Showing papers on "Hydroforming published in 2016"
TL;DR: In this paper, a new method denoted as electromagnetic incremental forming combined with stretch forming is proposed, which was adopted for manufacturing large-size and thin-walled ellipsoidal parts.
39 citations
TL;DR: In this article, an adaptive neuro fuzzy inference system (ANFIS) and genetic algorithm (GA) were used for pressure path optimization in hydrodynamic hydroforming process of cylindrical-spherical parts.
Abstract: One of the most important parameters in success of sheet hydroforming process is loading (pressure) path. Improper pressure of fluid chamber during the process may cause a number of defects such as necking, tearing, and wrinkling. Theoretical calculations and finite element trial-and-error simulations to find the optimum pressure paths are so costly and time-consuming. This study underlines the application of adaptive neuro fuzzy inference system (ANFIS) and genetic algorithm (GA) for pressure path optimization in hydrodynamic hydroforming process of cylindrical-spherical parts. In this research, an ANFIS model has been developed based on finite element simulation results to identify the effect of the pressure path on the maximum thinning in the critical region of the part. In subsequent step, the ANFIS model operated as an objective function for optimization process. For this purpose, GA was incorporated into the ANFIS model to acquire the optimal pressure path in order to obtain minimum thinning in the critical region of the part. The results showed that the combination of adaptive neuro fuzzy inference approach and optimization algorithm is a good scheme to predict an improved loading pressure path minimizing the thinning in the critical region of the part and avoiding numerous trial and error simulations or experiments.
38 citations
TL;DR: In this paper, a double-step hydroforming process is proposed for fabricating metallic bipolar plate of proton exchange membrane (PEM) fuel cells with thin slotted interdigitated serpentine pattern.
Abstract: Bipolar plate is considered as one of the main components of a fuel cell which has high weight and cost in the manufacturing of fuel cells. These plates are manufactured by different processes such as stamping, rubber pad forming, electromagnetic forming, and hydroforming, each of which has its own specific limitations. Among these processes, hydroforming is considered as a practical method in forming bipolar plates with complicated pattern due to its significant advantages. Bipolar plates have different flow field patterns including parallel, pin type, interdigitated, and serpentine patterns. Forming of slotted interdigitated serpentine flow field is very difficult due to its high geometrical complexity and accuracy of the flow pattern, small distance between slots, and very low thickness of sheet. To overcome this problem, a double-step hydroforming process is proposed in this work: an initial hydroforming step on a concave die and a final hydroforming step on a convex die. It is shown that the double-step hydroforming process is a feasible technique for fabricating metallic bipolar plate of proton exchange membrane (PEM) fuel cells with thin slotted interdigitated serpentine pattern.
27 citations
TL;DR: In this article, the authors theoretically and experimentally investigated the tribological behavior and its size effects in micro-hydromechanical deep drawing (MHDD) and found that the required fluid pressure for hydrodynamic lubrication significantly increases with scaling down micro-scale due to a high sealablity at small relative punch diameter to minimum thickness.
24 citations
TL;DR: In this article, the Explicit Finite Element Method with a Moisture and Temperature-Dependent Constitutive Model was used for the parametric study of Hydroforming of Paper Materials.
Abstract: Parametric Study of Hydroforming of Paper Materials using the Explicit Finite Element Method with a Moisture-and Temperature-Dependent Constitutive Model
22 citations
TL;DR: In this paper, the authors developed a technology by combination of hydroforming with moving dies similar to the forging process, known as a hydroforging technology, to avoid thinning, wrinkling, and bursting due to unreasonable selection of the internal pressure.
Abstract: In order to form the thin-walled hollow parts with large deformation, a technology has been developed in the present study by combination of hydroforming with moving dies similar to forging process, known as a hydroforging technology. Based on the finite elements simulation, the process of hydroforging was investigated to avoid thinning, wrinkling, and bursting due to unreasonable selection of the internal pressure. The suitable loading path was discussed. The results from simulation keep a reasonable agreement with that from experiment.
21 citations
TL;DR: In this paper, a dual response surface model-based multi-objective robust optimization method is introduced to deal with the uncertainties in the tube hydroforming process, which aims to maximize the protrusion height and minimize the thinning ratio; meanwhile, the variations of the objectives should be minimized.
Abstract: In this study, a dual response surface model-based multi-objective robust optimization method is introduced to deal with the uncertainties in the tube hydroforming process. The objective of this study is to maximize the protrusion height and minimize the thinning ratio; meanwhile, the variations of the objectives should be minimized. A valid finite element model obtained from experimental result and LS-DYNA is employed to simulate the T-shape tube hydroforming process. To improve computation efficiency, radial basis function combined with Latin hypercube and orthogonal design sampling strategies is employed to construct dual response surface model, which are the mean and standard deviation response of the hydroforming process, respectively. The robust Pareto solutions can be obtained using NSGA-II; meanwhile, the ideal point method is used to obtain the most satisfactory solution from the Pareto solutions for the design engineers. As a conclusion, a significant improvement of the robustness can be achieved; however, the mean performance of the protrusion height has to be sacrificed.
21 citations
TL;DR: In this paper, low activation martensitic steel/aluminum clad tubes were prepared by explosive bonding method in order to study its microstructure characteristics at the interface and to evaluate its performance.
Abstract: China low activation martensitic steel/aluminum clad tubes were prepared by explosive bonding method in order to study its microstructure characteristics at the interface and to evaluate its performance. The interface morphology of the different parts of the clad tube was characterized by scanning electron microscope and energy dispersive spectroscopy. Then, the performance of the clad tube, including its bonding strength and formability, was investigated. Microstructural results showed that existence of an under-fusion area at the head of the clad tube, diffusion of elements, and the metallurgical bonding was observed in the middle part while cracks and crushing particles appeared at the end of the clad tube. No separation after the cold extruding and hydroforming process showed that the middle part of the clad tube had excellent bonding properties and could endure the second plastic deformation.
20 citations
TL;DR: In this paper, the effect of forming media on the formation of cylindrical cups via hydrodynamic deep drawing assisted by radial pressure was investigated through finite element simulation and experiments.
Abstract: Apart from the punch and the die, a pressurized fluid (water or oil) is used in hydroforming. The presence of such pressure media is the main difference between hydroforming and conventional deep drawing. No comprehensive study has yet been conducted on the effect of forming media on the formation of cylindrical cups via hydrodynamic deep drawing assisted by radial pressure. This study investigated the formation of such cups through Finite element (FE) simulation and experiments. First, the process was modeled numerically using ABAQUS FE software. After simulation, copper and St14 sheets were formed with water and oil as the forming media. The effect of these forming media on thickness distribution and maximum punch force was investigated. By examining the thickness distribution curve of the hydroformed cup, a close agreement was found between experimental and numerical results. Using oil as the forming media reduced thinning at the corner radius zone of the punch and increased the maximum punch force. Changing the forming media does not significantly influence the maximum thickening at the cup wall region.
20 citations
TL;DR: In this paper, the 3A method is proposed to replace complex shaped, monolithic, metallic sheet parts with hybrid parts, which is based on simultaneous forming of any number of multiple metallic blanks in required shape by applying hydroforming technology.
Abstract: Being light weight and superior in characteristics, hybrid materials such as fiber metal laminate (FMLs) and functionally graded structures (FGS) are becoming increasingly popular in aeronautical, automobile and military industries. In the present work, an innovative methodology which hereafter will be named as “3A method” has been proposed to replace complex shaped, monolithic, metallic sheet parts with hybrid parts. This method is based on simultaneous forming of any number of multiple metallic blanks in required shape by applying hydroforming (HF) technology. Based on numerical simulations, forming limit diagrams (FLDs) are established for three types of blanks forming hemispherical shaped parts using Barlat 2000 yield criteria/DYNA Form/LS Dyna. To validate the simulation results, experimental study is accomplished and optimal process parameters are determined by varying the cavity pressure under constant die-binder gap. Effects of number of layers and thickness of blanks on thinning, wrinkling and punch force have been well studied for three types of blanks and a comparative analysis is made to investigate various failure modes. To achieve a composite layered structure, post forming procedure has been devised and implemented to get a final hybrid part. Furthermore, limitations of the 3A method in terms of final shape of parts are discussed. Good agreement can be found between numerical and experimental research. The new methodology is capable of employing any types of resins and composite materials at any required place in parts for desired characteristics. Elimination of repeated heating and solidification of blank assembly as well as precise punch force and speed requirements make this multilayer blank forming method more efficient, economical and user friendly for manufacturing of FMLs and FGSs at commercial scales.
19 citations
01 Jul 2016
TL;DR: In this article, the effects of pulsating pressure parameters on the parts' defects and shape accuracy were evaluated using 12 experiments with six parameters and two levels for each parameter, and three linear regressions without any interaction between the parameters.
Abstract: Tube hydroforming is a process that uses internal pressure and axial feeding simultaneously to form a tube into a desired shape. The internal pressure provides the stress required to yield the material while axial feeding eases metal flow helping to produce a part without wrinkles and with even wall thickness. Pulsating pressure hydroforming applies loading path with fluctuating pressures. In this study, pulsating pressure hydroforming of T-joint part was examined experimentally. Six process parameters in pulsating pressure loading path were selected. Using Taguchi design of experiments with six parameters and two levels for each parameter, 12 experiments were conducted to study the effects of pulsating pressure parameters on the parts’ defects and shape accuracy. Signal-to-noise ratio and analysis of variance were employed to determine the important process parameters affecting the final part in terms of wrinkling, bulge height and wall thickness. Three linear regressions without any interaction between ...
TL;DR: In this paper, an adaptive finite element analysis (FEA) was proposed for the industrial design of bimetal conical-cylindrical cup hydroforming, where the perfect and imperfect parts were concluded through adaptive FEA using the ANSYS parametric design language and effective parameters, including pressure loading path, layer placement order, and thickness ratio, were investigated for hydroforming of Al/St and Cu/St composite sheets.
Abstract: An adaptive Finite element analysis (FEA) was proposed in this paper for the industrial design of bimetal conical-cylindrical cup hydroforming. Forming circumstances for the perfect and imperfect parts were concluded through adaptive FEA using the ANSYS parametric design language. Effective parameters, including pressure loading path, layer placement order, and thickness ratio, were investigated for hydroforming of Al/St and Cu/St composite sheets. Experimental tests were implemented to validate adaptive finite element results. Rupture failure upon the pressure path occurred on the contact area between the blank and punch tip radius at low pressures and on the transition area of the conical-cylindrical portion at high pressures. The proposed method is applicable for any cylindrical, conical, or cylindrical/conical shapes with different materials and dimensions. Therefore, this method is beneficial as a practical design tool for engineers and researchers working in the process design of hydroformed shell products.
TL;DR: In this paper, the adaptive radial basis function (ARF) was used to determine the optimal loading parameters in T-shape tube hydroforming process and the results showed that a significant improvement in the contact area is achieved while the results of the minimum thickness and protrusion height do not become worse.
Abstract: The success of the T-shape tube hydroforming process requires a combination of internal pressure and axial and counter punch actions. The objective of this study is to introduce the adaptive radial basis function and demonstrate its accuracy and efficiency through a numerical example, to determine the optimal loading parameters in T-shape tube hydroforming process. The finite element model is developed with the explicit dynamic finite element code LS-DYNA and validated against the experimental work. The Taguchi method based on variance of analysis technique is used to screen the important loading parameters, which have a significant effect on the forming quality, such as the maximum thinning ratio, protrusion height and contact area, etc, from a number of potential loading parameters. The contact area is considered as the objective while the maximum thinning ratio and protrusion height are regarded as the constraints, and then the optimal loading parameters are obtained by adaptive radial basis function after several iterations. The results show that a significant improvement in the contact area is achieved while the results of the minimum thickness and protrusion height do not become worse.
TL;DR: In this paper, a single-step tube hydroforming process was retained based on pure expansion hydroforming with the conjunction of only internal pressure loading, and the distribution of thickness was studied under both dry and lubricated conditions.
Abstract: This paper presents an experimental study on corner filling in the tube hydroforming process. A single-step tube hydroforming process was retained based on pure expansion hydroforming with the conjunction of only internal pressure loading. Several hydroforming experiments were performed with differently shaped dies, such as a square, a rectangular, a trapezoidal, and a trapezoid-sectional die. The distribution of thickness was studied under both dry and lubricated conditions. The main results revealed that thinning occurred in the transition zone, between the corner radius and the straight wall, for both the square and rectangular dies. However, for the trapezoidal and trapezoid-sectional dies, the thinning took place in the sharp zone. The use of Teflon as a lubricant between the die and the tube led to significant changes in terms of thickness distribution and the reduction of thinning. For each of the various dies that were used, it was found that the lubrication of the contact tube/die offered a more uniform thickness for the final hydroformed product.
TL;DR: In this article, the optimal working conditions to manufacture an aluminium component by warm sheet HydroForming were determined based on numerical data and the effect of modeling different plastic behaviors through the implementation of two yield criteria (the anisotropic Barlat '89 criterion and the isotropic Von Mises one).
TL;DR: To investigate the capability of hydroforging process, an experimental setup was developed and used to hydroforge various geometries, which included hollow flanged vessels, hexagonal flanged parts, and hollow bevel and spur gears.
Abstract: Hydroforging is a hybrid forming operation whereby a thick tube is formed to a desired geometry by combining forging and hydroforming principles. Through this process hollow structures with high strength-to-weight ratio can be produced for applications in power transmission systems and other structural components that demands high strength-to-weight ratio. In this process, a thick tube is deformed by pressurized fluid contained within the tube using a multi-purpose punch assembly, which is also used to feed tube material into the die cavity. Fluid pressure inside the thick tube is developed by volume change governed by the movement of the punch assembly. In contrast to the conventional tube hydroforming (THF), the hydroforging process presented in this study does not require external supply of pressurized fluid to the deforming tube. To investigate the capability of hydroforging process, an experimental setup was developed and used to hydroforge various geometries. These geometries included hollow flanged vessels, hexagonal flanged parts, and hollow bevel and spur gears.
TL;DR: In this paper, the effect of various loading conditions, such as free loading, bulging with axial feeding and closed end, along with loading condition, die geometries with different corner radius and deformation width were studied on the strain path and plastic instability.
Abstract: Tearing as a factor that restricts formability of sheets and tubes is determined by forming limit diagram (FLD). The aim of the current study is to present a novel approach to achieve FLD of a metallic tube using hydroforming process. Here, for 304 stainless steel tubes, various loading conditions, namely free loading, bulging with axial feeding and bulging with closed end, were considered. Along with loading condition, die geometries with different corner radius and deformation width were studied on the strain path and plastic instability. The effects of process parameters on the strain path have been evaluated and simulated using ABAQUS/Explicit. Meshed tubes were bulged under controlled loading, and the FLD was drawn after measuring the major and minor strains close to the tearing location. Finally, the evaluation of the current method has been investigated by using the obtained FLD in the forming of an industrial part (i.e., the cam-shaped tube). The results revealed that the proposed approach has the capability to predict the formability of industrial components.
01 Feb 2016
TL;DR: In this paper, the effect of compressive normal stress has been considered in the determination of forming limit diagrams and forming limit stress diagrams to predict neck initiation failure in torsion control.
Abstract: In this study, the effect of a compressive normal stress has been considered in the determination of forming limit diagrams and forming limit stress diagrams to predict neck initiation failure in t...
TL;DR: In this article, a 3D finite element model for tube hydroforming was developed using Creo Parametric 2.0, pre-processed using HyperMesh and solved using LS-DYNA explicit solver.
TL;DR: In this paper, the authors used the interval optimization method to deal with limited information in T-shape tube hydroforming, where the contact area between the counter punch and the tube was taken as the objective function and the protrusion height and maximum thinning ratio as constraints.
Abstract: In this study, the interval optimization method, in which the bounds of uncertain parameters are only required and knowing their probability distributions are not needed, is introduced to deal with limited information in T-shape tube hydroforming. The contact area between the counter punch and the tube is taken as the objective function and the protrusion height and maximum thinning ratio as constraints. To control the possibility degree of failure associated to each constraint, the reliability-based possibility degree of interval method is adopted to evaluate the reliability of T-shape tube hydroforming process. Before optimizing the process, the finite element model is validated against experimental results, and Taguchi method is employed to screen key factors from a number of potential factors. In addition, to improve computation efficiency, the Kriging model is adopted to construct the surrogate model, and the performance of the resulting surrogate model is validated using cross-validated method. Finally, the Kriging based on interval optimization method is applied for loading path design in T-shape tube hydroforming, and the results show that the robustness and reliability of the process can be guaranteed.
TL;DR: In this article, a finite element codes LS-DYNA and DYNAFORM are used to analyze the plastic flow pattern of a tube hydroforming into a product with large expansion ratio and eccentric axes.
Abstract: In this paper, finite element codes LS-DYNA and DYNAFORM are used to analyze the plastic flow pattern of a tube hydroforming into a product with large expansion ratio and eccentric axes. Tube hydroforming with a movable die is proposed to enhance the forming capacity of tube hydroforming technology. The relative speed of the axial feedings to the movable die for obtaining a sound product is determined by a geometric analysis. The whole forming processes are divided into two stages. At the first stage, an internal pressure is applied on the inner surface of the tube and two axial feedings and a movable die move forward simultaneouly. At the second stage, one of the axial feedings keeps moving forward, whereas, the movable die moves backward. With this forming schedule for the axial feedings and movable die, products with more uniform thickness distributions are obtained. Finally, experiments of tube hydroforming with a movable die are conducted. Low-carbon steels are used as the tube specimen in the experiments. The simulation results of the product shape and thickness distributions are compared with experimental results to verify the validity of the finite element modeling and the proposed forming schedules.
Abstract: High-pressure pneumatic forming (HPPF) is an internal high-pressure forming process at elevated temperatures, which is based on quick plastic forming (QPF), hot metal gas forming (HMGF) and hydroforming. In this study, the HPPF experiments were performed on Ti-3Al-2.5V tubes using a square cross-sectional die at higher pressure levels and lower temperatures. The uniaxial tensile tests were carried out at various temperatures and strain rates before the HPPF experiments. The flow stress of Ti-3Al-2.5V tubes is evidently affected by both temperature and strain rate. Because of this, the corner radii all change linearly over time at the pressurization stage but exponentially over time at the constant pressure stage. The cooling effect of the inflow process on the tubes results in temperature differences between the centre of the straight wall areas and the corner areas of the tubes during the inflow process. Adopting the lower pressurization rate and filling regenerative materials into the tube are effective methods for decreasing or eliminating the temperature difference.
TL;DR: In this paper, a sheet metal forming process was proposed by the combination of sheet hydroforming process with multipoint tool to fabricate a variety of curved surface shells without the need of new tools for prototype development or low volume production.
Abstract: A newly developed sheet metal forming process was proposed by the combination of sheet hydroforming process with multipoint tool to fabricate a variety of curved surface shells without the need of new tools for prototype development or low volume production. An experimental hydroforming setup with multipoint punch was developed and performed to prove the feasibility of this process and investigate the combination effect. A half ellipsoid shell was employed as a case to investigate the deformation procedure of sheet metal. Stress and strain distributions were given by numerical simulations to evaluate the local dimpling and geometrical error caused by discrete pins. The influence of hydraulic pressure and cover sheet thickness on the surface quality and geometrical precision were analyzed both by experimental works and numerical simulations. It was shown that the geometrical shape error can be compensated by the reconfiguration of multipoint punch, and the geometrical deviation between the deformed shape and desired one can be restricted within the permitted value. This investigation reveals that the sheet hydroforming process with multipoint tool is a potential forming method for curved surface shells with low cost, high accuracy, and flexibility.
TL;DR: In this paper, the authors generalized the conventional M-K formability model to consider all possible loading conditions including normal and through thickness shear stresses, and applied the Newton-Raphson trend for solving the final system of equations to calculate limiting strains.
Abstract: Since necking in some novel processes such as hydroforming and incremental forming can occur at locations where in addition to the in-plane stresses normal and through thickness shear stresses are exerted on the sheet metal, the plane stress assumption is not proper for predicting forming limits in these processes. Consequently in this research, conventional Marciniak-Kuczynski formability model has been generalized to consider all possible loading conditions including normal and through thickness shear stresses. For this purpose, additional force equilibrium and geometrical compatibility have been supposed between groove and matrix and Newton–Raphson trend has been applied for solving final system of equations in the numerical model to calculate limiting strains. In order to validate the theoretical model, subsequent theoretical forming limit curves have been compared with published experimental data. It has been shown that the extended M–K model is in good compatibility with experimental results and increase in normal and through thickness stresses enhances forming limits.
TL;DR: In this article, numerical simulations of the hydroforming process of Ti/Al clad T-shapes were conducted by using finite element analysis software, which were used to optimize process parameters such as internal pressure, feed distance, and friction coefficient.
Abstract: Numerical simulations of the hydroforming process of Ti/Al clad T-shapes were conducted by using finite element analysis software. These simulations were used to optimize process parameters such as internal pressure, feed distance, and friction coefficient. Subsequently, hydroforming experiments were conducted based on these simulations. The results indicated that Ti/Al clad tubes could be obtained in the practical hydroforming process under the following forming conditions: internal pressure of 110 MPa, feed distance of punches of 25 mm, and a friction coefficient of 0.1. This resulted in well-bonded micro-interface between titanium and aluminum that is free from any delamination. The protrusion height of Ti/Al clad T-shapes were 25.5 mm and had high thickness uniformity.
01 Oct 2016
TL;DR: In this paper, an optimization process is employed to evaluate the appropriate external forces but defects are prevented, and the equivalent static loads method for nonlinear static response structural optimization is used for the optimization process because the tube-hydroforming process is analyzed by non-linear dynamic response analysis.
Abstract: In general, hydroforming optimization aims to make a desired shape of a plastically deformed structure under dynamic forces. The automotive industry has shown great interest in tube hydroforming, which is a metal-forming process. The forces from the hydraulic fluid are utilized to deform a tube. The internal pressures and the axial feedings (of the axial forces) determine the quality of the deformed product. In this research, an optimization process is employed to evaluate the appropriate external forces but defects are prevented. The equivalent static loads method for non-linear static response structural optimization is used for the optimization process because the tube-hydroforming process is analysed by non-linear dynamic response analysis. The equivalent static loads are the static loads that generate the same response field as that of non-linear dynamic analysis and are utilized as the loading conditions in linear static response optimization. A novel process is added to the original equivalent stat...
TL;DR: In this article, a modified Marciniak and Kuczynski (M-K) method is used with Barlat's 1989 anisotropic yield function and Voce equation to predict forming limit diagrams (FLDs) for AA6063 and AA6065 aluminum seamless extruded tubes.
Abstract: The purpose of this study is to predict forming limit diagrams (FLDs) for AA6063 and AA6065 aluminum seamless extruded tubes. The Modified Marciniak and Kuczynski (M-K) method is used with Barlat’s 1989 anisotropic yield function and Voce equation. Furthermore, a new calibration method for FLD determination based on the modified M-K method is also applied. The predicted forming limits correlate well with experimental data. It is shown that in comparison to other methods, this method is able to predict necking in tube hydroforming with more accuracy. Therefore, this method can be used to predict bursting in a wide range of practical tube hydroforming of aluminum alloys.
TL;DR: In this article, the wrinkling behavior and thickness distribution of 5A06 aluminum alloy sheets in an annealed state with thickness of 1.0mm and 2.5mm was numerically and experimentally investigated under different hydraulic pressures in the hydroforming of single-layer and double-layer sheets.
Abstract: In this article, the wrinkling behavior and thickness distribution of 5A06 aluminum alloy sheets in an annealed state with thickness of 1.0 mm and 2.5 mm was numerically and experimentally investigated under different hydraulic pressures in the hydroforming of single-layer and double-layer sheets. Note that, in double-layer sheets hydroforming, an upper-aided sheet is needed. The upper, thicker sheet synchronously deforms with the lower, thinner sheet during hydroforming. When the double-layer sheets are separated, a thinner curved sheet part will be manufactured. As can be seen from the simulation and experimental results, the upper, thicker sheet could effectively suppress the wrinkles of the lower, thinner sheet and improve the thickness distribution due to the increasing anti-wrinkle ability of the formed sheet and the interfacial friction between the double-layer sheets. In addition, the maximum hydraulic pressure can be decreased via hydroforming of double-layer sheets; this approach reduces the drawing force for large sheet parts and meets the requirement of energy conservation.
TL;DR: In this paper, an analytical model for stress component calculation for fixed-end tube under internal and external pressures was proposed to investigate the mechanical properties of anisotropic thin-walled tubes under three-dimensional stress state.
Abstract: Tube hydro-bulging test is a specialized method to obtain the mechanical properties of tubes when they are deformed under bi-axial stress states. However, the normal stress cannot be ignored in double-sided tube hydroforming process. In order to investigate the mechanical properties of anisotropic thin-walled tubes under three-dimensional stress state, an analytical model for stress component calculation for fixed-end tube under internal and external pressures was proposed. Furthermore, the equivalent stress and the equivalent strain were derived using the Hill 1948 yield criterion through plastic increment theory. A thin-walled AA5052-O aluminum alloy tubes were bulged under different external pressures using a dedicated testing apparatus for double-sided tube hydro-bulging tests. Then, hardening curves considering anisotropy were obtained for each external pressure condition, respectively. It is shown that the strain hardening exponent of AA5052 tube shows a slight increase with the increasing external pressure, and the external pressure of 85 MPa has little or no effects on the hardening behavior of tubes. Moreover, the anisotropy has a little effect on the strain hardening exponent, but has an obvious influence on the strength coefficient of the AA5052 tube. Therefore, for the measurement of the AA5052 tube’s mechanical properties under three-dimensional stress state, the effect of external pressure can be ignored but the anisotropy of tubes must be considered.
TL;DR: In this article, a blank bulging method was proposed to solve the problems of non-uniform thickness distribution and cracking failure of aluminum thin-walled corrugated sheet during the conventional hydroforming process.
Abstract: The explosively forming projectile (EFP) has been traditionally adopted for the manufacturing of aluminum thin-walled corrugated sheet. These components have large deformation ranges but inferior formability. Additionally, the process usually delivers inferior surface quality with long manufacturing cycle time and high cost. The active hydroforming process is suggested to solve these issues during EFP. A new technology named as blank bulging by turning the upside down active hydroforming technology is proposed to overcome problems like nonuniform thickness distribution and cracking failure of corrugated sheet during the conventional hydroforming process. FEM simulations and experiments were conducted to validate this new technology. The effects of strain rate on the formability of aluminum alloy AA2024-O during the active hydroforming process were investigated according to the bulging test with pressure rate control. Results indicate that aluminum alloy AA2024-O is not sensitive to pressure rate (strain rate) at room temperature. Furthermore, the deformation capacity of aluminum alloys can be improved effectively, and more uniform distribution of wall thickness can be obtained by this new method. It can be concluded that the new method is universal for thin-walled, shallow drawing parts having complex sections.