A brake can be described by basic parameters, such as the force or tonnage
and the working length. Additional parameters include the amplitude or stroke, the
distance between the frame uprights or side housings, distance to the backgauge, and
work height. The upper beam usually operates at a speed ranging from 1 to 15 mm/sec.
There are several types of brakes as described by the means of applying force:
mechanical, pneumatic, hydraulic, and servo-electric. In a mechanical press, energy is
added to a flywheel with an electric motor. A clutch engages the flywheel to power a
crank mechanism that moves the ram vertically. Accuracy and speed are two advantages
of the mechanical press. Hydraulic presses operate by means of two synchronized
hydraulic cylinders on the C-frames moving the upper beam. Servo-electric brakes use a
servo-motor to drive a ballscrew or belt drive to exert tonnage on the ram. Pneumatic
presses utilize air pressure to develop tonnage on the ram. Until the 1950s, mechanical
brakes dominated the world market. The advent of better hydraulics and computer
controls have led to hydraulic machines being the most popular.
Pneumatic and servo-electric machines are typically used in lower tonnage
applications. Hydraulic brakes produce accurate high quality products are reliable, use
little energy and are safer because, unlike flywheel-driven presses, the motion of the ram
can be easily stopped at any time in response to a safety device i.e. a light curtain.
Recent improvements are mainly in the control and a device called a backgauge. A back
gauge is a device that can be used to accurately position a piece of metal so that the
brake puts the bend in the correct place. Furthermore the backgauge can be programmed
to move between bends to repeatedly make complex parts. Early brakes relied on the
tooling to determine the bend angle of the bend(refer figure 2.2). The animation to the
right shows the operation of the backgauge, setting the distance from the edge of the
material or previous bend to the center of the die.