Showing papers on "Hydroforming published in 2014"

Global sensitivity analysis and multi-objective optimisation of loading path in tube hydroforming process based on metamodelling techniques

Abstract: Tube hydroforming process is widely used in various industrial applications which consists of combining internal pressure and axial displacement to manufacture tubular parts. Inappropriate choice as small changes in such variables may affect the process stability and, in some cases, lead to failure. Consequently, loading path should be optimised to better control the process and to guarantee hydroformed parts with desired specifications. However, optimisation procedure requires several evaluations of the real models which induces a huge computational time. To cope with this limitation, we propose to compare two metamodelling techniques to solve the problem efficiently: the response surface method and the least squares support vector regression. To enhance the metamodels precision, optimal latin hypercube design is used to generate sampled points. It is obtained through iterative optimisation procedure based on a modified version of the simulated annealing algorithm by minimising simultaneously two optimality criterions. Then, multi-objective optimisation problem is formulated to search for the Pareto optimal solutions. Fuzzy classification is then applied to rank the non-dominated solutions which helps designers in the decision-making phase. Before optimising the process, a global sensitivity analysis is carried out using the variance-based method by coupling metamodels and Monte Carlo simulations in order to identify the relative importance of the design variables in terms of internal pressure and axial displacement on the variance of the responses of interest defined to control the process.

Evaluating the flow stress of aerospace alloys for tube hydroforming process by free expansion testing

Abstract: In order to obtain accurate tube hydroforming (THF) simulation results, one of the important inputs in the finite element model (FEM) of the process is the mechanical response of the material during THF. Generally, the mechanical response is defined by the stress–strain behavior that can be determined from tensile testing of the specimens extracted either from the sheet used for roll forming of the tubes or directly from the tubes. More recently, free expansion testing has been used to characterize the mechanical response of the material for hydroforming applications. The free expansion test can emulate process conditions similar to those found during THF, and as such, can be used to obtain reliable and accurate information on the mechanical response/properties of the tubular material. The aim of this research is to present an approach for evaluating the stress–strain behavior of different materials using a 3D deformation measurement system in conjunction with an analytical model. Here, to characterize the mechanical response of the materials, free expansion and tensile testing were used for austenitic stainless steel types 321 (SS 321) and 304L (SS 304L), INCONEL® alloy 718 (IN 718), and aluminum alloy 6061 in the annealed “0” temper condition (AA 6061-0). The mechanical response of each material, measured through free expansion testing of tubular forms, was compared to the respective stress–strain behavior determined from the uniaxial tensile test using ASTM E8 geometry specimens extracted from the tubes. For each material studied in this work, the two flow stress behaviors were distinct, indicating that the test method can have a noticeable effect on the mechanical response. Finite element analysis (FEA) of the free expansion of each material was also utilized to simulate the THF process with the flow stress curves obtained experimentally; the predicted expansion and burst pressure results were close to the experimental data indicating that the approach developed and described in this work has merit for characterizing the mechanical response of aerospace alloys for hydroforming applications.

Improving formability due to an enhancement of sealing limits caused by using a smart fluid as active fluid medium for hydroforming

Abstract: Within this paper a new approach to enhance the process window in sheet metal hydroforming processes will be presented. The key idea of the technology is the local adaption of the properties of the active fluid medium. In this case the magnetorheological fluid (MRF) Basonetic® 5030 is used and the fluid behavior is changed due to a partially applied external magnetic field. Based on the new property distribution the medium can be used as forming and sealing medium at the same time. The results are compared to the values reached with mineral oil. The presented work covers all necessary steps for a successful application of the technology. After the presentation of the used fluids, a material characterization and the tools, which are developed for this reason, as the sealing limits for two different configurations are determined. Based on these investigations forming operations are carried out at the related process parameters to show up the potential of the MRF. At the end a numerical model is built up and validated for both fluids used to offer a qualified tool for process design.

Feasibility study on optimized process conditions in warm tube hydroforming

Abstract: 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.

Deformation Behavior of a Thin-Walled Tube in Hydroforming with Radial Crushing Under Pulsating Hydraulic Pressure

Abstract: Loading path plays a dominant role in tube hydroforming (THF), and the pulsating loading path has been reported capable of improving the formability of a tube in hydrobulging with axial feeding. As a new THF process, the tube hydroforming with radial crushing (THFRC) is receiving increasing attention; however, knowledge on the process still remains insufficient to extend its application to various other fields. In this study, the experiments of THFRC under both the pulsating and the linear hydraulic pressures were carried out to investigate the deformation behavior. The influences of the amplitude and the frequency of the pulsating hydraulic pressure on the shape precision, wall thickness, and the microstructures of the deformed parts were analyzed. Subsequently, metallographic examinations of the deformed specimens were conducted in an attempt to clarify the relationship between the microstructural evolution and deformation behavior. The mechanism of formability improvement in THFRC by the pulsating hydraulic pressure was explored from the perspective of microstructure. Compared with the linear hydraulic pressure, the pulsating hydraulic pressure could generate a higher shape precision, a more uniform wall thickness, as well as less martensites, and larger grain. The microstructural evolution induced by the pulsating loading path is supposed to contribute to the formability improvement of SUS304 stainless steel tubes.

Effect of bright annealing on stainless steel 304 formability in tube hydroforming

Abstract: Effects of bright annealing (BA) on enhancing formability of stainless steel 304 tube in a tube hydroforming (THF) process were studied. The tube material was the metastable austenitic stainless steel 304 with an initial thickness of 0.5 mm and an outer diameter of 31.8 mm. Both FEA and experimental results showed that THF process of the investigated part alone failed to achieve desired tube expansion of the diameter of 50.8 mm without severe fracture. Thus, a heat treatment process, also known as bright annealing (BA), which caused little to none oxide on the surface of annealed tube, was considered. Initially, effects of different annealing parameters such as temperature and holding time on the material formability were investigated using tensile tests. Stress–strain responses of various conditions were compared. As a result, an annealing process consisted of heating at the temperature of 1,050 °C, holding for 30 min, and rapidly cooling by purging N2 gas was identified. This annealing should be applied intermediately after a pre-forming step. With the aid of the BA process, tube deformation was significantly increased and the required tube expansion could be therefore attained. In addition, strain-induced martensitic transformation occurred during the forming process was examined by X-ray diffraction (XRD) method. The amounts of martensite taking place in tubes (pre-forming, post-forming, and after annealing) were determined and discussed.

Theoretical and Experimental Study of Bimetal-Pipe Hydroforming

Abstract: The corrosion of oil country tubular goods (OCTG) gets more and more serious especially in the acidic environment. So, it is very important to develop a perfect anticorrosion technology for exploring sour oil and gas fields economically and safely. Analysis indicates that the bimetal-pipe (BP) which consists of the base layer of low carbon steel and a corrosion resistant alloy (CRA) cladding layer is an economic and reliable anticorrosion technology and has broad application prospects in the transportation of acid medium. However, theoretical study of hydraulic expansion mechanism for BP is not enough. In this paper, the deformation compatibility condition of BP was obtained by studying the deformation rule of the (CRA) liner and the outer pipe of carbon steel in the forming process; the mechanical model which can compute the hydroforming pressure of BP has been established based on the nonlinear kinematic hardening characteristics of material; furthermore, based on the stress strain curve of inner pipe simultaneously, the calculation method of the plastic hardening stress has been proposed. Thus, the accurate method for computing the forming pressure was obtained. The experimental data show that results are consistent with results of the proposed model. It indicates that the model can be used to provide theoretical guidance for the design and production as well as use of BP.

Advances in Metal Forming : Expert System for Metal Forming

Abstract: Fundamental of Metalworking.- Sheet Deformation Processes.- Expert Systems And Artificial Intelligence.- Analysis of the Stamping Design Process.- Artificial Neural Network for Sheet Metal Forming.- Hybrid Intelligent System for Stamping Process.- Advances in Metal Forming Processes.- Fundamentals of Hydroforming.- Hydroforming for Enhanced Formability.- Fundamentals of Tailor Welded Blanks.

Influence of tube spinning on formability of friction stir welded aluminum alloy tubes for hydroforming application

Abstract: Due to economic and ecological reasons, the application of tailor-welded blanks of aluminum alloy has gained more and more attention in manufacturing lightweight structures for automotives and aircrafts. In the study, the research was aimed to highlight the influence of spinning on the formability of FSW tubes. The microstructural characteristics of the FSW tubes during spinning were studied by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The formability of the FSW tubes with different spinning reduction was assessed by hydraulic bulge test. It is found that the spinning process shows a grain refinement of the tube. The grains of the FSW tube decrease with increasing thickness reduction, and the effect of grain refinement is more obvious for the BM compared to that of the weld. The difference of grain size and precipitates between the weld and BM leads to an asymmetric W-type microhardness distribution after spinning. The higher thickness reduction of the tube, the more uniform distribution of grains and precipitates it shows, and consequently results in more significant increase of strength. As compared with the result of tensile test, the tube after spinning shows better formability when the stress state changes from uniaxial to biaxial stress state.

A technology to improve formability for rectangular cross section component hydroforming

Abstract: In order to overcome difficulties in non-uniform thickness distribution and cracking failure during rectangular tube quasi-static hydroforming, a new forming technology, named as electromagnetically assisted hydroforming, is put forward. Both experiment and finite element method were conducted to investigate corner deformability and deformation pattern and its effect mechanisms. Results indicate that both corner deformability and thickness distribution are improved greatly under electromagnetic-assisted hydroforming. The reason is that deformation behavior changed after electromagnetic force application. As electromagnetic force is applied, tine petal cross sections are periodically produced and flattened. Thus, petal-like preform continues to generate and play a useful role in corner filling. Such deformation pattern overcomes friction holding back defect and results in stress state going over from tensile stress to compressive stress, which helps to avoid cracking failure and greatly improve thickness uniformity. At the same time, it also contributes to improve surface quality and decrease forming pressure simultaneously.

Theoretical and experimental study on formability of laser seamed tube hydroforming

Abstract: As an effective method to evaluate the tube hydro-formability, forming limit curve (FLC) has been widely applied on the hydroforming process design. This paper mainly focuses on the study of evaluation of laser seamed tube hydro-formability. Based on the test methods of free bulging and elliptical bulging, hydroforming limit tests of the laser welded tube and the electric resistance welded tube (ERW) have been carried out. The cracking failure characteristics of the seamed tube above during hydroforming are analyzed, and then a new theoretical model which reflects the heterogeneity of material and the non-uniformity of curvature during seamed tube hydroforming is developed to predict FLC for seamed tube hydroforming. The comparison results show that the predicted FLCs are in agreement with the test data. The FLC analysis demonstrates that the laser welded tube exhibits a better hydro-formability than that of the ERW tube with the same size and tubular material, and that the hydro-formability of seamed tube is affected by its diameter and thickness.

Study of effective parameters in hydroforming of fuel cell metallic bipolar plates with parallel serpentine flow field

Abstract: هدافتسا لیذ ترابع زا هلاقم نیا هب عاجرا يارب دییامن : Please cite this article using: N. Mohammadtabar, M. Bakhshi-Jooybari, S.J. Hosseinipour, A.H. Gorji, Study of effective parameters inhydroforming of fuel cell metallic bipolar plates with parallel serpentine flow field, Modares Mechanical Engineering, Vol. 14, No. 8, pp. 17-27, 2014 (In Persian) ود تاحفص گنیمرفوردیهرد رثؤم ياهرتماراپ یسررب رایش اب یتخوس لیپ يزلف یبطق يزاوم چیپرام

Study on the forming of sandwich shells with closed-cell foam cores

Abstract: The efficiency and safety of vehicles represent today one of the most important lines of developing in the automotive industry, for example by the introduction of new materials. In fact, the investment in advanced materials represents one of the most important strategies to reduce injury among vehicle occupants in traffic accidents. Associated with the development of safety systems, there is also the possibility of improving efficiency by the introduction of materials that lead to weight reduction, having a direct impact on fuel consumption and carbon dioxide emissions. Metallic foams are one of these materials, due to the excellent ratio between mechanical properties and density. The main goal of this investigation is to study the mechanical behaviour of aluminium sandwich structures, composed by a metallic foam core with two outer layers of metallic sheets. With this work, the authors intend to contribute to a better understanding and consequently to provide design guidelines for the plastic forming of these composites. In order to correctly characterize the mechanical behaviour of the sandwich structure, the foam core and sheets were tested separately. For the aluminium sheet a series of tensile tests were performed, using samples obtained along three different angles to the rolling direction. For the metal foam core, uniaxial compression tests were used. Finally, with the numerical model defined considering isotropic and anisotropic constitutive models, a set of numerical and experimental bulge tests were performed to evaluate the capacity of forming of these panels, using hydroforming processes.

Determination of loading paths in warm hydroforming reinforced quadrilateral tubular components

Abstract: This paper investigates the formability of magnesium-based alloy (AZ31B) performed by loading paths for the quadrilateral tubular components fabricated by the warm tube hydroforming (THF) process. In this study, three loading path types and their formability were investigated via ABAQUS for simulation. Hydroforming experiments were carried out at 270 ± 10° C to fabricate the components for verification of the simulation results. The thickness distribution of simulation result and THF experiment of loading path Type III-3 indicated that the results obtained from simulation conform to the experimental results. The occurrence of wrinkling and local necking during warm THF process can be minimized.

Induction annealing as a method for expanded hydroformed tube formability

Abstract: A method of hydroforming a workpiece includes the steps of bending the workpiece into a first preliminary shape, pre-forming the workpiece into a second preliminary shape, induction annealing the workpiece at a temperature between 120-160° C. and hydroforming the workpiece to a desired shape.

Effect of Intercritical Annealing Time on Microstructure and Axial Mechanical Properties of TRIP Seamless Steel Tube

Abstract: The transformation-induced plasticity (TRIP) seamless steel tube, which is expected to be used in the hydroforming process, was prepared with piercing, cold-drawing and two-stage heat treatment process (intercritical annealing, “IA” and isothermal bainite treatment, “IBT”). The current study focused on the effect of IA holding time on microstructure and mechanical properties of TRIP seamless steel tube at a predetermined other heat treatment conditions, to maximize the volume fraction and stability of retained austenite as well as to obtain a TRIP seamless steel tube with good combination of strength and ductility. The microstructure and retained austenite volume fraction of the heat-treated steel tubes were studied via optical microscopy, transmission electron microscopy and X-ray diffraction. Two-stage heat treatment carried out in an electrical resistance furnace and a salt-bath furnace showed that for a predetermined IA temperature, IBT temperature and time, the content of retained austenite as well as total elongation increased first and then decreased with increasing IA time in the set time range in this study. When IA time was 10 min, the largest retained austenite volume fractions for both steel tubes was obtained. As a result, the TRIP seamless steel tube with an austenite volume fraction of 7.02%, total elongation of 35.5% and ultimate tensile strength of 618 MPa was successfully obtained.