Sheet Hydroforming Research Articles

Numerical simulation of sheet hydroforming taking into account analytical pressure and fluid flow

The paper treats the modeling and simulation of sheet metal hydroforming taking into account fluid pressure and fluid velocity effects. A hydro-mechanical model is proposed to determine the fluid flow and the pressure variation in the die cavity in case of sheet hydroforming. The hydrodynamical model for the fluid flow between the sheet and the blank holder is based on Reynold's equation. A numerical and experimental hydromechanical deep drawing of a cylindrical cup validates the predictions of the proposed approach.

Forming characteristic of sheet hydroforming under the influence of through-thickness normal stress

Sheet hydroforming is different from conventional sheet forming due to the existence of liquid pressure. Through thickness normal stress induced by liquid pressure is derived by solving the normal force equilibrium equation. The theoretical prediction is in a good agreement with that determined by experimental data at cup wall. As the third principal stress, through thickness normal stress cannot be reflected in two dimensional yield locus. The variables of η and ω as new coordinates were introduced. Accompanied with stress triaxiality βav and effective strain ɛeq, they were used to describe the change of typical stress states in sheet hydroforming. As liquid pressure increases to infinity, sheet hydroforming covers the stress states from equi-biaxial tension to uniaxial compression. The numerical simulation in Marc shows that, the stress states of non-free bulging zones are away from plane stress in the (βav, ɛeq) and (η, ω) based spaces.

Modeling of Microchannel Hydroforming Process With Thin Metallic Sheets

Micro/mesoscale metal sheet hydroforming (SHF) process is an efficient approach suitable for mass production to fabricate metal parts with micro/mesochannel features. In conventional sheet hydroforming process, the channel’s feature sizes (e.g., the channel width, fillet radius, etc.) are much greater than the sheet’s thickness, so that the influence of the fillet and the inhomogeneous stress/strain distribution through the thickness direction can be ignored. However, the influence becomes increasingly important, because the thickness of the sheet and the feature dimensions of the microchannel are in the same magnitude as the feature sizes of the material and tools reduced to micro/mesoscale. In this paper, an analytical model with consideration of the inhomogeneous stress/strain distribution was developed to predict the channel profile at different pressures in micro/mesohydroforming process. Plane-strain deformation behaviors in the section of the workpiece were studied, and the relation function between the pressure and the channel height was established. Via this function, the channel height could be accurately predicted for a given pressure. Furthermore, an experimental setup was prepared, hydroforming experiments using microchannel dies with various geometric dimensions were conducted, and the channel height of the workpieces was measured. It was found that the experimental results matched well with the simulation results, which confirmed the validity of the analytical model proposed in this study. It is expected that the model will be beneficial in the optimization of the microchannel hydroforming process.

Experimental springback evaluation in hydromechanical deep drawing (HDD) of large products

Springback is a really troublesome effect in sheet metal forming processes. In fact changes in geometry after springback are a big and costly problem in the automotive industry. In this paper the authors want to analyse the springback phenomenon experimentally in sheet metal hydroforming. Compared with conventional deep drawing, sheet hydroforming technology has many remarkable advantages, such as a higher drawing ratio, better surface quality, less springback, better dimensional freezing and capability to manufacture complicated shapes. The springback phenomenon has been extensively analysed in deep drawing processes but there are not many works in the literature about springback in sheet metal hydroforming. In order to study it, the authors have performed an accurate measuring phase on the chosen test cases through a coordinate measuring machine and the obtained measurements have been utilised for the determination of springback parameters, taking into account the method proposed by Makinouchi et al. The authors have focused their attention on the possibility of adopting a modified Makinouchi et al. approach in order to measure the springback of the large size considered test cases. Through the implemented methodology it has been possible to calculate the values of the springback parameters. The obtained results correspond to the observed experimental deformations. Analysing the springback parameter values of the different combinations investigated experimentally, the authors have also studied the pre-bulging influence on the springback amount.

The Effect of Polyurethane Hardness on the New Die-Set of Sheet Hydroforming Process Parameters

In recent years, several sheet hydroforming methods have been introduced by researchers. Despite the advantages of these methods, they have some limitations. The author [1] already proposed a novel sheet hydroforming method that is a combination of the standard and hydromechanical sheet hydroforming processes. The proposed method has the advantages of both processes and eliminates their limitations. In this method, a polyurethane diaphragm was used as a part of die-set to control the blank holder force. In this paper, the effect of polyurethane hardness on the effective parameters of the combined sheet hydroforming die-set such as forming pressure, thickness distribution of formed cup and maximum thinning zone of formed cup was investigated experimentally. It was shown that a softer polyurethane needs to a higher oil pressure to prevent wrinkling in the flange of the part. And tearing occurs at higher level of forming pressure. Also it was shown that by softer polyurethane, better thickness distribution was obtained.

Investigation of the Effect of Blank Shape on the Sheet Hydroforming Parameters

In the deep drawing processes, the use of an optimal blank shape not only saves the material but also it may reduce the occurrence of defects e.g. wrinkling and tearing. In addition, finding the desirable flange contour, eliminate the trimming step in the deep drawing of parts with flange. The main objective of this study is to optimize the blank shape in order to produce a cylindrical cup with desirable flange contour and investigation of its effect on important parameters. Presently, to overcome this issue, a very expensive and time consuming trial and error method is used. In this study, a systematic method based on sensitivity analysis has been used to find the optimal blank to obtain a desirable flange contour for a cylindrical cup by hydromechanical deep drawing process. With the aid of a well-known dynamic explicit analysis code ABAQUS; optimum initial blank shape has been obtained. With the predicted optimal blank, both computer simulation and experiment are performed and the effect of blank shape on the some parameters such as thickness distribution and forming pressure of the formed cups were investigated. It is shown that formed cup with an optimum blank shape has a better thickness distribution in the rolled direction.

Experimental Investigation on Hydromechanical Deep Drawing of Aluminum Alloy with Heated Media

AbstractTemperature controlled sheet hydroforming is known as the innovative processing of warm/hot sheet hydroforming. Cylindrical cup hydromechanical deep drawing (HMD) at elevated temperature is the typical process for basic research. Warm HMD process was carried out on a warm sheet hydroforming experiment platform to investigate the influences of key processing parameters on formability. The process window of successful forming versus liquid pressure was obtained, which was manifested as a shape of pyramid. The region of successful forming in warm/hot sheet hydroming is a father set of that in cold sheet hydroforming. The microstructure evolution of cups formed by using warm HMD under the effect of temperature was investigated. The grain growth was observed compared with cold HMD. The hardness of hydroformed cup was tested and no apparent reduction of hardness was detected.

Effect of Outflow Volume of Pressure Medium on Fluid-Lubrication Effect during Sheet Hydroforming

The effect of the outflow volume of the pressure medium on the fluid-lubrication effect during the sheet hydroforming was investigated experimentally. The hydraulic pressures in the flange area obtained for the sheet hydroforming during which the hydraulic pressure was pressurized using pump were higher than those of the sheet hydroforming during which the pump was not utilized. This might be owing to the difference in the outflow volume of the pressure medium. On the other hand, the drawability of the sheet was almost independent of with or without using pump. Examining the so-called effective punch force, we found that the effect of the difference in the outflow volume of the pressure medium on the fluid-lubrication effect was negligible. We concluded from these results that the fluid-lubrication effect was affected significantly by the existence or non-existence of the outflow of the pressure medium, i.e. the lubricant oil, but it was almost independent of the outflow volume of the pressure medium. Furthermore we also found that the hydraulic pressure distribution in the flange area would not affect the fluid-lubrication effect.

New Developments of Hydroforming in China

This paper reviews the recent developments of hydroforming technology in China. Limited corner radius, ring hoop tension test and tube bulging test were introduced on fundamentals of hydroforming. New hydroforming and hydro-bending process of ultra-thin tubes were investigated. Ultra-thin Y-shaped parts and complex section components were manufactured and applied in aerospace and aviation industry. Applications of tube hydroforming in automotive industry in China are also presented, including the hydroforming machines and production lines, typical automotive parts and potential market. New sheet hydroforming process with controllable radial pressure was proposed to increase the formability of sheets metals. Warm tube and sheet hydroforming were analyzed and discussed. [doi:10.2320/matertrans.MF201122]

Strain Hardening Analysis Coupled to Remeshing Procedure Application to Sheet Hydroforming Processes

In this study, we present an experimental/numerical methodology which aims to improve 3D thin sheet hydroforming considering coupled constitutive equations formulated in the framework of of irreversible processes accounting for isotropic hardening as well as isotropic ductile damage. The experimental study is dedicated to the identification of stress-strain flow from the global measure of pole displacement, thickness evolution and internal pressure expansion. Or during the hydroforming processes severe mesh distortion of element occur after a few incremental steps. Hence an automatic mesh generation with remeshing capabilities is essential to carry out the FEA. The proposed technique based on geometrical criteria includes adaptive refinement and coarsening procedure is integrated in a computational environment.

Strain Hardening Law Coupled to Damage and Remeshing Procedure Application to Sheet Hydroforming Processes

In this study, we present an experimental/numerical methodology which aims to improve 3D thin sheet hydroforming considering coupled constitutive equations formulated in the framework of irreversible processes accounting for isotropic hardening as well as isotropic ductile damage. The experimental study is dedicated to the identification of stress-strain flow from the global measure of pole displacement, thickness evolution and internal pressure expansion. Indeed, Hill48 yield surface anisotropy parameters and coefficients of the Swift law coupled to ductile damage allowing to locate plastic instability zones of hydroformed sheets are identified with three dies cavities shapes. Or during the hydroforming processes severe mesh distortion of element occur after a few incremental steps. Hence an automatic mesh generation with remeshing capabilities is essential to carry out the FEA. The proposed technique based on geometrical criteria includes adaptive refinement and coarsening procedure is integrated in a computational environment.

An Optimization of the New Die Design of Sheet Hydroforming by Taguchi Method

During the last few years, several sheet hydroforming processes have been introduced. Despite the advantages of these methods, they have some limitations. Of the processes, the two main ones are the standard hydroforming and hydromechanical deep drawing. A new sheet hydroforming die set was proposed that has the advantages of both processes and eliminates their limitations. In this method, a polyurethane plate was used as a part of the die-set to control the blank holder force. This paper outlines the Taguchi optimization methodology, which is applied to optimize the effective parameters in forming cylindrical cups by the new die set of sheet hydroforming process. The process parameters evaluated in this research are polyurethane hardness, polyurethane thickness, forming pressure path and polyurethane hole diameter. The design of experiments based upon L9 orthogonal arrays by Taguchi was used and analysis of variance (ANOVA) was employed to analyze the effect of these parameters on the forming pressure. The analysis of the results showed that the optimal combination for low forming pressure is harder polyurethane, bigger diameter of polyurethane hole and thinner polyurethane. Finally, the confirmation test was derived based on the optimal combination of parameters and it was shown that the Taguchi method is suitable to examine the optimization process.

Formability influenced by process loading path of double sheet hydroforming

Double sheet hydroforming can be used to manufacture hollow part with complicated section geometries by allowing material draw-in under an appropriate process loading path. Two major parameters, clamping force and liquid pressure, were studied for hydroforming of unwelded double sheets. A proposed limit liquid pressure corresponding to different clamping forces was calculated theoretically, which can be used to reveal the influence of process parameters combination on deformation behaviors. The calculated results were studied and verified by FE analysis and experiments. Two linear loading paths and a multi-step loading path were applied to study the sheet deformation behaviors and formability. The experimental results illustrate that the multi-step loading path shows better formability than other loading paths.

Optimization and Identification of the Characteristics of an Hydroformed Structures

In this study, we present an experimental/numerical methodology which aims to improve 3D thin sheet hydroforming. The experimental study is dedicated to the identification of stress-strain flow by using the Nelder-Mead simplex algorithm optimization from the global measure of displacement and force. Applications are made to the simulation of thin sheet hydroforming using different die geometry to show the efficiency of the proposed methodology to localize plastic instability, thinning of the blanks and damage initiation under different forming condition.

Deep Drawing of Aluminum Alloys Using a Novel Hydroforming Tooling

A simplified sheet hydroforming tooling was designed, fabricated, and tested. The advantage of the new tooling is its simplification of the tools, its requirement of lower hydraulic pressure for forming and decreasing the cost of the process. In this article, a new method of hydroforming deep drawing assisted by floating disk is proposed and investigated through experiments and simulation. Moreover, its advantages, such as simplifying the tools, decreasing the required medium pressure of the forming process, and elimination of some wrinkle due to ironing effect, have been discussed. An aluminum alloy, Al6061-T6, is formed successfully, and the influence of process parameters including the punch nose radius and friction are studied. It is determined that decreasing punch radii and friction, lead to a decrease in initial pressure and an increased safe zone, respectively. Working pressure curves, which guarantee sound workpieces, have been founded by series of experimental results. Wrinkling and fracture modes are studied and predicted in experiment and simulation. The finite element (FE) analysis is carried out. Hill–Swift and North American Deep Drawing Research Group (NADDRG) theoretical forming limit diagram (FLD) models are used to specify fracture initiation in finite element model (FEM), and it is shown that Hill–Swift model gives a better prediction. The simulated results are in good agreement with the experiment.

Contribution of Strain Hardening Law Coupled to Damage and Remeshing Procedure in the Localization of Plastic Instabilities Application to Hydroforming Processes

In this study, we present an experimental/numerical methodology, which aims to improve 3D thin sheet hydroforming considering coupled constitutive equations formulated in the framework of the thermodynamics of irreversible processes accounting for isotropic hardening as well as isotropic ductile damage. The experimental study is dedicated to the identification of stress-strain flow from the global measure of pole displacement, thickness evolution, and internal pressure expansion. During the hydroforming processes severe mesh distortion of element occurs and an automatic remeshing generation is essential to carry out the FEA. Some examples are given to demonstrate the efficiency of the proposed methodology.

Identification of the Characteristics of Hydroformed Structures Using Optimization Methods

In this study, we present an experimental/numerical methodology which aims to improve 3D thin sheet hydroforming. The experimental study is dedicated to the identification of stress-strain flow by using the Nelder-Mead simplex algorithm optimization from the global measure of displacement and force. Applications are made to the simulation of thin sheet hydroforming using different die geometry to show the efficiency of the proposed methodology to localize plastic instability, thinning of the blanks and damage initiation under different forming condition.

An Experimental Study on Robustness and Process Capability of the Warm Hydroforming Process

The warm sheet hydroforming process was investigated to determine the optimal process conditions of temperature, pressure, and pressurization rate for maximum formability of AA5754-O using an experimental stretch forming die shape. The optimal process conditions were evaluated to determine the robustness and process capability based on physical measurement of formed parts including thickness strain, cavity fill ratio, and radius of curvature. For the simple die shape investigated, a temperature of 268°C, a pressure of 25 MPa, and a pressurization rate of 0.22 MPa/s provided the most balanced combination of uniform thickness strain with the greatest cavity fill ratio and sharpest radius. Temperature had a greater effect on measured properties than either pressure or pressurization rate, although the effect of pressure increased as temperature decreased. The procedures demonstrated in this experimental study could be used to optimize process parameters for robust operation of production applications for more complex automotive body panels fabricated by the warm hydroforming process.

An Optimization of the New Die Design of Sheet Hydroforming by Taguchi Method

An Optimization of the New Die Design of Sheet Hydroforming by Taguchi Method

Comparative investigations on numerical modeling for warm hydroforming of AA5754-O aluminum sheet alloy

This study aimed to determine the proper combinations of numerical modeling conditions (e.g. solver, element type, material model) for warm hydroforming of AA5754-O aluminum alloy sheets. Assessment of finite element analyses (FEA) is based on comparison of numerical results and experimental measurements obtained from closed-die forming, hydraulic bulge and tensile tests at different temperature (25–300 °C) and strain rate (0.0013–0.013 1/sec) levels. Thinning (% t) and cavity filling ratios ( CFR) on the formed parts were taken as comparison parameters. Several numerical analyses employing different element types, solution methods and material models were performed using the commercially available FEA package LS-Dyna to determine the best combination of modeling options to simulate the actual warm hydroforming operation as accurately as possible. Analyses showed that relatively better predictions were obtained using isotropic material model, shell elements and implicit solution technique when compared with experimental results.