Sheet Hydroforming Research Articles

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.

The effect of upper sheet on wrinkling and thickness distribution of formed sheet part using double-layer sheet hydroforming

In the hydroforming of curved sheet parts with a small thickness-diameter ratio, qualified parts are difficult to be manufactured when using the traditional hydroforming process. To solve this problem, double-layer sheet hydroforming was proposed and the wrinkle-free sheet parts were obtained in the authors’ previous study, but the inhibition mechanism of forming defects is far from perfection. Therefore, in this paper, the inhibition mechanism of forming defects is investigated by the combination of FE simulations and technological experiments. Different from the previous research, 2198 Al-Li alloy sheet was selected as the lower sheet. Other conditions such as heat treatment status and thickness are the same as before. The principle of wrinkle elimination can be concluded into the following two aspects. On the one hand, the upper sheet cannot be wrinkled during hydroforming, On the other hand, the surface blank holder pressure is applied in the suspending area. In addition, the beneficial friction between this two sheets changes the radial stress state of the lower sheet and makes the radial strain at some specific area (punch contact area and die corner area) decreased. In conclusion, qualified sheet parts can be manufactured by double-layer sheet hydroforming.

An investigation into the production of a large-scale automotive part included small features using hydraulic sequential forming method

Aiming at the requirement of the formability and the surface quality of the large-scale aluminum alloy such as AA6016-T4, utilized in the automotive component with complicated structures, a sequential forming process is proposed. This method consists of sheet hydroforming technology and local shaping with rigid tools. Firstly, according to the hydroforming process, the small curvature surfaces with excellent surface quality and the partial deformation of the local small features are obtained. After that, the method of local shaping with rigid tools is adopted and causes to reduce the equipment tonnage. In this research, the sequential forming process is studied on the basis of numerical simulations and experiments. At the same time, substituting the conventional mechanical test, the influences of different loading modes on the mechanical properties of the material are studied further from the viewpoint of the microstructure analysis. So when the different forming process is finished, the material in different areas is sampled and the microstructure evolution law is observed. The research results are illustrated that the excellent agreement is found through the analysis and the comparison of the wall thickness values on different measuring sections in the experiments and simulations results and the part with excellent quality is obtained. Meanwhile, it is found that the change degree of the microstructure of the small local features in the local shaping is more intense than the hydroforming process, and the grain sizes in the local shaping are smaller than the hydroforming process, and it is illustrated that the sequential forming is essential to the production of the aluminum alloy part with excellent surface quality and accurate structure size.

Enhancement on plastic deformation of curved surface shell by sheet hydroforming with optimized pre-bulging process

For sheet metal components, the enhancement of formability during plastic deformation is a key criterion in the evaluation of forming quality. To realize homogenous deformation during the forming of curved surface shells, a pre-bulging process combined with sheet hydroforming technology was designed. The pre-bulging shape was optimized using response surface methodology. An experimental setup was manufactured to conduct pre-bulging and sheet hydroforming process. The distribution of strain and thickness were measured to present the formability of the parts. The stress distribution was calculated to analyze the deformation mechanism. Results show that when using appropriate pre-bulging and sheet hydroforming process, the average strain value and uniform deformation parameter can be improved simultaneously. The microhardness of formed shell is increased. The stress state in the center region after pre-bulging is changed to biaxial compression state. It can be concluded that the combination between optimized pre-bulging effect and sheet hydroforming process is a potential method for the enhancement of formability including deformation value and uniformity.

Evaluation of numerical and experimental investigations on the hybrid sheet hydroforming process to produce a novel high-capacity engine oil pan

The engine oil pan is used for restraining pollutant and gathering greasing oil from the engine components’ surface which is significant for thermal dissipation and preventing deterioration of oil quality. The study intended to investigate and develop a hybrid sheet hydroforming process for fabricating an innovative high-capacity oil pan that has the characters of asymmetrical cavity depth and major lateral bulging. Firstly, a two-stage hydromechanical deep drawing (HMDD) process was accomplished, which included precedingly regional and eventually integral deep drawing assisted by fluid counter force. The finite element modeling (FEM) was employed to study the impact of the die fillet dimension as well as the loading routes on the formability of the preformed part. The limited drawing ratio can be enhanced from 2.34 to 2.77 for AISI 304 by HMDD. Hydro-bulging was subsequently investigated by the simulations accompanied by the relatively experimental verification. Both the simulated and experimental results showed that there is a remarkable influence of lubrication condition and intermediate heat treatment on the formability of the final part. The cracks occurred at the corners of the main bulging area can be alleviated by reduction of friction coefficient. Furthermore, wrinkles and cracks have been completely eliminated and the thinning ratio can be reduced to 31.8% for the final part, when intermediate heat treatment is additionally employed. It was concluded that the present hybrid sheet hydroforming process is feasible and sufficient to manufacture a sound engine oil pan without any defects through the optimization of the process parameters.

Research on Al-alloy sheet forming formability during warm/hot sheet hydroforming based on elliptical warm bulging test

An elliptical warm/hot sheet bulging test under different temperatures and pressure rates was carried out to predict Al-alloy sheet forming limit during warm/hot sheet hydroforming. Using relevant formulas of ultimate strain to calculate and dispose experimental data, forming limit curves (FLCS) in tension–tension state of strain (TTSS) area are obtained. Combining with the basic experimental data obtained by uniaxial tensile test under the equivalent condition with bulging test, complete forming limit diagrams (FLDS) of Al-alloy are established. Using a quadratic polynomial curve fitting method, material constants of fitting function are calculated and a prediction model equation for sheet metal forming limit is established, by which the corresponding forming limit curves in TTSS area can be obtained. The bulging test and fitting results indicated that the sheet metal FLCS obtained were very accurate. Also, the model equation can be used to instruct warm/hot sheet bulging test.

Investigation into Composites Property Effect on the Forming Limits of Multi-Layer Hybrid Sheets Using Hydroforming Technology

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.

Application of a new integrated optimization approach in sheet hydroforming process

The purpose of this study is to produce a desired hydroformed product under the optimal pressure profile. To achieve this purpose, a new adaptive optimization approach is proposed based on fuzzy logic control (FLC) integrated with simulated annealing (SA) optimization technique and ANSYS parametric design language (APDL). An intermediate MATLAB code was developed and used to manage data transfer automatically between FLC, SA and APDL, in which there would be no need for any interaction of user/designer during the optimization process execution. This method aims to find the optimal pressure loading profile, prevent wrinkling and necking failures, reduce unsuccessful iterations, and enhance convergence precision. This method is capable of adaptively changing the process parameters in order to reach the optimized values with higher accuracy in a more reasonable time. The results show a good agreement between the proposed optimization approach and experiments. The developed optimization approach is a practical and reliable design tool for industrial production of any symmetric shell cups using hydroforming process.

Investigation of Forming Cylindrical Parts in a Modified Hydrodynamic Deep Drawing Assisted by Radial Pressure With Inward Flowing Liquid

Among the sheet hydroforming processes, hydrodynamic deep drawing (HDD) process has been used to form complex shapes and can produce parts with high drawing ratio. Studies showed that radial pressure created on the edge of the sheet can decrease the drawing force and increase drawing ratio. Thus, increasing of radial pressure to an amount greater than chamber pressure, and independent control of these pressures, is the basic idea in this study. In this research, the effect of radial and chamber pressures on formability of St13 and pure copper sheets in the process of hydrodynamic deep drawing assisted by radial pressure (HDDRP) with inward flowing liquid is investigated. Giving that a significant portion of the maximum thinning of the formed part occurs in the beginning of the process, the pressure supply system used in the experimental tests was designed in a way, which provides simultaneous control of the radial and chamber pressures throughout the process. Thickness distribution, forming force, and tensile stresses are the parameters that were evaluated in this study. Results indicated that using a higher radial pressure than the chamber pressure and controlling their values in the initial stages of the process enhances the thickness distribution of the formed part in all regions. A comparison between the thickness distribution and maximum forming force of the formed parts by the HDDRP and HDDRP with inward flowing liquid methods showed that by applying the later method, parts with more uniform thickness distribution and less maximum thinning and forming force can be achieved.

Micro Structural Features Induced by Sheet Hydroforming of Non- Ferrous Metals and Alloys

Micro Structural Features Induced by Sheet Hydroforming of Non- Ferrous Metals and Alloys

Quick establishment of backpressure path in sheet hydroforming process

Backpressure path is a vital parameter for the control of dimensional accuracy and shape integrity of the fabricated part and the improvement of material formability in sheet hydroforming. The optimal backpressure path is closely related to the unsupported wall region between the punch and the die, which is determined by the geometric characteristic of the fabricated part. To clarify the relation between the optimal backpressure path and part feature, the workpieces are classified into three types according to the various change patterns of the unsupported area during the hydroforming deformation. To establish the correlation of unsupported region with the reasonable loading locus, three different types of workpieces including a cylindrical part with constant unsupported area, a conical part owning continuous variable noncontact region and an irregular part with composite vacant area were selected to be produced via sheet hydroforming. The forming quality of the three parts was analyzed under different backpressure loci, and the relationship between the optimal backpressure path and the unsupported region was built.

Determination of critical pressure in analyzing of rupture instability for hydromechanical deep drawing using advanced yield criterion

Hydromechanical deep drawing (HMDD) is a sheet hydroforming process to produce complex workpieces with high drawing ratio. Fluid pressure used during the forming process is one of the most effective parameters in this process in which increasing critical pressure causes to rupture occurrence. Since the material properties in different angles respect to the rolling direction affect the amount of critical pressure, it is important to develop an appropriate theoretical model for prediction of plastic behavior of material with high precision. In this paper, a theoretical model based on BBC2008 yield criterion including 8 and 16 parameters (8p and 16p) is developed to determine critical pressure in HMDD process. With applying uniaxial and equi-biaxial tensile tests and optimizing an error-function by using Levenberg–Marquardt method, the parameters of BBC2008 yield criterion can be determined. Low carbon St14 steel sheets are utilized for experimental samples to verify critical pressure obtained from the proposed theoretical model. BBC2008 model with 8p and 16p is compared with Barlat–Lian 1989 and experiments. The results show that BBC2008-16p yield criterion can provide a more precise model of material behavior in planar anisotropy properties, while BBC2008-8p yield criterion have a better prediction of rupture occurrence in HMDD process.

Effect of stress distribution on springback in hydroforming process

Stress of sheet metal forming was analyzed by using the Hill theory, and the moment formula about bending shallow part was derived in sheet hydroforming. The offset distance in the stamping direction is as the size of the springback. The formulas about springback solution were obtained under the action of hydraulic pressure during the stretch bending. According to the formula, with the liquid chamber pressure increased, the force T increased, the moment M decreased, and the springback decreased. The neutral layer of stress moved to the inside of the plate under fluid pressure, and the sections of sheet are mostly in a tensile stress state and less springback after the end of hydroforming. Combined with the results of theoretical analysis and numerical simulation, the experimental method of getting the springback about bending sheet under liquid pressure is proposed, and the 3D model was got by using reverse engineering. It got the springback by comparing the punch surfaces. The test results show that the smaller the springback, the greater the fluid pressure in the forming pressure range about stainless steel metal, which accords with the theory analysis.

Influence Law of Initial Reverse Bulging on Sheet Hydroforming Process

In order to investigating the effect of the combination of two technological parameters such as the initial bulging height and the initial bulging pressure on the sheet , the sheet hydroforming process was studied. Firstly, by using the method of numerical simulation, the sheet hydroforming process with and without the initial bulging were discussed; Secondly, the effect of both the initial bulging height and the initial bulging pressure which were based on the hydroforming with the initial bulging on the forming of the part was studied; Thirdly, the result of the simulation was verified in the experiment. It was found that when the initial bulging height is 3.75mm and the initial bulging pressure is 2MPa, the maximum thinning ratio of the sheet is 4.803% at the end of the sheet hydroforming process. According to the hydroforming process without the initial bulging factors, the maximum thinning ratio is 5.123%. It can be found that the initial bulging factors play a key role in the sheet hydroforming process. The maximum thinning ratio of the wall thickness can be decreased effectively by the appropriate initial bulging height and bulging pressure, and the forming limit can also be improved at the same time. The results of numerical simulation have a reasonable agreement with the experimental results.

Study on hydroforming process and springback control of large sheet with weak rigidity

The control of instability and springback about large sheet with weak rigidity is difficult in the process. The hydroforming process of aluminum alloy engine cover, springback prediction and compensation were analyzed, and the manufacturing method of parts with high precision was obtained. In this paper, the effect of drawbead, pressure versus punch stroke, and blank holder force on the thinning rate of the plate was analyzed, and the phenomenon of wrinkling and fracture was judged according to the forming limit diagram. And springback is predicted through the method of the finite element and the surface of die was compensated by the iterative method. The results show that the quality of large aluminum alloy plate with weak rigidity is improved, the cost of the mould is reduced by the compensation, and the period of mold repair and commissioning is reduced by the sheet hydroforming, which is the flexible manufacturing process. Springback of large aluminum alloy sheet with weak stiffness is within 10mm through process optimization, and the surface of die was compensated in local region. The springback not only has been effectively controlled, but the accuracy of dimensional also is more than 90% of ± 0.5 mm.

A new simulation-based metaheuristic approach in optimization of bilayer composite sheet hydroforming

Simulated annealing which has been recently used in engineering applications is one of the most popular metaheuristic algorithms to solve optimization problems. In this work, an adaptive simulated annealing (SA) technique coupled with an adaptive finite element method is proposed and developed to optimize bilayer composite sheet hydroforming process. The aim of this combinatorial procedure is to obtain optimal forming pressure loading path to develop a new definition of SA algorithm parameters, to create an adaptive finite element (FE) code, to produce desired products with minimum thinning, and to avoid wrinkling and bursting failures. All of the effective SA parameters including Markov chain number, cooling function, initial temperature, and final temperature are redefined and developed to reduce excess iterations in FE simulations, hence saving the time and energy during the optimization process. The proposed optimization technique is employed to investigate the effect of layers sequence and thickness ratio on minimum cup thinning and optimal pressure load in hydroforming of aluminum/steel composite sheet. The experimental results demonstrated that the proposed adaptive method could be a reliable technique for optimization of processes with a large search space. It is also shown that it provides precise results in a shorter time by redefining the algorithm parameters.

段付き円筒カップを対象としたシートハイドロフォーミングにおける内圧経路と可変ブランクホルダー力の同時最適軌道設計

段付き円筒カップを対象としたシートハイドロフォーミングにおける内圧経路と可変ブランクホルダー力の同時最適軌道設計

Process window calculation and pressure locus optimization in hydroforming of conical box with double concave cavities

With the enhancement in the functional integration of components and concentration on lightweight materials, complex sheet metal parts are widely used in automobile and aviation industrial clusters. Consequently, the sheet hydroforming process has become an attractive fabricating technology for forming lightweight materials and complicated products. In this research, the hydrodynamic deep drawing (HDD) process of a composite conical box with double concave cavities was investigated through theoretical analysis, numerical simulation, and process experimentation. Furthermore, the process window diagram (PWD) was calculated using the stress analytical model combining material properties with workpiece geometrical features. The influence of cavity pressure loading locus on the forming quality of the fabricated part and the deformation behavior of aluminum alloy was explored. The forming results indicated that the initial pressure, full pressure, and loading locus are the fundamental parameters directly related to the forming quality and dimensional accuracy. For the conical part with composite features, the reasonable initial pressure value is crucial for the thickness homogeneity of the double concave characteristics, whereas the magnitude of the full pressure is vital for improving the quality of the conical feature. In addition, the optimal loading locus of the cavity pressure is characterized by two turning points, which are related to the punch corner radius, die shoulder radius, blank thickness, and angle of the conical feature.

Analysis of wrinkling during sheet hydroforming of curved surface shell considering reverse bulging effect

Wrinkling in unsupported region is a worthy problem to be solved in sheet metal forming process. Sheet hydroforming is advantageous in the prevention of unsupported wrinkles. However, the simply increasing of liquid pressure is not enough to suppress the wrinkling even though with the occurrence of “reverse bulging effect” .11Normally, the unsupported areas of sheet metals during hydroforming are easy to be bulged along the reverse direction of deep drawing, this phenomenon can be regarded as a “reverse bulging effect”. In order to predict and control the wrinkling quantitatively in unsupported region for thin-walled shells with curved surface, a theoretical model on critical wrinkling stress was proposed by considering proper “reverse bulging effect” based on energy method. The influence of liquid pressure and other parameters on the critical wrinkling stress was analyzed. The critical loading path of the liquid pressure to control wrinkling was obtained by combining critical wrinkling stresses and circumferential stresses. An experimental setup for an extremely thin-walled shell with semi-ellipsoidal geometry was designed and manufactured to verify the theoretical model. It is found that at a certain punch stroke, the magnitude of the critical wrinkling stress increases and that of circumferential compressive stress decreases with the improvement of the liquid pressure. The critical loading path can be utilized to get well formed shells with a ratio of thickness to diameter equals 0.27% in the experiments. The proposed method can be applied to predict and control wrinkling in unsupported region for hydroforming of thin-walled shell with high accuracy and considerably reduced simulation time.

Feasibility Study of Complex Sheet Hydroforming Process: Experimental and Modelling

The application of finite element method (FEM) in the area of metal forming and material processing has significantly increased in the recent years. The presented study provides details of the development of a finite element modelling approach to form a part via sheet hydroforming (SHF) process. Both FEM analysis and experimental trials were introduced in this study to produce a complex shape component from Inconel 718 material. The FEM provides a robust feasibility study for forming this part in terms of blank design, load path and process design optimisation. The simulated hydroformed part was validated by performing experimental trials. The analysis demonstrated close correlation between the predicted FE model and the physical trial.