a hydroforming cell having a fixed rigid structure including:

a base;

a top cross member surmounting the base and set at a distance therefrom; and

two shoulders, which connect the top cross member rigidly to the base; and

a hydroforming module, set within the cell between the base and said top cross member so that vertical forces that are generated during a hydroforming process are discharged on said shoulders, which are thus subject to tensile stress,

said hydroforming module comprising:

a top die and a bottom die, which can be displaced vertically with respect to one another between an open condition and a closed condition in which they define between them a forming cavity for a metal element, set between them;

means for supplying a liquid under pressure within said forming cavity; and

means for controlling a relative vertical movement of the two dies, said means comprising:

at least one hydraulic cylinder, set between one of said dies and the fixed structure; and

a vertically mobile member operatively connected to one of said two dies,

a pair of wedge-shaped members set opposite to one another, which can be displaced synchronously by means of actuator means in a horizontal direction over a horizontal supporting surface of the fixed structure of the hydroforming cell and having inclined surfaces co-operating with corresponding inclined surfaces of said vertically mobile member,

said vertically mobile member controlled by said wedge-shaped members which are horizontally mobile said at least one hydraulic cylinder and said vertically mobile member located between one die of said two dies of the hydroforming module and the fixed structure of said hydroforming cell, and

control means prearranged so that said at least one hydraulic cylinder is activated only for controlling a movement of the two dies between the open condition and the closed condition, and

said at least one hydraulic cylinder isolated with respect to a supply of hydraulic fluid so as to remain fixed at a desired size during the hydroforming process, said means for actuating the wedge-shaped members activated during the hydroforming process for applying to the two dies a force sufficient for preventing opening of said two dies during the hydroforming process, said at least one hydraulic cylinder functioning as a rigid transmission member for application of said force from the wedge-shaped members to the dies during the hydroforming process.