Rotary Punching, the concept, the types, and is it for you?
With manufacturing always looking for new ways to increase production, reduce labor cost and maximize floor space, with over 60 years in the development of rotary punching machinery, many features of new and existing piece parts can be looked at using the rotary technique. Not only does this mean various styles of punching and forming can now be done in rotary units, the piece parts are no longer restricted to a maximum material thickness of 1/16. With continued new advancements that allow certain features and pattern to be punched in material thickness up to .105” and line speed up to 700 feet per minute.
Rotary punching means that any of the below applications can be done by using a mating set of rolls, the diameter of which depends on the length of the pattern or multiples of patterns to be punched along with the line speed that the unit needs to achieve. For servo driven units, roll diameter is not as crucial as non servo units,
There are multiple styles of rotary units used in different applications and products, an example of some are as follows:
1. Single Pass (Cornerbead, Angles)
2. Multi Pass (Dense Patterns, RC channel)
3. Rotary Shear (Pre-Cut lines)
4. Rotary Lance (Soffit, Building Panels)
5. Rotary Punch (Holes, Oblongs, Squares, Rectangles)
6. Rotary Shearform
7. Rotary Form (Barbed Tape)
8. Rotary Semi Blank
ADVANTAGES OF ROTARY PUNCHING:
Depending on the application that is being evaluated for using rotary units, there are multiple factors that need to be addressed when weighing the options. Rotary units can be used in conjunction with a roll forming line or as a stand alone unit, in both cases not being restricted by a feed or press speeds, higher line speeds can be achieved.
There is decreased equipment cost because high sped presses with sophisticated feeds are no longer required. Rotary units are quieter than conventional presses due to the decreased noise and vibration because of the natural shearing action through the stock from the rotary motion. Less floor space is required because of their compact size and lack of a feed system, especially if a rotary unit can be designed to work mounted inside the roll former.
Another advantage is the low maintenance that is typically seen. As an example, in rotary punching units with multiple punches around the roll the normal punch and die wear that is seen in a standard stamping die is now spread over the roll diameter giving the unit longer run time, with more footage of material before sharpening and maintenance.
There are two distinct styles or rotary units one being a “Fixed” type punch or shear meaning that the punches do not move inside the upper roll (fixed). The other is a “Cammed” type where the punches move inside the punch roll and is activated by a solid or mechanical cam mechanism.
Both styles have similar construction; the rolls are made of eitherpre-hardened steel or tool steel hardened. The type of material used depends on many factors, the most im¬portant being the speed that the unit must run, the gauge material to be punched and the longevity required of the unit (low, medium or high production).
If at all possible (depends on the pattern to be punched) the rolls should be bushed with standard bushing. Even though this takes extreme measures at times, the unit can then be sharpened without losing diameter size and, therefore, pattern length. Louvers, shear-formed “loops”, slots (which can be punched on their sides only into discs) cut against the disc on each side of the slot and cut in the air, on its ends and therefore need no bushings. Some stamping and embossing operations do not need, or cannot use, bushings either.
The gears are usually very critical to successful operation of the unit when there must be accurate punch-to-die alignment in the direction of the rotary motion. In these cases, the gears should be hardened for wear and precision ground or wire EDM’d, when punching material thickness under .062 inches. This statement is very general and is only given as a rough guideline. An anti-backlash gear (split gear) should be used in most cases. This not only insures that the alignment is maintained but also insures that you will obtain increased life of all components in the rotary unit because of decreased chatter.
Quality rotary units will have certain construction features designed in that are helpful during the assembly and setups. Hardened alignment rolls (male/female) to keep the punch and die alignment 90 degrees to stock travel and a fine adjustment mechanism to precisely adjust alignment between punch and die. Some kind of pilot or alignment pin to insure that there is no shear¬ing of punches and dies during setup. When possible an easy method for removing punches in assembly. In all cases, be sure to use a large enough diameter shaft to insure little or no deflection and the roll stand bearings should be tapered roller bearings.
TYPES OF OPERATION
Rotary units are operated any of five different ways:
(1) The rotary unit has its own drive system and operates faster than line speed. It generates a free loop between it and the roll former and is turned on and off with a loop control on its exit side.
(2) The rotary unit has no drive system at all. The unit is rotated by virtue of the punches entering the stock continuously, or the rolls pinching on the stock continuously and the stock being pulled by the roll former.
(3) A combination of the two choices above is a drive unit is used with an overriding clutch in order to start up the unit without “snapping” the material. Then as the roll former picks up speed, the overriding clutch allows roll former to provide the power and requires no more power input from the rotary motor no matter how fast the roll former is running.
(4) If the unit does not have its own drive, the strip is usually hand cranked through the rotary puncher and up to the roll former in order to start up the line.
(5) A unit uses a computer controlled servo amplifier/drive system to drive the top or bottom roll with programmable motion control software and rotary encoder.
The roll assembly can be operated either in its own stand / housing or mounted in one of the stands on the roll former. If it is mounted in one of the roll former stands and if the rotary puncher is a precision punching unit, that stand must have its gears detached so that the stand shafts are free wheeling. Then the roll unit must always have its own set of gears attached to the rolls. If you do not do this, there could be shearing of the punches and die buttons and there might be buckling of the material in the roll former.
If a product has a large annual footage total, evaluate the features in the part, and determine if a certain style of rotary unit possible fits the application. If the answer is yes then do a cost justification to see if rotary punching can save money on each part you produce. Remember by the time you would buy a press, feeder and punching die for your application your overall cost could well exceed the cost of one single rotary punching machine.