Mühendislik Fakültesi, Makine Mühendisliği Bölümü, Makale Koleksiyonu

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https://hdl.handle.net/11492/876

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Effect of solution-blown polyamide-6 nanofiber interlayer on drilling performance of carbon fiber reinforced composites
(Sage Publıcatıons Ltd, 2025) Ayten, Ali Imran; Sahbaz, Mehmet; Morkavuk, Sezer; Polat, Yusuf; Seyhan, Aybeniz
This study examines the effect of solution-blown polyamide-6 (PA6) nanofiber interlayers on the drilling performance of carbon fiber reinforced polymer (CFRP) composites. Results demonstrate that PA6 nanofiber interlayers significantly reduce drilling thrust force and improve surface quality. Specifically, at a spindle speed of 1000 r/min and a feed rate of 1500 mm/min, the maximum thrust force was reduced by 17%, from 683.33 N in neat composites to 583.13 N in nanofiber-reinforced composites. At a higher spindle speed of 8000 r/min and a feed rate of 500 mm/min, thrust force decreased by 18%, from 80.22 N to 65.46 N. Surface roughness analysis revealed that nanofiber interlayers reduced Ra values by up to 44%, with a minimum roughness of 0.529 mu m compared to 1.196 mu m in neat composites. Optical and SEM analyses confirmed fewer plucking zones, reduced fiber pull-out, and improved fiber-matrix bonding in nanofiber-reinforced samples, particularly at higher spindle speeds. These findings indicate that PA6 nanofiber interlayers enhance drilling performance, offering reduced machining forces and superior hole quality for precision applications in the aerospace and automotive industries.
Metaheuristic optimization of an organic rankine cycle using advanced exergy analysis and artificial bee colony algorithm
(Begell House Inc, 2025) Yuce, Bahadir Erman; Eser, Sezgin; Arslanoglu, Nurullah
In optimizing thermodynamic cycles, selecting the objective function is crucial, and including advanced methods in addition to classical approaches can provide significant advantages to the optimization process. In this study, the condenser temperature, evaporator temperature, and turbine inlet pressure are considered as variables to be optimized in an organic Rankine cycle that extracts heat from a low-temperature geothermal water source. Total unavoidable exergy destruction, thermal efficiency, second-law efficiency, and network output are optimized individually. The artificial bee colony algorithm, a metaheuristic approach, is employed as the optimization method. R123, R11, and R245ca are considered to be the working fluids, and each objective function is applied individually. A total of 12 different optimization processes are conducted, and the achieved objective values are compared. Thus, not only identifying the fluid with the best potential, but also the selection of the most advantageous objective function is determined. In this study, it is observed that selecting R11 as the working fluid and applying total unavoidable exergy minimization optimization result in the best values for all objectives. While other fluids show relatively successful outcomes under different objectives, choosing total unavoidable exergy destruction as the objective function has consistently led to successful results in almost all cases. Maximum work output value was obtained with R11 as 298.45 kW.
The influence of drilling-induced damages and hole quality on hoop tensile and fatigue behavior of CFRP tubes
(Elsevier Ltd., 2024) Morkavuk, Sezer; Aslantaş, Kubilay; Gemi, Lokman; Köklü, Uğur; Yazman, Şakir
Filament winding and roll wrapping methods are widely used in the production of composite tubes. While the mechanical behavior of composites produced by different methods may be different, the effects of the damages that occurred while machining composite tubes on the mechanical behavior may also be different. In this study, the effects of drilling-induced damages and hole quality on the tensile and fatigue strength of the filament-wound and roll-wrapped composite tubes were experimentally investigated. Results showed that while the behavior of the filament-wound composite tube under hoop tensile load is better than the roll-wrapped composite tube, the roll-wrapped tube performs better than filament-wound tube under hoop fatigue load. It was also observed that different drilling conditions affect the mechanical behavior of filament-wound tube while it was found that drilling conditions do not have a significant effect on the mechanical behavior of roll-wrapped tube because manufacturing defects are more dominant.
Esnek uzuvlu bir manipülatörde yapay arı kolonisi algoritması ile optimize edilen kontrolcü parametreleri etkilerinin incelenmesi
(2023) Çetin, Sevda Telli; Eser, Sezgin
Bu çalışmanın temel amacı, esnek uzuvlu manipülatörün kontrol torku ifadesinde yer alan parametrelerin etkilerinin incelenmesidir. Çalışmada ilk olarak, esnek uzuv varsayılan modlar metodu ile modellenmiştir. Ardından, kontrol torku ifadesi sistem enerjisine bağlı olarak elde edilmiştir. Esnek manipülatör için gerçekleştirilen kontrolde amaç, uzvun istenen konuma ulaşması ve hareket sırasındaki salınımların sönümlenmesi olarak belirlenmiştir. Bu amaç doğrultusunda, tork ifadesinde yer alan katsayı parametrelerinin belirlenmesinde Yapay Arı Kolonisi (ABC) Algoritması kullanılmıştır. MATLAB ortamında gerçekleştirilen simülasyonlar literatürde ilgili tork ifadesini kullanan bir çalışma ile karşılaştırılmıştır. Son olarak tork ifadesinde yer alan tüm katsayı parametreleri için simülasyonlar tekrarlanarak ilgili parametrelerin optimizasyona dahil edilme gerekliliği incelenmiştir.
Makaslı bir platform için yükselme süresi ve hidrolik silindir kuvvetine etki eden tasarım parametrelerinin incelenmesi
(2023) Eser, Sezgin; Çetin, Sevda Telli
Makaslı platformlar sahip oldukları basit mekanik yapısı ve üretim kolaylığı sebebiyle endüstride yaygın olarak kullanılmaktadır. Platform için gerek duyulan hidrolik kuvvet ve platformun yükselme süresi, tasarımda önemli faktörler arasında yer almaktadır. Bu çalışmada, platformun uzuv boyu, hidrolik silindirin mafsal konumları ve hidrolik hızı değişken parametreler olarak seçilmiştir. Parametreler için öngörülen farklı değerlerin platformun yükselme süresine ve platformda ihtiyaç duyulan hidrolik kuvvetine etkileri incelenmiştir. Ayrıca, parametre seçimlerinde hidrolik silindirin maksimum strok değeri bir tasarım sınırı olarak dikkate alınmıştır. Hidrolik kuvvet ifadesi hem Virtüel İşler Prensibi (VİP) hem de Virtüel Güçler Prensibi (VGP) ile elde edilerek statik ve dinamik hesaplar arasında oluşan farklar belirlenmiştir. Simülasyonlar sonucunda, farklı tasarım ölçüleri ve hidrolik hızları ile elde edilen sonuçlar karşılaştırılarak yükselme süresini ve hidrolik kuvveti minimize etmek için uygun geometri belirlenmiştir.
Multiscale modelling and experimental analysis of ultrasonic-assisted drilling of GLARE fibre metal laminates
(Elsevier Ltd, 2024) Atif, Muhammad; Wang, Xibin; Xie, Lijing; Giasin, Khaled; Ma, Yuan; Köklu, Uğur
This study aims to evaluate the effectiveness of Ultrasonic-assisted drilling (UAD) of Glass laminate aluminium reinforced epoxy (GLARE) at high cutting speeds (Spindle speeds: 3000–7500 rpm; feed rates 300–750 mm/min) by analysing the thrust force and hole quality metrics (surface roughness, hole size, and burr formations. The research also presents numerical modelling of FMLs under conventional and UAD regimes to predict thrust force using ABAQUS/SIMULIA. The thrust force and exit burrs were reduced by up to 40.83 % and 80 %, respectively. The surface roughness metrics (Ra and Rz) were slightly higher using UAD but remained within the desirable limits of surface roughness for machined aeronautical structures. The discrepancy between the simulation and experimental results was adequate and did not exceed 15 %. The current study shows that it is feasible to drill holes in GLARE using higher cutting parameters and maintain excellent hole quality, which means increased productivity and reduced costs. © 2023 The Author(s)
The effects of support plate thickness on the drilling machinability of CFRP
(Sage Publications Ltd., 2023) Betgül, Çağlar; Köklü, Uğur; Morkavuk, Sezer
When carbon fiber reinforced plastics (CFRP) are drilled, delamination damage occurs at the hole entry and exit. An important method to reduce delamination at the hole exit is using a support plate. Therefore, sustainable drilling of CFRP to reduce the delamination damage is promising for modern industries. In this study, the effect of drilling CFRP composite plates using support plates of different thicknesses on thrust force, delamination, and borehole surface quality was experimentally investigated. The results showed that the thrust force increased as the support plate thickness increased at low spindle speed, but the support plate thickness did not significantly affect the thrust force at high spindle speed. While severe delamination damage occurred at the hole exit in the tests without the use of support, delamination damage was significantly reduced in the case of using a support plate. On the other hand, the severity of the damages decreased as the support plate thickness increased, especially unless very high feed rates were chosen. Consequently, the thickness of the support plate considerably influences the damage formation and severeness of the damages is significantly reduced when a support plate with sufficient thickness is used.
A metaheuristic approach for multi-objective optimization of the Stirling cycle with internal irreversibilities and regenerative losses using artificial bee colony algorithm
(Elsevier Ltd, 2023) Eser, Sezgin; Yüce, Bahadir Erman
This study aimed to investigate the multi-objective optimization of a Stirling cycle with a mathematical model that takes into account the dead volumes, effects of regenerative losses, and internal irreversibilities on the thermodynamic performance of the cycle. The optimization was carried out using the Artificial Bee Colony algorithm, which is a population-based metaheuristic method that mimics the foraging behavior of honeybees. The developed algorithm employs the concepts of Pareto frontier and ε-dominance to find the optimal solutions in the multi-objective space which is obtained with Artificial Bee Colony algorithm. The input parameters of the system are the maximum and minimum temperatures, compression and expansion volumes, and charge pressure which affect the thermodynamic variables of the cycle. The optimization process consisted of two stages: firstly, single-objective optimization was performed separately for each objective function to obtain the baseline results. Then, three different sets of triple-objective function groups were used to perform multi-objective optimization. These are Case 1 (net work output, thermal efficiency, irreversibility parameter), Case 2 (net work output, thermal efficiency, 2nd law efficiency), and Case 3 (net work output, thermal efficiency, entropy generation). The obtained results from the single and multi-objective optimizations were compared and analyzed. Since multi-objective optimization involves conflicting objectives, it does not result in a single optimal solution, but rather a set of optimal solutions that represent different trade-offs among the objectives. In order to achieve the optimum results with a good trade-off between solutions Pareto frontier method is used. In addition, to obtain a good distribution of solutions and filter very similar solution points in the solution space, ε-dominance was used to filter them. Finally, to select the final optimal solution from the Pareto frontier solution set, LINMAP was used as a decision-making tool which is a linear programming technique that assigns weights to each solution. The weights of the solutions are achieved according to the relative distance between objectives with their single optimal values achieved by single optimization. The best solution based on the net work output is achieved with Case 3 which includes entropy generation as different from other cases. Also, Case 3 has the lowest irreversibility parameter value even though the irreversibility parameter was optimized in Case 1. Entropy generation and mean effective pressure are quite sensitive due to the multiple solutions they have at each solution step when entropy generation is not an objective function.
Comparison of experimental and numerical analysis of Quasi-Static punch shear test for stainless steel sheet material
(Mersin Üniversitesi, 2022) Şahbaz, Mehmet
In this study, Quasi-Static Punch Shear Test (QS-PST) for AISI-304 stainless steel sheet material with 0.5 mm thickness was performed experimentally and numerically, then the results were compared. QS-PST was designed non-standard according to the need and is especially used to determine the puncture resistance of composite plate materials against low-speed loading. Since the results obtained from QS-PST are similar to those from ballistic tests, this has attracted the attention of researchers. The experimental study was carried out by integrating the die and punch which were specially produced for this test, into an electromechanical tensile-compression test device with a capacity of 100 kN. In order to define the material properties correctly in numerical analysis, the tensile tests of the relevant material were also carried out with the same device. Then, the CAD model of the experimental system was generated and Finite Element Analysis (FEA) was performed. In FEA, the mesh structure was determined as tetrahedral, since it gave closer results in such tests and the analyzes were performed by increasing the number of mesh from 16700 to 151800 elements. Finally, the experimentally and numerically obtained results were compared and it was observed that the result were very close depending on increasing the number of mesh.
Microstructure development and mechanical behaviour of pure copper processed by the novel TWO-CAP procedure
(Walter de Gruyter GmbH, 2023) Kaya, Hasan; Uçar, Mehmet; Şahbaz, Mehmet; Kentli, Aykut; Özbeyaz, Kerim; Öǧüt, Serkan
In this study, thin-walled open channel angular pressing (TWO-CAP) technique was applied to pure copper specimens as a novel severe plastic deformation (SPD) method. The TWO-CAP process was applied to the specimens up to four passes. After each pass, the microstructural and mechanical characterization of the material was investigated by tensile and hardness tests along with OM, SEM, EDS, TEM and XRD analyses. As a result, a highly increase in the mechanical properties was obtained, in addition satisfactory grain refinement was observed in microstructures. Strength and hardness values were positively affected from the minimizing the grain sizes after TWO-CAP process. Another reason of the improvements in mechanical properties can be explained as the increase in dislocation density. Furthermore, the effect of the TWO-CAP process on the dislocation density of the material has been demonstrated by XRD and TEM analyses in nanoscale. Moreover, the strain equation has been developed analytically and the effect of each pass on strain was calculated. Finally, the effect of the process on the stress-strain properties of the material was examined by the numerical analysis method and the study was verified.
Usage of 3D printing technology in centrifugal pumps and material selection
(SAGE Publications Ltd., 2023) Babayiğit, Osman; Sefaci, Selahattin; Şahbaz, Mehmet
The fused deposition modeling (FDM) technique which is one of the 3D printing technologies was used to produce a centrifugal pump impeller. The fabrication and investigation of the impeller were preferred because of its complex geometry and the difficulties encountered in its production. The most commonly used ABS, HIPS, PLA, and carbon fiber filaments were preferred to compare and determine the most suitable material for the production of the impellers. Firstly, mechanical test specimens from four different materials were printed in the 3D printer according to standards. Then the tensile tests and quasi-static punch shear tests (QS-PST) were applied to determine the mechanical properties of the 3D printed parts. Also, the mechanical tests were repeated to some specimen with the different fillings to define the optimum fill rates. Secondly, the impellers were fabricated from four materials by using the 3D printer in determined fill rates. Then, these impellers were mounted in the actual pump system, and pump performance tests were performed. In the pump performance tests, the head, pump efficiency, and electric power parameters were measured against the flow rate for each impeller. Finally, the mechanical properties and pump performance of the impellers compared with the GG25 cast iron impeller which is produced by traditional technique. As a result, PLA was selected as the most appropriate material for the production of the impellers. Furthermore, PLA showed superior performance compared to others when price, production time, and product weight parameters were considered.
An investigation of the impact of combustion chamber geometry on turbulent burning speeds in a thermodynamic model
(ASME, 2023) Kutlar, Osman Akın; Doğan, Hüseyin Emre; Demirci, Abdurrahman; Arslan, Hikmet
Combustion is the main parameter that affects efficiency and exhaust gas emissions. Recently, different studies have been carried out to increase the combustion rates due to the increasing use of the alternative fuels and lean mixtures in spark ignition engines. In general, in the absence of systems such as an optical access engine or ionization probes, combustion process evaluation is done based on cylinder pressure. In this study, the effect of different combustion chamber geometries on the turbulent burning speeds was investigated experimentally and theoretically. A three-zone, quasi-dimensional thermodynamic model for a spark ignition engine was constructed. Measured cylinder pressure data were used to establish the transition between the zones of the model and determine turbulent burning speeds. Two different turbulent speeds were calculated in the model, these are flame propagation and consumption speeds. It was seen that combustion chamber geometry significantly affected turbulent burning speeds. In MAN-Ricardo shapes and cylindrical shapes, the turbulent burning speeds decreased after it reached a maximum value in the combustion period. In flat geometry, without any bowl, speed continuously decreased different from other two designs. By means of a quasi-dimensional thermodynamic model, mean values of the turbulent burning and the flame propagation speeds can be calculated without having any optical observation.
The effects of aging process after solution heat treatment on drilling machinability of corrax steel
(Springer, 2023) Güldibi, Ahmet Serdar; Köklü, Uğur; Koçar, Oğuz; Kocaman, Engin; Morkavuk, Sezer
As a maraging steel, Corrax, is used in many engineering applications in the manufacturing, aerospace, and medical industries thanks to its properties such as high strength, hardness and corrosion resistance. However, these high specifications can cause some issues for manufacturing operations such as forging, machining, grinding. In addition to that, using heat treatment applications changes materials' mechanical specifications, affecting the material's behavior during machining. Therefore, it is important to characterize the influences of different heat treatment conditions on the material's property and behavior. In this study, the effects of heat treatment process on the mechanical properties, drilling machinability and corrosion resistance of Corrax steel were experimentally investigated with the samples of solution heat treated and aged at 400 °C, 525 °C, 600 °C, and 700 °C. The machinability was evaluated based on thrust force, chip morphology, hole quality, and tool wear. The results showed that the thrust force, torque and hole quality depend on feed rate, cutting speed, and mechanical properties affected by aging treatment. The highest hardness (47.4 HRC), ultimate tensile strength (1720 MPa), maximum elongation (33%), and toughness (198 jm-3) were obtained for the sample which aged at 525 °C for four hours, consequently the highest cutting force and surface roughness results were measured for this sample. Better hole surface quality and less burr formation were observed in the samples aged at 600 °C and 700 °C, and not-aged. On the other hand, while the highest value of corrosion potential were measured in the sample aged at 400 °C, the lowest corrosion potential value were measured in the sample aged at 700 °C. Graphical abstract: [Figure not available: see fulltext.].
Prediction of the mean turbulence intensity with a thermodynamic model for CNG and gasoline fuels
(Elsevier Ltd, 2023) Doğan, Hüseyin Emre; Demirci, Abdurrahman; Kutlar, Osman Akın; Arslan, Hikmet; Cihan, Ömer
Combustion is the main parameter that affects efficiency and exhaust gas emissions in internal combustion engines. In this study, the burning speed of gasoline and CNG were investigated quantitatively by calculating the mean value of turbulent consumption speed instead of qualitatively as is usually done. A three-zone quasi-dimensional thermodynamic model based on the measured cylinder pressure was created to calculate the mean value of turbulent consumption speed and turbulence intensity. The mass flow rate of air was kept constant in all experiments as much as possible, and the spark advance was kept constant at each relative air/fuel ratio. Thus, the effect of fuel and combustion chamber design on the consumption speed and turbulence intensity was directly determined. MR shape reached the highest consumption speed and turbulence intensity in all conditions. In the flat geometry, without any bowl, speed continuously decreased differently from the other designs. Natural gas burned clearly faster in the ultra-lean mixture. The increase in turbulence intensity has different effects on CNG and gasoline. The highest value of the mean turbulence intensity was calculated as approximately 3.4 m/s in the MR design. In the ultra-lean mixture, although the mass flow rate of air was constant, the mean value of the turbulence intensity changed in the same combustion chamber. Therefore, it has been determined that the combustion process affects the turbulence intensity. Using the quasi-dimensional thermodynamic model, mean values of the turbulent burning speeds and turbulence intensity might be calculated without having any optical observation and CFD analysis.
Investigation of burn parameters and cyclic variations of a spark ignition engine with different combustion chambers
(ASME, 2023) Demirci, Abdurrahman; Doğan, Hüseyin Emre; Kutlar, Osman Akın; Cihan, Ömer; Arslan, Hikmet
The tightening of the exhaust emission limits and the desire to reduce fuel consumption determine the direction of research on internal combustion engines. As it is known, the leaning of the mixture in spark ignition engines generally decreases fuel consumption and NOx emission together. Due to this fact, many researchers are focusing on lean combustion. The main purpose of this study is to compare the effect of different chamber geometries on combustion parameters of a spark ignition engine operated at lean and stoichiometric mixtures. One of the most important parameters of the combustion process is cyclic variations. It defines the stability of a spark ignition engine in operating conditions. Cyclic variations are increased with the leaning of the mixture in spark ignition engines. For lean mixture, a new combustion chamber was designed and manufactured for accelerating flow motions through its sickle and bowl shape. This chamber called MAN-Ricardo (MR) type decreased burn durations in the combustion process. While the start of the ignition for MR was later, the burn duration is shorter than that of the other two geometries. Therefore, MR type reduced the cyclic variations compared to other geometries in homogenous and lean mixtures. As a result, the combustion chamber must be designed to increase the turbulence intensity for a spark ignition engine to operate stably in lean mixtures, unlike the stoichiometric mixture.
Modelling and simulation of photovoltaic systems using MATLAB / Simulink
(World Scientific and Engineering Academy and Society, 2023) Çırak, Bekir
-The use of renewable energy sources has increased rapidly today, and the easy availability of solar energy and its abundance in nature are one step ahead of other renewable energy sources. The rapid increase in the technological infrastructure, especially to obtain electricity from solar energy by photovoltaic (PV) method, has also accelerated the process of integrating PV systems into people's daily life. In this study, the solar cell model was obtained by using a solar cell equivalent circuit with Matlab Simulink and a 5.3 kW PV generator was designed using this structure. Also, the performance of the PV module has been analyzed under different temperature and solar irradiation conditions. Thanks to the developed model, it is aimed to use PV model generators with different technical features and different installed power more easily. Methodology in this project study was to create a circuit model of a solar cell in the Matlab Simulink program, modeling this model as a subsystem.
Effect of machining parameters on surface quality of w-edmed Ti6Al4V alloy in ultrasonic assisted magnetic abrasive finishing technique
(Gazi Üniversitesi, 2023) Çelik, Mahmut; Gürün, Hakan; Çaydaş, Ulaş; Köklü, Uğur
In this study, a CNC milling machine was modified to include an ultrasonic system to finish Wire-EDMed Ti6Al4V alloy with Ultrasonic assisted magnetic abrasive finishing and the effects of machining parameters on surface quality and MRR were investigated. As seen in Figure A, improvements up to 90% occurred in surface roughness values. On the other hand, it was determined that ultrasonic support contributed 58% and 15%, respectively, in terms of surface quality and MRR. Purpose: The EDM method is frequently used in the machining of difficult-to-cut metals such as titanium alloys. As a result of the EDM method, unwanted formations such as recast layer, micro cracks and craters occur on the workpiece surface. These formations negatively affect the surface quality. In order to improve the surface quality of EDMed surfaces, a secondary finishing process is required. Magnetic abrasive finishing method is a method that can be used for this purpose. In this study, it is aimed to increase the surface quality of Wire-EDMed Ti6Al4V alloy with Ultrasonic assisted MAF method. Theory and Methods: In MAF technique, iron-based powders and abrasives are used together. These abrasives form a flexible magnetic brush assembly with iron powders along the magnetic field lines generated by the magnetic poles. The brush acts as a multi-point cutter. In this study, Wire - EDMed Ti6AL4V plates' surface quality was improved by ultrasonic assisted magnetic abrasive finishing method The experiments were carried out under the experimental conditions determined in the accordance of previous studies by CNC milling machine and improvement ratios of surface quality and material removal rates (MRR) were measured. Results: As a result of the experiments, an average improvement of 36 % and 57 % was observed in the Ra for MAF and UDMAF respectively. This improvement was found to be up to 81 % and 90 % in the appropriate experimental conditions. Additionally, MRR ratio was measured as 4.95 mg/min and 5.74 mg/min on average for MAF and UDMAF respectively. Conclusion: As a conclusion, MAF is a suitable method for improvement of surface quality of w-EDMed Ti6Al4V alloy. On the other hand, ultrasonic assist increased the efficiency of the method. © 2023 Gazi Universitesi Muhendislik-Mimarlik.
Machining GLARE fibre metal laminates: a comparative study on drilling effect between conventional and ultrasonic-assisted drilling
(Springer Science and Business Media Deutschland GmbH, 2022) Giasin, Khaled; Atif, Muhammad; Ma, Yuan; Jiang, Chulin; Köklü, Uğur; Sinke, Josg
GLARE laminates are multi-layered metal-composite materials created from bonding sheets of metallic alloys with carbon or glass fibre layers. The application of hybrid-conventional machining processes such as ultrasonic-assisted drilling (UAD) is becoming of great interest to the aerospace industry due to its capability in reducing the cutting forces and tool wear which are directly responsible for drilling-induced delamination. There is rich literature on the conventional drilling (CD) of GLARE, but no work reported using UAD process. This study will fill this gap and investigate the UAD of GLARE laminates using an indigenously developed UAD system. The influence of spindle speed and feed rate on thrust force and surface roughness metrics (Ra and Rz) were investigated under CD and UAD regimes. The quality of the borehole and damage mechanisms in the laminate constituents was examined using scanning electron microscopy (SEM). The contribution of the drilling parameters on the measured outputs was further evaluated using the analysis of variance (ANOVA) statistical analysis. It was found that UAD resulted in a significant reduction in thrust force by up to 65% while surface roughness metrics Ra and Rz were unaffected by the type of drilling process used. SEM analysis showed irregular and fuzzier surfaces in glass fibre layers in holes machined using UAD due to the longitudinal vibration of the tool.
Machinability and surface integrity investigation during helical hole milling in AZ31 magnesium alloy
(KeAi Publishing Communications Ltd., 2023) Adhikari, Raviraja; Bolar, Gururaj; Shanmugam, Ragavanantham; Köklü, Uğur
Conventional drilling has been widely used for making holes in structural materials. However, drawbacks like high cutting forces, poor surface finish, high cutting temperatures, excessive tool wear, and undesirable burr formation while drilling magnesium alloys have necessitated the development of alternative hole-making methods. Lately, the helical milling process has attracted interest in facilitating hole-making for assembly applications. However, the machinability of magnesium alloys using the helical milling process needs more investigation. Therefore, the presented work analyzed the influence of axial pitch, tangential feed, and spindle speed on cutting forces and surface integrity while milling AZ31 magnesium alloy. Axial feed was the most crucial factor contributing to the thrust force (71.8%), followed by tangential feed (13.2%). All three process variables impacted the radial force. Spindle speed was the most influential variable affecting the surface roughness (48.7%), followed by axial pitch (31.4%) and tangential feed (12.5%). Microhardness closer to the free surface of the hole was higher than the subsurface hardness. Moreover, microhardness showed an upward trend with the rise in axial pitch and tangential feed; however, it reduced with increased spindle speed.
Three-dimensional finite element modeling of drilling-ınduced damage in S2/FM94 glass-fiber-reinforced polymers (GFRPs)
(MDPI, 2022) Manzoor, Shahryar; Din, Israr Ud; Giasin, Khaled; Köklü, Uğur; Khan, K. A.; Panier, Stéphane
Considering that the machining of composites particularly fiber-reinforced polymer composites (FRPCs) has remained a challenge associated with their heterogeneity and anisotropic nature, damage caused by drilling operations can be considerably mitigated by following optimum cutting parameters. In this work, we numerically evaluated the effects of cutting parameters, such as feed rate and spindle speed, on the thrust force and torque during the drilling of glass-fiber-reinforced polymers (GFRPs). A meso-scale, also known as unidirectional ply-level-based finite element modeling, was employed assuming an individual homogenized lamina with transversely isotropic material principal directions. To initiate the meso-scale damage in each lamina, 3D formulations of Hashin’s failure theory were used for fiber damage and Puck’s failure theory was implemented for matrix damage onset via user subroutine VUMAT in ABAQUS. The developed model accounted for the complex kinematics taking place at the drill–workpiece interface and accurately predicted the thrust force and torque profiles as compared with the experimental results. The thrust forces for various drilling parameters were predicted with a maximum of 10% error as compared with the experimental results. It was found that a combination of lower feed rates and higher spindle speeds reduced the thrust force, which in turn minimized the drilling-induced damage, thus providing useful guidelines for drilling operations with higher-quality products. Finally, the effect of coefficient of friction was also investigated. Accordingly, a higher coefficient of friction between the workpiece and drill-bit reduced the thrust force.

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