Journal of Materials Processing Technology 177 (2006) 692–696 Optimized decision of the exact material modes in the simulation for the innovative sheet hydroforming method Lihui Lang a,∗ , Tao Li a , Xianbin Zhou a , Benny Endelt Kristensen b , Joachim Danckert b , Karl Brian Nielsen b a School of Mechanical Engineering and Automation, Beihang University, Beijing, PR China b Department of Production, Aalborg University, Aalborg, Denmark Abstract Although sheet hydroforming has gained increasing interest in the world, it is difficult to determine the optimal forming parameters in FEM due to the incorrect application of material property parameters. In this paper, the properties of the material used in sheet hydroforming were obtained to meet the reality based on the identification of parameters for constitutive models by inverse modelling in which the friction coefficients were also considered. With consideration of identified simulation parameters by inverse modelling, some key process parameters including tool dimensions and pre-bulging on the forming processes in sheet hydroforming were investigated and optimized. The paper shows that the results from simulation based on the identified parameters were in good agreement with those from experiment. © 2006 Elsevier B.V. All rights reserved. Keywords: Sheet hydroforming; Inverse modelling; Aluminium alloy; Simulation 1. Introduction Sheet hydroforming has gained increasing interest during the last couple of years, especially as application in the man- ufacturing of some components for automotive, aerospace, and electrical appliances [1,2]. Other alternative processes have been proposed, such as hydrodynamic deep drawing, aquadraw pro- cess, hydromechanical deep drawing, hydro-form process, radial pressure deep drawing with hydraulic counter pressure and reverse hydro-rim deep drawing and so on [3–6]. Compared with the above mentioned sheet hydroforming methods, the main advantage of this hydromechanical deep drawing comes from the uniform pressure onto the blank which was proposed by the authors and its clear boundary conditions. Fig. 1 shows the formed parts with the maximum drawing ratio of 3.11 for an aluminium alloy. In this paper, with respect to the results from experiment in hydromechanical deep drawing with uniform pressure onto the blank, the totally structured secant method proposed by Huschens [7,8] was used for approximation of the quadratic model, which describes the inverse problem, and the trust-region strategy was used to regulate the step size. By using the opti- ∗ Corresponding author. Tel.: +86 10 82317704; fax: +86 10 82317735. E-mail address: lang@buaa.edu.cn (L. Lang). mized material parameters, the key process parameters were ana- lyzed virtually, which will add more knowledge to the database of sheet hydroforming used for the further innovative design. To save CPU calculation time, the inverse problem was solved primarily based on explicit dynamic code LS DYNA. 2. Tools and materials The used material is 1.15 mm thick aluminium alloy (Al6016- T4). All the experimental results were based on the 375 tons Lagan double-action press. The punch speed can be adjusted from 10 to 30 mm/s freely. The pre-bulging function can be real- ized and the maximum pre-bulging pressure can reach 30.0 MPa. The flow rate of the pre-bulging pump is about 10 l/min. The liquid pressure in the die cavity was controlled by a propor- tional pressure valve the maximum pressure of which can reach 70.0 MPa. The punch diameter d p is 69 mm, the punch nose radius r p is 5.0 mm, the inside die diameter d d is 71.9 mm, the die entrance radius r d is 6.0 mm, the inside diameter of blank holder d BH is 70.0 mm and the blank holder entrance radius r BH is 3.0 mm. 3. Optimization strategy To evaluate the errors between the sampled results from experiment and the simulated results, non-linear least square 0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.04.100