The folding it is a cold mechanical process with which a typically flat product is deformed (sheet metal) applying forces to it by means of a punch, in order to obtain elements with open section of variable shape according to the matrix. In practice, the sheet is subjected to a bending stress with a load higher than the elastic limit, in order to obtain a permanent deformation. Mild steels with a low percentage of carbon are bendable (less than 0.2%) and low alloy steels (none of the added elements in the alloy reaches the 5%). The equipment used is a mold consisting of a punch and a matrix of suitable shape (typically V-shaped), according to the type of bending to be made. The punch is driven by a press brake which provides the bending force necessary to perform the machining.