Makine Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/263

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Now showing 1 - 14 of 14

Citation - WoS: 7
Citation - Scopus: 9
An experimental work on using conductive powder-filled polymer composite cast material as tool electrode in EDM
(Springer London Ltd, 2014) Yaman, Kemal; Çoğun, Can; Cogun, Can; 3837; Mekatronik Mühendisliği
This paper introduces the composite tool electrodes made of electrical conductive powder-filled polyester resin matrix material, providing promise for the electrical discharge machining (EDM) process. The dendrite-shaped copper powder, graphite powder, and their mixture were used as conductive fillers. Six different types of composite electrodes, namely, plain copper-polyester, pressed copper-polyester, furnaced copper-polyester, plain copper-graphite-polyester, pressed copper-graphite-polyester, and furnaced copper-graphite-polyester were prepared. It is found experimentally that increasing v (f) improved workpiece material removal rate, tool wear rate, relative wear, and electrical conductivity of electrodes. The pressed copper-polyester electrodes were found to be promising in the ED finishing of workpieces at low machining current settings. The practical applicability of the proposed composite electrodes in the industry was also illustrated.
Citation - WoS: 5
Citation - Scopus: 7
Combined use of ultrasonic-assisted drilling and minimum quantity lubrication for drilling of NiTi shape memory alloy
(Taylor & Francis inc, 2023) Akar, Samet; Lotfi, Bahram; Kilic, S. Engin; Yilmaz, Okan Deniz; Akar, Samet; 315516; Makine Mühendisliği
The drilling of shape-memory alloys based on nickel-titanium (Nitinol) is challenging due to their unique properties, such as high strength, high hardness and strong work hardening, which results in excessive tool wear and damage to the material. In this study, an attempt has been made to characterize the drillability of Nitinol by investigating the process/cooling interaction. Four different combinations of process/cooling have been studied as conventional drilling with flood cooling (CD-Wet) and with minimum quantity lubrication (CD-MQL), ultrasonic-assisted drilling with flood cooling (UAD-Wet) and with MQL (UAD-MQL). The drill bit wear, drilling forces, chip morphology and drilled hole quality are used as the performance measures. The results show that UAD conditions result in lower feed forces than CD conditions, with a 31.2% reduction in wet and a 15.3% reduction in MQL on average. The lowest feed forces are observed in UAD-Wet conditions due to better coolant penetration in the cutting zone. The UAD-Wet yielded the lowest tool wear, while CD-MQL exhibited the most severe. UAD demonstrated a & SIM;50% lower tool wear in the wet condition than CD and a 38.7% in the MQL condition. UAD is shown to outperform the CD process in terms of drilled-hole accuracy.
Citation - WoS: 5
Citation - Scopus: 6
Comparison of different yield criteria in various deep drawn cups
(Springer France, 2017) Cogun, Ferah; Çoğun, Ferah; Darendeliler, Haluk; 36624; 7702; Makine Mühendisliği
The aim of the study is to evaluate the performance of three recent yield criteria namely; BBC2008-8p, Yld2003-8p, Hu2003 through the simulation of the hemispherical, cylindrical and square cup drawing processes by comparing the results with the ones obtained by using the von Mises criterion for the isotropic, kinematic and combined hardening and the Hill'48 criterion. For this purpose, two different sheet materials, SS304 stainless steel and DKP6112 steel, and various punch travels were used in the simulations and experimental phases of this study. The BBC2008-8p, Yld2003-8p and Hu2003 models were implemented to the ABAQUS software through the user material subroutine VUMAT. The thickness strain distributions obtained from the simulations were compared with the experimental results to analyze the validity of the three aforementioned criteria. Compared with the other models, the material behavior in deep drawing cases of this study is better predicted with more recent models, namely BBC2008-8p, Yld2003-8p and Hu2003, which include anisotropy parameters found from uniaxial and biaxial tension tests.
Citation - WoS: 11
Citation - Scopus: 12
Effects of electrolytic copper and copper alloy electrodes on machining performance in electrical discharge machining (EDM)
(Taylor & Francis inc, 2022) Çoğun, Can; Simsek, Ulke; Cogun, Can; Esen, Ziya; Esen, Ziya; 52373; 3837; Mekatronik Mühendisliği; Ortak Dersler Bölümü
The most important cost element of electric discharge machining (EDM) is the production of tool electrode (shortly electrode). In the EDM process, copper and its alloys are often used as electrode materials. The machining with EDM without increasing the costs can be achieved by selecting the proper electrode with low production and material costs as well as high workpiece material removal rate (MRR), low electrode wear rate (EWR), and relative wear (RW = MRR/EWR). In this study, the EDM performance outputs, namely, MRR and RW were experimentally investigated for electrolytic copper, CuCr1Zr (with and without aging treatment) and CuCo2Be alloy electrode materials for varying machining parameters. The performance outputs were affected by the electrode material and the applied aging treatment. The aged CuCr1Zr alloy electrodes had higher electrical conductivity and better machining performance than the as-received alloy. The CuCo2Be alloy electrodes exhibited moderate to high MRR; however, their RW was the highest. Although the electrolytic copper has moderate MRR performance compared to the investigated alloys, its low cost increased its performance index, making it a more suitable electrode material for EDM applications.
Citation - WoS: 15
Citation - Scopus: 17
Electrostatic energy harvesting by droplet-based multi-phase microfluidics
(Springer Heidelberg, 2012) Yildirim, Ender; Yıldırım, Ender; Kulah, Haluk; 120121; Makine Mühendisliği
This paper presents an energy scavenging technique, merging microfluidics with electrostatic energy harvesting. The method employs droplet-based microflow of two phases with different electrical permittivities, resulting in a capacitance change across the microchannel, to harvest electrical energy. The technique is implemented on 3 mm wide, 1 mm deep minichannels. It is shown that 0.4 nW can be harvested using a single electrode pair, with air and water as the two phases flowing at 1 ml/min. The generated power can be increased significantly by microscale implementation, where the number of electrodes can also be increased for further improvement.
Citation - WoS: 5
Citation - Scopus: 5
Experimental investigation into the effect of magnetorheological fluid damper on vibration and chatter in straight turning process
(Elsevier Sci Ltd, 2023) Emami, Mohsen; Akar, Samet; Nasab, Vahid Hasan; Akar, Samet; Batako, Andre; 315516; Makine Mühendisliği
Magneto-Rheological (MR) dampers have received a great deal of attention in recent years due to the potential of offering semi-active control. MR dampers have been successfully applied in the vibration control of several machining processes. However, the effect of the material of the damper's fluid chamber on its magnetic prop-erties has not been studied much. In this study, an MR damper has been designed to control the chatter vibration of the straight turning operation. The magnetic properties of the MR damper are simulated in the FEM software COMSOL Multiphysics with two types of steel AISI 410 and AISI 1018, and the material with the best perfor-mance for constructing the fluid chamber is determined. Then, the MR damper with an assembly to hold the cutting tool was fabricated and experimentally tested during straight turning operation and its effect on the tool vibration, and work surface roughness was analyzed. From the result, it was observed that the MR damper reduced tool vibration and chatter effectively. The results obtained in this research confirm that the application of the MR damper in the straight-turning process can either suppress the chatter or greatly reduce the frequency amplitude of the chatter. The reduction of the tool's acceleration amplitude with the MR damper was more intense in the condition of chatter suppression and reached up to 89.42 %. Moreover, the MR damper reduced the roughness of the machining surface. This reduction was higher in cases where the chatter was suppressed and it was observed up to 29 %.
Citation - WoS: 2
Citation - Scopus: 3
Experimental investigation of laminar heat transfer inside trapezoidal duct having different corner angles
(Taylor & Francis inc, 2015) Onur, N.; Onur, Nevzat; Arslan, K.; 53858; Makine Mühendisliği
In this study, steady-state laminar forced flow and heat transfer in a horizontal smooth trapezoidal duct having different corner angles were experimentally investigated in the Reynolds number range from 10(2) to 10(3). Flow is hydrodynamically fully developed and thermally developing under a uniform surface temperature condition. Based on the present experimental data of laminar flow in the thermal entrance region, new engineering correlations were presented for the heat transfer and friction coefficients for each corner angle. The results have shown that as the Reynolds number increases heat transfer coefficient increases but Darcy friction factor decreases. Also, it is observed that average Nusselt number increases while average Darcy friction factor decreases with increasing corner angle of the duct.
Citation - WoS: 2
Citation - Scopus: 2
Hybrid Force and Motion Control of a Three-Dimensional Flexible Robot Considering Measurement Noises
(Mdpi, 2022) Kilicaslan, Sinan; Ozgoren, Mustafa Kemal; Ider, Sitki Kemal; 108608
This work addresses the end-effector trajectory-tracking force and motion control of a three-dimensional three-link robot considering measurement noises. The last two links of the manipulator are considered as structurally flexible. An absolute coordinate approach is used while obtaining the dynamic equations to avoid complex dynamic equations. In this approach, each link is modeled as if there is no connection between the links. Then, joint connections are expressed as constraint equations. After that, these constraint equations are used in dynamic equations to decrease the number of equations. Then, the resulting dynamic equations are transformed into a form which is suitable for controller design. Furthermore, the dynamic equations are divided as pseudostatic equilibrium and deviation equations. The control torques resulting from the pseudostatic equilibrium and the elastic deflections are obtained easily as the solution of algebraic equations. On the other hand, the control torques corresponding to the deviations are obtained without any linearization. Encoders, strain gauges, position sensors and force and moment sensors are required for measurements. Low pass filters are considered for the sensors. For the crossover frequencies of the sensors, low and high values are chosen to observe the filtering effect on the robot output.
Citation - WoS: 22
Citation - Scopus: 25
Investigation of surface integrity in the laser-assisted turning of AISI 4340 hardened steel
(Elsevier Sci Ltd, 2021) Khatir, Farzad Ahmadi; Akar, Samet; Sadeghi, Mohammad Hossein; Akar, Samet; 315516; Makine Mühendisliği
The use of laser-assisted turning (LAT) can improve different aspects of the machinability of high hardness/strength materials. The heat applied in this process reduces the strength of the material and upon a proper selection of laser heat source and machining process parameters, a significant improvement in the machining process can be achieved. This research studies the effect of machining and laser heat source parameters on the surface integrity of the LAT process of AISI 4340 hardened steel with a hardness of 560 HV using Response Surface Methodology (RSM). The effect of machining process parameters (feed rate, depth of cut and cutting speed) and laser power on the surface integrity characteristics of the machined surfaces (white layer thickness, microhardness, surface roughness, and surface chemical composition) are investigated. A detailed finite element simulation of the process has been performed to better understand the physics of the process and to interpret the experimental results. Laser power and feed rate are shown to be the most significant parameters affecting the surface integrity of the machined surfaces. It has been shown that a proper selection of machining and laser heat source parameters makes it possible to minimize the adverse effect of laser heating in the LAT process. This can pave the way for the widespread application of the LAT process by eliminating one of the most important obstacles of this process by controlling the laser heat diffusion into the workpiece.
Citation - WoS: 27
Citation - Scopus: 30
Investigation on replication of microfluidic channels by hot embossing
(Taylor & Francis inc, 2017) Çoğun, Ferah; Cogun, Ferah; Yildirim, Ender; Yıldırım, Ender; Arikan, M. A. Sahir; 31835; Makine Mühendisliği
In this study, effects of embossing temperature, time, and force on production of a microfluidic device were investigated. Polymethyl methacrylate (PMMA) substrates were hot embossed by using a micromilled aluminum mold. The process parameters were altered to observe the variation of replication rate in width and depth as well as symmetry of the replicated microfluidic channels. Analysis of variance (ANOVA) on the experimental results indicated that embossing temperature was the most important process parameter, whereas embossing time and force have less impact. One distinguishing aspect of this study is that, the channels were observed to be skewed to either side of the channel depending on the location of the protrusions on the mold. The mechanism of the skewness was investigated by finite element analysis and discussed in detail. Results showed that the skewness depends on the flow characteristics of the material and could be reduced by increasing the embossing temperature. The best replication rates were obtained at parameter settings of 115 degrees C, 10kN, and 8min for the molds with minimum 56 mu m wide features of 120 mu m depth. We also showed that the fabricated channels could be successfully sealed by solvent-assisted thermo-compressive bonding at 85 degrees C under 5.5kN force.
Citation - WoS: 10
Citation - Scopus: 11
Molecular dynamic approach to predict thermo-mechanical properties of poly(butylene terephthalate)/CaCO3 nanocomposites
(Elsevier, 2021) Seyedzavvar, Mirsadegh; Akar, Samet; Boga, Cem; Akar, Samet; Pashmforoush, Farzad; 315516; Makine Mühendisliği
Thermo-mechanical properties of poly(butylene terephthalate) polymer reinforced with carbonate calcium nanoparticles have been investigated using molecular dynamics simulations. Detailed analyses have been conducted on the effects of nanofiller content, at concentration levels of 0-7 wt%, on the mechanical properties of PBT, i.e. Young's modulus, Poisson's ratio and shear modulus. Thermal properties, including thermal conductivity and glass transition temperature, have been determined using Perl scripts developed based on nonequilibrium molecular dynamics and a high temperature annealing procedure, respectively. Experiments have been performed to verify the accuracy of the results of MD simulations. The CaCO3/PBT nanocomposites were synthesized using melt blending and mold injection techniques. The uniaxial tensile test, thermal conductivity, differential scanning calorimetry and x-ray diffraction spectroscopy measurements were conducted to quantify the thermo-mechanical properties of such nanocomposites experimentally. The results showed significant improvements in the mechanical properties by addition of CaCO3 nanoparticles due to strong binding between rigid particles and PBT polymer and high nucleation effects of nanoparticles on the matrix. Thermal conductivity and glass transition temperature of nanocomposites represented a consistent increase with the ratio of CaCO3 nanoparticles up to 5 wt% with an enhancement of 38% and 36% with respect to that of pure PBT, respectively.
Citation - WoS: 1
Citation - Scopus: 1
Motion Control of a Spatial Elastic Manipulator in the Presence of Measurement Noises
(Springer Heidelberg, 2021) Kilicaslan, Sinan; Ider, S. Kemal; Ozgoren, M. Kemal; 108608
This paper presents a method for the end effector motion control of a spatial three-link robot having elastic second and third links including measurement noises. In the derivation of equations of motion, not to face with complex equations of motion, each link is modeled as though the links are not connected and the restrictions on the links due to connecting them by joints are written as constraint equations. After that the Lagrange multipliers are eliminated and the constraint equations at the acceleration level are substituted into the equations of motion to reduce the number of equations. To handle the non-minimum phase property, the equations of motion of the elastic manipulator are divided as the equations corresponding to a pseudostatic equilibrium and the equations of the deviations from them. Definition of the pseudostatic equilibrium used in this study can be given as a hypothetical state in which the end effector velocity and the end effector acceleration possess their reference values while the elastic deflections are instantly constant. The advantages of this control method are that the elastic deflections and the control inputs required for the pseudostatic equilibrium are obtained by an algebraic method and the feedback stabilization control inputs for the deviation equations are determined without linearizing the dynamic equations. The required measurements are obtained from the strain gauges on the links, the encoders placed on the joints and the position sensors attached to the end effector. For each sensor, a low pass filter is used. Simulations are made with low and high values of crossover frequencies to show the positive and negative effects of filtering on the responses of the system.
Citation - WoS: 28
Citation - Scopus: 32
Performance and surface alloying characteristics of Cu-Cr and Cu-Mo powder metal tool electrodes in electrical discharge machining
(Taylor & Francis inc, 2016) Gulcan, Orhan; Çoğun, Can; Uslan, Ibrahim; Usta, Yusuf; Cogun, Can; 3113; 118190; 3837; Mekatronik Mühendisliği
The main objective of this study is to investigate the effect of Cu-Cr and Cu-Mo powder metal (PM) tool electrodes on electrical discharge machining (EDM) performance outputs. The EDM performance measures used in the study are material removal rate (MRR), tool electrode wear rate (EWR), average workpiece surface roughness (R-a), machined workpiece surface hardness, abrasive wear resistance, corrosion resistance, and workpiece alloyed layer depth and composition. The EDM performance of Cu-Cr and Cu-Mo PM electrodes produced at three different mixing ratios (15, 25, and 35wt% Cr or Mo), compacting pressures (P-c = 600, 700, and 800MPa), and sintering temperatures (T-s = 800, 850, and 900 degrees C) are compared with those machined with electrolytic Cu and Cu PM electrodes when machining SAE 1040 steel workpiece. Analyses revealed that tool materials were deposited as a layer over the work surface yielding high surface hardness, strong abrasion, and corrosion resistance. Moreover, the mixing ratio, P-c, and T-s affect the MRR, EWR, and R-a values.
Citation - WoS: 4
Citation - Scopus: 4
Prediction of white layer formation in μ-WEDM process of NiTi shape memory superalloy: FEM with experimental verification
(Springer London Ltd, 2021) Ilkhchi, Reza Najati; Akar, Samet; Akar, Samet; Meshri, Hassan Ali M.; Seyedzavvar, Mirsadegh; 315516; Makine Mühendisliği
Microscopic changes in the surface of nickel-titanium (nitinol) shape memory alloys (SMAs) in micro-wire electro-discharge machining (mu-WEDM) due to the formation of a resolidified layer on the machined surface, called white layer, are one of the main drawbacks in the processing of such alloys. Since these changes significantly affect the shape memory and elastic recovery characteristics of these alloys, reduction of the white layer thickness (WLT) based on the selection of optimum process parameters is essential to raise the quality of the machined parts. In this regard, a finite element model (FEM) has been developed to simulate the effects of mu-WEDM process parameters, including discharge current, pulse on-time, pulse off-time, and servo voltage, on the heat distributing in Ni55.8Ti SMA to predict the WLT. The flushing efficiency of electric discharges and the effect of flow regime of the dielectric fluid on the heat distribution in the workpiece and the formation of the WLT are analyzed. Experimental data are used to verify the accuracy of the FEM. The results show that the developed model can predict the WLT in mu-WEDM process of Ni55.8Ti SMA with an average error of 14%. The effects of discharge parameters on the formation of the WLT are discussed in details based on the results of the FEM.

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