Schobertechnologies introduced rotary punching technology to the paper, film and foil converting industry decades ago. The process offers a range of advantages, including higher output, efficiency, quality and precision, as well as high process reliability and production stability. It is also regarded as a comparatively environmentally friendly manufacturing method.
How rotary punching works
Rotary punching incorporates two cylinders. The upper one, featuring the male portion of the design to be punched and the bottom one featuring the female portion of the design.
Individual, exchangeable punches and dies with different geometries (round holes, squares, oblongs, rectangles, out-lines) are mounted into the punch and die cylinder. The proper phasing between the cylinders is achieved using alignment pins and anti-backlash format gears. Rotary punching is characterised by a shearing cut. The rotation creates punctual forces which are considerably lower than the surface power needed for stroke punching. While the material is fed through the rotating tools, the punches enter and exit the die at an angle, resulting in a shearing action. The slugs are removed through the centre of the die cylinder and can be safely removed by a suction system.
Module design and drive configuration
Even though the punching forces are considerably lower due to the shearing, or the scissor cut effect, rotary punching still requires special design considerations such as special bearings, high precision format gears and a heavy-duty frame design. The punching module can be geared up with an existing line shaft or can be powered via servo-drive.
Usually, the circumference speed of the punching tool is identical with the linear speed of the material to be punched. The length of the pattern, the line speed, the web width and the thickness of the material, determine the diameter of the punching tools. In some cases, more flexibility can be achieved by a vector-based servo drive. This scenario makes it possible to vary hole positions on the fly. The only time the punching tool rotates in synchronisation with the web is when the male punch is engaged with the female die. Otherwise, the rotary unit is accelerating or decelerating to position the next punch.
Advantages of rotary punching applications
The rotary punching process is suitable to produce high-volume goods and is mainly used in-line with converting lines. In some cases, “stand alone” machines are used, when lamination or other process steps are applied later.
The continuous punching process enables a significantly higher processing speed, which can be up to ten times faster depending on the materials to be punched. This speed increase now makes it possible to combine separate production areas like prefabrication and finishing into one step. Consequently, extensive handling and transporting is greatly reduced or illuminated. Additionally, the whole pro-cess becomes more “operator friendly”.
The rotary punching process provides further valuable advantages. These include a substantial noise and vibration reduction since the material rolling through the rotary punch is being sheared progressively. This smooth operation illuminates the requirement for noise insulating cabinets and foundations can be lighter because of greatly reduced vibration.
Due to the compact design and the fact, that the material is fed directly into the punching tool, no web loops before and after the punching station are required. Therefore, the floor space can be reduced significantly. If the punching module can be mounted directly inside the converting machine, no additional space is needed at all.
A presetting of the tools on a bench allows to shorten the make ready time. A new punching pattern can be introduced within a few minutes into the converting machine using change over cassettes.