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...

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A fracture criterion for sheet metals subjected to draw-bending is investigated using the concept of the forming limit stress criterion. An experimental apparatus that is capable of draw-bending sheet specimens with forming speeds (approximately 100 -1 mm s  ) comparable to those of real press forming machines is designed and built. The test materials are an ultralow-carbon steel sheet and a 590MPa high-strength steel sheet. Specimens undergo bending-unbending under tension when passing over a die profile. The magnitudes of true stress DB  at which the stretch-drawn specimens fractured are precisely determined from the measured data of the drawing force and the crosssectional area of the specimen after fracture. Moreover, multiaxial tube expansion tests are performed to measure the forming limit stresses PT  of the test materials under plane-strain tension. It is found that DB  is larger than PT  by 6-18%. Therefore, it is concluded that the forming limit stress criterion is effective for the fracture prediction in draw-bending.

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