PSI - Issue 5

Abdelouahid El Amri et al. / Procedia Structural Integrity 5 (2017) 363–368 Abdelouahid El Amri/ Structural Integrity Procedia 00 (2017) 000 – 000

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1. Introduction

Manufacturing technologies of sheet metal forming is rapidly developed in recent years. Nowadays; deep drawing, incremental sheet forming, and hot forming become very popular in sheet metal forming. Two different hot stamping processes exit as direct and indirect hot method. The direct process starts with a plain blank that is heated up to austenitization temperature, directly formed, and subsequently quenched in one process step. The indirect process uses a performed component which is heated up to austenitization temperature and quenched in a water cooled dies afterwards [1]. A 2D coupled thermo-mechanical FEM was developed to simulate sheet metal hot forming process for U channel part by Liu et al [2]. Several investigations were conducted to investigate the hot forming process [3-11]. The ductility of common aluminum alloys increases with temperature. Thus forming at elevated temperature close to the recrystallization temperature of about 300°C, also called warm forming, is another promising method to improve formability. The major disadvantage of warm forming of aluminium sheet metal is that there is very little experience with this process technology available. Thus engineers rely on expensive trial and error development. Therefore numerical simulation using the finite element method (FEM), which is nowadays almost indispensable for the design of a cold sheet metal forming process, is even more important for warm forming. Therefore an accurate warm forming simulation has to be thermomechanically coupled and has to incorporate flow stress and strain rate dependency on temperature [11]. So far researchers often had to focus on simulation of simplified isothermal and/or two- dimensional forming processes with very small deformation rates. In the manufacturing process, sheet is heated to the SHT temperature, and then transferred to a press for deformation. The transfer may take a few seconds, during which the sheet temperature decreases. A further decrease in temperature occurs during the forming process as heat transfers to the cold dies. Due to the lack of appropriate evidence to demonstrate the damage features under hot metal forming conditions, a series of hot tensile tests have been carried out on 6061-T5 Aluminium alloys for a range of deformation temperatures and strain rates. Thermal behavior of materials is a broader subject, more directly related to their general thermal properties than to thermal effects of specific interest. Thermal effects on materials may be used advantageously, or a nuisance. Most of the times, thermal effects are understood to focus just on materials, and to deal with the effects of a non-confort working temperature on some material properties, including the thermal processes used to produce, change or dispose of those materials. The main aim of this study is to achieve the art thermomechanically coupled simulation methods and their validation for hot forming process. The simulation results of the warm forming processing are compared with the corresponding hot forming processing.

Nomenclature  the yield stress p eff  the effective plastic strain p eff  the effective plastic strain rate s y  the quasistatic yield stress

C Material parameter p Material parameter c the sound velocity  the density  the Poisson’s ratio E

the Young’s modulus  mech t the explicit mechanical time step