Development of a non conventional bulging test through numerical simulation

The metal stamping is a forming process by plastic deformation of a metal surface carried by a punch in a die. During the process different deformation modes are possible. Thus, formability, the proneness of the material to be subjected to this kind of operation, it is very important for the process feasibility. If the blank is restrained between the die and the blank-holder, the metal stamping is said by stretching. In this case, the deformation status is of pure stretching. The Erichsen test is usually adopted to verify the material formability in this deformation conditions. In this test, the blank deformation is obtained thanks to a spherical punch. The friction in the contact of the sheet metal and the punch has influence in the deformations distribution. An alternative testing procedure for stretching conditions it is represented by the conventional bulging test. In this case, the deformation action is made by a pressurized fluid avoiding the effect of friction during the material deformation. This test condition better represents the deformation conditions when an unconventional process like direct hydroforming is adopted. In the present work authors have developed appropriate numerical models for the Erichsen test and, using the same tooling, except for the punch, a new bulging test has been developed. For the two different testing conditions the deformation status has been evaluated. The obtained results from the numerical analysis have confirmed a better formability in the case of the non conventional bulging test, with a more uniform distribution of the plastic deformation and of the thickness percentage reduction of the formed blank.