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Diecutting 101

Details: Written by Robert Larson

The Diecutting Process is rather simple and basic. Well almost!

What is Diecutting? The process of using sharp edged cutting dies to cut out identical shapes or component parts of a product from a wide array of soft to semi-hard materials using cutting dies of a flatbed, multi-contour or rotary cutting press. It also involves pressing a sharp edged cutting die blade through the material to be cut or trimmed either into or onto a cutting surface to obtain a good clean cut. Sounds simple enough if you know all the basics involved in the diecutting process.

Having said the above then why is diecutting, in many cases, so complex and challenging? The reason is that there are a vast number of soft to semi-rigid materials that can be diecut, in varying densities and thicknesses. Different materials react in different ways. There are different solutions on how to best diecut different materials to obtain an accurate die cut part. There are a number of different diecutting systems that can be used to diecut different materials and a whole range of diecutting tooling solutions to be used on diecutting press systems.

The key to success in diecutting is to produce die cut parts in the most efficient manner possible at the lowest cost per cut piece. This is the ideal scenario but many diecutters seldom if ever use all of the correct elements of diecutting to attain that goal.

For example, the school solution for obtaining a good clean accurate diecut from a soft sponge foam rubber material is different from diecutting a molded ½” plywood chair seat. The solution for diecutting paperboard is different from diecutting cotton fabric materials. Diecutting a ream of paper to cut out a stack of envelopes is different from cutting and creasing a single lay of paperboard for a folding carton.

Many diecutters in different industries have figured out what best combinations of diecutting press system, cutting surface and cutting dies are best to use in producing diecut component parts for their products. Some diecutters are still trying to figure out the most cost effective methods to diecut their component parts.

Introduce a new material with different cutting characteristics and a diecutter may be bewildered as to how to determine the best combination of elements to diecut the new material and get desired results. Many times a diecutter will attempt to use the same old die cutting press that he has used for many years to cut out component parts of a product. Product lines change and so do materials. Is that experienced diecutting press the best choice to cut out different materials? It just may be that the diecutting press system and cutting dies that they used for one material may not be the appropriate solutions for diecutting a new unfamiliar material.

To add some light onto the challenge of diecutting different materials, here are some considerations to ponder in selecting the best combination of elements to successfully diecut different materials.

What is the density of the material?

As I have mentioned diecutting with a sharp edged cutting die is intended to be used with soft to semi-rigid materials. The density or compression characteristic of the material is a prime factor in successful diecutting. One consideration of diecutting any material is that the diecutting action begins after the material is compressed to its thinnest possible thickness to get a good accurate die cut. It is at that point the sharp edge of the die blade starts to burst its way through the material and complete the cutting action.

The more firm or dense materials have little or no compression before the sharp edge die blade starts its cutting action. For example in diecutting paper, paperboard or cardboard you never want to diecut all the way through the material. As the die blade bursts it way though the paper based material, when the die blade get approximately 90% through the material, the material naturally bursts apart to complete the cutting action. The same situation is prevalent in diecutting many denser plastic materials. If you were to look at the diecut edge of a part of dense material you can see where the cutting action stops and the burst action begins.

How thick is the material to be diecut?

The thickness or thinness of the material determines what type of cutting blade that you should use to get a good diecut as well as the construction of the die blade. Again compressibility plays a factor in diecutting. In this case I want to discuss diecutting denser or more rigid materials.

When diecutting firmer or denser materials, you have to allow some sort of clearance or relief in the die cavity to allow the diecut part of self eject itself from the die cavity without getting bound up inside the die. When using a steel rule die, you have a straight inside wall to the die with no relief or clearance to relieve the pressure imposed on the die blade during the cutting action. Therefore, more rigid materials tend to get stuck up inside the die or the die blades tend expand out of original shape and eventually break.

In those cases it better to use an all steel seamless clicker type die. Clicker type dies can be constructed with blades that provide clearance or relief for ejecting more rigid materials. We will discuss this in more detail in Part 4 under Diecutting Tooling.

Should the material be cut one layer at a time or in multiple layers?

If your diecutting and creasing folding cartons or corrugated boxes, you only want to cut one layer at a time. On the other hand if your diecutting shirt collars out of some type of fabric you can stack up many layers of material to cut many parts in one stroke of the die press. If you have to register the material to a die configuration, you must only put one thickness at a time. In the shoe industry where you are diecutting component shoe parts from a hide of leather, you would only cut one hide at a time. It is import that a diecutter determine the best areas of the hide to make the die cuts as the diecutter has to avoid any scars or damaged areas of the hide.

Of course you diecut many parts from one single sheet of material. For example in diecutting cigarette boxes, you may diecut up to 20 cavities in one stroke of the press. With automated diecutting presses with material nesting capabilities, you can cut different parts from a single lay of material.

Does the material have threads as in textile materials?

When diecutting fabrics it is best to use a seamless clicker die vs. a steel rule die. Steel rule dies have butted joints where one section of a die blade buts up against another section of blade. If you are cutting any material with a thread in the material, the threads will forced up into the butted area, tending to open up the jointed area. The result is that when you make a diecut, not all of the threads in the die cut part will be die cut and some of the uncut threads will pull in part damaging the diecut part.

Should material be with or against the bias of the material?

In diecutting fabrics, you have to consider the stretch or bias of the material.

Should the material be allowed to relax before the diecutting process?

When diecutting from a roll of material it is often preferable to relax the tension of the material before the material goes under the cutting head of the diecutter. This can be accomplished by allowing the material to fall into a loop that relaxes the material. Material that is not relaxed before diecutting can alter the size of the diecut parts.

Does heat affect the diecutting process?

Yes, in several ways. For example, some materials have to be heated to get a good diecut. I have seen cases where a material needs to be cols or even frozen to result in a good die cut.

What about static electricity?

Static electricity can build up when material is transported on a layout table to the diecutting area. The static build up can cause the material to cling to the head of the press causing the die cut parts not to flow properly through the diecutter. This can be prevented by applying an anti static coil or device right before the diecutting head to eliminate any static charge in the material.

Is the surface of the material to be diecut slippery?

Some materials that are diecut in multiple layers man have smooth or slippery surfaces and move while being transported to the diecutting area. This can solved by clamping the layers together to prevent the layers from shifting.

Does humidity affect diecutting?

Humidity can affect paperboard and corrugated board materials when diecut. Paper and paperboard material are hydroscopic in that they grow as humidity increases. As the material is exposed to a humid surroundings, the moist air impregnates the material. After a part is diecut and stored in a less humid area, as the humidity decreases, the size of the part will change. This may or may not be important in the converting process where one or more parts are assembled into a product. What about static electricity?

Is the surface of the material to be diecut slippery?

Does humidity affect diecutting?

Humidity can affect paperboard and corrugated board materials when diecut. Paper and paperboard material are hydroscopic in that they grow as humidity increases. As the material is exposed to humid surroundings, the moist air impregnates the material. After a part is diecut and stored in a less humid area, as the humidity decreases, the size of the part will change. This may or may not be important in the converting process where one or more parts are assembled into a product.

Should the material be pre-treated before diecutting?

There are some materials that have to be allowed to set for some time before diecutting. This again allows the material to relax or stabilize before the material is diecut. In some cases, the material may have to be heated up or frozen to stabilize the material to assure getting the desired diecut.

Can die cut part change dimensions after diecutting?

Yes it can in some cases. In high humidity situations, paperboard, for example can absorb moisture and tend to enlarge the material. When the material is moved to an area with less humidity, the diecut parts can slightly shrink. Depending on the tolerance requirements of the die cut part, this can create a problem when parts are assembled into a final product.

Do different manufacturing lots of a similar material have the same cutting characteristics?

Yes and no. Now there is a definitive answer. If you are using a specified material from one supplier, you should be assured that every shipment of materials is identical and will diecut just like the last lot of material. What if your material supplier changes some aspects of the product? What if your purchasing department sources a similar material at a lower cost from another supplier? Will the new material cut the same as the original material? Maybe yes or maybe not. Before you put a new lot of material into the diecutting process it may be prudent to make some test cuts and check tolerances and cutting characteristics. It’s better to find out any differences before you cut up $50,000 worth of material only to find out that something is different in the material.

What about maintaining close tolerances?

If you are diecutting a material that requires a close tolerance finished part, you have insure that your using a cutting die that is constructed so that it can be held to a close tolerance. For example, most cutting dies are made to a commercial tolerance of +/- 0.15” or 1/64^th of an inch. That tolerance is satisfactory for many diecutting. Applications. If you need to use a die that could maintain a closer tolerance, you should use a die that could maintain a tolerance of +/- 0.005”. Here again, you should be aware that different materials react differently when relaxed before diecutting begins. Again, humidity can affect the size of a part.

Should I use solid ejection materials in my cutting dies?

Ejection materials in a die perform two basic functions. In a steel rule die it is necessary to have ejection materials to strip the die cut part out of the die during the diecutting action. Another consideration is that to diecut many materials you have to compress the material to its thinnest thickness before the die blade starts the cutting action. This is especially important in diecutting soft foam materials. If the material is not uniformly compressed before the diecutting action starts, then the material may have a concave edge depending on the loose thickness of the foam material. If the material is uniformly compresses, you will get a good straight cut edge.

So many things to consider. So many variables that can affect an outcome to deliver that perfect diecut. Nobody said the process was easy. Experience in diecutting many different types of materials can be of valuable assistance in determining what elements should to put together for the best results. Let face it, not everyone knows how to perfectly diecut all types of materials.

Let’s say that old Joe has been your main resource in diecutting knowledge in your company for many years. He retires or is run over by a truck. He is now longer available to solve your diecutting problems. Where do you go to get solutions, to get the right answers to diecut a special diecutting application? The new kid right off the street that has been on the diecutting press for 3 days probably isn’t the one to ask.

If you have a question on how best to cut a specific material you could always ask your material supplier for his or her suggestions. Your cutting press manufacturer could be a good source of information. After all, they have been exposed to many types of diecutting applications and should have the answers on the best way to diecut many materials. Contact a diecutting consultant. Contact the International Association of Diecutting and Diemaking (IADD) www.iadd.org. The IADD’s Tech Team has access to industry experts that can find answers to almost and diecutting question that you can throw at them.

Types of Diecutting Equipment

In Part 3 of this book I will describe the different types of flatbed, multi-contour and rotary die cutting systems. At this point, I can make two general observations. There are many types of diecutting equipment that have been developed to best cut specific materials. For example, a rotary label diecutter has been developed to cut many types of labels. Automatic and semi-automatic platen diecutting/creasing diecutting presses have been developed to cut single layers of paperboard and corrugated board materials. Other types of diecutting presses tend to be more general purpose diecutting press systems that have the ability of die cutting a wide variety of materials.

The number of parts that can be diecut in an hour of use varies dramatically depending on the type of diecutting press system that you use. For example, a Bobst SPrintera automatic platen diecutter/creaser system can make up to 12,000 impressions per hour. The Sprintera can feed sheets of material, die cut the material, blank and strip the waste within the cut blank and stack the die cut parts on a pallet. This is indeed a truly impressive fast operating machine.

There are other diecutting press systems that can make 100 to 300 impressions per hour. Much slower indeed, but very adequate for many diecutting applications. The speed of a diecutting press is also dependent on the type of tooling that is used on the diecutter. For example, a diecutting press may be rated as being capable of producing 9,000 sheets per hour may only be capable of cutting 6,000 sheets per hour. There are a number of reasons for this. It may be the cutting die that is being used was nor built to provide optimum diecutting speeds. It may be that the stripping materials being used in a steel rule die may not be the best or most advanced materials. It could be the inexperience of the diecutting press operator. Finally, it may be a conscious decision of a diecutting manager to run a press at less than optimum speeds because of the lack of diecutting orders.

Another consideration to be explored is that in many diecutting situations, a company may be using the wrong type of diecutting equipment or the wrong type of tooling to obtain optimum results. This may be as simple as relying on an older press that the company has been using for many years and is reluctant to invest in as more modern more efficient system.

The Bottom Line

The bottom line in any diecutting operation is to die cut parts at the lowest possible cast per die cut part. The more efficient a diecutting system is can have a direct result in being able to die cut part the lowest cost per cut piece. An efficient material handling system can have a great effect on how efficient a total diecutting press system can be.