Calculating Die Cutting Tonnage Continued...

Let’s Get Really Technical:
 
A couple of us have actually talked about developing an on-line tonnage calculating website. It would be comprised of a database that held values and asked questions like; Strength values (Tensile) for most common materials (A), Shear strength values for several processes/rule types/ejection, etc…(B), Number of inches being cut (C), Thickness of the material (D). A X B X C X D = Tons 2,000

In fact, this is exactly how many software stress analysis programs work. They take a set of very obvious variables and make a simple calculation based on these (and other) numbers. It gives you a very consistent way of looking at every project you take on. Right or wrong, the answer is a base number to start with, and that is what we have gathered is the trick to determining proper starting tonnage numbers. Once you have this standard formula in place and trust that it will give you that base number, you can then depend on it and translate it to work in different machinery on your shop floor. Perhaps you have a string of ten punch presses and they all cut a little different. One is hydraulic, one is pneumatic, one is mechanical off a simple small cam while another throws off a giant flywheel that was welded back together by Uncle Joe a few years back. They all cut differently but they all have a factor you can use as a multiplier against that base number we just calculated out. It’s beautifully simple really, it just takes some time to develop and work out in your own shop, on your own equipment. Once you have that number, everyone can plan around the equipment you have vs. the projects you have with more confidence.

So then the formula may look like this;
(A X B X C X D) F = Tons (Where F is a press factor based on experience and/or a manufacturers guidelines.) 2,000 Putting this into a real life situation may look something like this; I have a ten up steel rule die cutting and creasing .018” paperboard. There are 1,000 total inches of cutting, creasing, stripping, support knives etc… I am using modern ejection materials. I am cutting on a platen style press.
17000(A) X 1(B) X 1,000(C) X .018(D) X 1(F) = 153 Tons. 2,000
Simple Formulas from above; C/6.5 = Tons (1,000 / 6.5 = 153.8 Tons) or (C X 400) / 2,000 = Tons (1,000 X 400) / 2,000 = 200 Tons

Both formulas work and give us a range that is safe and a good starting point.

Now Let’s Get Really Simple:
 
What seems to happen with all this fancy calculating in real world situations is that the base theory gets boiled down to simple formulas that work for similar situations. Most of us deal in very similar tooling and materials everyday and having a very fast and simple way of coming up with a safe base number is natural. If you are always working in paperboard in about the same caliper, taking the total periphery and dividing by a single proven number is a fantastic way to approach tonnage calculating. The same goes for plastic, steel, leather, or anything else you cut on a regular basis.

So, this article is not going to give a catch-all formula for determining tonnage for all materials on all press types, with all tools, because there are too many factors involved and nobody would ever use it in real life. What we can do is offer a base calculation where you plug in your own numbers based on experience. Your own situation will provide the best formula for you.

That base calculation would look like this;
Total Periphery to Convert X Material Factor / 2,000 = Tons Needed

Developing a living chart of MATERIAL FACTORS will then be the key to making this work in your business. We’ve been using paperboard a good deal in our discussions and it seems that a starting point for a folding carton manufacturer on a Flatbed style press would be a MATERIAL FACTOR of 300. The heavier gauge the material is the bigger the Material Factor. (1,000 Inches X 300) / 2,000 = 150 Tons Keep in mind that if your cutting process changes, maybe it’s as simple as going to a harder rubber or steeper bevel rule, you will have to use a multiplier to compensate for this change.

There is no trick of the trade in calculating the tonnage you need for a project but as you develop a more and more sophisticated list of materials and how they process on your equipment, you will have an estimating and production tool that will help you predict with greater accuracy how well a job will run, where it should run, how many up it can run, and whether or not it will run at all. You will have a leg up on the competition that is still shooting from the hip and this will really put the pressure on them…..

We’d like to thank all of the operators out there that are trying to improve their production techniques and came to The TECHTEAM with their questions!

Calculating Die Cutting Tonnage

Compiled & Written by The IADD TECHTEAM

Knowing How Much Pressure It Will Take To Convert Your Product Is One More Key To Success
 
Here on the TECHTEAM we sometimes see the same question more than once. The question of “how much tonnage will it take to cut this product?” is the most common, and also one of the hardest to answer because of the complexities involved in calculating a perfect number. In fact the question should probably be, “is it possible to calculate exactly the tonnage it will take to cut a specific product, in a specific material, on a specific press?” This article outlines the basic theory of calculating tonnage needed to cut and will give most readers a base starting point they can feel comfortable with for their business.

Here’s my problem with the idea of tonnage. It’s an intangible sort of a concept that really has no place at all in my business. It seems to change and move and act quite slippery and I really just don’t think I need to deal with it. That is true until I find out that the machine I just planned a job for in a very specific factory, on a very specific machine, on a very specific tool, in a very specific material, will not run because the machine doesn’t have the guts to get the job done. Then it becomes a factor that I should have paid allot more attention to right from the get go.

For most of us, the machines we plan around have all the tonnage we’ll ever need for 99% of the jobs we will ever see. I’d bet most estimators never even look at this factor when they plan a job. For many diecutters the advantage of knowing how to accurately calculate tonnage needed makes the biggest difference in faster make-readies, and that alone is well worth the effort of knowing how to at least get a good starting number. For some of us it will only make a difference when we are planning an usual job that needs to run perfectly the first time around, and that alone is also worth knowing exactly what you are talking about.

So, where on Earth do we start? How about a bit of theory? The tonnage needed to cut/emboss a material is strictly a function of the strength of the material, the shear power of the process being used to cut, the size of the image to cut, and other factors like flex in the machinery, ejection materials, air pressure build-up’s, etc… That being the case then we should be able to use a simple formula that says – This is the amount of image I have to cut/crease/emboss/etc. that has value A. This is how thick the material is and it has value B. This is the material that I am cutting and it has value C. Calculate them all out and I get an exact number that works every time. Answer D.

Straight from the from Machinery's Handbook 25th ED. P1924 “P = periphery x thickness x tensile strength(PSI) where P is cutting force in pounds.” That was easy! And in fact for many cases it may be a number that is good enough to get started. The problem lies in the fact that there are many different processes and techniques for cutting and each holds a different value that must be factored in, and there must be a starting value for the material you are cutting.

Over the past year we’ve been answering tonnage calculating questions and it’s really interesting to take a look at all the formulas being used out there. Here’s a typical and really great question. "Thanks for taking my call. Here is my question. I need to be able to figure if my die cutting press has enough tonnage for different jobs that we produce. We die cut anything from 10 pt to 100 pt. paper in different shapes and sizes. Sometimes they are 1 up, sometimes they are 100 up. Is there a formula that I can use to determine if I can run a job 2 up as oppose to 5 or 6 up? Something like 1 ton of press is equal to 6 in of cutting rule when cutting 18 pt. and 5 in of rule when cutting 24 pt. This would greatly help when trying to quote jobs knowing that I can't die cut as many up as I print. Thanks in advance for your help.”

Here’s a sampling of formulas and answers that worked for this and other applications;

• 6.5 inches of cut rule with ejection = 1 ton pressure This should be good for paper up to .030 thick for thickness .031 - .050 reduce the inch count by 10% for thickness .051 - .070 reduce the inch count by by 20% for thickness .071 - .100 reduce the inch count by by 30%
• Total inches x thickness x (some material strength factor you know to be correct) /2,000 is one way to get total tonnage needed.
• For each inch of rule, you will need 300 lbs of pressure and for each square inch of rubber; you will need approximately 50 lbs of pressure. So if a die has 1000 inches of cutting rule and is rubbered in strips of ½” wide on each side of the knife, it will calculate to 1000 x 300 and 1000 x 50 or 350,000 lbs of pressure or 175 tons.
• We use a factor of 400 pounds per linear inch of rule up to 500 pound per inch depending upon material being cut. Paper is 400 pounds. Ejection rubber can add up to 20% more pressure needed, depending upon amount of rubber in die.
• I have looked over the information you supplied me and I feel fairly confident your 50 ton press would be able to cut your material to the size and # up you are considering. The most basic formula many of us in the industry use is 6.5 inches of cut knife requires 1 ton of cutting pressure to cut and eject a paper sheet .018 thick. Considering other factors such as the die area, serrated rule and the fact that I feel that a press can be called upon from time to time to cut up to 110% of its tonnage rating. If I didn't know for sure that it did not have the ability to cut to this pressure I would take a chance and build this die and use it as a "benchmark" as what the press is capable of cutting. If you would like me to go into further detail please contact me.