Once again the English language proves to be a baffling tongue. Depending on context the word die can either mean the singular of dice, the act of ‘taking the dirt nap’, or a complicated cutting tool for making labels. Sometimes I think a rotary cutting die for labels can cause almost as much angst as the other two meanings at times. That may be a bit of an exaggeration because certainly crapping out with big bucks on the table, or an acquaintances extinction cannot be taken lightly. But die issues with pressure sensitive labels are usually the most complicated, costly, and take the longest to fix of any label production issue. There are a few things that can be done however, to avoid the Claymore mine-like effect of things ‘blowing up’ on press with die issues.
The most important thing is to tailor the die, or tool as we refer to it, to the job. Our tooling options at AW range from inexpensive magnetic tooling to really expensive rotary EDM engraved dies on very high Rockwell hardness steel. Both types are in the image to the right. Factors to be considered are what are you cutting, how are you cutting it, and how long do you want to cut it for? A few thousand paper labels, linered and on a roll, would probably point toward inexpensive rotary tooling. On the other end of the spectrum, large runs of Tyvek lidding material, cutting against a hardened steel anvil roll rather than a nice forgiving paper liner, would require bringing out the big, expensive guns. How many cavities a die is built with impacts cost as well. Dies are typically costed with a charge for a blank and a gear based upon circumference and then a dollar per inch of tooling charge based on the grade of steel used. If talking about a simple rectangle, let’s say a 3.0 x (4.0), cavities can be added by building more across or around the web. What he doing with those parentheses around the 4, you ask? I use that to indicate the around the web dimension; it guarantees zero errors. That roll of labels would be 3″ wide and cut every 4″ on the roll. A (2.0) x 4.0 label would be a 4″ wide roll cut every 3″. For a few thousand labels, a one across die would probably be the way to go. For a few million labels, maxing out number across based on press size, eg. 2 across on a 7.5″ press, 3 across on a 10″, and 4 across on a 13″ press would be the way to go. The rule of thumb for number around is that the circumference be greater than the press width. Therefore two 4″ cavities around on the 7.5″, three on the 10″, and four on then 13″ would be prudent.
A couple more elements of die design to consider is how close cutting edges can be and the normal tolerances needed for producing pressure sensitive labels using rotary tooling. If you think of the blade shape, it’s more like a triangle with the sharp edge on the top and a flat base. If you envision this triangle shaped blade it make sense that blades can’t be right up against one another; they should be at least .125″ apart. Tolerances vary depending on the diemaking process and the grade of steel. EDM dies are a bit more accurate than the more conventional CNC dies but both will produce a label die that’s within the +/-.005-.007 range. Frankly, there just aren’t that many pressure sensitive label applications that require that much accuracy. Die to die accuracy (jobs that have more than one die in the press) and print to die tolerance is more typically in the +/-.03″ or .75mm range. Once again this is usually plenty tight for most label applications.
Dies do get dull, with the number of revolutions depending on the answer to the three ‘what’, ‘how’, and ‘how long’ questions listed above. A half million to a million revolutions is not uncommon. When it needs to be resharpened, the cost is roughly 30% of the cost of a new tool. One of the tests we perform is to test the die cut using dye, another aggravating quirk of the English language. We take a red dye and wipe the silicone side of the paper liner and flip it over. If red dye comes through the back side of the liner, it indicates the tool has cut through the silicone and nicked the paper. Another sure visual is when labels start going up with the waste matrix. When we see either of those things it’s time to retool.
This post had been a fairly technical, relatively dry essay, although there is some valuable basic information buried in it. If you really have critical die questions, call, email, or (the best way) stop by the Advanced Web booth at Healthpack in Louisville next month. Not only can you discuss somewhat mundane die issues but you can also race horses! Yes, Churchill Downs and Keeneland have not begun their meet yet but you can gamble on horses at the Advanced Web booth in Louisville. Details and valuable prizes are being firmed up but the vintage battery powered HORSE RACING DERBY game will be at the booth. Certain packaging professionals whom I know will not be allowed to play due to that choking hazard for three year olds mentioned on the box, but most will be green lighted to win, place, or show. Heck we may even need an exacta bet. See you in Louisville!