Warm Hydroforming Research Articles

Failure analysis and formability improvement of GLARE laminates in warm active hydroforming technology: Experimental and numerical approach

Warm hydroforming shows considerable promise as a forming technology for Fiber Metal Laminates (FMLs) parts due to its capacity to enhance the formability of materials. However, a detailed investigation into the failure behavior during hydroforming is still lacking. In this paper, a systematic experiment was performed to analyze the possible failure modes for GLARE in warm active hydroforming. Five main defect modes have been identified, including fiber crack, combined Al & fiber crack, wrinkle, low resin, and voids defects. The related formation mechanisms have been analyzed based on both experiments and numerical methods. Additionally, the effects of critical process parameters, including the blank holder force (BHF), liquid pressure rate (PR), and temperature (T) on failure behavior are thoroughly investigated and quantified. The use of step-loading BHF was recommended to enhance formability, which caused a nearly 36% decrease in the prepreg tensile damage criteria coefficient. Conversely, decreasing PR or increasing T significantly improved the formability of GLARE but resulted in low resin content and significant void defects. Consequently, a feasibility map that quantified the BHF and liquid pressure effects on various defects was developed, leading to optimized parameters for manufacturing a box-shaped part. This study not only explores the failure model of FMLs but also offers valuable insights for process parameter improvement and how to optimize key parameters in engineering processes.

A novel active hydroforming & curing process to manufacture GLARE laminates: Numerical and experimental investigations

Fiber Metal Laminates (FMLs) are preferable thin-walled structures in several fields for their exceptional mechanical properties. However, how to manufacture thin-walled FMLs structures with complex shapes and guarantee the high mechanical properties is still a challenge. To address these, this paper proposes an innovative hybrid forming method, referred to as active warm hydroforming and curing, to enhance the formability and performance of FMLs in GLARE form by combining the forming and curing process into a single step. The hybrid method was verified on a box-shaped part as a proof-of-concept to assess the feasibility and parameter influence. Online curing was utilized to enhance efficiency and quality. The outcomes revealed that the new method increases the ultimate tensile stress by 12.1 % and reduces curing deformation from 3.1 mm to 1.3 mm compared to the vacuum bagging method. Furthermore, the critical parameters in forming of thin-walled structures, including blank holder force (BHF), pressure rate (PR), maximum pressure (MP), and forming temperature (FT), were identified using experimental, mathematical, and numerical approaches. Four defects in the formed thin-walled structures were observed and successfully eliminated through the control of these parameters. The method and results presented in this paper also provide direct guidance for optimizing the process parameters of FMLs warm hydroforming.

Modeling of constitutive behavior and ductile fracture of AA5A06 aluminum alloy sheet in warm hydroforming process

In order to predict the formability of lightweight materials, the flow stress and fracture behavior of AA5A06 aluminum alloy which is very sensitive to temperature and strain-rate were investigated in this study. First, a modified Misiolek constitutive equation with a work-soften term is proposed to calculate the flow stress of the sheet metal. To predict ductile fracture in sheet forming operations, Cockcroft-Latham damage criterion is applied here and ductile fracture threshold under each condition is estimated using Response Surface Method. Finally, warm hydroforming deep drawing tests were conducted at various conditions and the experiment results are compared with the numerical simulation result to evaluate the new model’s feasibility and accuracy in forecasting the mechanical response of the material in warm forming conditions. Results show that the proposed model has a good accuracy compared with the traditional power law models and the FEM simulation conforms well to the tests.

Numerical simulation and experimental study of warm hydro-forming of magnesium alloy sheet

The uneven forming temperature during warm hydro-forming of magnesium alloy sheets is one of the main causes of defects in formed parts. In order to completely solve this problem to obtain products with good forming quality, a new warm forming method for magnesium alloy sheet is proposed: the magnesium alloy sheets and forming die are immersed in hot oil to achieve constant temperature forming. In addition, a hot oil warm hydro-forming device for magnesium alloy sheets was designed and developed. This work also carried out the numerical simulations and forming experiments, this study to investigated the effects of forming concave die chamfer, temperature, friction coefficient, hydraulic pressure, and blank holder force on the warm hydro-forming of magnesium alloy sheet. The simulation results are in good agreement with the experimental ones, and the feasibility of warm hydro-forming of magnesium alloy sheet is verified. According to the numerical simulations and forming experiments, the best process window for warm hydro-forming of l mm thick AZ31B magnesium alloy sheet was obtained. The hot oil constant temperature hydraulic forming technology can enrich the forming process of magnesium alloy and provide a new perspective and technical basis for warm forming of other hard-to-deform metal materials.

5A06-O aluminium–magnesium alloy sheet warm hydroforming and optimization of process parameters

The uniaxial tensile test of the 5A06-O aluminium–magnesium (Al–Mg) alloy sheet was performed in the temperature range of 20–300 °C to obtain the true stress–true strain curves at different temperatures and strain rates. The constitutive model of 5A06-O Al–Mg alloy sheet with the temperature range from 150 to 300°C was established. Based on the test results, a unique finite element simulation platform for warm hydroforming of 5A06-O Al–Mg alloy was set up using the general finite element software MSC.Marc to simulate warm hydroforming of classic specimen, and a coupled thermo-mechanical finite element model for warm hydroforming of cylindrical cup was built up. Combined with the experiment, the influence of the temperature field distribution and loading conditions on the sheet formability was studied. The results show that the non-isothermal temperature distribution conditions can significantly improve the forming performance of the material. As the temperature increases, the impact of the punching speed on the forming becomes particularly obvious; the optimal values of the fluid pressure and blank holder force required for forming are reduced.

Investigation on precision warm hydroforming with independent circumferential pressure of high-performance aluminum alloy parts with special-shaped bottom

High-performance aluminum alloy is light, has high strength, but is very difficult to be formed. In the forming process of aluminum alloy parts with special-shaped bottom, there are defects such as poor fittability accuracy, instability, and cracking at the complex bottom, and the forming accuracy is an important performance index to characterize the forming quality. In this paper, a precision warm hydroforming scheme of pre-bulging and deep drawing is designed, and a method of applying independent circumferential pressure on the periphery of the flange in the later stage of pre-bulging is proposed to maintain the shape of the bottom and improve the fittability accuracy. The effects of temperature difference and independent circumferential pressure on the wall thickness and fittability of the part are studied. At the same time, response surface method is used to study the interaction among pre-bulging pressure, liquid chamber pressure, and circumferential pressure, and the optimal forming conditions are obtained after optimization and compared with the test piece. The results show that independent circumferential pressure can significantly improve the ability of the bottom of the pre-bulged part to maintain the acquired shape, and the temperature difference can effectively improve the plasticity of the sheet, the depth of drawing, and the quality of the part. After optimization by response surface method, the minimum wall thickness of the part is 0.8013 mm and the fittability is 94.2%. The forming quality parameters of the test piece are in good agreement with the numerical simulation parts, which indicates that this simulation can effectively predict forming situation of the part, and provides scientific guidance for precision forming of complex-shaped bottom parts.

Mechanics analysis of aluminum alloy cylindrical cup during warm sheet hydromechanical deep drawing

To obtain the stress states of the sheet metal and understand the potential forming mechanism under the influences of fluid pressure and temperature during the warm hydroforming of 5A06-O aluminum alloy sheets, mechanics analysis was conducted for the warm hydromechanical deep drawing of a cylindrical cup, taking into account through-thickness normal stress induced by fluid pressure. By considering the additional stress during bending using a variable-stiffness pure bending model as equal to that determined using a bending moment model, the additional stress at the die corner during bending was solved. The force equilibrium equations for the cup near the die corner, which were classified by whether the blank contacted the die, were also established and the results were in good agreement with those obtained via the finite element method. Furthermore, mechanics analysis was also performed for the straight-wall region, and the results revealed that the error was slightly greater when the liquid pressure was used to approximately equal to through-thickness normal stress because the ratio of thickness to radius was not sufficiently large.

Effect of flow stress calculation on formability of aluminum alloy warm sheet hydroforming

Effect of flow stress calculation on formability of aluminum alloy warm sheet hydroforming

Investigation on the Effect of Type of Cooling on the Properties of Aluminum Alloy during Warm/Hot Hydromechanical Deep Drawing

The warm sheet cylindrical deep drawing experiment of aluminum alloy was carried out and macro-mechanical properties and microstructure evolution of hydro-formed cups with different cooling medium were analyzed, which aimed to investigate the effects of different types of cooling on mechanical properties and microstructure of cylindrical cups hydro-formed by warm Hydro-mechanical Deep Drawing (HDD). Results show that, under the condition of warm hydroforming, the mechanical properties such as yield stress and ultimate strength were influenced very little by air or water cooling. Grain coarsening of these hydro-formed cups can be inhibited to a certain extent with subsequent rapid water cooling. Moreover, it shows that the processing with warm sheet hydroforming and subsequent rapid cooling of 7075-O aluminum alloy has a positive significance in maintaining the stability of macro mechanical properties and inhibiting the degradation of the microstructure of materials.

Investigation about the Oil Pressure Rate in the Warm Hydroforming of an Al-Mg Alloy Component

In this work, the hydroforming process in warm conditions was used for manufacturing an Al-Mg alloy (AA5754) benchmark component displaying different strain levels due to its geometry. The attention was focused on the effect of the rate to increase the forming pressure (PR), strictly related to the strain rate the material is subjected to. In fact, preliminary tensile and Nakajima tests (both at room temperature and in warm conditions) revealed that the mechanical and formability properties of the investigated alloy are strongly affected by the strain rate. Warm Hydroforming tests were conducted in order to investigate both the working temperature and the parameter PR. The Blank Holder Force profile was varied according to an experimentally determined profile able to avoid oil leakages. Experimental results were collected in terms of output variables related to the die cavity filling and to the strain level reached on the component: in such a way a multi-objective optimization could be carried out using the commercial integration platform modeFRONTIER. The best compromise between the high level of the component deformation and the cycle time could be obtained by conducting the warm hydroforming process at the temperature of 250°C and setting the parameter PR equal to 0.1 MPa/sec.

Experimental and numerical analysis of hydrodynamic deep drawing assisted by radial pressure at elevated temperatures

Nowadays, due to the demand for lightweight construction and fuel consumption reduction, especially in automotive and aerospace industries, the use of aluminum alloys has drawn much attention. Nevertheless, poor formability at room temperature is the main drawback of using these alloys. To overcome the problem, the work material is formed at elevated temperatures. In the present paper, Hydrodynamic Deep Drawing assisted by Radial Pressure (HDDRP) process has been selected over other forming methods. The aim of the study is to investigate the applicability of this process in conjunction with warm forming. For this purpose, experimental and numerical attempts have been made on warm forming of flat-bottom cylindrical cups in isothermal condition. At first, a series of warm hydroforming experiments were performed to determine the effect of tool temperature and forming speed on the thickness distribution of the final part and on the required forming load. Then, a set of finite element analyses (FEA) were performed using ABAQUS explicit to extend the findings. The Response Surface Method (RSM) was then used to build the relationship between the input parameters such as temperature and forming speed, and output responses including minimum part thickness and maximum punch force. It is demonstrated that the required forming force was decreased with increase in punch speed and tool temperature. Additionally, minimum thickness of the part is increased with increasing temperature and decreasing punch speed. Studying the Limiting Drawing Ratio (LDR) revealed that elevating the forming temperature causes reduction in LDR, while rising the punch speed leads to a slight enhancement in it. For the evaluation of part dimensional changes after forming, springback analysis was done via studying the through-thickness hoop stress distribution. It is found that using warm isothermal HDDRP in high forming rate results in more uniform stress distribution and lower level of stress and so a better springback behavior.

Design, Fabrication, and Experimental Validation of a Warm Hydroforming Test System

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 °C using induction heaters in the die and blank holders (BH), whereas the punch can be cooled down to temperatures of around 10 °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.

Warm HydroForming of the heat treatable aluminium alloy AC170PX

In this work the Warm HydroForming process of a 6xxx series Al alloy has been investigated in order to find suitable process parameters for successfully forming a benchmark component displaying varying deformation ratios due to its geometry. Since the attention was focused on the 6xxx series alloy AC170PX, belonging to the group of the age-hardenable Al alloys, the process conditions affecting the ageing, such as temperature and duration of heating exposure, the rate to increase the oil pressure, had to be determined. A preliminary mechanical characterization on artificially aged specimens was thus necessary both at room temperature and in warm conditions to investigate the influence of the ageing phenomenon on the mechanical and deformation behaviour at temperatures ranging from 150°C to 350°C. Based on the results of the tensile tests, preliminary Warm HydroForming experiments were conducted by changing the most influencing process parameters: working temperature, heating time and the time needed to increase the oil pressure up to the maximum value. It was found that the optimum working temperature was 200°C and that the exposure of the material to the employed warm-forming temperature had to be minimized. Final Warm HydroForming tests were thus carried out using different rates to increase the oil pressure for comparison purposes, revealing that employing higher rates, i.e. increasing the strain rate, was beneficial, in terms of die cavity filling and sheet thinning, to obtain sound products.

Modified MK model combined with ductile fracture criterion and its application in warm hydroforming

A modified MK model combined with ductile fracture criterion (DFC-MK model) is proposed to compute the forming limit diagrams (FLDs) of 5A06-O aluminum alloy sheet at different temperatures. The material constant (C) of ductile fracture criterion and initial thickness imperfection parameter (f0) at various temperatures are determined by using a new computing method based on wide sheet bending test. The FLDs at 20 and 200 °C are calculated through the DFC-MK model. The DFC-MK model, which includes the influence of through-thickness normal stress, is written into the subroutine VUMAT embedded in Abaqus/Explicit. The cylindrical cup hydroforming tests are carried out to verify the model. The results show that compared with experimental observations, the predicted FLDs based on DFC-MK model are more accurate than the conventional MK model; the errors between the simulations and experiments in warm hydroforming are 8.23% at 20 °C and 9.24% at 200 °C, which verify the effectiveness of the proposed model.

Multi-Objective Optimization of the Hydroforming Process Considering Different Plastic Yield Criteria

The present work aims at determining the optimal working conditions for the manufacturing of the AA6061-T6 Al alloy by the hydroforming process. As case study a stepped geometry was used. A numerical model was created using the commercial explicit Finite Element code LS-DYNA. The plastic behaviour of the investigated alloy was modelled implementing experimental data (flow stress curves, Lankford coefficients and Forming Limit Curves) and using two different yield criteria: an anisotropic one (Barlat ‘89) and the conventional isotropic one (Von Mises). Finite Element models were tuned using experimental data from warm hydroforming tests: comparing both the sheet thinning and the die cavity filling, quite different friction conditions had to be supposed for obtaining a good fitting with both the yield criteria.Finite Element models were finally used for evaluating the working range of the hydroforming process: results from a CCD simulation plan were imported within an integration platform (modeFRONTIER) to evaluate the optimal hydroforming conditions based on a multi-objective genetic algorithm optimization. Quite different results in terms of optimization and working range were obtained when adopting different yield criteria.

Mechanics analysis of axisymmetric thin-walled part in warm sheet hydroforming

To obtain the influence of fluid pressure and temperature on warm hydroforming of 5A06-O aluminum alloy sheet, the unified mechanics equilibrium equations, which take through-thickness normal stress and friction into account, were established in spherical coordinate system. The distribution of through-thickness normal stress in the thickness direction was determined. The relation between through-thickness normal stress and fluid pressure was also analyzed in different regions of cylindrical cup. Based on the method of subtracting one increasing function from another, the constitutive equation of 5A06-O applied to warm hydroforming was established and in a good agreement with uniaxial tensile data. Based on whether the thickness variation was taken into account, two mechanic models were established to do the comparative study. The results for the studied case show that the calculated stress values are pretty close according to the two models and consistent with results of finite element analysis; the thickness distribution in flange computed by the second model conforms to the experimental data. Finally, the influences of fluid pressure on the flange thickness and radial stress were analyzed.

Application of the Warm Hydroforming Process to the Manufacturing of Pre-Aged 6xxx Series Components Using a Numerical/Experimental Approach

In this work the Warm Hydroforming (WHF) process for the production of a 6xxx series Al alloy component has been investigated using a numerical/experimental approach: both experimental and numerical hydroforming tests were carried out using the alloy AC170PX, a pre aged (T4 condition) Al alloy often adopted for automotive applications. In order to evaluate both the mechanical and strain behaviour of the material, tensile tests were carried out at different temperature and strain rate levels using the Gleeble system 3180, keeping also into account the ageing effect; in addition, formability (Nakazima) tests in warm conditions were performed by means of a specific equipment and the Forming Limit Curves at different temperature levels were evaluated according to the ISO standard 12004-2. Hydroforming experiments were carried out using a prototypal press machine specifically designed for WHF and SuperPlastic Forming tests. Such tests, scheduled by a DoE approach, were aimed at investigating the suitability of using the investigated Al alloy in the WHF process: attention was thus focused on those parameters mainly affecting the aging phenomenon (temperature, heating time and cycle time). In order to overcome the actual physical limitation of the hydroforming facilities, a Finite Element (FE) model of the WHF process was also created implementing experimental data (flow stress curves and FLCs) and tuned using data from preliminary WHF tests. In particular, after setting the Coefficient Of Friction (COF) according to temperature and verifying the robustness of numerical simulations, the FE model was used for investigating: (i) the influence of the Blank Holder Force (neglected in the experimental campaign); (ii) the adoption of quite smaller values of the parameter cycle time (being the aim to determine higher strain rates in the material). Through the definition of proper response variables (Flatness, Bursting Pressure and Thickness Ratio) both experimental and numerical results were analyzed by means of polynomial Response Surfaces in order to evaluate the optimal process conditions.

Prediction of bulge height in warm hydroforming of aluminum tubes using ductile fracture criteria

Warm hydroforming is used widely to increase the formability of aluminum and magnesium tubes. Prediction of forming limit is a vital problem in designing the warm hydroforming process of tubes. In this paper, bulge height of aluminum tubes AA6063 is predicted using ductile fracture criteria at high temperatures. Ductile fracture criteria were calibrated by performing several uniaxial tensile tests at different temperatures and strain rates. Fracture strain and work functions were obtained based on Zener–Holloman parameter. Free bulging process of tubes was simulated using finite element method and different loading curves were used to bulge the tubes. Prediction of ductile fracture was compared with the experimental results measured on a warm free bulging set-up. The comparison shows that Ayada ductile fracture criterion is able to predict the bulge height of aluminum tubes at high temperatures.

Feasibility study on optimized process conditions in warm tube hydroforming

Feasibility study has been performed to estimate the optimized process conditions in warm tube hydroforming based on the simulated annealing optimization method. Precise prediction and control of process parameters play an important role in forming at warm conditions. Optimal pressure and feed loading paths are obtained for aluminium AA6061 tubes through the simulated annealing algorithm in conjunction with finite element simulations. Numerous axisymmetric geometries are investigated and the effects of expansion ratio, corner fillet to thickness ratio, and initial diameter to thickness ratio are studied. For the feasibility estimation, warm hydroforming experiments have been conducted on aluminum AA6061 under optimal designed conditions. The results show that the optimization procedure used in this research is a reliable and feasible tool in determination of optimal process conditions for the sound warm hydroforming process.

Progress on High Pressure Pneumatic Forming and Warm Hydroforming of Titanium and Magnesium Alloy Tubular Components

Complex structural tubular components of Titanium and Magnesium alloy can be obtained at a certain temperature by high pressure pneumatic forming (HPPF) with gas medium or warm hydroforming with pressurized liquid medium. At 800°C, through experimental research on HPPF of TA18 Ti-alloy tube with expansion ratio of 50%, the influence of axial feeding on thickness distribution of the workpiece was studied. Using reasonable loading curve, the component with large ratio can be formed with a small thinning ratio as 13% with total axial feeding amount of 40mm. At 850°C, HPPF experiments of TA18 Ti-alloy component with square section were carried out. The influence of gas pressure on thickness distribution and corner filling process were analyzed. The larger the pressure, the sooner the displacement changes at the corner, and the shorter corner filling term. At pressure of 30 MPa, small corner with the relative corner radius of 2.0 can be obtained within 168s. For Mg-alloy tubular part, warm hydroforming with non-uniform temperature field was studied. By using reasonable axial temperature field and loading path, the maximum thinning ratio of Mg-alloy tubular component with expansion ratio of 35% was reduced from 21.6% to 11.6%.