Abstract: A hydraulic press assembly for forming a U-profile from a rectangular plate comprises horizontally and vertically reciprocatable press members each having two hydraulic actuating cylinders. The horizontal cylinders are energized by respective variable-displacement pumps provided with servomechanisms operated by an electronic control circuit for selectively varying pumping rates to center a plate prior to a first bending phase in which the pump output ducts are connected to the vertical cylinders. During the first bending phase, synchronization of the action of the vertical cylinders is effectuated via control-circuit adjustment of the pump servomechanisms, while horizontal centering is maintained by means of an additional hydraulic circuit connectable by the control circuit to the horizontal cylinders.