With rotary dies, there are a number of factors involved with the tool’s lifespan. Some are based on mechanics. Some on environment. But many are under your control.
DIE CUTTING DEFINITION: WHAT IS THE DIE CUTTING PROCESS?
The die cutting process involves using a die to cut specific shapes from webs of different materials. The materials used – such as foil, paper, cloth, fiberboard, plastic – primarily dictate the type of die used for the job.
Industrial die cutting is typically done either on flatbed or rotary presses. Flatbed die cutting does not have the efficiency of rotary die cutting, and is used primarily when the advantages of rotary die cutting cannot be applied to the material or the application.
TWO TYPES OF ROTARY DIE CUTTERS: FLEXIBLE AND SOLID
- Rotary die cutting involves either a flexible or solid rotary die. These dies are both cylindrical dies.
- A flexible die is made of a thin sheet of steel, and folds around a magnetic cylinder.
A solid die is a solid steel cylinder, and is traditionally used in more long run applications for extended die life.
WHICH ROTARY DIE SHOULD YOU CHOOSE?
For the most part, both dies will convert most types of materials. According to Cris Slay of RotoMetrics, the vast majority of materials can be converted with a flex die. These include:
- Papers
- Films
- Pressure-sensitive labels
- Through cut parts
However, there are several different situations that dictate whether you should choose one type of die over the other. Let’s break down the advantages of each type of die.
ADVANTAGES OF FLEXIBLE DIES
- Flexible dies are less expensive
Because flexible dies are a thin sheet of metal as opposed to a solid drum, they’re less expensive to manufacture and to ship. - Flexible dies can be created and delivered quickly
The delivery time is based on the type of die being manufactured, the majority of flexible dies can be shipped within 48 hours and many can be produced and shipped in the same day. - Flexible dies can be durable
While you are limited in the types of steels you can choose, hardening on the tips of the blade and other surface treatments can increase longevity, including non-stick coating.
Flexible dies cover most materials
Flexible dies are used for to-liner cutting in the majority of typical label jobs. As we mentioned, you’re likely to cover most of the typical converting tasks with flexible dies.
Flexible dies require less storage and floor space
Inventory can be an issue with larger solid rotary dies. Flexible dies can be stacked or stored on racks requiring less floor space.
However, it must be noted, in a conventional environment involving multiple magnetic cylinders, the supporting roll on which the flexible die is attached must be held in inventory. Typically, one for each circumference will need to be produced. For initial conversions to flexible die usage, this can be a very significant investment.
ADVANTAGES OF SOLID DIES
Solid dies are superior at material handling, or scrap removal
Slug removal or material management requires drilling into solid dies and installing equipment to aid in the removal of scrap or movement of small parts along the web. We’ve touched on slug removal in a previous post. Later in this post, Cris Slay details RotoMetrics’ pin-eject technology that dramatically improves material handling.
Solid dies have the ability to convert more difficult & challenging materials
Very thick materials can be difficult for a flexible die to cut. Solid dies give you the ability to cut through very abrasive materials or substrates with messy adhesives, multi-layer constructions and gasket materials.
Solid dies are more durable
Naturally, solid dies are much more durable. They’re better suited to withstand high pressure applications and more abrasive materials. “It depends on the materials you choose, but typically a solid die will last 2-3 times longer than a flexible die.
In addition, a solid die can be “re-sharpened” multiple times. A flexible die must be replaced when worn.
Solid dies are more flexible
Aren’t flexible dies, you know, more flexible? Literally, they are, but solid rotary dies can be constructed out of a variety of different steel types. It allows for different blade shapes, hardness, and material movement options.
THE KEY TO CHOOSING THE RIGHT ROTARY DIE: KNOW YOUR MATERIALS
Knowing your materials is critical when choosing the right die, and it requires a holistic approach. “Analyze your entire process. Know your requirements, and work toward a value-driven solution. The testing is extremely important, as customers are pushing material manufacturers to develop new solutions. Naturally, this leads to pushing the envelope on what can and can’t be converted by a rotary die.
THE MECHANICAL ASPECTS: DEALING WITH THE DOOMSDAY EQUATION
The simple equation explaining the main mechanical issue that can potentially spell doomsday for your rotary die.
Pressure = Friction = Heat = BAD
Perhaps it’s not an equation that you encountered in any engineering classes, but the logic behind it is rather straightforward. Heat is bad for steel. Because pressure causes friction, and friction then causes heat, you get BAD as a result.
Lubrication
To deal with friction, the best tool is lubrication. Pressure is required to get the blades of the die to pierce the material. Naturally, with pressure, friction occurs. Lubrication can help you reduce the friction caused by the pressure. This is regular (daily) maintenance that an operator must perform. But, as Slay notes, this isn’t always the case. “If someone gets busy, they may forget to do the task.
Pressure Monitoring
We know that pressure results in friction, so your goal should be to run the die with the least amount of pressure possible to get a successful conversion. Granted, you have to apply enough pressure to initiate cutting, so it’s a bit of a balancing act.
Hydrajack devices can help you minimize excessive pressure. These tools monitor the pressure being applied into the die cutting system and then supply a data point, which can be used by the operator in this battle against premature die wear.
For example, if the pressure is set when the machine is cool and heat starts to build up over time, you will see the thermal expansion caused by the heat register on the Hydrajack pressure gauges.
Pressure monitoring can also be accomplished with die-equalizers.
Reducing the pressure back down to the minimum required operating pressure will reduce the friction which will in turn reduce the heat, allowing us an opportunity to manage this “vicious cycle.”
Adjustable Clearance Anvil (ACA)
Discussions about die life have to include Adjustable Clearance Anvils. ACAs allow an operator to change the depth of cut, on the fly. This allows the management of two key factors.
- The first factor is the liner strike. Being able to adjust the depth of cut allows us to “dial in” the liner strike. We can create a lighter or deeper liner strike adjustment with just a turn of a dial. This can help with the inconsistencies of difficult conversions of multiple layers but may also allow you to reduce your die inventory. You may be able to have one die convert multiple materials.
- The second factor is die life. Being able to adjust the anvil instead of only adding more pressure (with all the negative effects that brings) will allow you to get every revolution out of your tooling. You just might be able to squeeze out that last 5,000 feet after all.
Care and Handling. There is a human element – the operator’s specific care and handling of the die itself.
Both solid and flexible dies are high tolerance pieces of equipment. Only the top .0003 of the blade is involved in the actual cutting. If this small area gets damaged in any way – mishandled, dinged, mashed – the die stops working. If that happens, the rest of the usable life of the die is potentially lost. In the case of a solid die, you would need a repair. If damage occurs to a flexible die, you’ll probably need to order a new one.
Operators needs to handle the die with great care, including:
- Don’t let the die blades come in contact with anything metallic.
- Don’t put the die on a bench or table where the blades aren’t protected by something soft.
- Always handle the die cautiously. Remember that it is delicate, sharp and most of the time, a heavy piece of equipment.
- “Take a beat” and think about keeping yourself safe when you handle the die. If you keep yourself safe, you will keep the die safe.
You can also use die carriers to move the die carefully and safely.
IT’S A MATTER OF TIME, BUT…
Die cutting is a physical action. You are using a steel blade to separate something into two pieces. The material you are cutting will always cause wear and tear on the die. It’s just a matter of time.
But managing the lifespan of your die is well within your power. With the right upfront planning, and smart operator practices, your die can live a profitable lifespan for your company.
Author : Mohammed Abdul Haleem
Email : packagingprinting@consultant.com
With almost 26 years of experience in the Printing industry, he offers proactive recommendations, for flexographic printing plates,Mounting tapes, Anilox rolls, Sleeves selection specifications, testing, inventory management, flexographic equipments applications,training, drawing from experience in technical sales,marketing,production,technical service,parts and supplies. His experience covers the spectrum of flexographic markets including: wide web film, narrow web, tag & labels,foil, folding carton, corrugated packaging applications.