom Sadu, koji se odnose na vizuelizaciju rada složenih tehnoloških sistema u području proizvodnog mašinstva, kao segmenta ukupne virtualne realnosti.
VIZUELIZACIJA RADA FLEKSIBILNOG TEHNOLOŠKOG MODULA ZA BRUŠENJE U MATLAB/SIMULINK OKRUŽENJU
(Elektrotehnički fakultet, Univerzitet u Istočnom Sarajevu, 2010-03) Košarac, Aleksandar; Zeljković, Milan; Požar, Atila
Kako bi se projektovana struktura mogla bolje razumjeti, procijeniti, prostudirati, pogotovo u fazi projektovanja koncepcionog rješenja, kada su najmanji troškovi eventualnih izmjena, tehnlogija virtualne realnosti ima veliki potencijal kao nadopuna mogućnostima računarske grafike i konvencionalnih CAD sistema. U radu je prikazan postupak vizuelizacije i animacije rada fleksibilnog tehnološkog modula (FTM) za obradu brušenjem rotacionih dijelova u MATLAB/SIMULINK okruženju. Kao primjer je prikazan FTM koga sačinjavaju sledeće komponente: brusilica za okruglo brušenje, portalni manipulator, sistemske palete i indikciono vođena kolica. Virtualni model fleksibilnog tehnološkog modula je dobijen eksportovanjem 3D modela razvijenog primjenog programskog sistema CATIA u VRML. VRML model je posredstvom VR toolbox-a povezan sa upravljačkom strukturom koja je razvijena u SIMULINK-u.

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