Punch Presses Mechanical

The Punch Press
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.

For 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 Additionally, a device to hold the material in place as the punch is withdrawn, call a stripper, is often an integral part of the punch tool.

The 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.

A 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.

Tool 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.