Rotary Die Cutting via Matched Metal

In a continuing series of Technical Projects that focus upon rotary diecutting and the tools that go with the processes, we must explore the very exciting method of using the male/female die with a small twist. Actually a very large and fast twist may be a bit closer to the mark as this type of cutting system is designed to turn very quickly and very accurately for a growing number of converted products. There seems to be no specific name that has emerged as the common term for this type of cutting. Some common names for the process include; compression cutting, pressure cutting, male female rotary cutting, and rotary pressure cutting - so for the sake of this writing let's call the method the MMRC or (Matched Metal Rotary Cutting).

 
Rotary Die Cutting 1

 As a guy with a semi-flat background (careful), I remember seeing one of these tools at the CMM show in Chicago back in the early 1990's. I was amazed. This was probably the most complicated looking monstrosity I had ever seen. It looked to be made in one piece, had to be made to an accuracy that just blew me away, was at least the width of the widest tool I had ever made 60"(1,520mm) and the contraption was round! I mean there were two of them and they were cylinders that matched one another perfectly. Now if I had a hard time getting our flat dies to come up and kiss a flat plate, how in the world could these guys get these things to work. I stood and stared until a salesman explained a little more. Slowly it all began to gel - I was the only sane one in the booth, everyone else had to be nuts! Well, nearly ten years later a good customer of mine has made the decision that this type of MMRC will be the best bet to improve the overall production quality for a particular long run product. I was one of the people that recommended the process to them and in retrospect to that earlier experience in Chicago, the people in that booth were among the savviest converters at the show. The balance of this article will try to explain why.

 
Rotary Die Cutting 2

 What is a Matched Metal Rotary Cutting System? Instead of using a crushing cut where a knife like cutter rolls against a solid anvil to make the cut, a shear type cut is made by passing two precisely machined blocks or cutters by or through one another without ever touching anything but the material to be cut. The material is actually squeezed or compressed to the point of bursting without the two parts of the tool ever touching. The two cylinders that make up the tool set both rotate at exactly the same rate in order to create a perfect match to one another through the cut. The two can be brought closer, moved apart, and can even be slid parallel to one another in order to maintain the quality of the cut during the run. The fact that the tools and the system that the tools ride in are so accurate and never actually come in contact with one another creates a unique opportunity for perfect quality and long tool life.What type of products can and should be cut on these tools? The tooling that make this type of operation a success can be expensive. They last for a very long time but usually the cost translates into making products that have a large volume and have specific quality requirements that are hard to accommodate with other methods. Material thickness up to .125" (3.175mm) and no less than .007" (.177mm) can be cut. Some typical materials that convert well include paperboard, high-density plastics, corrugated, recycled paperboard, and specialty coated boards. Folding cartons are a very common product followed by gaskets and then specialty items. What is the quality of product difference? When compared to standard crush cut rotary or flatbed cutting the major product quality improvement issues that make a difference include; less dusting, less slivering, less burring, less nicking - both natural and production oriented, and greater accuracy.

 What are the main production advantages?

• Feed rates are not limited by the cutting operation! Now there's a statement. These tools will spit out finished product as fast as you can push it through the press. Usually another process like in-line printing or part delivery systems will limit the feet per minute speed of the line.
• Stripping is done at the cutting stage by either a series of fingers, a through the cylinder collection of waste, or other techniques that remove all waste before the part is delivered to the back side of the die. There is no separate stripping stage and parts are delivered waste and web free. "Stream Stripping" is a term used to describe the waste being removed as a continuous stream as it is pulled into a vacuum tube.
• Tool life is typically measured in millions of revolutions. Depending on the operator, the material being cut, and the method used to manufacture the dies, cases are reported of solid dies lasting up to 350,000,000 *(yes, that's 350 million) revolutions before needing a sharpening. Flexible dies will typically max out earlier than solid tools somewhere in the range of 4 to 5 million revolutions. This long tool life usually translates into less down-time overall and can translate into lower overall tooling costs when compared to other methods.

Rotary Die Cutting 3

What about the tools?

• The tooling for this type of process is made in both flexible plate and solid machined configurations. The flexible plate tools are usually made via chemical or standard machining or through a combination of the two and are wrapped around a cylinder that stays in the press. The solid machined cylinders are typically made using EDM (Electronic Discharge Machining) or standard direct machining or through a combination of the two.
• Hardening and finishing techniques for the cutting surfaces can include laser hardening and cladding as well as specialty coatings and platings. All are designed to improve tool life.
• Web widths can range from 6" to 60" (152.4mm to 1,524mm)
• Tool diameters can range from 3" to 24" (76.2mm to 610mm)
• Accuracy is ±.002" (.05mm)
• Costs for a single matched tool: $1,000.00 to $250,000.00 US That's a huge range and it can vary greatly depending on the image to be cut, the style you choose - flexible or solid, the stripping requirements, the surface finishes, the number of rolls you put in line, etc… Flexible tooling tends to range from $1,000.00 to $3,000.00 US with most narrow web applications falling under the $2,000.00 mark
• Solid tools can typically be sharpened about five times before they are retired and they can be reworked. Flexible plate tools cannot be sharpened or reworked.
• Just like male/female cutting in a flat operation, the tolerancing and adjustments made to offsets allow for just about any material to be cut accurately and with ease.

How is a Crease, Emboss or a Perf produced?
The MMRC technique will only cut through material. Just like with a pair of scissors or a steel rule bridger, it's tough to make a kiss cut or a dent with a male/female tool. When a crease or an emboss or a perf need to be produced a crushing operation must be added. A blade like or crease like male is added with a hard anvil counter on the opposite cylinder. Because the upper and lower cylinders are both being machined, reverse scores and reverse cut-scores can be created as easily as the standards. These can be incorporated into the tool that does the perimeter cut or can be incorporated into a second set of die cylinders that fall before the final cut stage. Separating the stages has the advantage of creating a long life tool and a shorter life tool that can be worked on individually.

Are there specialty machines that are needed to run this type of tooling?
There are many companies that make presses to accommodate rotary cutting. This type of tooling and process (MMRC) can be used in many of them. In general the die manufacturers that make this type of tooling will do their best to build a tool that will work in your press.
Finishing UpEveryone has their own take on techniques used in our industry. What the future will hold for MMRC will most likely be embroiled in what happens to run lengths, corporate consolidations/product consolidations, and mechanization of other attached packaging processes. For the time being this technique has a growing number of markets that it plays very well to. The cheaper flexible and magnetically mounted tooling is being pushed hard right now by a couple of tool manufacturers. Although this type of flexible tooling will never replace the need for the more expensive solid tools it will more than likely allow more converters to use this type of cutting technique on a more regular basis. As more rotary converters discover the benefits, for those special jobs, the technique will flourish. I predict that this will lead to an explosive market over the next twenty years where once again our productivity as converters advances by leaps and bounds.As lessons go, this ten year process of becoming familiar with MMRC has been too slow but has taught me to listen a little longer and a little harder to everyone I meet. I hope you too find a product that can use this process to your full advantage, and that the IADD has once again started you off in the right direction.*At printing of this article the production was closing in on 400,000,000 revolutions (not parts). This solid machined tool was made by Bernal Technologies and is cutting .018" Poly coated SBS. Wow! Not all solid tools will last this long. It all comes down to materials, machines, and operators.

Support for this writing came from several sources including:

Marc Voorhees - Bermaxx LLC / Bernal TechnologiesMarc Love - Atlas Chem-MillingJim Redd - XynatechRon Brenwall of Maxim InternationalPhotos courtesy of Bermaxx LLC / Bernal Technologies.

Thank-you very much!