crank press[′kraŋk ‚pres]
a machine with a crank-slide mechanism; designed for stamping. The working part (tool) of the crank press is a stamp, whose fixed part is mounted on the table of the press and whose movable part is mounted on the press slide. The slide is moved by the crank-slide mechanism. In one turn of the crank the connecting rod makes a complete pass; the stamping takes place during the forward motion of the slide.
The force of the crank press is created by the torque transmitted to the crankshaft by the electric drive, which consists of an electric motor, a flywheel, an insert coupling, a brake, and a reduction gear through which the rotation is transmitted to the crankshaft. The electric motor turns the flywheel and a torque moment is generated on the crankshaft because of the inertial force of the flywheel. The press may operate in individual passes —that is, with disengagement of the coupling after each complete pass—or automatically, with constant engagement of the coupling. The most important characteristics of a crank press, which together determine its technical capabilities, are the size of the table, the slide path, the rated force, and the number of slide passes per minute in the automatic mode. Various types of crank presses are used in closed impression die forging and sheet-metal stamping.
Crank presses for closed impression die forging include horizontal forging machines, automatic cold upsetters, coining presses, and swaging presses. Crank presses for hot stamping are characterized by high speed of operation and have a highly rigid construction, which is necessary to reduce elastic deformations and produce precise dimensions of the forged pieces. Such presses are constructed with a rated force of up to 100 meganewtons (MN), or 10,000 tons-force (tf).
Crank presses for sheet-metal stamping are divided into single-action, double-action, and triple-action presses and automatic presses. Single-action presses are designed for punching, bending, and light drawing and have a single slide driven by one, two, or four cranks. Single-action presses used instead of special cutting presses also serve for trimming forged pieces.
Drawing is done on double-action presses. The special feature of such presses is the presence of two slides, an outer slide for cutting and clamping of the piece and an inner slide for stretching. Triple-action crank presses have three slides. Particularly complex drawing is done on such presses. Crank presses for sheet-metal stamping that are constructed with supports located behind the table are called open presses (rated force, up to 4 MN, or 400 tf), and those with supports to the side of the table are called closed presses (rated force, up to 40 MN, or 4,000 tf).
Many crank presses have special attachments that permit mechanization and automation of a number of operations, such as the removal of forged pieces on swaging presses, feeding of blanks, and removal of waste products.
REFERENCESIgnatov, A. A. Krivoshipnye goriacheshtampovochnye pressy. Moscow, 1953.
Ekspluatatsiia goriacheshtampovochnykh pressov. Moscow, 1963.
Magaziner, V. V., V. N. Tynianov, and I. N. Fil’kin. Ekspluatatsiia odnokrivoshipnykh pressov prostogo deistviia. Moscow, 1964.
V. V. MAGAZINER