Papers by Keyword: Sheet Hydroforming

Abstract: In regard to shaping up a complex-shaped, largely strained industrial forming part, sheet hydroforming (SHF) is one of the primary processes utilized to address these challenges. Before actual tooling fabrication, the finite element (FE) simulation is, nowadays, commonly employed to assess the feasibility of the process and tooling design. Therein, material modelling, especially of the distinguishing deformation anisotropy unavoidable in cold rolled sheet metal, plays a vital role. This study, therefore, seeks to enhance the capability of the FE simulation on sheet hydroforming of an SPC270 mild steel sheet comparatively through the von Mises, Hill’48, and Yld2000-2d yield criteria. Additionally, the hybrid Swift-Voce (HSV) model is applied to refine and extend the experimentally determined uniaxial flow stress curve. The prediction accuracy is evaluated on the basis of two geometrical deviations such as the sheet thickness distribution and tank surface profile. The results show that the Yld2000-2d yield model obviously leads to the most accurate geometric estimation for both evaluation criteria.

Abstract: 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.

Abstract: In this paper, the sheet hydroforming process of 2A12 aluminum alloy with uniform die cavity pressure on to the blank is proposed and investigated both primarily through the finite element method (FEM) and experiments. The influence of the die cavity pressure curve on the quality of the products was explored and the measures to promote the sheet formability were discussed. The results from the studied case indicate that the profile of the cavity pressure was one of the fundamental parameters directly related to the product's quality and precision. Excessive or insufficient initial pressure is not conducive for the reduction of wall thickness thinning and guarantee of wall thickness uniformity. And the wall thickness thinning is reduced and the thickness evenness is improved by increasing the maximum cavity pressure within a proper range. Moreover, an optimum cavity pressure curve generated by the numerical and experimental methods was properly applied in forming the aluminum alloy part without rupture and with slight wrinkle in the flange area. The study demonstrates that the results of simulations based on the identified parameters were in reasonable agreement with those from experiments.

Abstract: Sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as higher forming potentiality, good quality of the formed parts which may have complex geometry. The main advantage is that the uniform pressure can be transferred to any part of the formed blank at the same time. This paper reports numerical and experimental correlation for symmetrical hydroformed component. Experimental tests have been carried out through the hydroforming cell tooling, designed by the authors thanks to a research project, characterized by a variable upper blankholder load of eight different hydraulic actuators. The experimental tests have been carried out following a factorial plane of two factors, with two different levels for each factor and three replicates for each test with a total of 12 tests. In particular two process parameters have been considered: blank holder force, die fluid pressure. Each factor has been varied between an High (H) and Low level (L). The order in which have been conducted the tests has been established through the use of the Minitab software, in order to ensure the data normality and the absence of auto-correlation between the tests. An ANOVA analysis has been performed, in addition, with the aim of evaluating the influence of process parameters on the thickness distribution of the component, its formability and feasibility. Finally, finite element analysis (FEA) was used to understand the formability of a material during the hydroforming process. In this paper, the commercial finite element code LS-Dyna was used to run the simulations. A good numerical – experimental correlation has been obtained.

Abstract: The authors have investigated, in other paper, the problem related to the definition of a “set of shape factors” in order to declare the feasibility of a product through sheet hydroforming. In particular the defined shape factors are three different a-dimensional coefficients by which it is possible to declare the feasibility of a product through the calculation, in different sections, of the three previous shape factors. The robustness of this methodology is related to the correct calculation of the “limit value” of each shape factor. In fact the feasibility is reached if, in any section, the calculated shape factors are higher than their respective limit values. In this paper the authors have performed an extensive numerical and experimental campaign, taking into account a different geometry respect to that of the first paper, in order to: re-calculate the limit value for each shape factor and, then, verify the correctness of the limit values exposed in the previous first paper. The numerical campaign has been used, after the evaluation of the accuracy of the numerical model, in order to study the feasibility of the product without engaging the hydroforming machine. Finite Element Analysis (FEA) has been extensively used in order to investigate and define each shape factor with a proper comparison to the macro feasibility of the chosen component geometry. The limit values that have been calculated by the authors in this paper are slightly different from those calculated in the first paper. From this point of view it is possible that, although the shape factors are a-dimensional coefficients, they are affected by different choices of the users as, for example, the dimensions of the initial blank. Anyway, the small differences in the shape factors limit values do not adversely affect the use of the shape factors in order to predict the feasibility of the product.

Abstract: The success of sheet hydroforming process largely depends on the loading pressure path. Pressure path is one of the most important parameters in sheet hydroforming process. In this study, a combination of finite element simulation, artificial intelligence and simulated annealing optimization have been utilized to optimize the pressure path in producing cylindrical-spherical parts. In the beginning, the finite element model was verified based on laboratory experimental results. The experiments were designed and a radial basis neural network model was developed using data generated from verified finite element model to predict the thickness in the critical region of the product. Results indicated that the neural network model could be applied successfully to predict the sheet thickness in the critical region. In addition, the neural network model was used as a fitness function in simulated annealing algorithm to minimize the thickening in the above mentioned critical region. The final results showed that utilization of the optimized pressure path yields good thickness distribution of the part.

Abstract: nfluence of friction and lubrication on formability of an aluminium alloy (AA5182) in hydroforming of square cups has been studied experimentally and numerically. Three friction conditions were created at the blank-die interface using hydraulic oil, Teflon and dry condition (no lubrication). Maximum thinning and minimum radius at the cup corners were taken as criteria for formability evaluation. Formability improved to a great extent with Teflon sheet as the lubricant. Lower friction allowed better draw-in of the material with higher uniformity of strain distribution and the maximum pressure that the material can sustain has significantly increased.

Abstract: This paper discusses the application of sheet hydroforming technology to the forming of deep draw aluminum automotive body panels. Currently, the amount of aluminum in vehicle architectures is somewhat limited due to cost and also the inability to incorporate common body panel design to aluminum sheet due to lower formability. Typical aluminum sheet has approximately about 30~40% of the formability of comparative steel grades. Automotive designers have been hampered by this fact and have not been able to successfully introduce aluminum sheet for wide range of panels. Sheet hydroforming, however, has a formability advantage over many types of forming methods. This paper will discuss those advantages and show some successful applications to the automotive industry.

Abstract: Sheet hydroforming process of one irregular box with unequal height and flat bottom was investigated by numerical simulation and experiment. The effect of blank shape and pressure loading path on the forming result was discussed. The key process parameter was optimized. The results have shown that the round blank is the best shape blank. The part can be formed with the appropriate blank shape and die cavity pressure.

Abstract: The demand for complex sheet parts has increased more and more in the modern lightweight construction, especially in the automotive industry. Complex drawn sheet parts can be usually achieved in one step with using the hydroforming technology. As the demand for the complex products increase, the need of hydroforming process will greatly expanded around the world due to its many advantages. Complex parts have many convex and/or concave features on it. The shapes, dimensions and the positions of the features are important for manufacturing high quality products. So understanding these geometrical parameters on the product quality has great importance. In this study, the effects of the geometrical parameters of the complex stepped parts on the manufacturability by using sheet hydroforming process were numerically investigated for AA5754 aluminum alloy and some of results were experimentally confirmed.