Rotary punching revisited
Taking a new look at an old friend
New ways to increase production, reduce labor costs, and maximize floor space may be found by revisiting a 50-year old technology—rotary punching. Many part features and patterns can be punched and formed using pull-through rotary units at up to 300 feet per minute(FPM) in materials as thick as 1/16 inch. In addition, cam technology allows rotary punching and forming of material thicknesses up to 0.105 in. (12 gauge). Servo drives empower line speeds as fast as 650 (FPM).
New ways to increase production, reduce labor costs, and maximize floor space may be found by revisiting a 50-year-old technology—rotary punching.
Many part features and patterns can be punched and formed (see Figure 1) using pull-through rotary units at up to 300 feet per minute (FPM) in materials as thick as 1/16 inch. In addition, cam technology enables rotary punching and forming of material thicknesses up to 0.105 in. (12 gauge). Servo drives empower line speeds as fast as 650 FPM.
What It Can Do
Examples of rotary-punched or formed features and components are:
- Holes, oblongs, squares, and rectangles, which are made using a simple rotary punch. Corner bead for drywall and angles can be punched on a rotary punch, as well as dense patterns (see Figure 2), RC channels, starter strips, nail holes for siding, and filters (see Figure 3).
- Precut lines, which are sheared using rotary shear rolls.
- Soffits and building panels, which are punched using a rotary lance or open-slot-style unit (see Figure 4).
- Barbed tape, which can be formed using a rotary form roll.
Multiple factors need to be addressed when deciding if rotary technology is right for the application.
The first is to determine which features, if any, can be made in the rotary unit by consulting the manufacturer and running tests.
Then determine whether the unit can be used in a roll forming line or as a stand-alone unit. If the profile requires only forming and no punched holes, or if the part cannot be roll-formed, such as an aluminum extrusion, it may be able to be processed in a stand-alone unit.
How Rotary Works
Rotary punching uses a set of mating rolls. The top roll has punches and the bottom roll has die openings. The material is punched, lanced, or formed as it is pulled through the rotating rolls and the punches in the top roll meet their mating roll die openings using alignment rolls and wire EDM antibacklash gears.
The length of the pattern or patterns to be punched, as well as the line speed that needs to be achieved, determines the diameter of the rolls. The roll diameter is not as critical for servo-driven units as for nonservo units.
Fixed or Cam Style. Two distinct styles of rotary units are fixed and cam. With a fixed punch or shear, the punches do not move inside the fixed upper roll. This style normally is used when the part features, such as holes, are continuous down the length of the part (see Figure 5).
In a cam-in rotary unit, a solid or mechanical cam activates the punches so they actually move up and down inside a punch roll, similar to the movement of a punching machine. This means that structural components with material thicknesses up to 12-gauge, such as building joists, can be punched with rotary units.
A cam-in and some fixed-style units can be programmed to punch in specific locations, thereby allowing the punching of irregular patterns that are not continuous down the length of the part.
Both styles have similar construction. The rolls are made of either prehardened steel or are tool steel-hardened.
The type of roll material used depends on many factors, the most important of which are the speed that the unit must run; the gauge of the material to be punched, lanced, or formed; and the durability required (low, medium, or high production).
Four Common Rotary Punch Units
Rotary units are operated in one of four different ways:
- The rotary unit has its own drive system and can operate faster than the line speed. It generates a free loop between itself and the roll former. However, this configuration is rarely used to avoid starting and stopping the rotary unit or roll former.
- The rotary unit has no drive system at all. The strip usually is hand-cranked through the rotary puncher and hand-fed into the roll former to start up the line. Then the unit rotates as the punches enter the material continuously, or as the rolls pinch the stock continuously and the roll former pulls the stock.
- A combination of the self-driven unit and the no-drive system unit is used with an overriding clutch to start up the unit without snapping the material. Then as the roll forming machine picks up speed, the overriding clutch provides the power, so that the rotary motor no longer needs to input the power, no matter how fast the roll former is running.
- A computer-controlled servo amplifier-drive system drives the top or bottom roll via programmable motion control software and a rotary encoder.
Advantages and Applications
Rotary punch equipment costs can be low, because these pull-through units do not require sophisticated feeds normally associated with high-speed presses.
In addition, minimal floor space is required because no feed system or punch press is needed and the rotary punch unit is compact—typically about 3 by 3 feet. Space can be conserved even more if the rotary unit is mounted inside the roll former.
A rotary unit is relatively quiet. Vibration is minimal, because it shears through the material progressively in a radial motion rather than all at once, as a punching die does.
Another advantage is its low maintenance requirements. Because its punch and die wear is spread over the roll diameter, the rotary punch unit usually can punch material for a very long time before sharpening and maintenance are needed (see Figure 6).
Disadvantages and Limitations
The material thickness that can be punched on a rotary machine is limited to 12-gauge or thinner.
Rotary punch technology can be inflexible in terms of how many different applications it can be used for. The rolls are the tooling, so they cannot be switched with other tooling in the same way that punch tooling can be on a turret punch press. The roll diameter is determined by the part specifications, and different parts may require different vertical roll spacing, for example.
A rotary unit is not suitable for short runs. To achieve cost efficiencies, it must be dedicated to one job for an extended period of time.In the Long Run
If a million feet of product is run per year, it is a good candidate for rotary punching.
Rotary punching less than a million feet per year can be cost-justified if the part has uncomplicated features.
If the volume of the component to be punched, lanced, or formed is high enough, evaluate the features in the part, and then determine if a rotary unit fits the application. If it does, then perform a cost justification to see if rotary punching can save money on each part to be produced.
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.