Showing papers on "Hydroforming published in 2015"

Ultrafine-grained magnesium–lithium alloy processed by high-pressure torsion: Low-temperature superplasticity and potential for hydroforming

Abstract: A Mg–Li alloy with 8 wt% Li was processed by severe plastic deformation (SPD) through the process of high-pressure torsion (HPT) to achieve ultrafine grains with an average grain size of ~500 nm. Tensile testing with an initial strain rate of 10 −3 s −1 showed that the alloy exhibited superplasticity at a temperature of 323 K or higher. Tensile testing in boiling water confirmed that the specimens were elongated to 350–480% at 373 K under the initial strain rates of 10 −3 s −1 to 1 0 −2 s −1 with a strain rate sensitivity of ~0.3. The current study suggests that not only superplastic forming but also superplastic hydroforming should be feasible after the grain refinement using the HPT method.

Recent developments in hydroforming technology

Abstract: This article is the review of hydroforming technologies that have been used increasingly in various industries including automotive applications. General concepts and technological developments in tube hydroforming and sheet hydroforming are presented with recent research and development activities. Then, the theoretical background associated with the plasticity and constitutive laws and their implementation to the computational modeling of the hydroforming process are discussed.

60 Excellent Inventions in Metal Forming

Abstract: Preface -- Introduction -- Material characterization and simulation -- Sheet Metal Forming -- Hydroforming -- Bulk forming -- Impulse forming -- Bending -- Multi-material forming -- Future studies.

Analysis on critical conditions of sidewall wrinkling for hydroforming of thin-walled Tee-joint

Abstract: Based on the sidewall wrinkling phenomena in hydroforming of thin-walled Tee-joint, an analytical model for tube wrinkling under double side constraints was proposed to calculate the critical wrinkling stress. The effects of stress ratio, diameter-to-thickness ratio and tube material properties on critical condition of sidewall wrinkling were investigated. It is found that the middle of the main tube side wall is the most dangerous position for wrinkling within hydroforming of thin-walled Tee-joint. At a certain internal pressure, the critical wrinkling stress increases with increasing of ratio of hoop stress to axial stress and material strength coefficients, but decreases with increasing of work-hardening exponent and ratio of diameter to thickness. Through the analytical model combining FEM simulation, the critical wrinkling loading path according to the relation between axial feeding and internal pressure was obtained. Experimental results validates that wrinkle can be avoided if the pressure is above the critical wrinkling loading path, otherwise, wrinkle occurs. It is also verified that the analytical model of critical wrinkling stress is reasonable for the thin-walled Tee-joint hydroforming process.

Investigation on the effect of through thickness normal stress on forming limit at elevated temperature by using modified M-K model

Abstract: The formability can be improved in warm/hot sheet hydroforming due to two important factors of temperature and through thickness normal stress. An extension of the M-K model was presented in this paper with the liquid pressure induced through thickness normal stress taken into account. The through thickness normal stress was introduced by using the general form of the Hill48 criterion. The combined effect of temperature and through thickness normal stress on the increase of FLD0 is achieved by applying a proposed temperature dependent constitutive equation for 5A06 aluminum alloy (a Chinese designation of Al-Mg alloy, corresponding to the ASTM designation of 5056 aluminum alloy) into the M-K approach. The Newton–Raphson method is used in the numerical procedure and it is proved to be stable and correct. The yield loci show a significant dependence on temperature and through thickness normal stress. Both size shrinking caused by the elevated temperature and location shifting due to the increasing thickness normal stress of the yield loci are observed. Comparison of the experimental FLDs of AISI-1012 low carbon steel (an AISI designation of steel) at plane stress and room temperature, STKM-11A steel (a Japanese designation of Steel Tube Kozo Machine) for tube hydroforming at room temperature and 5A90 aluminum alloy (a Chinese designation of Al-Li alloy) at plane stress and elevated temperature with the theoretical results show good agreements. The effect of key parameters, such as inhomogeneity factor f0, n value, m value and initial thickness T0, grain size d, initial surface roughness R0, show a strong dependence on FLDs and increase of FLD0. The increase of FLD0 is formulized in a full quadratic form, which is a function of temperature and through thickness normal stress. The left quadrant of FLD was determined by the cylindrical warm hydromechanical cup deep drawing, which shows a good accordance with the predicted results by using the modified M-K model.

A new process of forming metallic bipolar plates for PEM fuel cell with pin-type pattern

Abstract: Bipolar plates are the most important and expensive components of a fuel cell. These plates can be fabricated by different processes, such as machining graphite plates, producing composite materials, and forming metallic sheets. Due to some benefits of the metallic plates, especially with stainless steel sheets, they have recently been more noticeable. There are various flow field patterns with different applications in these plates, being classified into simple and complex ones in forming process for spiral or parallel and multi-array pin-type examples, respectively. In this study, hydroforming, stamping, and hybrid hydroforming–stamping methods have been used to investigate the forming capability of multi-array pin-type pattern, and, consequently, to compare the results of filling percentage and thickness distribution of these methods. According to the results, samples formed by the hybrid method have shown desirable filling percentage and thickness distribution. The effect of preload pressure of this method on thickness distribution has subsequently been studied and it was observed that the thickness distribution of the formed sample was enhanced by maximizing the pressure of the hydroforming stage.

Forming limit prediction of anisotropic material subjected to normal and through thickness shear stresses using a modified M–K model

Abstract: In some recent sheet metal forming processes such as hydroforming and incremental forming processes, normal and through thickness stresses are induced over the metal sheet, and therefore, prediction of forming limits requires considering effect of these stresses. In this investigation, a modified M–K model has been utilized to consider general stress state including normal and through thickness shear stresses on anisotropic metal sheet. This is achieved by assuming additional force equilibrium and geometrical compatibility between groove and matrix, and the numerical model has been solved by Newton–Raphson method to calculate the limiting strains. Forming limit diagrams resulting from this model have been evaluated with some published experimental data, and a good accordance between the results has been observed. It has also been concluded that exertion of normal and through thickness stresses enhances forming limits significantly.

Strength and Formability Improvement of Al-Cu-Mn Aluminum Alloy Complex Parts by Thermomechanical Treatment with Sheet Hydroforming

Abstract: Normally, the strength and formability of aluminum alloys can be increased largely by severe plastic deformation and heat treatment. However, many plastic deformation processes are more suitable for making raw material, not for formed parts. In this article, an experimental study of the thermomechanical treatment by using the sheet hydroforming process was developed to improve both mechanical strength and formability for aluminum alloys in forming complex parts. The limiting drawing ratio, thickness, and strain distribution of complex parts formed by sheet hydroforming were investigated to study the formability and sheet-deformation behavior. Based on the optimal formed parts, the tensile strength, microhardness, grain structure, and strengthening precipitates were analyzed to identify the strengthening effect of thermomechanical treatment. The results show that in the solution state, the limiting drawing ratio of cylindrical parts could be increased for 10.9% compared with traditional deep drawing process. The peak values of tensile stress and microhardness of formed parts are 18.0% and 12.5% higher than that in T6 state. This investigation shows that the thermomechanical treatment by sheet hydroforming is a potential method for the products manufacturing of aluminum alloy with high strength and good formability.

Formability improvement of austenitic stainless steel by pulsating hydroforming

Abstract: Pulsating hydroforming process has been verified to prevent the thickness of tube wall thinning and obtain a uniform expansion, which can improve the hydroformability effectively. In the present work, the experimental research was carried out on the influence of pulsating load on the formability of austenitic stainless steels. The results showed that the formability of austenitic stainless steel can be improved by pulsating load in which the effect on formability should be understood from two different aspects of process parameters and material properties. The mechanical property of austenitic stainless steel is obviously improved through loading and unloading mode. The fraction of the strain-induced martensite is increased by pulsating load, which leads to enhance the transformation-induced plasticity effect. Meanwhile, axial feeding process can be motivated during the process of loading and unloading. Consequently applying pulsating load with large amplitude can achieve a more uniform deformation with a...

Global optimisation of the production of complex aluminium tubes by the hydroforming process

Abstract: With the recent development of analysis software products, designers and engineers are able to design more complex parts to obtain better performance in the final products. In this study, the tube hydroforming process, including preceding processes, i.e. variable thickness tube drawing and two-step bending, are globally optimised to obtain parts without any problems like bursting or un-filled zones at the end of the forming processes. Unlike most previous studies which searched for an optimum hydroforming process by changing two hydroforming parameters, i.e. axial load feeding and internal pressure, in this study, the distribution of initial tube wall thickness and the variation of thickness due to bending steps will be taken into account in a global optimisation algorithm. The developed algorithm is a general-purpose algorithm that can encompass different processes and change various parameters in each process to be able to reach the global objective. The case study used was a part that needs two-step variable thickness tube drawing, and two bending steps before hydroforming. To verify the numerical results in each forming stage and at the end of all forming processes, extensive experiments were performed, and acceptable agreements were observed.

The study of forming concave-bottom cylindrical parts in hydroforming process

Abstract: Among the sheet-hydroforming techniques, hydrodynamic deep drawing assisted by radial pressure has introduced good results for forming parts with high drawing ratio. Forming concave-bottom cylindrical parts is complicated through conventional deep drawing and requires several steps. Hydroforming is one of the techniques that can resolve such problems. In this paper, forming of concave-bottom parts has been studied by using finite element simulation and experiment through hydrodynamic deep drawing assisted by radial pressure. The effects of pressure path and geometrical parameters of the punch on thickness distribution and punch force have also been investigated. The results illustrate that after forming the concave profile of the part, by increasing the maximum fluid pressure, the thickness of critical regions does not change. Thus, the pressure path with the lowest maximum pressure that can form the concave profile of the part is the best pressure path for forming a concave-bottom part. Meanwhile, increasing the concavity height and punch corner radius affects thickness reduction in critical regions, but these parameters do not have any significant effects on maximum punch force.

Research on hydro-pressing process of closed section tubular parts

Abstract: A hydro-pressing method was proposed to solve the problems in tube hydroforming process, such as too high pressure, nonuniform thickness distribution, and difficult forming of section corners. The process of hydro-pressing a tube seems like pressing of a solid bar. Theoretical analysis was performed, and the calculation formulas of hydro-pressing process parameters were given. Experimental research was conducted on hydro-pressing process of rectangular cross section with curved sides and bowtie cross-sectional components. The effects of supporting pressure, displacement of the pressing on section shape, and thickness distribution were investigated. The difference was compared between the hydro-pressing forming and the conventional mechanical pressing. It is demonstrated that the supporting pressure and pressing displacement are the essential parameters that influence cross-sectional shape and thickness. The dent defect disappears gradually as the supporting pressure increases and the thickness varies unobvious during hydro-pressing process of a rectangular cross section with curved sides. When the supporting pressure is 15 MPa, the maximum thinning of the rectangular cross section with curved sides is only 1.92 %. For a bowtie cross section, the required pressure is far less than that of conventional hydroforming for the same corner radius. Thickness distribution of section corner zone is more uniform than that formed by conventional hydroforming. Compared with conventional hydroforming, the hydro-pressing is a valid method to form the closed section tubular parts with the same perimeter and different cross-sectional shapes, which remarkably improves thickness distribution and reduces the forming pressure.

Formability and microstructure evolution during hydroforming of drawing quality welded steel tube

Abstract: Tube hydroforming is an advanced manufacturing process in which a tube is placed inside a die cavity and plastically deformed under hydraulic pressure, so that it takes the shape of the die. This process is commonly applied in the automotive and aerospace sectors. Welded tubes are commonly used in the hydroforming process. In this work, therefore, the entire study is carried out on resistance-welded tubes. Forming limit diagram is a measure of formability of any forming process; and in the case of the tube hydroforming process, it was obtained by deforming the tubes under different strain paths. A simulation of the hydroforming process was carried out using the finite element–based commercial software, PAM-STAMP 2G. The forming limit diagram obtained through experiments was predicted using this simulation. A fractography study revealed that in the case of axial feed, the nature of fracture was ductile; whereas in the fixed condition, some brittle characteristics were seen. In these experiments, it was obs...

Research on deformation and stress in hydroforming process of an ellipsoidal shell without constraint

Abstract: In order to the study the deformation of die-less hydroforming of ellipsoidal shell under the condition of without restricting the elongation of short axis, experimental research on hydroforming of an ellipsoidal shell with the initial axis length ratio 1.8 was carried out to analyze the effect of internal pressure on the variation of shell shape, volume, and wrinkling. The results show that as the internal pressure increases at the early stage of deformation, the short axis elongates; correspondingly, the volume varies slightly; wrinkling occurs on the equatorial plane when the internal pressure is up to 1.0 MPa, and it becomes severe when the internal pressure is 2.2 MPa; as the internal pressure continuously increases, the long axis begins to shrink rapidly, but the shell volume has a very tiny change within the range of internal pressure 2.2–3.5 MPa; when the internal pressure is 3.8 MPa, the wrinkling is eliminated completely, and the shell volume suddenly increases; when the internal pressure is up to 5.5 MPa, the equatorial plane is no longer shrinking but expanding and the out-of-roundness approaches zero; finally, when the internal pressure is 6.8 MPa, the ellipsoidal shell with the axis length ratio 1.06 is obtained, and the variation of long axis, short axis, and volume are −2.9, 64.6, and 52.7 %, respectively. Simulation was also carried out simultaneously to analyze the stress locus of typical points. It has indicated that the compressive stress in the circumferential direction is the reason of wrinkling occurring; accordingly, the tensile stress in the circumferential direction is the reason of wrinkling disappearing.

Research on the effect of flow stress calculation on aluminum alloy sheet deformation behavior based on warm bulging test

Abstract: Confirmation of material properties is an important research area for determining metals deformation behavior. In order to research the effect of flow stress calculation on aluminum alloy sheet deformation behavior, warm sheet bulging test was carried out to obtain bulging height - pressure curves with different bulging heights and diameters in this study. Based on the bulging parts profile data measured by three coordinate measuring machine, the least square circle fitting radius were fitted. Existing theoretical models for radius of curvature and thickness were compared and best models were selected to obtain more accurate stress — strain curves by calculating the bulging flow stress. Combination model was used to calculate the bulging height — pressure curves obtained by bulging test and the stress-strain curves with different temperatures and pressure rates were obtained. A monotonous increasing function was resulted which is of great significance in the area of formability and deformation behavior of warm sheet hydroforming.

Deformation analysis of hydro-bending of bi-layered metal tubes

Abstract: Bending of an aluminum alloy thin-walled tube with larger diameter-to-thickness ratio is more difficult than that of a mild steel or stainless steel tube due to its low elastic modulus and yield strength. To solve this problem, experiments were conducted on hydro-bending of bi-layered tubes, which consist of an outer mild steel tube and an inner aluminum alloy thin-walled tube. The wrinkling behavior, springback, cross-sectional non-circularity, and wall thickness variation of the inner aluminum alloy tube were analyzed. It has been shown that the internal pressure plays a prominent role in preventing the wrinkling due to an additional axial tensile stress being introduced to the inner tube through welding the inner tube ends onto the surface of the outer tube. By increasing the internal pressure to a critical value, it is helpful to reduce the magnitude of compressive stress at the inner side of bent tubes, so the onset of winking is prevented. The springback and the cross-sectional non-circularity become smaller, while the thinning rate gets bigger with pressure increasing. Finally, a sound aluminum alloy thin-walled tube with diameter-to-thickness ratio of 63 and relative bending radius of 2.2 was successfully formed under the internal pressure of 25 MPa.

Developments of New Sheet Metal Forming Technology and Theory in China

Abstract: Developments of new sheet metal forming technology and theory in China are reviewed in detail in this paper. Advances of crystal plasticity on the deformation mechanism of Mg alloy are firstly described, especially its applications on the prediction of sheet forming process. Then, a new macroscopic constitutive model is introduced, which possesses an enhanced description capacity of tension/compression anisotropy and anisotropic hardening. In order to take into account the twinning process of hexagonal close-packed material, a modified hierarchical multi-scale model is also established with adequate accuracy in a shorter computational time. The advanced forming limit of sheet metal, mainly about aluminum alloy, is also investigated. Besides the above theory developments, some new sheet metal forming technologies are reviewed simultaneously. The warm forming technology of Mg alloy is discussed. New processes to form sheet parts and to bend tubes are proposed by using hard granules. On the other hand, a new kind of ultra-high-strength steel based on typical 22MnB5 by introducing more residual austenite and Cu-rich phase to increase the elongation and strength and its novel forming method that integrates hot stamping and quenching participation are proposed. Progresses in sheet hydroforming, press forging and electromagnetic forming of sheet metal parts are also summarized.

Feasible pressure and axial feed path determination for fuel filler tube hydroforming by genetic algorithm

Abstract: Successful fuel filler tube hydroforming largely depends on proper loading paths, that is, application of internal pressure and axial feeding during the forming time duration. Generally, two part quality criteria are considered in selecting the feasible loading paths: (a) minimum part wall thinning and (b) part wrinkle free. Due to the highly nonlinear nature of the tube hydroforming process, iterative finite element analyses with adjustments based on forming experience are typically conducted to design the loading paths. In this research, genetic algorithm was integrated into the finite element analysis–based optimization, resulting in enhanced determination of the feasible loading paths. Genetic algorithm is a heuristic search based on mechanics of natural selection. A pair of pressure and axial feeding profiles was represented by connecting genes making up to be a chromosome. In each search, mutation and crossover operations generated a new generation of chromosomes. Fitness functions were formulated t...

Comparative Study of Finite Element Analysis in Tube Hydroforming of Stainless Steel 304

Abstract: This research conducts a comparative study of finite element analysis (FEA) in tube hydroforming (THF) The investigated tube is stainless steel grade 304 (SS304) of as received and after annealing (AN) Three different finite element modeling techniques have been examined and compared with corresponding experimental results The main modeling parameters of interest range from element technologies, symmetry modeling, and solving schemes Other parameters being sensitive to each model are discussed Formability issues have been investigated through FEA and forming limit diagram (FLD) Computational aspects have been illustrated and discussed for simulating THF and an intermediate AN Prediction of the required forming pressure is challenging Both shell and continuum elements have different advantages and drawbacks in simulating THF A shell element with explicit time integration tends to underpredict the required forming pressure while both axisymmetric and 3D continuum elements with implicit time integration tend to overpredict the required forming pressure The draw-in observation can also provide an insight of the state of deformation

Hydroformability assessment of AA6063 tubes using the polar effective plastic strain diagram

Abstract: Conventional forming limit diagram concept to determine the forming severity in tube hydroformed products might be restrictive because materials experience complex stress and strain path changes during the shaping process. In this study, a polar effective plastic strain diagram approach was adopted as a strain path–insensitive measurement to establish a criterion for evaluation of necking and, consequently, bursting failures in the tube hydroforming process. The polar effective plastic strain–based failure prediction uses information of the effective plastic strain and the direction defined by the arctangent of the current strain-rate ratio. These values were measured and calculated from free-expansion tests of straight AA6063 tubes for various combinations of axial feed and internal pressure using a stereo vision-based surface strain measurement system. The polar effective plastic strain diagram was constructed and applied to finite element analysis to predict the forming limit of AA6063 tubes. The effec...