a machine with static (nonimpact) action for working metals by means of pressure. Presses are widely used in various branches of industry for the processing of metals, plastics, rubber, agricultural and food products, and other materials. They are also used for the study of the properties of these materials under high pressures. Presses have their widest range of application in the metalworking industry, where they are used for forging, for stamping solid stock and sheet metal, and for forming extrusions. They are also used for metalworking assembly operations, such as press-fitting of gears, pins, and bearing races, and for mechanical testing.
Historical information. Manually operated screw presses were used as early as the 15th and 16th centuries in such trades as butter-making, viticulture, printing, and bookbinding, which are not connected with metalworking. At the end of the 17th and beginning of the 18th century, screw presses were used for working metals under pressure, specifically for minting coins and medals, and later, for stamping. Hydraulic presses became common in the mid-19th century in the forging and stamping industry. With the development of large-series and mass production, crank presses, which constitute the largest group of forging and stamping machines, came to be widely used, especially after the invention of electric motors.
Design and principles of operation. The basic parts of a press are the slide, a bed with guides for the slide and bolster plate, drive and control mechanisms, mechanization and automation devices, and the tool. The moving part of the tool is attached to the slide, which performs a reciprocating motion, and the stationary part is attached to the bolster plate. The article is shaped by compression of the blank between the moving and the stationary parts of the tool. The principal parameters of the press, which, taken as a whole, determine its technical capacity and construction features, are nominal strength, stroke and velocity of the slide, and dimensions of the bolster plate.
Basic types. According to the drive used, presses are classified as hydraulic, mechanical (crank, screw, and friction types), and hydromechanical. In hydraulic presses, the slide is actuated by the pressure exerted by water, emulsion, or oil, which functions as the carrier of energy. Upon entering the cylinder, the hydraulic fluid displaces a piston that is connected to the slide. A crank press works by using a crank gear to transform the rotary motion of the drive into the reciprocating motion of the slide. The screw press uses a screw mandrel with a non-self-braking thread to impart motion to the slide. The mandrel is rotated either by an electric motor acting through a friction gear (friction press), or by fluid pressure (hydraulic screw press). Depending on the intended use, presses have slides that move either vertically, for example, for stamping, or horizontally, for example, for forming.
Hydraulic presses are the most powerful. Hydraulic stamping presses develop forces of up to 735 meganewtons, (MN), or 75,000 tons-force (tf); hydraulic presses for the production of diamonds develop forces of up to 490 MN, or 50,000 tf. Crank presses produce a maximum force of about 100 MN, and screw presses produce a maximum force of about 125 MN.
I. A. SHUR