Although the punching of holes is often accomplished with die
sets that also perform bending and forming, a punch press is designed
specifically for the making of various shaped holes and cutouts
on sheet metal and plate material. The punch press is fitted with
punches and dies of the size and shape of the hole required.
irregular and non-standard holes, the modern punch press is capable
of nibbling. This refers to a series of successive hits
following a predetermined pattern that creates the cutout. The
punching action is accomplished by a vertical moving ram that
forces the punch through the material and into a die through which
the resulting slug is ejected. Additionally, a device to hold
the material in place as the punch is withdrawn, call a stripper,
is often an integral part of the punch tool.
press ram may be activated manually, mechanically, or hydraulically.
Mechanical punch presses use a system of flywheels, gears, and
eccentrics to stroke the ram. This can generate from 8 to 60 tons
of force with some larger models creating over 150 tons. Mechanical
presses can operate faster than hydraulic models. Press Capacity
is determined by not only available tonnage, but also by effective
throat depth. This determines how large a workpiece the press
can accommodate. Throat depth is measured from the center of the
punching tool to the rear of the press. Other capacities are the
movement of the carriage on which the work is mounted and the
weight of the workpiece.
press may have a single tool mounting station or multiple stations
mounted in a revolving turret. Very heavy punching in plate structurals
is done in the ironworker. These perform cutting and
parting in addition to punching. Turret punches can hold from
12 to 70 punch assemblies and can be rotated depending on the
press type, manually or automatically with a CNC system.
changing can also be done in semi- and full automatic modes. By
rapidly revolving and presenting a specific punch to the work,
the punching speed is then determined by how fast the workpiece
can be moved and positioned under the turret. CNC punching stations
can achieve 500 strokes per minute.