جستجوی مقالات مرتبط با کلیدواژه "tube hydroforming" در نشریات گروه "مکانیک"

The main objective in this study is to model the hydroforming process for Mg tube and obtain the forming limit diagram (FLD) using finite element method. In the first step, three -dimensional finite element modeling of hydroforming process of AL-7020-T6 tube was performed to plot FLD. In order to identify the appropriate criterion for the onset of necking, the hydroforming process modeling was performed by considering the four criteria including of the second derivative of minimum principal strain, maximum principal strain, thickness strain and equivalent plastic strain. Comparison between simulation and experimental results indicated that the second derivative of minimum principal strain, max principal strain and equivalent plastic strain were appropriate criteria for simulation. After validation of the hydroforming process modeling with experimental result, the FLD of the Mg tube was extracted. The results show that in the loading with different axial feeding, the necking time and the amount of stress and strain change. Therefore, various limit strains are obtained by changing the loading conditions. Also, according to the FLD, the higher ratio of axial feed to internal pressure causes the limit strain shifts to the left in FLD plane.

In recent years, aluminum and magnesium alloys have attracted the attention of researchers and engineers due to higher strength to weight ratio, compared with steels. The main limitation of these alloys is the low formability at room temperature. In order to overcome this limitation, researchers have shown that the formability of aluminum alloys increases at high temperatures. Tube hydroforming is known as a novel metal forming process in which the fluid internal pressure and the axial force are applied simultaneously to the tube. In this study, the formability of 6063 annealed aluminum tube has been investigated in warm tube hydroforming process. The effects of pressure and axial feed on the thickness distribution, bursting pressure and the respecting bulge height at different temperatures have been studied experimentally and numerically. In order to numerically predict the onset of fracture in the process, three criteria, namely equivalent plastic strain acceleration (second derivative), major strain acceleration, and thickness strain acceleration were used. Moreover, a geometrical method was adopted in the simulation to determine the wrinkling. By comparing the results, there was an acceptable accordance between experimental and simulation results. By using experimental tests and finite element simulation, the process windows of the 6063 annealed aluminum tube were obtained at the temperature of 25 °C and 250 °C. According to the process window obtained at 25 °C compared with the one obtained at 250 °C, the pressure interval in the safe zone is about twice but the axial feed interval becomes nearly half.

Today, Production in the shortest possible time, with the lowest cost and highest quality is the one of the most important criterions in the industry. Tube hydroforming (THF), because of its unique feature, increasingly used in military, industries, automobile manufacturing, aerospace, and bicycle industries. Most tube hydroformed parts are produced by a multistage loading process which the suitable loading condition in THF with regard to internal pressure and axial feeding should be designed to improve formability and to avoid failure modes on the final hydroformed product. This study deals with the procedure for the determination of the proper loading path in THF using a fuzzy logic control algorithm, which avoids the failure of the tube due to excessive induced strain during the forming process. For this purpose, Mamdani fuzzy control algorithm was used in conjunction with Abaqus FEA code for simulation of the THF process. The wrinkling measurements and the thickness variation obtained from simulation are used as input in fuzzy control and fuzzy control outputs are used to set the loading path. A controlled algorithm is designed to maximize the expansion of the tube and minimize the thickness variation of the wall and wrinkling at the same time. The numerical results were verified and validated by conducting experiments where a good agreement was obtained between the experimental results and simulations

Due to the increasing use of tubular components in various industries such as automotive and military industries, tube hydroforming process has been widely welcomed due to its advantages over traditional methods. The Y-shaped product is an asymmetric part that requires expensive asymmetric axial feed control equipment for its production. In this paper, by designing the tube in symmetric pairs and applying the same axial force on two sides of the tube, the hydroforming process of the double of Y-shaped is improved. Then, the process is three-dimensionally simulated using the Abaqus software by finite element method and the conditions for the improvement of the shape were investigated. In order to validate the modeling, the experimental product and the simulation model were compared, which showed a good agreement. Using the design of experiment method, the effects of tube length, the distance between the two bulges, internal pressure and axial feeding are investigated on the height of the bulge and the thinning percentage..

There are many industrial applications, such as in aerospace, nuclear and petrochemical industries, that involve using metal bellows. Tube hydroforming is the major process by which the metal bellows are produced. Although many parameters may affect the final product, the fluid pressure can be regarded as the most important parameter in hydroforming a metal bellows. Low pressure may result in some defects such as wrinkling. On the other hand a high pressure may lead to a highly thinning and even rupture. In the previous researches, no theoretical criterion has been proposed to predict the allowable forming pressure. In this paper, an analytical equation is proposed for determining the allowable pressure, based on thin-walled cylindrical vessels. Neglecting the elastic deformation, Swift equation along with von-misses yield criterion was used to model tube deformation. The analytically computed pressure compared with the existing experimental results and a close agreement was observed. This evidently shows the validity of the propose model.

In this paper, a new sealing method has been applied to eliminate the friction force between the tube and the die. The new sealing method was experimentally examined in the free bulge test of AA6063 aluminum tubes and necking limit strains, thickness and bulge height of specimens were measured. Results showed that the new sealing method compared to the conventional sealing method improves the material flow to the deformation zone and, therefore, increases the bulge height of aluminum tubes. Finite element simulations of the free bulge test were performed in ABAQUS software under the different process parameters. In these simulations, forming limit curve obtained from the experimental tests was utilized to predict of the necking. Results showed that an increase of friction coefficient, axial feed and initial length tub increases the bulge height of aluminum tubs in the new sealing method compared to the conventional sealing method.

One of the most common non-traditional forming process, is the tube hydroforming, which is widely used for to form various tubular parts. To produce final product without any failure, tube hydroforming process is strictly dependent on load path, internal pressure-axial feed. Major modes of failure which may be occur in tube hydroforming process are necking, bursting, buckling and wrinkling. Predicting and preventing each of these failures are very important and leads to defects-free products. In this study, geometrical criteria for detecting wrinkling in numerical methods such as finite element analysis are reviewed. This type of identifying the wrinkling can be pointed out such as the first derivative or geometric slope and length to area indices criteria. In this paper, a new geometric method as a center of volume is introduced. In this case, the center of volume of wrinkled part is not equal with the wrinkled-free one. In order to verify, the results of this new criterion were compared with the results of previous measures and experimental tests in published articles.

Tube bending is widely used in the aerospace and automotive industries. Of the main difficulties of this process are wrinkling, rupture and incomplete filling of the die. If the ratio of the bend radius to tube diameter (R/D) in the bending process is between 1 and 1.5, the bending cannot be performed by conventional methods. Therefore, it is important to develop a new technique in this respect. In this study, at first, closed-end seamless tubes were produced by multistage deep drawing and ironing processes. Then, the proposed hydroforming process of square cross-section tubes with the ratio of R/D=1 has been examined experimentally and by FEM. It is illustrated that the square cross section tubes with low R/D can successfully be produced by the developed technique. In addition, the effect of internal fluid pressure and die bend angle on the thickness distribution of the inner, outer and lateral walls of the bending area has been investigated. It is shown that with increasing the pressure, the thickness of the inner, outer and lateral tube walls increases. The reduction in the thickness is much greater for the external wall. The tube in the R / D = 1 was formed with multi of bending angles. The results exhibit with increasing the bending angle, the pressure of forming was decreased.

Achieving sharp corners in hydroforming process is difficult or impossible in experimental producer. Also, augmenting pressure for producing sharp corner and filling the die is caused local thinning and fracture in the corners of tubes. Then, the corner of tubes has the less thickness compared with the other parts. In new dies which leads sharpen corners, tube forming contains two phases, bulge and forming. In current paper, a new die for producing bended SS-316L tubes with non-uniform bending radius and diatreme has been offered by considering experimental tests and finite element modelling. Having two movable bushes for producing completely filled steps is one of the merits of new die. Movement of movable bushes can omit the friction between die and bushes while the specimen is feeding. Another advantage of this die is having less forming pressure and non-complicated die structure. In addition, thickness distribution of tubes which was produced in this die is more uniform than the previous dies.

Aluminum alloys, due to their light weight and resistant against corrosion, play a significant role in aviation and automobile industries. Hydroforming process can be used for the formation process of Aluminum alloys. In some applications such as in transferring very high temperature corrosive fluids use of multilayered pipes are recommended. This paper is divided in to two parts: in the first part, formation process of a two layered isotrope Aluminum-Copper pipe is simulated using a 3D finite element method. In the second part, to validate the simulation results, an experimental machine of hydroforming pipe with the capability of controlling the internal pressure and axial feeding is designed and built. Linear loading curve was selected as the best loading curve for the formation process based on a comparison between three different types of loading curves (linear, step-wise, and spline). Also, comparison between thickness distribution of hydroforming of single layer and two layered pipes showed that two-layered pipe has more homogenous distribution. According to the results, wrinkles created befor bulging the pipe playes the role of axial feeding very well and the pipes have better thickness distribution.Experimental results verified simulation outcome that can be used to predict loading curves with a reasonable tolerance.

Tube multi-point hydroforming is a new flexible forming technology for manufacturing of various tubular parts that presented and investigated in this paper for first time in the world. In this process¡ one die is enough to deform tubes to different shapes by utilizing high pressure fluid. In conventional hydroforming¡ it is necessary to manufacture different dies for producing different geometrical parts. This requires higher process time and cost. In present novel¡ tube multi-point hydroforming is investigated via FE simulation and experiments. In this process a new die based on multi point forming were designed and manufactured. Due to good formability of brass 70/30¡ a bulged tube and a rectangular tabular cross section of brass with initial thickness of 2mm are produced by applying this die to the process. The main difference between multi-point die and conventional dies is substituting the rigid surface by wide spaced pins. By adjusting the pins height¡ different tubular cross sections could be produced. This process is simulated and verified experimentally and defects are predicted. In order to decrease these defects an elastic layer of polyurethane is used. According to the simulation¡ maximum decreases in thickness are 11% and 17% for the bulged and rectangular cross section samples. These results are matched with the experiment.

Internal pressure and axial feeding are the most important factors in tube hydroforming process. The internal fluid pressure and the material feeding that is produced by punch axial loading form the tube. How to apply these two parameters simultaneously in combination has effects on the quality, thickness and forming limit of the final piece. In this paper, the effects of internal pressure and axial feeding paths were investigated to improve the thickness distribution of stepped cylindrical tubes and the wrinkles in the loading path were used to create a new method for removing the wrinkles. Firstly, the constant pressure loading paths with various pressure levels were investigated. Then, the pressure levels in which the parts weren’t burst and formed perfectly or formed with wrinkles were chosen and the effect of axial feeding on these paths were examined separately. The results showed that the axial feeding in the initial step of increasing pressure improves the part thickness distribution in final step. In addition, through using this new method, the wrinkles on tube body were eliminated at the end of the process by changing the direction of axial feeding, and consequently the sound part with better thickness was obtained. Furthermore, using stepped loading path improved thickness distribution uniformity through applying this new method of wrinkle elimination.

Recently, tube hydroforming had been developed in many industry. Prediction and prevention of possible defects such as wrinkling and failure are the major issues when it comes to hydroforming technique. These flaws are directly dependent on the initial and ultimate pressures and axial feed in this method. Thus, selecting an appropriate pressure path in a proper correlation with axial feed is crucial. In this paper, a new die capable of producing two-step box shaped pure copper specimens is presented by experimental test and finite element simulation. Compared with conventional hydroforming dies, it consists of four moving bushes to produce completely filled steps. Moving bushes can be considered as one of the advantages of the new die. When feeding, the movement of the specimen is accompanied by the movements of the bushes which results in elimination of friction. Also, sliding between the die and the specimen decreases to zero, so the produced specimen has filled and complete corners. Besides low forming pressure, simple die structure and cheaper machining costs as compared with conventional hydroforming dies can be considered as other advantages of the proposed die.

Bursting is the most important defect in tube hydroforming. Prediction of bursting can help to design the process. Aim of this paper is the application of ductile fracture criteria for prediction of bursting, forming limit curve at neck and forming limit curve at fracture in tube hydroforming process. Different ductile fracture criteria have been calibrated and applied in simulation to identify the best criterion for prediction of fracture zone. A free bulge setup has been manufactured to verify the simulation results. This setup has fixed bulging length and the ability of applying axial feed. To bulge the tube under fixed strain ratio, different loading curves (internal pressure versus axial feed) have been created. Using loading curves and prediction of ductile fracture criteria, FLCN and FLCF have been obtained and compared with experimental ones. Predicted FLCN using ductile fracture criteria have been compared with M-K Model too. Results show that the criteria which consider the effect of stress triaxiality on the prediction of fracture are more appropriate for tube hydroforming. Prediction of Ayada' s criterion and Rice' s criterion have the best conformity with the experimental results.