Simulation of Hammering Hydroforming by Static Explicit FEM

Abstract

Recently, tube hydroforming is receiving increasing attention. Knowledge on the process is, however, still insufficient to produce high-quality products in an efficient way. Hammering hydroforming, in which the hydraulic pressure is pulsated synchronously with axial feeding, is an effective method of improving forming ability. However, the factors that cause the improvement are still unclear. In the research reported in this paper, simulations of an automotive component produced by hammering hydroforming have been performed using a static explicit finite-element method code, which was developed in this study. The simulation results showed a good agreement with the experiment, thus validating the hammering hydroforming simulation by the developed code. The factors that improve the forming ability were also investigated by simulation. It was clarified that the hammering forming has the advantage of obtaining enough expansion as well as the regular forming with the lower friction force by using the lower pressure history. Moreover, that roughly the same effect as lowering the friction coefficient could be achieved by the hammering hydroforming.KEY WORDS: tube hydroforming; hammering forming; static explicit finite-element method; strain path, displacement in the longitudinal direction.tions. 23) An updated Lagrangian rate formulation is used to describe the finite deformation. The rate form of the equilibrium equations and boundary conditions are equivalently expressed by the principle of virtual velocity in the form 24) ..................... (1) where V and S denote, respectively, the domain occupied by the body and its boundary at time t. s is the Cauchy stress tensor, t J is the Jaumann rate of the Kirchhoff stress tensor, L is the velocity gradient tensor, and D is the strain rate tensor, which is the symmetric part of L. dv is the virtual velocity field satisfying the condition dvϭ0 on the velocity boundary. S G is the part of the boundary S on which the rate of hydraulic pressure p is prescribed. S C is the part of the boundary S on which the rate of traction f (other than the hydraulic pressure) is prescribed.As for constitutive equations, small strain linear elasticity and large deformation rate-independent work-hardening plasticity are assumed. Hill's quadratic yield function 25) and the associated flow rule are used. The equation can be written in the formijkl are the tangent elastoplastic moduli. The solution procedure for the formulation stated above follows the standard way of static explicit analysis using the r-minimum strategy. 26) Simulation Model Suspension ComponentIn this study, the forming processes of a suspension component of an automobile shown in Fig. 1(a) 2) were simulated. This component is formed through multistage processes: the pre-bending process, the die-closing process, and the hydroforming process. During the hydroforming process, pressure up to 140 MPa and axial feeding up to 200 mm are applied. Ultimately, 43 % of maximum expansion is achieved.In the actual industrial production...

Improvement of formability in T-shape hydroforming of tubes by pulsating pressure

“…Hama et al [7] have claimed that the same effect achieved by lowering the friction coefficient could be obtained by pulsing the pressure. However, since the frequency of the ultrasonic vibration is much higher than that used in pulsating hydroforming, a different mechanism to achieve this aim is still required [11].…”

Formability of tube hydroforming under various loading paths

“…The effect of loading path on the formability has been investigated by many researchers [3][4][5] and the guideline on designing the loading path is gradually acquired. Recently, the loading paths in which the hydraulic pressure is raised to a certain magnitude in advance of the axial pushing and then the hydraulic pressure and the axial pushing are simultaneously given, are considered to be effective to obtain the good formability, and are employed to product many practical components [2,6]. This type of loading path is generally called the pressure advanced type and this knowledge is also found in the experiments conducted by Yoshida et al [4].…”

Formability improvement of austenitic stainless steel by pulsating hydroforming

“…4 Mori and colleagues [5][6][7] examined the mechanism of improvement of formability by experiments and simulations of tube hydroforming under monotonic increasing internal pressure and pulsating internal pressure. It was found that the occurrences of bursting and buckling were prevented by the oscillation of pressure, and the wall thickness of the formed tube was also improved by the oscillation.…”