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Öğe Comparison of Flow Curves of AA 5457-O Sheet Material Determined by Hydraulic Bulge and Tensile Tests at Warm Forming Temperatures(AMER SOC TESTING MATERIALS, 2016) Sukur, Emine Feyza; Turkoz, Mevlut; Dilmec, Murat; Halkaci, Huseyin Selcuk; Halkaci, MehmetThe deformation behavior of sheet materials changes according to temperature. It is possible that the formability of a material for different temperatures is investigated and the flow curves are obtained by using a hydraulic bulge test. Generally, biaxial stress state occurs in real forming processes. Flow curves can be derived from the hydraulic bulge test for the biaxial stress state, and the higher strain values can be achieved in comparison to the tensile test without extrapolation. Hydraulic bulge tests are preferred instead of tensile tests on account of presuming the problems can occur during the formation process of sheet material, being informed about the formability of material at the current pressure and temperature states, and obtaining flow curves to perform more accurate process simulations. In this study, the flow curves for the material AA5754-O were obtained using the warm bulge test and by considering the strain rates. The sections of the curves that can be used in simulation were identified, and these curves were comparatively investigated with respect to the curves obtained from the tensile test. In addition, case studies were performed in order to conduct more realisitic simulations using the results of the flow curves obtained from the bulge and tensile tests.Öğe Design of Sheet Hydroforming Press Body(IEEE, 2017) Turkoz, Mevlut; Avci, Semih; Dilmec, Murat; Ozturk, Ekrem; Halkaci, Mehmet; Halkaci, H. SelcukIn this research, the body of a sheet hydroforming press, which can produce an industrial product, was designed and dimensioned. Initially, the required pressure and forces to produce the industrial product were determined by finite element analysis. Then, structural analysis of the press body was conducted by using these forces in Solidworks Premium simulation module. The strain gauges were bonded on various critical areas of the press body. The strains were measured for various loading conditions and compared with the analysis results. According to the results obtained, the strain values obtained from the analysis and measured experimentally are in good agreement with each other.Öğe Design, Fabrication, and Experimental Validation of a Warm Hydroforming Test System(ASME, 2016) Turkoz, Mevlut; Halkacr, Huseyin Selcuk; Halkaci, Mehmet; Dilmec, Murat; Avci, Semih; Koc, MuammerIn this study, a hydroforming system was designed, built, and experimentally validated to perform lab-scale warm hydromechanical deep drawing (WHDD) tests and small-scale industrial production with all necessary heating, cooling, control and sealing systems. This manuscript describes the detailed design and fabrication stages of a warm hydroforming test and production system for the first time. In addition, performance of each subsystem is validated through repeated production and/or test runs as well as through part quality measurements. The sealing at high temperatures, the proper insulation and isolation of the press frame from the tooling and synchronized control had to be overcome. Furthermore, in the designed system, the flange area can be heated up to 400 degrees C using induction heaters in the die and blank holders (BH), whereas the punch can be cooled down to temperatures of around 10 degrees C. Validation and performance tests were performed to characterize the capacity and limits of the system. As a result of these tests, the fluid pressure, the blank holder force (BHF), the punch position and speed were fine-tuned independent of each other and the desired temperature distribution on the sheet metal was obtained by the heating and cooling systems. Thus, an expanded optimal process window was obtained to enable all or either of increased production/test speed, reduced energy usage and time. Consequently, this study is expected to provide other researchers and manufacturers with a set of design and process guidelines to develop similar systems.Öğe Detailed Investigation of Forming Limit Determination Standards for Aluminum Alloys(AMER SOC TESTING MATERIALS, 2013) Dilmec, Murat; Halkaci, H. Selcuk; Ozturk, Fahrettin; Turkoz, MevlutIn this study, experimental studies were conducted to evaluate the differences between the ASTM E2218-02 and ISO 12004-2 standards that are used for construction of the forming limit curve (FLC) and that made various assumptions, which create dissimilar FLCs for the same material. The comparison was made for two materials which have moderate brittle and ductile characteristics, AA2024-T4 and AA5754-O alloys, respectively. The effects of a specimen's geometry, lubrication condition, and determination methods of limit strains on FLCs were considered and compared. Because the same strain evaluation method should be used for the standards, so as to be able to investigate the effect of only standards, a simple method in the computer grid analysis system was used. To test the validity and the reliability of the method, limit strains on the same specimens were also determined with using a real-time measurement method for the ISO experiments, and the results reveal that the method is reliable. Failure mechanisms were inspected for further investigation. The Nakajima specimens formed with the two standards showed different failure mechanisms. Finally, conducting the case studies, it was concluded that ISO 12004-2 yields more reliable and reproducible results than the ASTM standard.Öğe Determination of optimal loading profiles in hydromechanical deep drawing process using integrated adaptive finite element analysis and fuzzy control approach(SPRINGER LONDON LTD, 2017) Ozturk, Ekrem; Turkoz, Mevlut; Halkaci, H. Selcuk; Koc, MuammerIn this paper, an improved approach is proposed to determine the optimal profiles of two controllable process parameters (hydraulic pressure and blank holder force), which improve the forming condition and/or make better use of forming limits in hydromechanical deep drawing (HMD) process. A method based on adaptive finite element analysis coupled with fuzzy control algorithm (aFEA-FCA) was developed using LS-DYNA to determine the optimal loading profiles and thus to maximize the limiting drawing ratio (LDR). Maximum thickness reduction, maximum wrinkle height in the flange region of the sheet metal blank, and position of the nodes in the unsupported portion of the sheet metal blank between punch and die were used as criteria in the fuzzy control algorithm. Different rule-based matrices were compared by considering the maximum thinning occurred in the sheet metal blank, and thus, the most accurate matrices were determined for the control algorithm. The optimal loading profiles could be determined in a single FEA, thus reducing the computation time. The proposed approach enables determining the optimal loading profiles and also could be applied to complex parts easily. In addition, effects of initial blank diameter and coefficient of friction between the sheet-blank holder and sheet-die on the optimal loading profiles were investigated. An attainable LDR of 2.75 for AA 5754-O sheet material in hydromechanical deep drawing process was proven experimentally using the optimal loading profiles determined by adaptive FEA.Öğe EFFECT OF SHEET THICKNESS ON THE ANISOTROPY AND THICKNESS DISTRIBUTION FOR AA2024-T4(INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2013) Dilmec, Murat; Halkaci, Huseyin Selcuk; Ozturk, Fahrettin; Turkoz, MevlutIn this study, the effect of sheet thickness on the anisotropy and thickness distribution at room temperature (RT) was investigated for AA2024-T4 sheets. The anisotropy was determined using automated strain measurement with a grid analysis and profile-projector methods. The results indicate that the effects of the thicknesses of 0.8 mm, 1 mm, and 2 mm on the anisotropy were insignificant. In addition to the anisotropy measurement, the thickness variation of the specimens was also monitored. Besides the anisotropy values, no significant differences were observed between various thicknesses and directions.Öğe The Effect of Temperature and Strain-Rate Sensitivity on Formability of AA 5754(TRANS TECH PUBLICATIONS LTD, 2012) Turkoz, Mevlut; Halkaci, H. Selcuk; Koc, MuammerAluminum alloys have limited usage because of their limited formability at room temperatures. In order to design and develop more parts made of aluminum, new forming techniques such as hydroforming, warm forming and warm hydroforming have been researched to overcome the low formability issues. This, in turn, necessitates understanding and modeling the behavior of aluminum alloys at different temperatures and strain rates. This paper deals with the investigation of the effect of temperature and strain rate sensitivity on the formability of AA 5754 aluminum alloy. Tensile tests were carried out at temperatures of 20,100,180 and 260 degrees C and forming rates of 25, 100 and 250 mm/min. The mechanical properties and flow curves were obtained and the strain rate sensitivities were calculated at different strains and temperatures. The effects of temperature and strain rate sensitivity on the formability were introduced.Öğe Effects of Heat Treatment Conditions on the Mechanical Properties of AA 2024 Alloy(TRANS TECH PUBLICATIONS LTD, 2012) Halkaci, Huseyin Selcuk; Turkoz, Mevlut; Yigit, OsmanAluminum alloys have good properties such as high strength-to-weight ratio, corrosion resistance and relatively low cost. Nowadays they are primarily used as wrought and cast in many industries such as automotive, aviation and aerospace because of these properties. Aluminum alloys are classified into two categories as non-heat-treatable and heat-treatable. The mechanical properties of the heat-treatable alloys are improved by solution heat treatment and controlled ageing. While mechanical properties of some heat-treatable alloys, especially 2XXX series, become stable with natural ageing at room temperature within a few days, some of them are unstable and exhibit significant changes in properties even after many years. Heat treatment process of AA 2024 is very sensible and critical and therefore should be carefully performed. In this research, effects of the solution temperature, soaking time, heating rate and quenching delay condition of AA 2024 on the mechanical properties were investigated.Öğe Enhancing formability in hydromechanical deep drawing process adding a shallow drawbead to the blank holder(ELSEVIER SCIENCE SA, 2014) Halkaci, Huseyin Selcuk; Turkoz, Mevlut; Dilmec, MuratIn this paper, a new method was proposed in order to enhance the limiting drawing ratio (LDR) of AA5754-O in the hydromechanical deep drawing process (HDD). In the proposed method, a shallow drawbead was added to the blank holder to increase LDR so as to provide strain hardening of a large region on the flange of the sheet material in addition to pre-bulging process which affects particularly only the initial stage but not the later ongoing process. So the LDR of the AA5754-O was increased from 2.65 to 2.787 by enlarging the region of strain hardening in the flange and partially reducing wrinkling tendency due to occurred tensile stresses using the convenient pressure and blank holder force profiles. The importance levels and their convenient values for height of drawbead, pre-bulge height and pressure, surface roughness of the punch were determined with analysis of variance (ANOVA) is a statistical method. ANOVA analysis illustrated that adding a shallow drawbead to the blank holder is the most effective factor between the investigated factors for the HOD process. While the effects of the pre-bulging pressure and pre-bulging height were determined as quite small, the surface roughness of the punch was found unimportant compared to the effect of the shallow drawbead. The highest LDR value was obtained with 1 mm drawbead height, 5 mm pre-bulging height, 10 MPa pre-bulging pressure and 2.8 mu m surface roughness of the punch. (C) 2014 Elsevier B.V. All rights reserved.Öğe Investigation of the effect of hydromechanical deep drawing process parameters on formability of AA5754 sheets metals by using neuro-fuzzy forecasting approach(IOS PRESS, 2015) Tinkir, Mustafa; Dilmec, Murat; Turkoz, Mevlut; Halkaci, H. SelcukAdaptive neural-network based fuzzy logic inference system (ANFIS) is a useful method instead of costly Finite Element Analysis (FEA) in order to reduce investigation cost of forming processes. In this research, the effect of hydromechanical deep drawing (HDD) process parameters on AA5754-O sheet was investigated by FE simulations with analysis of variance (ANOVA) and Adaptive Neuro-Fuzzy Modeling approach. In order to determine the prediction error of the ANFIS model according to FEA, firstly a series of FEA of the HDD process were conducted according to Taguchi's Design of Experiment Method (DOE). The results of the FEA were confirmed by comparing the thickness distributions of the formed cups by experimentally and numerically. Moreover an adaptive neural-network based fuzzy logic inference system (ANFIS) was created according to results of simulation to predict the maximum thinning of AA5754-O sheet without needing FE simulations. The calculation performances of the ANFIS model were determined by comparing the estimated results with the results of the FE simulations. By using the results of the FE simulations which were conducted according to a matrix plan, the effects of the parameters to the thinning of the blank were determined by the analysis of variance (ANOVA) method. ABAQUS and MATLAB/ANFIS/Simulink softwares were used to realize and simulate proposed techniques. Mean error of prediction result of ANFIS is found as 0.89% according to FEA.Öğe Investigation on Earing Behavior of AA 2024-T4 and AA 5754-O Aluminum Alloys(TRANS TECH PUBLICATIONS LTD, 2011) Turkoz, Mevlut; Dilmec, Murat; Halkaci, Huseyin SelcukDeep drawn parts usually have different wall heights because of earing behavior. This behavior is due to the planar anisotropy (Delta r) of sheet metals. A measure of the variation of normal anisotropy with the angel to the rolling direction in sheet plane is known as planar anisotropy. If the magnitude of the planar anisotropy is relatively large as absolute value, the earing behavior becomes more effective so larger ears occur. Furthermore, the orientation of the sheet with respect to the die or the part to be formed will be important. In addition, cutting of scraps in the parts which have ears leads to material waste. The scope of this study is to determine the planar anisotropy of AA 5754-O and AA 2024-T4 aluminum alloys and to investigate the earing behavior by the way of deep drawing of cylindrical cups.Öğe A new method for determining limit strains of materials that show post-uniform elongation behavior(SAGE PUBLICATIONS LTD, 2014) Turkoz, Mevlut; Halkaci, Huseyin S.; Yigit, Osman; Dilmec, Murat; Ozturk, FahrettinIn this study, a new method is proposed to determine limit strains at the onset of localized necking for ductile materials that show post-uniform elongations. The new method is first applied for AA 5754-O using the ISO 12004-2 forming limit diagram determination standard. The method is also applied for ductile materials of 7114 steel, 304 stainless steel, and CuZn37 brass and finally for AA 2024-T4 having brittle fracture behavior. The results indicate that the new proposed method is quite successful, easy, and accurate for ductile materials that show post-uniform elongations.Öğe A Study on DOE Methods for Hydromechanical Deep Drawing Process Parameters(TRANS TECH PUBLICATIONS LTD, 2012) Halkaci, Mehmet; Halkaci, H. Selcuk; Turkoz, Mevlut; Daghan, BehcetFormability of sheet metals can be increased by Hydromechanical Deep Drawing (HDD) process. Formability of the deep drawn cups is generally assessed by Limiting Drawing Ratio (LDR) which is the ratio of the blank diameter to punch diameter. In order to increase LDR by HDD, process parameters of the HDD should be arranged properly. Arranging of the process parameters requires a great knowledge about the effects of the process parameters to certain performance criteria of the process. Determining of the effects of the process parameters by full factorial experiments is a hard duty. Hence certain statistical methods that decrease the number and the cost of the experiments and reduce the time should be used to find effective parameters and their appropriate levels. In this study orthogonal experimental array was applied and effective process parameters were determined by analyzing predicted data with Taguchi's robust parameter design method and ANOVA method. Then the results were compared with each other to evaluate differences between the methods. By using the appropriate levels of the parameters the LDR of AA 5754 aluminum alloy which uses in automotive industry intensely was determined.
