Machine tool vibrations consist of a self-stimulating mechanism during chip removal by machining ... more Machine tool vibrations consist of a self-stimulating mechanism during chip removal by machining operations. The system, which is a structural mode of the tool-workpiece, is initially stimulated by a force. In turning operations, a wavy surface is formed on the workpiece because of both the previous revolution and structural vibrations. The maximum chip thickness may exponentially increase due to the phase shift between two consecutive waves, while the system oscillates at a chatter frequency very close to its structural mode. Variable growth in chip thickness increases vibrations, cutting forces and tool wear and causes a wavy surface. The purpose of the study is to compare different cutting tool inserts in terms of stable cutting depths. First, an experimental study was carried out and the stable cutting depths without chatter vibrations were determined in turning operations using various materials (AISI-1010, AISI-1050, Al-7075). Alumina inserts (Al2O3) were used in the study. Stable cutting depths were compared with a literature study that was performed using Titanium carbide (TiC) inserts. A paired t-test was used for the comparison. After the experimental study, a statistical/ optimization study was performed to optimize stable cutting depths. It was observed that the chatter frequency was generally higher than the natural frequency of the cutting tool. Also, it was observed that the decrease in the number of revolutions, tool overhang lengths and yield strength of workpiece results in higher stable cutting depths. When the number of revolution is 125 rpm, the overhang length is 70 mm, and the yield strength is 124 MPa, the stable cutting depths maximize. In addition, stable cutting depths were higher when using Al2O3 cutting tool inserts and chatter vibrations were prevented. There was a significant difference between the two inserts (p<0.05). It was found that the Al2O3 cutting tool inserts had better performances than TiC cutting inserts for the hard materials.
Shear thickening fluid (STF) is a kind of smart material showing increasing viscosity under loadi... more Shear thickening fluid (STF) is a kind of smart material showing increasing viscosity under loading. This unique behavior is benefitted in various applications however, STF usage in machining tools has not been investigated in literature. In this study, a novel tool was designed by integrating STF into conventional cutting tools for turning operations. Thanks to this design, the non-Newtonian rheology of STF contributes to the vibration damping properties of cutting tools and thereby suppressing the chatter vibrations during machining operations. For this reason, STF integrated cutting tools provide enhanced stability in the operations, which leads to an improvement in the surface quality of workpieces.
Ultrasonik yardımlı işleme, takıma veya iş parçasına belirli bir titreşim uygulanarak iş parçasın... more Ultrasonik yardımlı işleme, takıma veya iş parçasına belirli bir titreşim uygulanarak iş parçasının işlenmesi süreci olup son işlem uygulamalarında yüzey özelliklerinin iyileşmesi, kesme kuvvetlerinin azalması ve takım ömrünü arttırılması amacıyla uygulanır. Sıcak işleme ise talaş kaldırması zor olan malzemelerin termal yumuşamasını sağlayarak kesme işleminin kolaylaştırılmasını amaçlayan bir işlemdir. Bu işlem sayesinde kesme kuvvetlerinde azalma ve takım ömründe artış görülmektedir. İşlenebilirliği zor malzemeler için son yıllarda ortaya çıkan en önemli melez yöntemlerden biri ise sıcak titreşim yardımlı talaşlı işlemedir. Bu işlem ultrasonik yardımlı işleme ile sıcak işlemeyi birleştiren yeni bir melez imalat yöntemidir. Bu çalışma kapsamında ülkemizde yaygın olmayan bu üretim tekniği için yeni bir imalat ünitesi tasarımı yapılmıştır. Bu yeni üretim yöntemi ile özellikle savunma ve havacılık sektöründe işlenebilirliği düşük olan süperalaşım, paslanmaz çelik gibi malzemeler hem yüzey kalitesi arttıralarak imal edilebilecek hem de takım maliyeti gibi masraflar azaltılacaktır. Yöntemin hayata geçmesiyle de savunma ve havacılık gibi kritik bir alanlarda ileri teknoloji edinilerek milli bir birikim sağlanmış olacaktır. Tasarlanan imalat ünitesi üniversal torna tezgahlarına ilave bir modül olarak eklenebilmekte ve ileride CNC tezgahlar için de yaygınlaştırılabilme potansiyeline sahiptir.
Since the beginning of the 18th century, ergonomics and work studies have been used in the manufa... more Since the beginning of the 18th century, ergonomics and work studies have been used in the manufacturing industry. Because of the developments in mechanization, the work force has been significantly reduced. To efficiently use the resources of manufacturing systems, ergonomics and work studies are important and effective methods. Therefore, manufacturing firms are advantageous for evaluating different opportunities related to ergonomics.
In this study, an ergonomical study was conducted to improve the flow of processes for assembly in a cable manufacturing company. Then, newly improved processes and machine systems were proposed. Unnecessary work was eliminated, and a significant gain in time was obtained.
Conventional manufacturing methods are limited in the machining of newly developed high strength,... more Conventional manufacturing methods are limited in the machining of newly developed high strength, precision/brittle and complex shaped parts. Non-conventional manufacturing methods are required to machine such parts. Choosing the most suitable manufacturing method for the part is a vital decision-making problem and the solution of this problem is very important for today's manufacturers. In this study, three different Full Consistency Method (FUCOM) methods were combined with fuzzy Technique for Order Preference by Similarity to Ideal Solution method (fuzzy TOPSIS) and fuzzy weighted aggregated sum product assessment (fuzzy WASPAS) techniques. In order to test these developed methods, the selection of non-traditional manufacturing methods from the literature was taken as a case study. It is seen that the model produced successful results.
High-strength steel alloys, titanium, ceramics, composites are in the group of materials that are... more High-strength steel alloys, titanium, ceramics, composites are in the group of materials that are hard to machine. Conventional manufacturing techniques are not sufficient to machine these materials. For this reason, these materials are generally machined with non-conventional manufacturing methods. In this study, a fuzzy application of Best–Worst method and a novel hybrid decision-making model (Best–Worst decision-making approach with fuzzy TOPSIS) are proposed to solve different non-traditional machining method selection problems which were taken from the literature. Using these models, the Best–Worst method shortens the steps of solutions in the fuzzy environment compared to the AHP/ANP-based fuzzy solutions in the literature. The proposed models produce successful results.
The optimum selection of material in manufacturing environment should be investigated using a str... more The optimum selection of material in manufacturing environment should be investigated using a strategic perspective because of its complex nature. The ideal alternative cannot be found easily due to the different criteria, so the decision maker has to consider several factors for selecting the appropriate material. As a result, the decision maker should design a proper form of decision support system to solve the given problem. From decision-maker perspective, it is not easy to determine criteria weights of materials selection problem. Especially, several criteria cause inadequate subjective evaluation. In order to prevent this, different novel hybrid models were developed by using Indifference Threshold-based Attribute Ratio Analysis (ITARA), VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and Multi-Objective Optimization on the Basis of Ratio (MOORA) methods. Two case studies (material selection of flywheel and cryogenic storage tank) were taken from the literature to use these models. ITARA is used to calculate the criteria weights in the problems, and the final rankings are obtained by using VIKOR, TOPSIS and MOORA. The results indicate that the proposed methods produced successful results in terms of material selection perspective.
Vibration attenuation performance of structures is significantly important in aerospace, automoti... more Vibration attenuation performance of structures is significantly important in aerospace, automotive, sport and medical equipment applications. In order to enhance the vibration absorption properties, shear thickening fluid (STF) is a candidate component in the structures due to its viscoelastic behavior. In this study, the vibration characteristics of carbon fiber reinforced polymer (CFRP) tubes were investigated. To compensate the lack of vibration isolation behavior of CFRP tubes, a natural STF was filled into the tubes and thus, the thickening rheology of this smart fluid was benefited in the STF/CFRP structures. The damping properties of the structures were investigated with modal analysis and the natural frequencies and damping ratios were calculated for two different boundary conditions (single and double-fixed ends). The results showed that the STF integration into the CFRP tubes significantly enhances the natural frequency of the structures as well as providing higher damping ratio in the STF/CFRP systems.
In the present study, different turning operations (conventional, ultrasonic assisted and hot ult... more In the present study, different turning operations (conventional, ultrasonic assisted and hot ultrasonic assisted operations) of Ti6Al4V alloy were investigated by using a new multi-criteria decision-making method. In the first part of the study, conventional turning (CT), UAT and HUAT operations were conducted, and they were compared to each other. The modal/chatter tests were performed through a hammer and recording chatter sound. Cutting velocity (10-40 m/min), and cutting tool overhang lengths (60 and 70 mm) were used as cutting parameters in the experiments. The full factorial experimental design was used. In the comparison of the turning operations, surface roughness, stable cutting depths, and maximum cutting tool temperatures were considered. Also, variance analysis was carried out to optimize machining outputs. In addition, chip formation was observed. In the second part of the study, multi-criteria decision making (MCDM) analysis was performed by using Reference Ideal Method which has been recently presented in the literature to optimize machining outputs. Surface roughness, stable cutting depths, and maximum cutting tool temperatures were selected as criteria to rank all the experiments. Based on MCDM results, higher cutting speeds, lower tool overhang lengths and ultrasonic assisted turning are the appropriate levels of the cutting parameters. As a result, this study helps to understand new nontraditional machining methods in terms of MCDM perspective
Chatter vibration in turning and milling operations is one of the most critical problems that cau... more Chatter vibration in turning and milling operations is one of the most critical problems that causes low workpiece quality and manufacturing efficiency. Therefore, the determination of stable cutting depths is crucial for these operations. Several vibrational characteristics (natural frequency (wn), stiffness coefficient (k) and damping coefficient (s)) affect stable cutting depths. The vibration characteristics of these operations show randomness for every setup conditions. For this reason, the randomness of the vibration characteristics should be modeled. In this study, a probabilistic approach and regression model are combined for turning operation. Also, a probabilistic approach and analytical model are integrated for milling operation. The purpose of these models is to establish confidence intervals for stability diagrams. As a result, the operators can work in a secure region during the operations.
Nickel-based alloys provide high corrosion resistance and high-temperature strength but these all... more Nickel-based alloys provide high corrosion resistance and high-temperature strength but these alloys possess poor machinability. Hastelloy-X is a nickel based alloy that has been used for high temperature use. There are many studies about finite element modeling of aerospace alloys but studies in literature with Hastelloy-X are limited. In the present work, machining characteristics of Hastelloy-X were investigated and a numerical model was developed for the turning operation of Hastelloy-X. Two input parameters (cutting speed and feed rate) were variated in the operations and the results were evaluated considering process outputs such as cutting forces, cutting temperature, effective stresses and chip morphology. Based on the verification of the numerical model using experimental results, presented material model is appropriate for the turning operation of Hastelloy-X at low and medium cutting speed machining conditions.
In this study, different non-traditional turning operations were investigated using various soft ... more In this study, different non-traditional turning operations were investigated using various soft computing methods. In these operations, cutting speed, machining method, material type, and tool overhang lengths were used as machining inputs. Surface roughness, stable cutting depths, and maximum cutting tool temperatures were considered as machining outputs. In the first stage, Artificial Neural Network (ANN), Classification and Regression Tree (CART) and Support Vector Machine (SVM) models were developed to predict these outputs. In the second stage, an optimization study (regression analysis) was conducted. CART model produced better prediction results compared to the other methods. In CART models, 0.991, 0.998 and 0.959 values of correlation coefficients were calculated for the prediction of surface roughness, stable cutting depth, and max. cutting temperatures, respectively. In the optimization study, ultrasonic-assisted/hot ultrasonic-assisted turning methods, a tool overhang length of 60 mm, and a cutting speed of 10 m/min provide optimum conditions. The proposed soft computing models will help to understand these nontraditional machining methods. These models will give a preliminary idea before the experiments. These models can be used as an alternative instead of 2D finite element machining simulations. Less analysis time is required compared to the finite element simulations.
Structural health monitoring (SHM); isthe tracking method used to determine the location and size... more Structural health monitoring (SHM); isthe tracking method used to determine the location and size of the damage to the structure and the life of the structure. In this study, the behavior of a free piezoelectric sensor was experimentally tested using theelectromechanical impedance method (EMI), taking into account the structures exposed to varying environmental conditions, and simulation studies were performed using the ANSYS finite element program. In the experimental study; impedance measurements were performed between -10 °C and -45 °C after impedance measurements of the piezoelectric sensor were completed at room temperature. The frequency and amplitude have increased with decreasing temperature. In the simulation studies, harmonic analysis results were obtained by using the ANSYS finite element program of the piezoelectric sensor used in the experimental study. The frequency and amplitude increased as the temperature decreased, as in the results obtained from the experimental studies. The results obtained from experimental and simulation studies were found to be close to each other
Shear thickening fluid (STF) is a kind of non-Newtonian fluids exhibiting drastic viscosity jump ... more Shear thickening fluid (STF) is a kind of non-Newtonian fluids exhibiting drastic viscosity jump under an increasing shear rate. Even though these fluids are single-phase suspensions including nano-sized particles in a carrier liquid, various additives have been included in the suspensions to form multi-phase shear thickening concept. Despite novel concepts in compositions, rheological models have been studied only for single-phase STFs until this time. In the present work, multi-phase suspensions were fabricated adding aluminum oxide particles in a nano-silica/PEG based STF. Additive amount and temperature were selected as variables in the rheological measurements. Upon obtaining experimental data from the rheological tests, viscosity curves of the multi-phase STFs were adapted for a phenomenological model which was suggested for single-phase STFs. According to the results, the model gave proper fitting for the flow curves beyond the thickening point. However, it yielded a lower performance to predict the shear thinning region prior to the thickening onset. Therefore, a modified model was developed to fully cover the rheological behavior of multi-phase STFs. By the modified model proposed in this study, flow prediction of multi-phase STFs was improved due to the enhanced fitting performance, especially in the shear thinning region.
In this article, a novel method is suggested for solving heuristic optimization problems. A pre-s... more In this article, a novel method is suggested for solving heuristic optimization problems. A pre-study was performed to define proper bounds. Different problems with these bounds were solved using genetic, accelerated particle swarm, and cuckoo search algorithms. Three different problems (multi-pass turning, welded beam design, and tension spring) were used as case studies. The results of the studies were compared with the earlier studies. As a result, the proposed method requires less computing time and has better objective function values compared to the solutions in the literature. The proposed method provides effective decision-making for operators and engineers dealing with different design and manufacturing environments in terms of cost and time.
New materials lead to the occurrence of high technology industries. These materials are high stre... more New materials lead to the occurrence of high technology industries. These materials are high strength, corrosion and heat resistant steel alloys, titanium, ceramics, composites, and other non-metallic materials. Conventional machining methods are not proper to machine these materials in terms of high surface quality. Such materials are generally processed using non-traditional machining methods. Multi criteria decision making models (MCDM) are extensively used in material-process selection, and optimization of machining problems in engineering. In this study, a novel hybrid optimization model is proposed. Taguchi method is hybridized with Reference Ideal Method. The model is tested in two case studies (conventional and non-traditional machining problems) taken from literature. The proposed model can be used by engineers and operators in manufacturing environment.
In this article, surface roughness, cutting forces and material removal rates of different materi... more In this article, surface roughness, cutting forces and material removal rates of different materials are examined in different cutting conditions in turning operations. First, vibration characteristics (natural and chatter frequency, stiffness coefficient and damping ratio) are determined by different cutting tests. Surface roughness, material removal rate and cutting forces are measured during experiments. By using these experiments, five different hybrid multi-criteria decision making models are proposed. Cutting parameters are optimized by maximizing material removal rate and minimizing surface roughness and cutting force. This study will enable the operators and engineers to work more efficiently in the machining operations.
Aviation alloys exhibit superior properties such as high strength-to-weight ratio and corrosion r... more Aviation alloys exhibit superior properties such as high strength-to-weight ratio and corrosion resistance but these alloys possess poor machinability. In order to overcome this disadvantage, new machining methods (Ultrasonic assisted machining, hot machining etc.) are developed. Hot ultrasonic assisted turning (HUAT) is a new hybrid machining method which changes the cutting system between tool and workpiece therefore reduced cutting forces and better surface finish for workpiece are obtained. In this study, 2D finite element (FE) analysis is carried out to investigate the effects of these machining methods on titanium and Hastelloy-X alloys in terms of cutting forces, cutting tool temperatures and effective stresses. DEFORM-2D software is used during analyses. Also, an experimental study is conducted to verify numerical results. During verification, cutting tool temperature is taken into consideration. It is confirmed that HUAT technique reduces cutting forces and effective stress significantly but cutting temperature increases compared to conventional and ultrasonic assisted turning.
Ultrasonic assisted machining is a machining operation based on the intermittent cutting of mater... more Ultrasonic assisted machining is a machining operation based on the intermittent cutting of material which is obtained through vibrations generated by an ultrasonic system. This method utilizes low amplitude vibrations with high frequency to prevent continuous contact between a cutting tool and a work piece. Hot machining is another method for machining materials which are difficult to cut. The basic principle of this method is that the surface of the work piece is heated to a specific temperature below the recrystallization temperature of the material. This heating operation can be applied before or during the machining process. Both of these operations improve machining operations in terms of work piece-cutting tool characteristics. In this study, a novel hybrid machining method called Hot Ultrasonic Assisted Turning (HUAT) is proposed for the machinability of Hastelloy-X material. This new technique combines Ultrasonic Assisted Turning (UAT) and hot turning methods to take advantage of both machining methods in terms of machining characteristics, such as surface roughness, stable cutting depths and cutting tool temperature. In order to observe the effect of the HUAT method, Hastelloy-X alloy was selected as the work piece. Experiments on conventional turning (CT), UAT and HUAT operations were carried out for Hastelloy-X alloy, changing the cutting speed and cutting tool overhang lengths. Chip morphology was also observed. In addition, modal and sound tests were performed to investigate the modal and stability characteristics of the machining. The analysis of variance (ANOVA) method was performed to find the effect of the cutting speed, tool overhang length and machining techniques (CT, UAT, HUAT) on surface roughness, stable cutting depths and cutting tool temperature. The results show both ultrasonic vibration and heat improve the machining of Hastelloy-X. A decrease in surface roughness and an increase in stable cutting depths were observed and higher cutting tool temperatures were obtained in UAT and HUAT compared to CT. According to the ANOVA results, tool overhang length, cutting speed and machining techniques were effective parameters for surface roughness and stable cutting depths at a 1% significance level (p≤0.01). In addition, cutting speed and machining techniques have an influence on cutting tool temperature at a 1% significance level (p≤0.01). During chip analysis, serrated chips were observed in UAT and HUAT
Springback is inevitable phenomenon in bending operations. For the geometrical accuracy in manufa... more Springback is inevitable phenomenon in bending operations. For the geometrical accuracy in manufacturing, springback should be predicted and required compensation should be applied to the operation. Numerical method is very popular approach to predict the material behavior in the operations. This method provides reduction in time, effort and cost in comparison with trial and error method. In this study, springback in three-point bending operation of AA6082T6 tubes is investigated. A numerical model is established and results are compared with experimental outputs for verification of the model. Effects of indenter travel distance and wall thickness of tube in springback are studied
Machine tool vibrations consist of a self-stimulating mechanism during chip removal by machining ... more Machine tool vibrations consist of a self-stimulating mechanism during chip removal by machining operations. The system, which is a structural mode of the tool-workpiece, is initially stimulated by a force. In turning operations, a wavy surface is formed on the workpiece because of both the previous revolution and structural vibrations. The maximum chip thickness may exponentially increase due to the phase shift between two consecutive waves, while the system oscillates at a chatter frequency very close to its structural mode. Variable growth in chip thickness increases vibrations, cutting forces and tool wear and causes a wavy surface. The purpose of the study is to compare different cutting tool inserts in terms of stable cutting depths. First, an experimental study was carried out and the stable cutting depths without chatter vibrations were determined in turning operations using various materials (AISI-1010, AISI-1050, Al-7075). Alumina inserts (Al2O3) were used in the study. Stable cutting depths were compared with a literature study that was performed using Titanium carbide (TiC) inserts. A paired t-test was used for the comparison. After the experimental study, a statistical/ optimization study was performed to optimize stable cutting depths. It was observed that the chatter frequency was generally higher than the natural frequency of the cutting tool. Also, it was observed that the decrease in the number of revolutions, tool overhang lengths and yield strength of workpiece results in higher stable cutting depths. When the number of revolution is 125 rpm, the overhang length is 70 mm, and the yield strength is 124 MPa, the stable cutting depths maximize. In addition, stable cutting depths were higher when using Al2O3 cutting tool inserts and chatter vibrations were prevented. There was a significant difference between the two inserts (p<0.05). It was found that the Al2O3 cutting tool inserts had better performances than TiC cutting inserts for the hard materials.
Shear thickening fluid (STF) is a kind of smart material showing increasing viscosity under loadi... more Shear thickening fluid (STF) is a kind of smart material showing increasing viscosity under loading. This unique behavior is benefitted in various applications however, STF usage in machining tools has not been investigated in literature. In this study, a novel tool was designed by integrating STF into conventional cutting tools for turning operations. Thanks to this design, the non-Newtonian rheology of STF contributes to the vibration damping properties of cutting tools and thereby suppressing the chatter vibrations during machining operations. For this reason, STF integrated cutting tools provide enhanced stability in the operations, which leads to an improvement in the surface quality of workpieces.
Ultrasonik yardımlı işleme, takıma veya iş parçasına belirli bir titreşim uygulanarak iş parçasın... more Ultrasonik yardımlı işleme, takıma veya iş parçasına belirli bir titreşim uygulanarak iş parçasının işlenmesi süreci olup son işlem uygulamalarında yüzey özelliklerinin iyileşmesi, kesme kuvvetlerinin azalması ve takım ömrünü arttırılması amacıyla uygulanır. Sıcak işleme ise talaş kaldırması zor olan malzemelerin termal yumuşamasını sağlayarak kesme işleminin kolaylaştırılmasını amaçlayan bir işlemdir. Bu işlem sayesinde kesme kuvvetlerinde azalma ve takım ömründe artış görülmektedir. İşlenebilirliği zor malzemeler için son yıllarda ortaya çıkan en önemli melez yöntemlerden biri ise sıcak titreşim yardımlı talaşlı işlemedir. Bu işlem ultrasonik yardımlı işleme ile sıcak işlemeyi birleştiren yeni bir melez imalat yöntemidir. Bu çalışma kapsamında ülkemizde yaygın olmayan bu üretim tekniği için yeni bir imalat ünitesi tasarımı yapılmıştır. Bu yeni üretim yöntemi ile özellikle savunma ve havacılık sektöründe işlenebilirliği düşük olan süperalaşım, paslanmaz çelik gibi malzemeler hem yüzey kalitesi arttıralarak imal edilebilecek hem de takım maliyeti gibi masraflar azaltılacaktır. Yöntemin hayata geçmesiyle de savunma ve havacılık gibi kritik bir alanlarda ileri teknoloji edinilerek milli bir birikim sağlanmış olacaktır. Tasarlanan imalat ünitesi üniversal torna tezgahlarına ilave bir modül olarak eklenebilmekte ve ileride CNC tezgahlar için de yaygınlaştırılabilme potansiyeline sahiptir.
Since the beginning of the 18th century, ergonomics and work studies have been used in the manufa... more Since the beginning of the 18th century, ergonomics and work studies have been used in the manufacturing industry. Because of the developments in mechanization, the work force has been significantly reduced. To efficiently use the resources of manufacturing systems, ergonomics and work studies are important and effective methods. Therefore, manufacturing firms are advantageous for evaluating different opportunities related to ergonomics.
In this study, an ergonomical study was conducted to improve the flow of processes for assembly in a cable manufacturing company. Then, newly improved processes and machine systems were proposed. Unnecessary work was eliminated, and a significant gain in time was obtained.
Conventional manufacturing methods are limited in the machining of newly developed high strength,... more Conventional manufacturing methods are limited in the machining of newly developed high strength, precision/brittle and complex shaped parts. Non-conventional manufacturing methods are required to machine such parts. Choosing the most suitable manufacturing method for the part is a vital decision-making problem and the solution of this problem is very important for today's manufacturers. In this study, three different Full Consistency Method (FUCOM) methods were combined with fuzzy Technique for Order Preference by Similarity to Ideal Solution method (fuzzy TOPSIS) and fuzzy weighted aggregated sum product assessment (fuzzy WASPAS) techniques. In order to test these developed methods, the selection of non-traditional manufacturing methods from the literature was taken as a case study. It is seen that the model produced successful results.
High-strength steel alloys, titanium, ceramics, composites are in the group of materials that are... more High-strength steel alloys, titanium, ceramics, composites are in the group of materials that are hard to machine. Conventional manufacturing techniques are not sufficient to machine these materials. For this reason, these materials are generally machined with non-conventional manufacturing methods. In this study, a fuzzy application of Best–Worst method and a novel hybrid decision-making model (Best–Worst decision-making approach with fuzzy TOPSIS) are proposed to solve different non-traditional machining method selection problems which were taken from the literature. Using these models, the Best–Worst method shortens the steps of solutions in the fuzzy environment compared to the AHP/ANP-based fuzzy solutions in the literature. The proposed models produce successful results.
The optimum selection of material in manufacturing environment should be investigated using a str... more The optimum selection of material in manufacturing environment should be investigated using a strategic perspective because of its complex nature. The ideal alternative cannot be found easily due to the different criteria, so the decision maker has to consider several factors for selecting the appropriate material. As a result, the decision maker should design a proper form of decision support system to solve the given problem. From decision-maker perspective, it is not easy to determine criteria weights of materials selection problem. Especially, several criteria cause inadequate subjective evaluation. In order to prevent this, different novel hybrid models were developed by using Indifference Threshold-based Attribute Ratio Analysis (ITARA), VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and Multi-Objective Optimization on the Basis of Ratio (MOORA) methods. Two case studies (material selection of flywheel and cryogenic storage tank) were taken from the literature to use these models. ITARA is used to calculate the criteria weights in the problems, and the final rankings are obtained by using VIKOR, TOPSIS and MOORA. The results indicate that the proposed methods produced successful results in terms of material selection perspective.
Vibration attenuation performance of structures is significantly important in aerospace, automoti... more Vibration attenuation performance of structures is significantly important in aerospace, automotive, sport and medical equipment applications. In order to enhance the vibration absorption properties, shear thickening fluid (STF) is a candidate component in the structures due to its viscoelastic behavior. In this study, the vibration characteristics of carbon fiber reinforced polymer (CFRP) tubes were investigated. To compensate the lack of vibration isolation behavior of CFRP tubes, a natural STF was filled into the tubes and thus, the thickening rheology of this smart fluid was benefited in the STF/CFRP structures. The damping properties of the structures were investigated with modal analysis and the natural frequencies and damping ratios were calculated for two different boundary conditions (single and double-fixed ends). The results showed that the STF integration into the CFRP tubes significantly enhances the natural frequency of the structures as well as providing higher damping ratio in the STF/CFRP systems.
In the present study, different turning operations (conventional, ultrasonic assisted and hot ult... more In the present study, different turning operations (conventional, ultrasonic assisted and hot ultrasonic assisted operations) of Ti6Al4V alloy were investigated by using a new multi-criteria decision-making method. In the first part of the study, conventional turning (CT), UAT and HUAT operations were conducted, and they were compared to each other. The modal/chatter tests were performed through a hammer and recording chatter sound. Cutting velocity (10-40 m/min), and cutting tool overhang lengths (60 and 70 mm) were used as cutting parameters in the experiments. The full factorial experimental design was used. In the comparison of the turning operations, surface roughness, stable cutting depths, and maximum cutting tool temperatures were considered. Also, variance analysis was carried out to optimize machining outputs. In addition, chip formation was observed. In the second part of the study, multi-criteria decision making (MCDM) analysis was performed by using Reference Ideal Method which has been recently presented in the literature to optimize machining outputs. Surface roughness, stable cutting depths, and maximum cutting tool temperatures were selected as criteria to rank all the experiments. Based on MCDM results, higher cutting speeds, lower tool overhang lengths and ultrasonic assisted turning are the appropriate levels of the cutting parameters. As a result, this study helps to understand new nontraditional machining methods in terms of MCDM perspective
Chatter vibration in turning and milling operations is one of the most critical problems that cau... more Chatter vibration in turning and milling operations is one of the most critical problems that causes low workpiece quality and manufacturing efficiency. Therefore, the determination of stable cutting depths is crucial for these operations. Several vibrational characteristics (natural frequency (wn), stiffness coefficient (k) and damping coefficient (s)) affect stable cutting depths. The vibration characteristics of these operations show randomness for every setup conditions. For this reason, the randomness of the vibration characteristics should be modeled. In this study, a probabilistic approach and regression model are combined for turning operation. Also, a probabilistic approach and analytical model are integrated for milling operation. The purpose of these models is to establish confidence intervals for stability diagrams. As a result, the operators can work in a secure region during the operations.
Nickel-based alloys provide high corrosion resistance and high-temperature strength but these all... more Nickel-based alloys provide high corrosion resistance and high-temperature strength but these alloys possess poor machinability. Hastelloy-X is a nickel based alloy that has been used for high temperature use. There are many studies about finite element modeling of aerospace alloys but studies in literature with Hastelloy-X are limited. In the present work, machining characteristics of Hastelloy-X were investigated and a numerical model was developed for the turning operation of Hastelloy-X. Two input parameters (cutting speed and feed rate) were variated in the operations and the results were evaluated considering process outputs such as cutting forces, cutting temperature, effective stresses and chip morphology. Based on the verification of the numerical model using experimental results, presented material model is appropriate for the turning operation of Hastelloy-X at low and medium cutting speed machining conditions.
In this study, different non-traditional turning operations were investigated using various soft ... more In this study, different non-traditional turning operations were investigated using various soft computing methods. In these operations, cutting speed, machining method, material type, and tool overhang lengths were used as machining inputs. Surface roughness, stable cutting depths, and maximum cutting tool temperatures were considered as machining outputs. In the first stage, Artificial Neural Network (ANN), Classification and Regression Tree (CART) and Support Vector Machine (SVM) models were developed to predict these outputs. In the second stage, an optimization study (regression analysis) was conducted. CART model produced better prediction results compared to the other methods. In CART models, 0.991, 0.998 and 0.959 values of correlation coefficients were calculated for the prediction of surface roughness, stable cutting depth, and max. cutting temperatures, respectively. In the optimization study, ultrasonic-assisted/hot ultrasonic-assisted turning methods, a tool overhang length of 60 mm, and a cutting speed of 10 m/min provide optimum conditions. The proposed soft computing models will help to understand these nontraditional machining methods. These models will give a preliminary idea before the experiments. These models can be used as an alternative instead of 2D finite element machining simulations. Less analysis time is required compared to the finite element simulations.
Structural health monitoring (SHM); isthe tracking method used to determine the location and size... more Structural health monitoring (SHM); isthe tracking method used to determine the location and size of the damage to the structure and the life of the structure. In this study, the behavior of a free piezoelectric sensor was experimentally tested using theelectromechanical impedance method (EMI), taking into account the structures exposed to varying environmental conditions, and simulation studies were performed using the ANSYS finite element program. In the experimental study; impedance measurements were performed between -10 °C and -45 °C after impedance measurements of the piezoelectric sensor were completed at room temperature. The frequency and amplitude have increased with decreasing temperature. In the simulation studies, harmonic analysis results were obtained by using the ANSYS finite element program of the piezoelectric sensor used in the experimental study. The frequency and amplitude increased as the temperature decreased, as in the results obtained from the experimental studies. The results obtained from experimental and simulation studies were found to be close to each other
Shear thickening fluid (STF) is a kind of non-Newtonian fluids exhibiting drastic viscosity jump ... more Shear thickening fluid (STF) is a kind of non-Newtonian fluids exhibiting drastic viscosity jump under an increasing shear rate. Even though these fluids are single-phase suspensions including nano-sized particles in a carrier liquid, various additives have been included in the suspensions to form multi-phase shear thickening concept. Despite novel concepts in compositions, rheological models have been studied only for single-phase STFs until this time. In the present work, multi-phase suspensions were fabricated adding aluminum oxide particles in a nano-silica/PEG based STF. Additive amount and temperature were selected as variables in the rheological measurements. Upon obtaining experimental data from the rheological tests, viscosity curves of the multi-phase STFs were adapted for a phenomenological model which was suggested for single-phase STFs. According to the results, the model gave proper fitting for the flow curves beyond the thickening point. However, it yielded a lower performance to predict the shear thinning region prior to the thickening onset. Therefore, a modified model was developed to fully cover the rheological behavior of multi-phase STFs. By the modified model proposed in this study, flow prediction of multi-phase STFs was improved due to the enhanced fitting performance, especially in the shear thinning region.
In this article, a novel method is suggested for solving heuristic optimization problems. A pre-s... more In this article, a novel method is suggested for solving heuristic optimization problems. A pre-study was performed to define proper bounds. Different problems with these bounds were solved using genetic, accelerated particle swarm, and cuckoo search algorithms. Three different problems (multi-pass turning, welded beam design, and tension spring) were used as case studies. The results of the studies were compared with the earlier studies. As a result, the proposed method requires less computing time and has better objective function values compared to the solutions in the literature. The proposed method provides effective decision-making for operators and engineers dealing with different design and manufacturing environments in terms of cost and time.
New materials lead to the occurrence of high technology industries. These materials are high stre... more New materials lead to the occurrence of high technology industries. These materials are high strength, corrosion and heat resistant steel alloys, titanium, ceramics, composites, and other non-metallic materials. Conventional machining methods are not proper to machine these materials in terms of high surface quality. Such materials are generally processed using non-traditional machining methods. Multi criteria decision making models (MCDM) are extensively used in material-process selection, and optimization of machining problems in engineering. In this study, a novel hybrid optimization model is proposed. Taguchi method is hybridized with Reference Ideal Method. The model is tested in two case studies (conventional and non-traditional machining problems) taken from literature. The proposed model can be used by engineers and operators in manufacturing environment.
In this article, surface roughness, cutting forces and material removal rates of different materi... more In this article, surface roughness, cutting forces and material removal rates of different materials are examined in different cutting conditions in turning operations. First, vibration characteristics (natural and chatter frequency, stiffness coefficient and damping ratio) are determined by different cutting tests. Surface roughness, material removal rate and cutting forces are measured during experiments. By using these experiments, five different hybrid multi-criteria decision making models are proposed. Cutting parameters are optimized by maximizing material removal rate and minimizing surface roughness and cutting force. This study will enable the operators and engineers to work more efficiently in the machining operations.
Aviation alloys exhibit superior properties such as high strength-to-weight ratio and corrosion r... more Aviation alloys exhibit superior properties such as high strength-to-weight ratio and corrosion resistance but these alloys possess poor machinability. In order to overcome this disadvantage, new machining methods (Ultrasonic assisted machining, hot machining etc.) are developed. Hot ultrasonic assisted turning (HUAT) is a new hybrid machining method which changes the cutting system between tool and workpiece therefore reduced cutting forces and better surface finish for workpiece are obtained. In this study, 2D finite element (FE) analysis is carried out to investigate the effects of these machining methods on titanium and Hastelloy-X alloys in terms of cutting forces, cutting tool temperatures and effective stresses. DEFORM-2D software is used during analyses. Also, an experimental study is conducted to verify numerical results. During verification, cutting tool temperature is taken into consideration. It is confirmed that HUAT technique reduces cutting forces and effective stress significantly but cutting temperature increases compared to conventional and ultrasonic assisted turning.
Ultrasonic assisted machining is a machining operation based on the intermittent cutting of mater... more Ultrasonic assisted machining is a machining operation based on the intermittent cutting of material which is obtained through vibrations generated by an ultrasonic system. This method utilizes low amplitude vibrations with high frequency to prevent continuous contact between a cutting tool and a work piece. Hot machining is another method for machining materials which are difficult to cut. The basic principle of this method is that the surface of the work piece is heated to a specific temperature below the recrystallization temperature of the material. This heating operation can be applied before or during the machining process. Both of these operations improve machining operations in terms of work piece-cutting tool characteristics. In this study, a novel hybrid machining method called Hot Ultrasonic Assisted Turning (HUAT) is proposed for the machinability of Hastelloy-X material. This new technique combines Ultrasonic Assisted Turning (UAT) and hot turning methods to take advantage of both machining methods in terms of machining characteristics, such as surface roughness, stable cutting depths and cutting tool temperature. In order to observe the effect of the HUAT method, Hastelloy-X alloy was selected as the work piece. Experiments on conventional turning (CT), UAT and HUAT operations were carried out for Hastelloy-X alloy, changing the cutting speed and cutting tool overhang lengths. Chip morphology was also observed. In addition, modal and sound tests were performed to investigate the modal and stability characteristics of the machining. The analysis of variance (ANOVA) method was performed to find the effect of the cutting speed, tool overhang length and machining techniques (CT, UAT, HUAT) on surface roughness, stable cutting depths and cutting tool temperature. The results show both ultrasonic vibration and heat improve the machining of Hastelloy-X. A decrease in surface roughness and an increase in stable cutting depths were observed and higher cutting tool temperatures were obtained in UAT and HUAT compared to CT. According to the ANOVA results, tool overhang length, cutting speed and machining techniques were effective parameters for surface roughness and stable cutting depths at a 1% significance level (p≤0.01). In addition, cutting speed and machining techniques have an influence on cutting tool temperature at a 1% significance level (p≤0.01). During chip analysis, serrated chips were observed in UAT and HUAT
Springback is inevitable phenomenon in bending operations. For the geometrical accuracy in manufa... more Springback is inevitable phenomenon in bending operations. For the geometrical accuracy in manufacturing, springback should be predicted and required compensation should be applied to the operation. Numerical method is very popular approach to predict the material behavior in the operations. This method provides reduction in time, effort and cost in comparison with trial and error method. In this study, springback in three-point bending operation of AA6082T6 tubes is investigated. A numerical model is established and results are compared with experimental outputs for verification of the model. Effects of indenter travel distance and wall thickness of tube in springback are studied
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Papers by Alper Sofuoğlu
uygulamalarında yüzey özelliklerinin iyileşmesi, kesme kuvvetlerinin azalması ve takım ömrünü arttırılması amacıyla uygulanır.
Sıcak işleme ise talaş kaldırması zor olan malzemelerin termal yumuşamasını sağlayarak kesme işleminin kolaylaştırılmasını
amaçlayan bir işlemdir. Bu işlem sayesinde kesme kuvvetlerinde azalma ve takım ömründe artış görülmektedir. İşlenebilirliği zor
malzemeler için son yıllarda ortaya çıkan en önemli melez yöntemlerden biri ise sıcak titreşim yardımlı talaşlı işlemedir. Bu işlem
ultrasonik yardımlı işleme ile sıcak işlemeyi birleştiren yeni bir melez imalat yöntemidir. Bu çalışma kapsamında ülkemizde yaygın
olmayan bu üretim tekniği için yeni bir imalat ünitesi tasarımı yapılmıştır. Bu yeni üretim yöntemi ile özellikle savunma ve
havacılık sektöründe işlenebilirliği düşük olan süperalaşım, paslanmaz çelik gibi malzemeler hem yüzey kalitesi arttıralarak imal
edilebilecek hem de takım maliyeti gibi masraflar azaltılacaktır. Yöntemin hayata geçmesiyle de savunma ve havacılık gibi kritik
bir alanlarda ileri teknoloji edinilerek milli bir birikim sağlanmış olacaktır. Tasarlanan imalat ünitesi üniversal torna tezgahlarına
ilave bir modül olarak eklenebilmekte ve ileride CNC tezgahlar için de yaygınlaştırılabilme potansiyeline sahiptir.
In this study, an ergonomical study was conducted to improve the flow of processes for assembly in a cable manufacturing company. Then, newly improved processes and machine systems were proposed. Unnecessary work was eliminated, and a significant gain in time was obtained.
uygulamalarında yüzey özelliklerinin iyileşmesi, kesme kuvvetlerinin azalması ve takım ömrünü arttırılması amacıyla uygulanır.
Sıcak işleme ise talaş kaldırması zor olan malzemelerin termal yumuşamasını sağlayarak kesme işleminin kolaylaştırılmasını
amaçlayan bir işlemdir. Bu işlem sayesinde kesme kuvvetlerinde azalma ve takım ömründe artış görülmektedir. İşlenebilirliği zor
malzemeler için son yıllarda ortaya çıkan en önemli melez yöntemlerden biri ise sıcak titreşim yardımlı talaşlı işlemedir. Bu işlem
ultrasonik yardımlı işleme ile sıcak işlemeyi birleştiren yeni bir melez imalat yöntemidir. Bu çalışma kapsamında ülkemizde yaygın
olmayan bu üretim tekniği için yeni bir imalat ünitesi tasarımı yapılmıştır. Bu yeni üretim yöntemi ile özellikle savunma ve
havacılık sektöründe işlenebilirliği düşük olan süperalaşım, paslanmaz çelik gibi malzemeler hem yüzey kalitesi arttıralarak imal
edilebilecek hem de takım maliyeti gibi masraflar azaltılacaktır. Yöntemin hayata geçmesiyle de savunma ve havacılık gibi kritik
bir alanlarda ileri teknoloji edinilerek milli bir birikim sağlanmış olacaktır. Tasarlanan imalat ünitesi üniversal torna tezgahlarına
ilave bir modül olarak eklenebilmekte ve ileride CNC tezgahlar için de yaygınlaştırılabilme potansiyeline sahiptir.
In this study, an ergonomical study was conducted to improve the flow of processes for assembly in a cable manufacturing company. Then, newly improved processes and machine systems were proposed. Unnecessary work was eliminated, and a significant gain in time was obtained.