|This article does not cite any references or sources. (December 2012)|
A press has a bolster plate, and a ram.
The bolster plate (or bed) is a large block of metal upon which the bottom portion of a die is clamped; the bolster plate is stationary. Large presses (like the ones used in the automotive industry) have a die cushion integrated in the bolster plate to apply blank holder forces. This is necessary when a single acting press is used for deep drawing. The ram is also a solid piece of metal that is clamped to the top portion of a (progressive) stamping die and provides the stroke (up and down movement). This action causes the die to produce parts from the metal being fed through it.
Stamping presses can be subdivided into mechanically driven presses and hydraulically driven presses.
The most common mechanical presses use an eccentric drive to move the press's ram, whereas hydraulic cylinders are used in hydraulic presses. The nature of drive system determines the force progression during the ram's stroke. The advantage of the hydraulic press is the constant press force during the stroke. Mechanical presses have a press force progression towards the bottom dead center depending on the drive and hinge system. Mechanical presses therefore can reach higher cycles per unit of time and are usually more common in industrial press shops.
Another classification is single-acting presses versus double- (seldom triple) acting presses. Single-acting presses have one single ram. Double-acting presses have a subdivided ram, to manage, for example, blank holding (to avoid wrinkles) with one ram segment and the forming operation with the second ram segment.
Typically, presses are electronically linked (with a programmable logic controller) to an automatic feeder which feeds metal raw material through the die. The raw material is fed into the automatic feeder after it has been unrolled from a coil and put through a straightener. A tonnage monitor may be provided to observe the amount of force used for each stroke.