All photos courtesy of Bernal
When specifying rotary dies for folding carton conversion, it is important to identify several key aspects in your technical communication: your OEM’s rotary equipment capabilities, annual volume requirements of your products, the types of solid rotary tooling, and the applications and processes for which they are designed.
Equipment Rotary Capabilities
During any design or concept phase within the folding carton industry, it is imperative to understand what capabilities and limitations exist within your OEM’s physical equipment and plant setup. Today’s OEM supplier capabilities vary widely. Some OEMs will have broad ranges of capabilities spanning many customizable processes incorporating one-, two- or three-station converting modules. Others may have limited processes that will be static in their ability to expand. Your OEM’s capabilities should be a key factor in deciding what will be possible.
Your rotary die supplier will be most interested in the capabilities of your production equipment (web width, printing press repeat, OEM manufacturer) along with the technical features of your carton’s production needs. Supplying a comprehensive dimensional diagram or drawing of your desired product will help define your expectations, illustrate key aspects of your product and guarantee successful implementation. A key feature to focus on are the overall dimensions of the finished carton. This will give your rotary die maker an adequate idea of the requirements to accommodate your product.
Another important variable in any folding carton process is defining the right tooling to achieve the desired outcome and meet customer expectations. Much of what the OEM and rotary die manufacturer will be concerned about has to do with the tolerances required by the design for all cuts, creases, paperboard type and thickness of your end product. All converting processes have manufacturing specification boundaries. Some rotary cutting tools are more precise than others and, in turn, have a higher price tag.
There are typically two techniques for cutting folding cartons today: crush cut and rotary pressure. Different types of dies can perform a wide variety of tolerances at many varying speeds. These two processes have numerous variables and capabilities. Rotary pressure cutting requires a “precision” cutting station/module with the ability to make multiple adjustments to maximize an RP die’s features.
No matter the product packaging you will be producing, the greatest concern should always be producing the highest quality carton in the most efficient way possible. The variable in the efficiency formula is the quantity of the packaging to be produced. An accurate count of the volume required in a given year of a product will define the most efficient production process. It should be a priority of defining a cutting technique along with equipment process to reduce the “cost per thousand” of the product.
Material’s Effect
Since each product has a set of its own branding requirements, product materials, inks and coatings are crucial to ensure you are selecting the best possible production options for the desired package. Material options (paperboard) include: virgin board such as solid bleached sulphate (SBS), recycled paperboard (i.e. clay-coated-news (CCN), and poly-coated paperboard (PCP).
Each of these materials can be supplied in varying thicknesses and have widely different abrasive natures. SBS paperboard printed with an ink that includes titanium dioxide (TiO2), can be extremely abrasive on rotary diecutting tooling due to its pigment and reflective coating. These kinds of product material combinations may require a special consideration in steel selection of the rotary die or more frequent tooling sharpenings, which increases costs.
Selecting your carton’s material includes several determining factors that may require asking your rotary die manufacturer for recommendations.
Cutting Technologies & Multi-Station Applications
Beyond the before-mentioned considerations, there can be many other configurations of cutting technology that may enhance or limit your package’s successful production. Some OEMs use multiple stations in producing folding cartons. These stations may perform different functions like embossing, creasing, scoring or cutting. Your equipment may only have a single processing station where you are required to cut and score in the same tool set. Creasing tools, for example, rarely need to be replaced since the wear effect of the material against scoring dies is minimal and outlasts the cutting tools. Rotary cutting tools can also be configured with interchangeable segments where high-wear areas exist to extend the life of the entire tool.
Other variables that impact the cost of producing folding cartons are the speed and whether the scrap or waste can be removed at the required/desired production speeds from the inline process. Some cutting tool carton “geometry” is more accepting of waste removal than others, based on the layout and nesting of a product. The process of scrap/waste removal can restrict running speeds.
The following types of rotary tooling can be manufactured using three different configurations: solid, partially segmented and fully segmented. If you’re looking to reduce costs for tooling, a solid component is the most economical option. But remember, the fixed cost of die tooling needs to be weighed based on the “cost per thousand” of the final product. The ability to change out a portion of a rotary die may allow for easy product adaptation without producing a new set of tools. This allows a segment of a tool to be changed out to accommodate minor product variations for multiple package designs.
Left, a rotary pressure cutting profile. Right, a crush cutting blade profile.
Crush Cut vs. Rotary Pressure Dies
When deciding between crush cut and rotary pressure tooling or a combination of both, there are several considerations to make before finalizing your decision. Following are recommendations of each cutting technique.
Crush Cut Dies: Crush cut dies are made up of two steel cylinders—one upper machine-tooled cylinder and one lower smooth anvil. Crush cut tooling offers a number of solutions to meet cutting requirements. The initial cost is lower and crush cut offers tool life up to 12 million revolutions between sharpenings on SBS paperboard. While your first cut offers the highest quality, the die life does degrade after that initial cut.
Other notable features of crush cut dies include:
- Capable of high-speed operation
- Machine sharpening for accuracy
- Fully-hardened, solid steel construction for strength and longevity
- Dies can be partially or fully segmented
- Capable of quick-changing
- Precise cutting shape tolerances
- In-die waste/scrap stripping
- Lower initial cost
- Capable of combining cutting, creasing and embossing in one tool set
- Maximum 12 million revolutions between sharpening (three possible) on SBS paperboard
Rotary Pressure Dies: Rotary pressure dies are made up of two solid steel cylinders, where both the upper and lower cylinders are machined with cutting edges. The set of tools cuts the material using force from both the top and bottom cutting edges. These dies provide significantly longer life than conventional rotary dies, while maintaining like-new cutting quality and minimizing waste by using shearing blades on both the upper and lower dies. While the cost of this option is higher initially, the die life is three to five times longer than a crush cut tool depending on product material.
Other notable features of rotary pressure dies include:
- Cleanest cut for the longest period during production: SBS paperboard 40 million-60 million revolutions between sharpenings (three to four total) on fully-hardened tooling. Recycled paperboard 20 million-40 million revolutions between sharpenings (three to four total) on fully-hardened tooling
- No metal-to-metal contact between die surfaces
- Dies can be partially or fully segmented
- Capable of quick-changing
- Precise cutting shape tolerances
- Low operator maintenance
- High-speed operation
- In-die waste/scrap stripping
- Capable of combining cutting (rotary pressure and crush cut), creasing, and embossing in one tool set
The variability of modern converting technologies has significantly increased the flexibility of today’s packaging diversity and greatly increased the number of features that can be included in any packaging design. This technological advancement has added to the value offering of packaging to most products. The package is now viewed as a feature or enhancement to many products. Unfortunately, this innovation has increased the number of variables that must be considered in designing and concepting your product’s package. In the case of rotary converting tooling for folding cartons, it is important to understand the requirements of your end product, and the variables and experience that are offered in the market from the rotary die manufacturer to enhance the implementation of your next folding carton project.
About the Author: Bernal LLC performance has become a benchmark for high-speed rotary die cutting and has established a new standard for inline web printing and converting. Born as Bernal Rotary Systems, the company has pioneered the development of web converting for the folding carton and consumer products markets since 1972. Bernal offers extensive options for rotary tooling including cutting, creasing/scoring, anvils. Its tooling offers various levels of tooling life with the mix roll materials and additional coatings when applicable.