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Showing papers on "Hydroforming published in 2019"


Journal ArticleDOI
21 Jun 2019
TL;DR: In this article, the development and perspectives of several extreme forming technologies were reviewed, including the sheet hydroforming of ultra-large curved components, die-less hydroforming, radial-axial ring rolling of rings, in situ manufacturing process of flanges, and local isothermal forging of titanium alloy components.
Abstract: In order to meet the requirements of high reliability, long-lifetime and lightweight in a new generation of aerospace, aircraft, high-speed train, and new-energy power equipment, integrated components are urgently needed to replace traditional multi-piece, welded components. The applications of integrated components involve in a series of large-size, complex-shaped, high-performance components made of difficult-to-deform materials, which present a huge challenge for forming ultra-large size integrated components. In this paper, the developments and perspectives of several extreme forming technologies were reviewed, including the sheet hydroforming of ultra-large curved components, die-less hydroforming of ellipsoidal shells, radial-axial ring rolling of rings, in situ manufacturing process of flanges, and local isothermal forging of titanium alloy components. The principle and processes for controlling deformation were briefly illustrated. The forming of typical ultra-large size integrated components and industrial applications were introduced, such as the high strength aluminum alloy, 3 m in diameter, integrated tank dome first formed by using a sheet blank with a same thickness as the final component, and a 16 m diameter, integrated steel ring rolled by using a single billet. The trends for extreme forming of ultra-large size integrated components were also discussed with a goal of providing ideas and fundamental guidance for further development of new forming process for extreme-size integrated components in the future.

60 citations


Journal ArticleDOI
TL;DR: In this article, an experimental and numerical investigation on a micro/meso scale hydroforming process of pure copper sheet metals was conducted as a case study, and the experimental results reveal evident size effect: the pressure and maximum height onset of failure decrease as the grain size approaches the thickness.

44 citations


Journal ArticleDOI
TL;DR: In this article, the roll forming process is employed for the first time to form thin stainless steel sheets to micro-scale channel sections of the kind required for bipolar plates, and the final part quality is evaluated in terms of material thinning, longitudinal bow and cross-sectional shape.

38 citations


Journal ArticleDOI
TL;DR: In this paper, a tailor layered tube (TLT) hydroforming process is proposed to fabricate hollow tubular parts with dissimilar thicknesses by using TLTs without welding.
Abstract: To produce highly functional tubular parts with locally different properties, tailor welded tubes (TWTs), which are made by tube-to-tube welding of tubes having different thicknesses or mechanical properties, are hydroformed. Notwithstanding the numerous applications of TWT hydroforming processes, TWT presents some disadvantages and considerable risk owing to the presence of a weld seam. This study proposes and characterizes the tailor layered tube (TLT) hydroforming process, which can fabricate hollow tubular parts with dissimilar thicknesses by using TLTs without welding. The proposed TLT hydroforming process was implemented and characterized both numerically and experimentally to validate its feasibility. The optimal loading path to prevent defects including insufficient bulging and wrinkle were analytically determined and verified by experiments. The deformation behaviors of TLT were also characterized at various processing parameters. The results demonstrate that the proposed TLT hydroforming process can be a feasible alternative for achieving tailored properties even with dissimilar thicknesses, with high reliability.

34 citations


Journal ArticleDOI
TL;DR: The main focus of the study will be on the chain of conceptual design, experimentation and subsequent work processes, right through to the final assembly of car exterior skin parts of a streamlined vintage concept car.

21 citations


Journal ArticleDOI
TL;DR: In this article, the influence of process parameters (peak pressure, pressure path, and blank holding force) on formability of 1 mm thick AA5182 aluminum alloy sheets in deep drawing of square cups by hydroforming was investigated through numerical simulations and validated with experimental work.
Abstract: The formability of 1 mm thick AA5182 aluminum alloy sheets in deep drawing of square cups by hydroforming was studied. The influence of process parameters (peak pressure, pressure path, and blank holding force) on formability was investigated through numerical simulations and validated with experimental work. The experiments were designed using the Taguchi method. The minimum thickness in the formed cups (at the bottom corners) and the minimum corner radius that can be achieved were considered as the criteria for evaluation of formability. The peak pressure was the most important process parameter affecting thinning and the minimum corner radius that can be achieved. The variation of the pressure path had the least effect on formability. Regression models were developed for prediction of minimum thickness in the cup and the corner radius as a function of peak pressure and blank holding force.

20 citations


Journal ArticleDOI
Guannan Chu1, Lei Sun1, Guodong Wang1, Zhigang Fan1, Hang Li1 
TL;DR: In this paper, the axial hydro-forging sequence was proposed to overcome the problems in forming the variable-diameter tubes by tube hydroforming, such as excessive thinning and high internal pressure.

20 citations


Journal ArticleDOI
TL;DR: In this article, a collet-type tool design was proposed to provide a non-isothermal condition for tube hydroforming (THF) magnesium alloy within an appropriate pre-heating time after die closing.

18 citations


Journal ArticleDOI
TL;DR: In this paper, the feasibility of utilizing fiber-metal materials in the form of laminates was investigated under the condition of uniform blank holder force for three-layered aluminum and aluminum-composite Laminates using orthogonal carbon and Kevlar as well as glass fiber in the middle.
Abstract: Fiber-metal laminates (FMLs) such as Kevlar reinforced aluminum laminate (ARALL), Carbon reinforced aluminum laminate (CARALL), and Glass reinforced aluminum laminate (GLARE) offer great potential for weight reduction applications in automobile and aerospace construction. In order to investigate the feasibility for utilizing such materials in the form of laminates, sheet hydroforming technology are studied under the condition of uniform blank holder force for three-layered aluminum and aluminum-composite laminates using orthogonal carbon and Kevlar as well as glass fiber in the middle. The experimental results validate the finite element results and they exhibited that the forming limit of glass fiber in the middle is the highest among the studied materials, while carbon fiber material performs the worst. Furthermore, the crack modes are different for the three kinds of fiber materials investigated in the research. This study provides fundamental guidance for the selection of multi-layer sheet materials in the future manufacturing field.

16 citations


Journal ArticleDOI
TL;DR: In this article, a finite element (FE) model was used to evaluate high strain rate (HSR) formability of Al-Cu-Mg 2B06-O sheets by impact hydroforming.

15 citations


Journal ArticleDOI
Xu Xuefeng1, Wu Kongwei1, Wu Yiwang1, Xiao Jie1, Fu Chunlin1 
TL;DR: In this paper, a novel lubrication approach for T-shaped tube hydroforming is developed to reduce the forming defects referred to the wrinkles that called intermediate semiring differential lubrication (ISDL), which reduced the dependence of the internal pressure and axial-feeding loading paths to make forming process easily.
Abstract: In this work, a novel lubrication approach for T-shaped tube hydroforming is developed to reduce the forming defects referred to the wrinkles that called intermediate semiring differential lubrication (ISDL), which reduced the dependence of the internal pressure and axial-feeding loading paths to make forming process easily. The T-shaped tube was divided into four zones: bulging zone, guiding zone, back zone, and middle back zone, and the ISDL method was to coat the bulging zone and whole or part of guiding zone with PTFE film and others with MoS2. Experimental results show that the ISDL method greatly reduced wrinkles in middle back zone of the T-shaped tube without wasting time to adjust the loading path again and again. Also, formulas related to the length and width for lubrication area of ISDL method was derived to guide the tube hydroforming process. The modified tribological performance by employing regional lubrication method improved the T-shaped tube hydroforming ability.

Journal ArticleDOI
TL;DR: In this paper, the 3D drawing software UG was used to establish the geometric modeling of T tube for hydroforming process, and the software DYNAFORM is used to simulate the forming performance of T-shaped tube under different loading paths to obtain the simulation value of forming performance parameters.
Abstract: In this paper, the 3D drawing software UG is used to establish the geometric modeling of T tube for hydroforming process, and the software DYNAFORM is used to simulate the forming performance of T-shaped tube under different loading paths to obtain the simulation value of forming performance parameters. Next, the response surface method is used to analyze the influence of the main factors on hydroforming formability. The loading path, including axial feeding, internal pressure, and backward displacement, and friction coefficient are included in the main factors; the minimum thickness value, the height of branch tube, and the radius of limiting circle angle are considered as important characteristics that govern the forming performance. According to the optimization evaluation criteria, the perturbation plots and the interaction effect of different test factors, the main factors are optimized, and the best value of loading path was selected. Finally, the comparison of simulation and experiment under the optimal loading path shows that the error between experiment and simulation is within 5%, indicating that the loading path optimization method has high accuracy and good feasibility.

Journal ArticleDOI
TL;DR: In this article, a novel electromagnetically activated high-speed hydroforming process (EAHF) is introduced, which can be used for metals and non-metals with low electrical conductivity.
Abstract: In this paper, a novel electromagnetically activated high-speed hydroforming process (EAHF) is introduced. The EAHF process is compared with the electromagnetic forming process (EMF) in the forming of a low-conductive steel sheet, forming of a high-conductive thin aluminum sheet and also, in the multistage forming of an aluminum sheet. Furthermore, the effect of the process parameters on the EAHF process is investigated by the Taguchi design of experiments. Based on the results it can be concluded that the presented process is an efficient high-speed forming process that can be used for metals and non-metals with low electrical conductivity. This process has more uniform pressure and hence more uniform geometry compared to the EMF process. Furthermore, by a proper design of the process, EAHF can be used for the simultaneous forming and trimming operation.

Journal ArticleDOI
TL;DR: In this paper, an attempt has been made to enhance formability of AA5083 alloy sheets (annealed at 275°C for 15min) in deep drawing of flat bottom square cup-shaped parts by hydroforming.
Abstract: In this paper, an attempt has been made to enhance formability of cryorolled AA5083 alloy sheets (annealed at 275 °C for 15 min) in deep drawing of flat bottom square cup-shaped parts by hydroforming. Numerical simulations based on finite element method have been carried out to study the effect of important process parameters (fluid pressure and sealing force) on formability. The minimum corner radius and the maximum depth that can be achieved without failure and the maximum percentage thinning at the corners have been considered as measures of formability. The results have been compared with conventional deep drawing. The simulation results have also been validated with experimental work in both hydroforming and conventional forming. A process window with optimum combination of peak sealing force and peak pressure has been identified to form the cups up to full depth of the die without failure at die entry or bottom corners. Lubrication between the die and the blank reduced the minimum possible corner radius to nearly 16 mm with thinning less than 6%. In conventional forming only 70% of the full depth could be obtained before failure with 16 mm punch corner radius due to much higher thinning at the corners. This work demonstrates that, by hydroforming, formability of high strength cryorolled Al alloy sheets can be enhanced due to lower thinning and more uniform strain distribution and hence this process route (cryorolling followed by hydroforming) is a potential technique to produce complex parts from lightweight high strength Al alloy sheets due to enhanced formability.

Journal ArticleDOI
TL;DR: In this article, the effects of mechanical property parameters on the wrinkling behavior of thin-walled tubes for hydroforming application were investigated and the numerical simulation results showed that the effect of elastic modulus is very small and ignorable, but the initial yield stress and tangent modulus of tubes have an obvious effect on their wrinkling behaviour.
Abstract: In tube hydroforming, some controllable wrinkles can be used to improve the formability of tubes, so as to obtain the tubular parts with large expansion ratio and relatively uniform wall thickness. In this paper, finite element analysis and experimental research with 5052 aluminum alloy and 304 stainless steel tubes are used to investigate the effects of mechanical property parameters on wrinkling behavior of thin-walled tubes for hydroforming application. The numerical simulation results show that the effect of elastic modulus is very small and ignorable, but the initial yield stress and tangent modulus of tubes have an obvious effect on their wrinkling behavior. Tubes with higher initial yield stress and lower tangent modulus tend to possess three axisymmetric wrinkles within the lower internal pressure range. Moreover, it is found that the ratio of initial yield stress to flow stress of the tubes, σs/σf, is a significant factor to their wrinkling behavior. Three axisymmetric wrinkles could be produced on the tubes with higher σs/σf under a lower internal pressure. All of these were verified by the experimental results of 5052 aluminum alloy and 304 stainless steel tubes, whose wrinkles obtained under wrinkling internal pressure of 1.8 ps and 1.2 ps can be flattened completely in the calibration stage. These research findings are extremely meaningful to get controllable wrinkles for different kinds of tubes.

Journal ArticleDOI
TL;DR: In this paper, a finite element (FE) analysis was conducted with various combinations of wires and the reinforcement effects of the wire-reinforced aluminum tubes were verified according to the number of reinforcing wires and their diameters.
Abstract: Aluminum composites have been widely used in a variety of applications requiring high strength levels and low weights. This paper proposes an innovative hydroforming process for the manufacturing of wire-reinforced aluminum tubes. To characterize the proposed hydroforming process for the manufacturing of wire-reinforced tubes (WRTs), a finite element (FE) analysis was conducted with various combinations of wires. The reinforcement effects of the WRT were verified according to the number of reinforcing wires and their diameters. Based on the equivalent plastic strain and tube wall thickness values of the inner tube as derived via the FE analysis, appropriate loading paths for hydroforming experiments were derived according to various combinations of reinforcing wires. Through hydroforming experiments, WRTs without process-induced defects such as insufficient bulging, wire buckling, and tube bursting were successfully obtained. To estimate the mechanical performance of the WRT when under a load, the structural strength was experimentally evaluated through a lateral three-point bending test. The measured structural strength values demonstrate the superior reliability and applicability of the WRT manufactured in this study.

Journal ArticleDOI
TL;DR: In this paper, a tube hydro-mechanical forming (THMF) process was proposed to form an integral automobile exhaust manifold that has the characters of large deformation and small corner.
Abstract: The automobile exhaust manifold regularly has a multi-valved shape that used to be formed by the combination of stamping and welding. The current study intended to investigate and develop a tube hydro-mechanical forming (THMF) process to form an integral automobile exhaust manifold that has the characters of large deformation and small corner. It included three stages such as pre-forming stage, die-forming stage, and calibration stage. In addition, the non-feasibility of one-step hydroforming process was proved by FE modeling and experimental for the target component. An optimal loading path was obtained through the principle of dichotomy for pre-forming stage and die-forming stage, corresponding to the maximum thinning ratio of 19.7% and 13.27% respectively. The variation of stress and strain states were analyzed for the whole process. As a consequent, the thickness distribution exhibited a V-shaped along axial direction at each stage, while a fluctuated distribution after die-forming was presented along radial direction in the multi-valved area. For the final component, a maximum thinning ratio of 28.53% and the large deformation above 60% obtained from FE modeling kept a reasonable agreement with that achieved from experiments. It showed that THMF has advantages of not only decreasing the internal pressure but also improving the formability of tube.

Journal ArticleDOI
TL;DR: In this paper, microstructural evolution and cracking behavior of an extrusion welded aluminum alloy blank tube were characterized to uncover the failure mechanisms during hydroforming process using backscattered diffraction, transmission electron microscope, and scanning electron microscope.
Abstract: During hydroforming of Al alloys, cracking often limits the production of specific frames for next-generation transportation vehicles. In this study, microstructural evolution and cracking behavior of an extrusion welded aluminum alloy blank tube were characterized to uncover the failure mechanisms during hydroforming process. Electron back-scattered diffraction, transmission electron microscope, and scanning electron microscope were employed to characterize the grains, textures, and local micro-crack sites. Experimental results demonstrated that grains in the welds region were significantly larger than those in the neighboring regions. Along the weld region, large grains typically with high-misorientation with respect to neighboring grains were identified as the preferred crack nucleation sites. Plastic incompatibility due to preferential yielding in the larger (softer) grains as compared to the surrounding finer (harder) grains is postulated as the origin for local strain localization that leads to cracking in the weld regions during hydroforming.

Journal ArticleDOI
TL;DR: In this article, the authors explored the possibility of using additive manufactured (AM) polymer die as direct rapid tool (RT) for metal bellow hydroforming using finite element analysis (FEA) to simulate bellow forming and to evaluate the compatibility of AM die.
Abstract: Custom-designed metal bellows require alternate ways to produce the die to shorten lead time. The purpose of this study is to explore the possibility of using Additive Manufactured (AM) polymer die as direct rapid tool (RT) for metal bellow hydroforming.,Finite element analysis (FEA) was used to simulate bellow forming and to evaluate the compatibility of AM die. Fused deposition modelling (FDM) technique is used to fabricate die with Acrylonitrile Butadiene Styrene (ABS) material. To validate, the width of the metal bellow convolutions obtained from the FEA simulation is compared with convolution formed during the experiment.,FDM-made die can be used for a short production run of bellow hydroforming. FEA simulation shows that stress developed in some regions of die is less and these regions have potential for material reduction. Use of RT for this particular application is limited by the die material, forming pressure, width, convolution span and material of bellow. This supports the importance of FEA validation of RT before fabrication to evaluate and redesign die for the successful outcome of the tool.,The given methodology may be followed to design a RT with minimum material consumption for bellow forming application. Whenever there is a change in bellow design or the die material, simulation has to be done to evaluate the capability of the die. As this study was focused on a short production run for manufacturing one or few bellows, the die life is not a significant factor.,This paper demonstrates about rapid tooling for metal bellow manufacturing using FDM technique for low volume production. Further, FEA is used to identify low stress regions and redesign the die for material reduction before die manufacturing. AM die can be used for developing customized metal bellow for applications such as defense, aerospace, automobiles, etc.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the hydraulic pressure control of reinforced s-shaped bellows in the hydroforming process and revealed the key factors affecting plastic strain and wall thickness thinning.
Abstract: Reinforced s-shaped bellows is a kind of typical reinforced metal bellows that can withstand high pressure. Hydroforming process and its simulation technology of reinforced s-shaped bellows were investigated in this paper. The hydroforming technology of reinforced s-shaped bellows is a severe plastic deformation process. Most area of the bellows is in the state of severe plastic yielding with a maximum equivalent plastic strain of 30.6%. At the same time, the wall thickness shows a linear thinning trend from wave trough to peak. The control of hydraulic pressure is a key factor of hydroforming process. The best hydroforming hydraulic pressure is 12 MPa, which is in good agreement with the designed shape. At last, the key factors affecting plastic strain and wall thickness thinning of the hydroforming process were revealed. Plastic strain and wall thickness thinning of the large-pitch bellows in the hydroforming process are obviously higher than those of the small-pitch ones. The waveform parameters directly affect the hydroforming process. However, the influences of initial wall thickness and number of layers of the bellows were not obvious. The maximum thinning rate of the bellows basically maintains around 20%.

Journal ArticleDOI
TL;DR: In this paper, the effects of some geometrical parameters, such as the die profile radius and the gap between the die and the blank holder, and some process parameters such as pressure path and friction coefficient are investigated on thickness distribution of cylindrical cups and punch force.
Abstract: Among the various techniques of sheet hydroforming, hydrodynamic deep drawing assisted by radial pressure (HDDRP) has showed good results to shape parts with uniform thickness distribution and high drawing ratio. In this paper, improving formability of the parts in HDDRP is taken into consideration and the effects of some geometrical parameters such as the die profile radius and the gap between the die and the blank holder, and some process parameters such as pressure path and friction coefficient are investigated on thickness distribution of cylindrical cups and punch force. The pressure path has a great effect on the formability. The results showed that increasing the maximum pressure reduces part thinning in the critical regions. Increasing the pressure above a certain value does not have a significant effect on the part forming, but it increases the punch force. The most appropriate pressure path for forming the part studied in this paper is 27 MPa. Furthermore, thinning of the part and maximum punch force decreases by decreasing the friction between the sheet and blank holder. Moreover, increasing the friction coefficient between the punch and sheet to a certain value (0.2) improves forming condition that results in decreasing thinning of the part. Increasing the friction coefficient more than this value does not have a significant effect on forming the part. Friction between the punch and the sheet does not affect the maximum punch force. The results also illustrated that by increasing the gap between the blank holder and the die to 1.2 mm which is more than the thickness of the sheet, thickness reduction of the part and maximum punch force decreases. Increasing the gap above this value does not have a significant effect on ease of sheet flow and improving part formability.

Journal ArticleDOI
TL;DR: In this article, a multiobjective optimization methodology based on the Taguchi method is proposed in order to make these processes robust and unresponsive to material variations, and the design of experiments and process simulation are combined in the methodology, using the nonlinear finite element method.
Abstract: The aluminium alloy sheet forming processes forging in rubber pad and diaphragm presses (also known as hydroforming processes) are simple and economical processes adapted to aeronautical production. Typical defects of these processes are elastic recovery, necking, and wrinkling, and they present difficulties in control mainly due to property variations of the sheet material that take place during the process. In order to make these processes robust and unresponsive to material variations, a multiobjective optimization methodology based on the Taguchi method is proposed in the present study. The design of experiments and process simulation are combined in the methodology, using the nonlinear finite element method. The properties of sheet material are considered noise factors of the hydroforming process, the objective being to find a combination of the control factors that causes minimal defects to noise factors. The methodology was applied to an AA2024-T3 aluminium alloy sheet of 1 mm thickness stamping process in a diaphragm press. The results allowed us to establish the optimal pressure values, friction coefficient between sheet and block, and friction coefficient between sheet and rubber to reduce the elastic recovery variations and the minimal thickness before noise facts.

Journal ArticleDOI
Zheng Liu1, Lihui Lang1, Shangwen Ruan1, Meng Zhang1, Fengli Lv, Jun Qi 
TL;DR: In this paper, the effect of different pressures on forming performance was discussed and the thickness distribution could be improved effectively after hydroforming within an appropriate supporting pressure range during preforming, which has been theoretically proved that circumferential bending moment in the V-shape region is an important contributing factor toward the depth of dent between up die and tube.
Abstract: With the growing application of advanced high-strength steel in automobile components, hydroformed hollow parts become popular because of the advantages of high strength and high stiffness. Hydroforming process of CP800 high-strength steel torsion beam was researched by numerical simulation and experiment in order to avoid defects and improve thickness distribution. It had been theoretically proved that circumferential bending moment in the V-shape region is an important contributing factor toward the depth of dent between up die and tube, which has a significant effect on forming performance after hydroforming. Therefore, supporting pressure was carried out in the hydropressing process to make a better preparation for hydroforming. And the effect of different pressures on forming performance was discussed. It showed that the thickness distribution could be improved effectively after hydroforming within an appropriate supporting pressure range during preforming. In hydroforming process, the effect of supporting pressure during axial feeding was developed by an experiment based on the simulation numerical simulation. It showed that an appropriate internal pressure could avoid wrinkle and improve thickness distribution nearby the end area of tube effectively. Finally, a qualified hydroformed torsion beam was manufactured.

Journal ArticleDOI
11 Oct 2019
TL;DR: A toolbox is created that is suitable for a screening process of different flow field design variants and provides information about optimum channel geometry and the best choice of the general flow field layout at the beginning of the design process.
Abstract: Metallic flow field plates, also called bipolar plates, are an important component of fuel cell stacks, electrolyzers, hydrogen purification and compression stacks. The manufacturing of these plates by means of stamping or hydroforming is highly suitable for mass production. In this work, a toolbox is created that is suitable for a screening process of different flow field design variants. For this purpose, the geometry and computational mesh are generated in an automated manner. Basic building blocks are combined using the open source software SALOME, and these allow for the construction of a large variant of serpentine-like flow field structures. These geometric variants are evaluated through computational fluid dynamics (CFD) simulations with the open source software OpenFOAM. The overall procedure allows for the screening of more than 100 variants within one week using a standard desktop computer. The performance of the flow fields is evaluated on the basis of two parameters: the overall pressure difference across the plate and the relative difference of the hydrogen concentration at the outlet of the channels. The results of such a screening first provide information about optimum channel geometry and the best choice of the general flow field layout. Such results are important at the beginning of the design process, as the channel geometry has an influence on the selection of the metal for deep drawing or hydroforming processes.

Journal ArticleDOI
TL;DR: In this paper, a self-developed measurement system was used to investigate dynamic frictional characteristics in the guiding zone of TP2 copper tubes under different loading and fluid velocities.
Abstract: Tube hydroforming (THF) experiments were performed on TP2 copper tubes under different loading velocities and fluid velocities using a self-developed measurement system to investigate dynamic frictional characteristics in the guiding zone. The results show that the coefficient of friction (COF) dynamically changes during forming experiments and decreases with tube deformation. The average descending rate and amplitude of the COF increase with increasing loading velocity. Microscopically, the micro-protrusions on the tubular surface are flattened, and the surface scratches are finer and more uniform, as the loading velocity increases, resulting in a decrease in COF. At the same external loading velocity, the COF increases with increasing fluid velocity and is also extremely sensitive to it. Moreover, improving and predicting the formability of such tubes by accurately adjusting and controlling fluid velocity in THF is valuable and critical for the future.

Journal ArticleDOI
TL;DR: In this article, a non-uniform geometric model for tube hydroforming is proposed, which combines finite element (FE) simulation with a non uniform geometric model to predict the ultimate strain of tubular blanks with initial nonuniform thickness.
Abstract: Tube hydroforming (THF) is a unique forming technique, which can transform metal tubes into complex hollow parts using hydraulic fluid as the forming medium. The initial non-uniform thickness of as-received practical tubes significantly affects their formability in the hydroforming process. A forming limit diagram (FLD), also called as the forming limit curve (FLC), is often adopted to evaluate the forming behaviour of sheet metals in plastic forming processes to avoid forming failures. The purposes of this research are fivefold, namely to establish the FLCs of tubular blanks with varied initial thickness deviations in tensile and compressive strain states by means of finite element (FE) modelling of THF, to construct a non-uniform geometric model for practical tubes, to analyse the impact of initial thickness deviation on the FLCs, to clarify the differences in the FLCs obtained using three different instability criteria, and to validate the proposed non-uniform geometric model by conducting hydro-bulging experiments. Results show that it is possible to accurately predict the FLCs of practical tubes with initial non-uniform thicknesses using FE simulation combined with the proposed non-uniform geometric model. We found that the displacement of FLCs occurred in the major- and minor-strain coordinates because the thickness is initially not uniform; however, no significant discrepancies were observed in the FLCs obtained using the three instability criteria. The proposed approach, which combines FE simulation with a non-uniform geometric model, can be easily employed to predict the ultimate strains of tubes with initial non-uniform thicknesses in THF to avoid forming defects.

Journal ArticleDOI
TL;DR: In this article, a stress-based forming limit diagram has been developed for AA 5182 alloy sheets modifying the analytical procedure, proposed by Stoughton, to determine forming limits in stress space from failure strains incorporating anisotropy using Balart's yield criterion.
Abstract: Prediction of failure in sheet metal forming processes accurately is very important for successful production and optimization of parameters. A major problem of conventional strain-based forming limit diagrams (FLDs) is their inability to predict failure accurately in processes such as sheet hydroforming where there is a change in strain path and mode of deformation. In the present work, a stress-based forming limit diagram has been developed for AA 5182 alloy sheets modifying the analytical procedure, proposed by Stoughton, to determine forming limits in stress space from failure strains incorporating anisotropy using Balart’s yield criterion. The developed stress-based FLD has been used to predict failure in sheet hydroforming of square cups. Results are compared with Hill’s quadratic yield criterion. Significant difference has been found in failure prediction between strain-based and stress-based criteria when they are applied to sheet hydroforming. A change in strain path has been observed at the critical corner regions in hydroforming of square cups due to initial drawing and then biaxial stretching during calibration. The experimental validation clearly showed that accuracy in failure prediction can be improved in sheet hydroforming by using a stress-based forming limit diagram.

Journal ArticleDOI
TL;DR: In this paper, the authors performed a comprehensive experimental study on the convolution height and thickness of the top point of a metallic bellows and developed a mathematical model according to the second-order linear regression equations.
Abstract: In this paper, for the first time, a comprehensive experimental study is performed on hydroforming process of metallic bellows. For this purpose, the effects of the main process parameters and their interactions on the characteristics of hydroformed metallic bellows are investigated using Response Surface Methodology (RSM). The selected parameters as input variables are internal pressure, die stroke and die fillet. The measured characteristics of metallic bellows are convolution height and thickness of the top point of bellows congress. A set of experiments are carried out and the convolution height and thickness of the top point of bellows congress are measured. Then a mathematical model is developed according to the second-order linear regression equations to maximize the convolution height and thickness of the top point of bellows congress. The results show that the increase in the convolution height and decrease in the thickness of the top point of bellows congress will occur by increasing the internal pressure and die stroke. Also, the convolution height and thickness of the top point of bellows congress are increased with an increase in the die fillet.

Journal ArticleDOI
TL;DR: In this paper, the first systematic investigation of the edging process was conducted and a new analytical model which can be used to enable the design of edging processes was presented. And the results showed that edging technique was effective in sharpening the flange radius from 10mm to 4mm or from 6mm to 2mm in thickness of 2.1mm and 1.2mm respectively.
Abstract: This paper presents the first academic study of a hydroforming process known as edging. An edging process allows a smaller radius to be produced with a lower pressure than a standard sheet hydroforming process and is currently developed by trial and error that relies heavily on operator experience. This paper reports the first systematic investigation of the edging process that concludes in a new analytical model which can be used to enable the design of edging processes. It was found that in each of the three aerospace nickel alloys tested, the edging technique was effective in sharpening the flange radius from 10 mm to 4 mm or from 6 mm to 2 mm in thicknesses of 2.1 mm and 1.2 mm respectively. This radius is equivalent to between 1.5 and 1.8 times the material thickness (1.5 t to 1.8 t). These results were achieved by using edging heights of between 2.5 to 5 mm (2.5 t to 3 t). At the limits of successful edging operations, (under 2 t) three different kinds of phenomena were observed: crushing of the top of the component, radii which were pushed inwards, and the generation of an underside lip which protruded from the bottom of the samples. This paper discusses the benefits of hydroforming with an edging operation, explores the limitations of the edging process, derives an equation which can be used to estimate the sharpness of an edged radius and finally defines a model which enables the design of an edging operation. The work reported here is particularly relevant to aerospace applications because it will enable lighter components to be formed with lower pressures with nickel based superalloys.

Journal ArticleDOI
TL;DR: In this paper, a reconfigurable tube multi-point hydroforming die was designed and fabricated, where the main difference of this die with conventional types is substitution of the rigid surface with a set of spaced pins.
Abstract: It is necessary to fabricate individual dies in conventional hydroforming, to produce different tubular parts. This procedure is costly and time-consuming. Tube multi-point hydroforming is a new flexible forming technology which facilitates producing various tubular products by only one die. In this study, a new reconfigurable hydroforming die was designed and fabricated. The main difference of this die with conventional types is substitution of the rigid surface with a set of spaced pins. Different tubular sections could be produced by adjusting the pins position. Due to the low cost of changing the tool into a new die, this process is appropriate for producing small batch numbers of a tubular product. Numerical simulations were employed to determine the effects of pin diameter and polyurethane layer thickness on the characteristics of final products. Increasing the number of pins was found out to improve dimensional accuracy and surface quality. On the other hand, while using a thicker polyurethane layer reduced dimpling, it led to a poor dimensional accuracy. A bulged and a square brass 70/30 tube were produced with an initial thickness of 2 mm. Thereafter, experimental tests were performed to compare distribution of the thickness and variation of dimensions with the numerical results.