Nathalie Boudeau

Study of Localized Thinning of Copper Tube Hydroforming in Square Section Die: Effect of Friction Conditions

The friction conditions are responsible of the thickness distribution in a part realized by tube hydroforming. Then it is essential to have a good evaluation of the friction coefficient for running predictive finite element simulations. The tube expansion in a square die is one of tests proposed for the friction evaluation. In the literature, several analytical models have been developed for this specific test. The present paper concentrates on one of this model and results obtained from the analytical analysis, FE simulations and experiments are compared. The repartition of the thickness over the shaped tube and its evolution during the process are studied. The tendencies are in agreement but some complementary evaluations are proposed for using the proposed approach for the evaluation of the friction coefficient with the analytical model.

On the friction effect on the characteristics of hydroformed tube in a square section die: analytical, numerical and experimental approaches

A focus on the effect of friction condition on tube hydroforming during corner filling in a square section die is proposed. Three approaches have been developed: an analytical model from the literature has been programmed, finite element simulations have been conducted and experiments have been carried out. Effect of friction coefficient on the thickness distribution in the square section of the hydroformed tube is studied. Critical thinning is found to take place in the transition zone between the straight wall and the corner radius and this minimal thickness seems to be the more appropriate parameter for the evaluation of the friction coefficient.

Numerical Study of Localized Necking in the Strain Path of Copper Hydroformed Tube: Effect of Friction

The effect of the friction coefficient in the strain path of hydroformed tube is discussed in this paper. A finite element simulation with the LS-DYNA/Explicit software has been performed and experiments have been carried out. The localized thinning can be related to necking and then, the use of the Forming Limit Curve (FLC) and the analysis of the strain path can give some indications on the risk of fracture in the hydroformed part. FE simulations have been performed with different friction coefficients to study their effect on the resulting strain path and to predict the localized thinning during tube hydroforming in a square section die. Hydroforming experiments have been performed on deoxidized copper (Cu-DHP) tubes to validate the finite element results. When the pressure increases, the strain increases firstly in the transition zone, that next leads to severe thinning in the corner zone and finally, in the straight wall. The comparison between the results obtained with the finite element and experiments confirms that the thickness reduction is more important in the transition zone between the straight- wall and the corner radius and the localized necking occurs in the transition zone. It is then possible to define the limits of the process and enhance the necking prediction.