Specialty Features & Function Of Rotary Tooling
There is a general rule in rotary die cutting that says, “Don’t expect your rotary die to fix every converting issue.” Converters often attempt to solve common problems that stem from lack of control over rotary press parameters by modifying the cutting die. For example, improper web tension and speed may produce die cut parts that are too long (or too short) in the web travel direction, but changing dimensions of the die cavity will not solve the problem. However, there are many die cutting challenges that can be addressed by adding features to the rotary die.
Special features and function of rotary tooling discussed in this section will pertain only to solid tooling, which allow significant customization not feasible with flexible dies.
Certain applications benefit from additional die clearance, or cavity depth, to avoid web speed problems or damage to the converted products. For example, pouched products or thick foam materials can be accommodated by deep cavity machining.
Web Waste Removal
The act of die cutting parts from rolled material always results in the creation of waste material. Waste may be the remaining web material outside of the die cut parts (the matrix), or material internal to the die cut part that must be removed (slugs), or both. Many methods have been developed to efficiently remove both types of web waste during high speed converting. These methods vary in cost, effectiveness, and feasibility, and should be evaluated relative to each specific application.
Ejection foam – A simple and inexpensive method to keep slug waste from building up in die cavities. Various thicknesses of foam are available to be applied to specific cavities within the die to aid in ejection on problematic areas or foam can be applied to the entire cutting surface of the die.
Spring plungers – A mechanical method for avoiding slug build up in cavities, spring plungers provide more force than ejection foam. Spring plungers are threaded into machined holes in each die cavity and are typically used when die cutting stiff or rigid materials.
Standard air ejection – An air probe inserted into a specially designed die directs pressurized air through small internal channels, forcing waste slugs out of the web as they are die cut.
Focused air ejection (Pulse-AirTM) – In some ways similar to standard air ejection, this method utilizes a manifold to deliver a more concentrated burst (or pulse) of high-pressure air through internal die channels at a specifically determined point in the die’s rotation. Benefits include reduced compressed air usage and higher slug removal force.
Vacuum transfer with focused air eject (Pulse-AirTM) – This method adds the capability of determining exactly where to eject the slug by incorporating vacuum pressure to secure the slug in the cavity until a preferred point in the die’s rotation is reached. This allows the converter to direct slug waste into existing waste collection systems, or away from critical areas where slug waste buildup would be detrimental to press operation.
Stripping pins – This method is a mechanical means of removing slug or matrix waste using pins mounted in the anvil to pierce and carry waste away from the cutting interface. Waste is then stripped from the anvil with a series of specially designed combs, preventing waste buildup. Removing matrix waste with stripping pins is common in paperboard carton production where web speeds range in the hundreds of feet per minute.
Vacuum-through die inserts – For small slugs, this method pulls waste into the core of the die and out through the die journal, rather than pushing or blowing them out and away from the die. Specially designed die inserts prevent slug buildup in the cavities. The advantage of this method is better control over where the waste travels, but there are limitations based on slug geometry and thickness, and presence of adhesive in the part material.
Some special converting applications benefit from heated dies. Heated dies allow for a cleaner cut for certain materials that are prone to extraneous fibers at the cut edge, such as poly fabrics and nonwovens. Heat applied at the die blade/material interface serves to seal the edge of die cut parts for many fibrous materials. Heated dies may also be used to seal layers of substrate together using specially designed flat blades that apply pressure and heat, but do not cut through the material. Sealing may be performed alone, or in conjunction with die cutting in the same press station. For heated applications the die is fitted with a heat probe that is inserted into the die, and the appropriate die temperature is maintained using an infrared sensor and feedback controller
Embossing / Debossing
Embossing dies produce a raised feature in the converted material, while debossing dies produce the reverse, a sunken or relief feature. Embossing/debossing is achieved through use of a specialized die, and may be incorporated into the cutting die, consolidating cutting and embossing in the same step.
For large dies where very heavy tooling may cause handling difficulty and added press wear, a hollow die design can significantly reduce the overall tool weight, in turn reducing shipping cost. Hollow tooling also allows for pumping heated or chilled fluid through the die for controlling temperatures of the web for certain applications, such as a chill roll to set adhesives on hot melt coating lines.
Removable Blade Sheeting
Although sheeting blades are routinely engraved into solid tooling, it is also possible to incorporate
removable steel rule blades into the tool design, allowing for simple and inexpensive blade
replacement. Removable blades also allow for varying the position and number of sheeting blades
around the die, which allows a single die to do the job of many for a given repeat length.
Matched Set Tooling
There are several configurations that are used with matched set tooling to achieve different outcomes. Many folding carton applications require cutting and creasing performed in a single die station, which is achieved with a complimenting male/female die set. The male die has cutting and/or creasing blades and the coinciding matched female die has recessed relief grooves that align with the crease blades to create a deeper crease. Similar to this concept, dual function die sets (also called “stacked dies”) allow cutting from the top and bottom of the web in a single die station. Each die has cutting blades and coinciding anvil pads on the opposite die to cut against. Island placement, or the transferring of a cut part to a different web, is achieved with matched set tooling as well by the use of a vacuum anvil. Stripping pin anvils are another example of matched set tooling (mentioned previously in slug removal section). All matched set tooling options eliminate registration requirements between stations and in turn lowers tooling cost, set up time, and material waste.