A machine press is a machine tool that uses pressure to cut or shape pieces as part of a manufacturing process. Machine presses use a variety of means to apply pressure, including hydraulic, pneumatic, and mechanical, such as in the screw or rolling press. The particular type of machine press used may be dependent on the material to be shaped or cut, as well as the specifications of the end product. Examples of types of machine presses go back several centuries, though the specific methods of applying pressure have changed over the years with ongoing innovation.
Varieties of the machine press are used throughout manufacturing, from shaping sheet metal for use in automotive manufacture to pressure-shaping plywood to create curved pieces for furniture. Through the use of die, a machine press may be used to cut shapes or punch holes into sheets of material. A single press, fitted with a variety of cutting and shaping pieces along its length, may be used in metal forming to shape and cut a one piece, such as the tab for a pop can, by advancing a sheet of metal each time the press is raised. By this method, each individual step in the piece's creation is completed by separate die along the length of the single press.
Two of the most popular types of machine press used in industry are pneumatic and hydraulic presses, both depending on fluids to exert pressure. A pneumatic press depends on a pump to build air pressure in a reservoir, which is released as needed in order to apply pressure. A hydraulic press consists of two cylinders of differing sizes joined by a tube, and the entirety is filled with liquid, usually oil, and sealed. When pressure is exerted on the smaller piston, due to the Law of Conservation of Energy, greater force over a shorter distance is applied to the larger piston.
A pneumatic press is capable of moving much faster and may perform several cycles in the time it would take for a hydraulic press to complete a single cycle. The trade-off for speed is power, as a hydraulic press may be able to exert several times the pressure of a pneumatic press of comparable size. Though mostly automated, safety concerns exist as a pneumatic press may move too quickly for a human operator to react. A hydraulic press may move slow enough to be interrupted mid-cycle by cutting power, but the need for more operator interaction actually poses greater risks.
Other types of machine presses use mechanical leverage, such as the screw press, which applies pressure through the leverage created by turning a screw. In the case of a rolling press, pressure is applied when the material passes through a set of rollers, such as in a manual printing press, though the method is used to cut and shape sheet metal as well. The arbor press has a notched rod that matches to a gear, and when the gear is turned, the rod applies pressure. The knuckle-joint press depends on the movement of a knuckle-joint, with the pressure being applied in a classic fulcrum-and-lever configuration. All of these and other mechanical presses may use hydraulic or pneumatic pressure as a power source, or they may get power from a mechanical engine.