Issue 49

M. Abbadeni et alii, Frattura ed Integrità Strutturale, 49 (2019) 282-290; DOI: 10.3221/IGF-ESIS.49.28 284 The previous work on modeling and simulating the HDD process of cylindrical parts by the authors [15] has established the reliability of the proposed approach in the modeling of process parameters. An analytical model was proposed to consider the non-uniform pressure distribution in the cavity and for the hydrodynamic pressure of the fluid film in the blank-die contact region. Based on this previous work, this study focuses on the comparison of conventional and hydromechanical deep drawing processes by performing a finite element analysis. The fluid cavity pressure effect on the plastic strain and the thickness distribution has been investigated. N UMERICAL MODELING Finite element model inite elements simulations of conventional and HDD of a cylindrical cup are performed using the ABAQUS/Explicit software. In the numerical modeling, the two processes (CDD and HDD) are involved at the same initial conditions: the same geometry of the instrument, the same boundary conditions, the same applied loads, etc. The deep drawing process involves a blank and an instrument consisting of three main parts: blank holder, punch and die (Fig. 1 and Fig. 2). In this case, considering the cylindrical symmetry, only one half of the blank and the instrument are analyzed in 2D. In the meshing of the blank the following initial conditions are used: continuum media; axial symmetry; and four node elements (CAX4R). During the process, the punch, the blank holder and the die are considered as rigid, while the blank is deformable. The die is constrained fully and the punch can move only along the vertical direction. The punch motion is prescribed with a constant velocity. A constant blank holder force throughout the process is applied. Uniform friction conditions are assumed for all contacting surfaces. The Coulomb friction model is used to describe the contact between the blank and the tooling surfaces. The friction coefficients are adopted based on previous works in this field [17-19]. Tab. 1 summarizes the friction coefficient values for different contacts. Table 1 : Friction coefficient values. The fluid pressure variation in the die cavity is one of the most important parameters in the HDD process, because wrinkles appear if the pressure is not sufficiently high. In contrast, the blank is damaged by fracture if the pressure is too high [4]. During the simulation of this process, the modeling of the fluid-structure interaction is the principal difficulty. In a previous work [15], the authors give a detailed study of this problem. The fluid was represented by a non uniform pressure load applied on the lower surface of the blank. An analytical model was given to define the variation of the pressure in the cavity and the distribution of the pressure of the fluid between the blank and the die, this analytical model was implemented into the ABAQUS/Explicit code using the user defined subroutine VDLOAD. This developed program is used in the present work to take into account the fluid pressure in the cavity and the hydrodynamic pressure of the fluid film between the blank and the die. Material parameters The blank thickness is 1.12 mm. The blank is made of an aluminum alloy (AA5086). Elasto-plastic material behavior with isotropic hardening is supposed. Hooke’s model with a Young modulus E=67293 MPa and a Poisson ratio ν = 0.3 is used to describe the elasticity. The Von Mises yield criteria is used for the plasticity to describe the isotropic characteristics of the blank material. The hardening behavior is described by following relation:        0 n k (1) F Contact zone Friction coefficient HDD CDD Blank-Die 0.05 (Presence of fluid) 0.08 (Boundary contact) Blank-Punch 0.1 (Dry contact) 0.1 (Dry contact) Blank-Blank holder 0.08 (Boundary contact) 0.08 (Boundary contact)