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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, Mehmet
The 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.
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, Mehmet
The 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.
Design, Fabrication and Performance Tests of a Double-sided Sheet Hydroforming Test System
(Natl Inst Science Communication-Niscair, 2023) Urmamen, Mustafa Kemal; Atas, Gurkan; Dilmec, Murat; Turkoz, Mevlut; Ozturk, Osman; Halkaci, Huseyin Selcuk
In this study, a double-sided sheet hydroforming (DSH) test system, which contains dies, sealing, pressure intensifiers, and a control unit, has been designed, built, and tested. The hydraulic numerical control system, which is currently used, has been modified as afour-axis where parameters are forming pressure, back pressure, punch position, and blank holder force. A hydromechanical deep drawing press has been modified in terms of die and sealing. New sealing components have been used to prevent leakage during the forming process because one side of the sheet is exposed to the forming pressure, and the other side is exposed to both the back pressure and the moving punch. Performance tests have been carried out to determine the limitations and capacity of the system. After the performance tests, it has been concluded that; the higher forming rates all along the process curve, the higher the pressure and force differences. However, the resultant error of the corresponding points has been only higher at the beginning of the process curve. In addition, the higher slopes in process curves have increased the pressure and force differences. A conical industrial part has been deformed by using hydromechanical deep drawing and DSH processes to test the performance of the DSH press. The wrinkling defect that occurred in previous hydroformed parts has been reduced remarkably by using back pressure in the DSH process. As a result, a double-sided sheet hydroforming test press has been successfully designed and manufactured. Finally, this study provides technical knowledge and can be used as a guideline for the design and performance evaluation of similar manufacturing systems.
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, Muammer
In 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.
Determination of Limit Drawing Ratio of SS 304 Steel using Sheet Hydroforming Process with Female Die
(Natl Inst Science Communication-Niscair, 2022) Dilmec, Murat; Buluc, Vehbi
Sheet hydroforming with female die process (SHF-D) is easily applicable without controlling of pressure and blank holder force paths compared to the hydroforming with punch process. Shallow parts can be produced easily with using SHF-D process which is used a lower cost production method in a wide variety of sectors. Limiting drawing ratio (LDR) is indication of formability of sheet metals is determined by using cylindrical punch die. In this study, for the first time, the LDRs of the SS 304 material with different thicknesses was determined experimentally by using the SHF-D instead of sheet hydroforming with punch unlike in the literature. FEA of SHF-D process has been performed. The results showed that relatively shallow sheet metal parts can be easily produced without there is no need to be optimizethe pressure and blank holder force paths by means of SHF-D using obtained LDR. It is important to know the forming limit in the SHF-D, since it can be a more economical production method, especially in the manufacture of shallow and large parts used in the automotive and aerospace industries and obtain more quality products than that from classical deep drawing process. By knowing these ratios, die design and parts manufacturing can be realized less costly. The LDR was experimentally obtained as 1.82 with using the SHF-Dfor the SS 304. The FEA results are in good agreement with experimental results. So, it is useful to analyze the FEA before designing the dies that will be used with the SHF-D.
Effect of geometrical and process parameters on coefficient of friction in deep drawing process at the flange and the radius regions
(Springer London Ltd, 2016) Dilmec, Murat; Arap, Mustafa
In the deep drawing process analyses, generally a single friction coefficient is taken into account for the flange and radius regions of the dies. In fact, friction coefficients between these regions and sheet metal are different from each other. Using of a single friction coefficient for different regions would lead to performing of unreal analyses. In this study, coefficient of friction which is one of the most important parameters affects the deep drawing process for flange and radius regions were determined experimentally. A new friction test apparatus which could determine the friction coefficients for both the flange and the radius regions with only a single experiment was designed and manufactured. Hence, the time and the cost have been reduced. After the tests, it was shown that the friction coefficients are considerably different from each other. By the help of the determined friction coefficients for flange and radius regions contacting to sheet metal, it is concluded that deep drawing analyses can yield more accurate results; thus, time, labor force, and money consumption because of trial-and-error process can be eliminated during die design and process analyses. For this purpose, case studies were experimentally and numerically conducted by using the obtained friction coefficients for flange and radius regions so as to validate the results. Moreover, effect of die radius, surface roughness of the tools, drawing speed, blank holder force, and lubrication type on dynamic coefficient friction between flange and radius regions of the tools and sheet metal were investigated by using ANOVA analysis method. According to the results, lubricant type was found to be an effective parameter for the flange and radius regions. On the other hand, the next effective parameter was surface roughness of the tools and the die radius for radius region, the blank holder force, and drawing speed have small effect for both flange and radius regions. The suitability of separately using of coefficients of friction for the flange and radius regions was verified to obtain closer results to the process.
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, Mevlut
In 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.
Effects of sheet thickness and anisotropy on forming limit curves of AA2024-T4
(Springer London Ltd, 2013) Dilmec, Murat; Halkaci, H. Selcuk; Ozturk, Fahrettin; Livatyali, Haydar; Yigit, Osman
In this study, the effects of sheet thickness and anisotropy of AA2024-T4 on forming limit curve (FLC) are experimentally investigated according to ISO 12004-2 standard. A new limit strain measurement method is proposed by using the grid analysis method so as to determine limit strains conveniently and reliably. In addition to the regular test specimens, various widths are added to enhance the FLC's accuracy at the plane strain condition (PSC). The accuracy and reliability of the proposed method are verified for different materials. Results illustrate that an increase in the sheet thickness increases the FLC level. The additional experiments for additional widths improve the accuracy of the FLC at the PSC, and the position of the lowest major strain value differs from the literature. However, the effect of anisotropy on the FLC is found to be insignificant. Finally, experimental and numerical case studies are carried out for conventional deep drawing, stretch drawing, and hydraulic bulge processes. Results reveal that different FLCs are necessary for different thicknesses for accurate predictions.
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, Murat
In 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.
Formability improvement in Ti-6Al-4 V sheet at room temperature by pulsating hydraulic bulging: experimental and numerical investigations
(Springer London Ltd, 2023) Ozturk, Osman; Korkmaz, Habip G.; Atas, Gurkan; Aydin, Mevlut; Turkoz, Mevlut; Toros, Serkan; Dilmec, Murat
Ti-6Al-4 V sheets possess limited formability at room temperature due to low ductility with almost no strain hardening. Pressure pulsation during hydroforming may bring significant improvement as an alternative to the widespread solution hot forming. However, much uncertainty exists on the deformation mechanism and effects of pulsating on difficult-to-form materials. In this study, the effect of pulsating pressure on the hydraulic bulge test was investigated to increase the limited formability of the Ti-6Al-4 V sheet at room temperature. Experimental results of thickness distribution and bulge height obtained from the bulge tests were compared with the finite element simulation results. The results show that the tests with pulsation allow a higher thickness reduction with a slightly more homogenous thickness distribution. Pulsation causes a delay in the material's failure resulting in a 15.4% increase in the dome height with a 17% increased burst pressure compared to monotonic loading. The underlying microstructural phenomena of increased formability were elaborated using dislocation estimations, fracture surface analysis, and hardness. Test results suggest that pulsation improves formability by 47% in terms of maximum elongation due to stress relaxation.
INVESTIGATION INTO REASONS FOR MINIMUM MAJOR STRAIN OFFSETTING OF FORMING LIMIT CURVE OBTAINED WITH NAKAJIMA TEST FOR AA 2024-T4
(Gazi Univ, Fac Engineering Architecture, 2014) Dilmec, Murat; Halkaci, Huseyin Selcuk; Ozturk, Fahrettin
In a typical forming limit curve (FLC), the minimum major strain where the minor value is equal to zero is located at y axes. In many forming processes, failure occurs at this region. Many studies in literature indicates that minimum major strain value is obtained about at y axis. In this study, the minimum major strain value is not determined on the y axes and it was found to be offsetted from the y axes to the right about 0.04 strain for AA 2024-T4. This value could be important for evaluations of sheet metal forming processes. In this study, the reasons for the minimum major strain of setting of the forming limit curve for AA 2024-T4 were investigated. It was found that drawbead and heat treatment were most effective parameters for this offsetting. It is observed that offsetting result from pre-strain which occur for conducted tests with using draw-bead and residual stress arising from T4 heat treatment.
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. Selcuk
Adaptive 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.
Investigation on the Optimal Geometrical Parameters for Cylindrical Cups in Warm Hydromechanical Deep Drawing Process
(IEEE, 2017) Turkoz, Mevlut; Acar, Dogan; Dilmec, Murat; Halkaci, H. Selcuk
Warm sheet hydroforming process has being investigated in recent years with its high formability feature. Warm hydromechanical deep drawing (WHDD) which is a type of the warm sheet hydroforming process is important for deeper parts. To determine the formability of the WHDD process the most convenient tool is Limiting Drawing Ratio (LDR). But determination of the LDR accurately needs using of the most convenient tool dimensions. In this study optimal geometrical parameters were investigated by FE Analyses of the process. Consequently optimum punch and die diameters and optimum punch nose and die entrance radiuses were determined for accurate LDR value.
Microstructural Characterization of Improved Formability of Ti-6Al-4V Sheet by Pulsating Hydraulic Bulging at Room Temperature
(Springer, 2023) Yapan, Yusuf Furkan; Ozturk, Osman; Turkoz, Mevlut; Dilmec, Murat; Livatyali, Haydar; Halkaci, Huseyin Selcuk; Kotan, Hasan
This study aims to increase the limited formability of the Ti-6Al-4V sheet at room temperature using the pulsating hydraulic bulging and to investigate the microstructural reasons for the increased formability. Accordingly, monotonic and pulsating hydraulic bulge tests (HBTs) were applied to Ti-6Al-4V sheets with 0.55 mm thickness at room temperature, and the underlying microstructural reasons for the improved formability were investigated by conducting detailed microstructural characterizations. The experimental results showed that the pulsating HBT samples reached 15.4% higher bulge dome height than the monotonic HBT samples, and a more homogeneous thickness distribution was achieved by pulsating bulging. The thickness and microhardness distributions, dislocation density estimations, and fracture surface analysis were utilized to correlate the increased formability with the microstructure. It was determined that stress relaxation occurred during the pulsating HBT, resulting in the achieved improved formability. The decrease in the dislocation density in the early stage of forming prevented the locking of the dislocations and delayed the occurrence of the damage, i.e., leading to the increased bulge dome height. The higher plastic deformation resulting from the increased formability also increased the hardness along the cross-section. The increased formability of the Ti-6Al-4V sheet during the pulsating HBT and the underlying microstructural phenomena elaborated in this study are expected to make significant contributions to the current literature on the sheet metals with limited formability at room temperature.
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, Fahrettin
In 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.
Numerical Investigation of Manufacturability of Various Compound Shapes Using Sheet Hydroforming Process
(Trans Tech Publications Ltd, 2012) Dilmec, Murat
The demand for complex sheet parts has increased more and more in the modem lightweight construction, especially in the automotive industry. Complex drawn sheet parts can be usually achieved in one step with using the hydroforming technology. As the demand for the complex products increase, the need of hydroforming process will greatly expanded around the world due to its many advantages. Complex parts have many convex and/or concave features on it. The shapes, dimensions and the positions of the features are important for manufacturing high quality products. So understanding these geometrical parameters on the product quality has great importance. In this study, the effects of the geometrical parameters of the complex stepped parts on the manufacturability by using sheet hydroforming process were numerically investigated for AA5754 aluminum alloy and some of results were experimentally confirmed.
Numerical optimization of warm hydromechanical deep drawing process parameters and its experimental verification
(Elsevier Sci Ltd, 2020) Turkoz, Mevlut; Cora, Omer Necati; Gedikli, Hasan; Dilmec, Murat; Halkaci, Huseyin Selcuk; Koc, Muammer
Warm Hydromechanical Deep Drawing (WHDD) is considered as an effective sheet metal forming process to overcome low formability problems of lightweight materials, such as aluminum and magnesium alloys, at room temperature. WHDD process combines the advantages of Hydromechanical Deep Drawing (HDD) and Warm Deep Drawing (WDD) processes. In this study, interactive and combined effects of Pressure (P) and Blank Holder Force (BHF) variation on the formability of the AA 5754 aluminum alloy sheets in the WHDD process were investigated experimentally and numerically. Different from available studies, the optimal fluid pressure (P) and blank holder force (BHF) profiles, which were determined numerically using adaptive FEA integrated with fuzzy logic control algorithm (aFEA-FLCA), were validated experimentally for the first time in literature. Consequently, limiting drawing ratios (LDR) of AA5754 material were recorded as 2.5, 2.625, and 3.125 for HDD, WDD, and WHDD processes, respectively. Thus, it was demonstrated that the formability of lightweight materials, such as AA5754, could be increased significantly using the WHDD process through the proposed optimization method. This method was also implemented into the WHDD of an industrial part with complex geometry, successfully forming sharp features with minimal thinning at reduced levels of force, pressure, and time. Consequently, it is reasonably to state that the method developed in this study can be adopted for the manufacturing of any other part using the WHDD process.

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