Abstract: An auxiliary supporting structure for presses, having an auxiliary mold platen having a front surface designed to firmly, but removably, support a half-mold; a number of hydraulic supporting cylinders, which project from the rear of the auxiliary mold platen, in a direction parallel to a reference axis perpendicular to the plane of the auxiliary mold platen; mounting means for firmly, but removably, fixing the hydraulic cylinders to the front surface of a movable mold platen of the press; a hydraulic distributor for regulating pressurized-oil flow to and from each hydraulic cylinder independently of the others; and an electronic central control unit for controlling the hydraulic distributor as a function of signals from a number of external sensors, to enable the hydraulic cylinders to instantaneously compensate any asymmetric distribution of the mechanical forces exerted on the half-mold as the plastic material is injected.