Hydroforming of inhomogeneous sheet pairs with counterpressure

Double sheet hydroforming is a technology which allows to manufacture lightweight hollow components with complex geometries in one forming operation. One major challenge in hydroforming regards the manufacturing of inhomogeneous double sheet parts, i.e., of components, where the two halves are made up of different materials or have a different initial thickness. The failure mechanisms taking place in this case are due to the different amount of draw-in of material in the die during the preforming, which causes the occurrence of wrinkling in the flange, and to the different bursting pressure of the two blanks during the successive calibrating stage. An innovative strategy is proposed, in which a counterpressure is applied at the outer surface of one of the two sheets in order to compensate the different behaviors of the two forming partners, allowing thus to exploit their forming potential.