Presses are machines used in the sheet metal processing able to generate a continuous and progressive pressure in order to cut or deform the material placed in the mold. Generally they are composed of a base, a frame, the columns, the engines for the generation of the force and the control systems of the moulding phase.
The fixed part of the mold is clamped on the base, while the mobile part is connected to the press base of the casing. The frame has the task of counterbalancing the force impressed on the mold, while the columns or guides guarantee perfect alignment of the parts of the mold.
Depending on the system with which the applied force will be produced, the presses are classified into two distinct categories: mechanical presses and hydraulic presses.
Mechanical presses are also sub-categorised into screw presses or eccentric presses.
Screw presses are mainly used for sheet metal extrusion and hot forging operations. Screw presses are equipped with a tool-holder slide, moved by a screw that fits into the fixed nut in the frame. The stroke is obtained by rotating the screw alternately in one direction or the other.
Eccentric presses are mainly used in the cold working of sheet metal for shearing and punching operations. The engine drives the flywheel by means of gears or belts and the energy is transmitted via a gear device to an eccentric or crank shaft which, by means of a connecting rod, controls the stroke of the ram.
Hydraulic presses instead produce work by the action of a liquid under pressure.
Hydraulic presses are preferred to the mechanical presses when it is necessary to regulate the pressure and keep it constant for a given time, this is what happens for example in the forming operations.
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