Product Reviews

Rotary Dies & Tooling

July 20, 2005

The search for the perfect cut leads die makers to pursue new technologies.

A cutting die is a timeless tool. The power to create a shape in a substrate, be it a hole, a border, a crease or a perforation, has changed the packaging industry over the years. The web fed press gave rise to rotary tooling, which is the predominant type used in the narrow web industry today.

For a while it seemed that the creation of dies would also remain consistent. Fashioned from steel using engraving techniques, the nearly finished rotary die goes for its final baptism to the hand finisher, the skilled worker who uses the human eye to bring the cutting edge to perfect sharpness. Dies are still made that way throughout the world. But changes are taking place that could have a significant effect on the sharpening process.

“Most of the time the label producer doesn’t know how a die is sharpened,” says David McLaughlin, technical support manager for American Die Technology, Suwanee, GA. “The bottom line is that every label company in the world orders a die and expects it to cut. They don’t just hope it cuts. I don’t think it matters that much to them how it is sharpened.

“We’re always looking into new technologies to improve our products,” McLaughlin says. “There is more than one way to sharpen a die, whether by hand, by machine, by laser, whatever people are trying these days. Right now people are looking into machine sharpening of dies. But the feedback is that it’s not as consistent enough as hand sharpening is.”

Die manufacturers, a competitive group, don’t talk much about the new processes they are using. Some generalities are forthcoming, however.

“We produce dies in a number of ways — there are all kinds of methods,” says Gary Smith, vice president of sales for RotoMetrics, Eureka, MO. “We don’t publicly tell how a tool is finished. We don’t sell the process; we sell the right tool for the right application.”

There is talk in the industry about sharpening dies using laser beams. “We do that on occasion, where the application requires,” says Smith, “but again, we don’t sell the process.”

Using lasers to put the final sharpness on a rotary die is viewed by some as having the potential for a better tool, but the jury appears to be out. “It’s possible that the cutting edge could last longer,” Smith adds, “but for the most part, and for most companies, hand finishing is still the predominant method.”

“The push these days is toward getting dies consistently manufactured throughout the process, instead of having the craft of the hand work in it,” says Jim Breig, sales manager for Lederle Machine Co., Pacific, MO. “Everyone is trying to achieve processes that will come up to the standard of hand work.

“It could involve lasers,” Breig adds, “but it still involves machined rotary engraved dies that are heat treated and sharpened. The question is how we do that mechanically.

“There is some feedback that machine sharpening works better, but I think it’s a bit too early to say that those who are experimenting with it are getting better results.”

Machine sharpening
One company that is using lasers in its rotary die manufacturing process is Wilson Manufacturing, of St. Louis, MO. The company has been working on a new process for the past four years, and has been testing the new dies with customers.

“The blades are still carved out the same way, but the sharpening is different,” says Wade Fouts, sales manager. “A single machine will engrave it, treat it and sharpen it. You have one set-up, and the die is done and ready for testing. From there it’s ready to be shipped.”

Fouts is reticent about discussing the proprietary process, but says that the feedback from customers is positive.

“With a conventional die you can tool it to cut thermal transfer stock, but on 2 mil polyester it doesn’t work, as a rule of thumb. It’s not as sharp. This new die will cut them all, as long as you don’t change your liner. It’s very precise, and it doesn’t matter if the die is tooled for paper or polyester. You can run paper, synthetic paper or film on a liner.”

The new method of sharpening, Fouts adds, is “so much more accurate than hand sharpening.”

Wilson Manufacturing developed the entire process in-house, says Fouts. “We wrote the software ourselves, and did everything internally. The only thing done outside is the machines.”

As for the life span of the new style of die, Fouts is pleased with the results. “We shipped the first one for testing in April of 1999, and it outperformed anything the customer ever ran, longevity-wise. They were running very abrasive computer-printable film that was eating their dies up — they would go through five or six dies to get through the run. So I asked him if he wanted to be a guinea pig for the new die, and he said sure. He ran the whole job on one die, and that’s when we knew we were really on to something big.”

The new dies don’t react the same way with every substrate. “There are so many variables,” says Fouts, “so it’s not fair to compare one converter’s results to another. But the gist is that the results have been phenomenal across the board.”

Fouts says the new generation of dies has another benefit: “Typically, with a conventional die the life expectancy becomes less and less with each retool. The first run is longest, the second will be less. Usually you can get three, four, maybe five retools out of one die. The blade gets shorter and the angle changes.

“The great part about the new dies is that they are machine sharpened, and you get the same angle every time. On the third retool you get the same die you started with.”

Manufacturing time for the new tooling is similar to that of conventional tools, “maybe a little bit faster.”

A punch unit manufactured by Tools & Production to display the various punching capabilities

Laser consolidation
On the horizon for rotary dies is a revolutionary process called laser consolidation. Research on the method has been under way for a couple of years at the National Research Council of Canada’s (NRC) Integrated Manufacturing Technologies Institute, in London, ON. Prototypes of this next generation of dies are being worked on by Rotoflex International, in Mississauga, ON.

Laser consolidation produces a die that is made in a manner opposite to that of conventional dies. Whereas conventional dies begin as a steel cylinder whose cutting shape is created by removing metal, the laser consolidation die is made by building up the cutting edge onto a cylinder.

According to an abstract published by NRC, the dies are made as follows: a Nd:YAG laser beam is focused on the blank surface of the cylinder to create a molten pool, while metal powder is simultaneously injected into the pool. The blank is mounted on a stage, and the stage moves according to the die design to form the cutting pattern. “A layer of molten material is deposited on the blank surface which rapidly re-solidifies and forms a metallurgical bond to the substrate and forms the first layer of the cutting blade to be built. Subsequent passes are then deposited on the previous pass until the desired height of the blades is achieved. The process produced fully dense and metallurgically sound cutting blades without porosity or cracks.”

“We’ve been working with NRC of Canada for well over a year on this,” says Val Rimas, vice president of sales and marketing for Rotoflex. “Here’s the advantage we saw: We’re going into a green revolution, and we have to consider what to do with the old dies that are out there. We could see this process as allowing us to take older dies and build blades on them through the laser process. We also saw that different blades could be made using different materials, to get the correct hardness.”

Rotoflex currently is in the prototype stage. “We’ve manufactured a number of these dies, which are being used by our customers, and we’re getting data back from them now,” Rimas adds. “The response so far is fantastic. The dies perform better than conventional tooling.”

The company also is working on laser sharpening of dies, as well as machine sharpening.

Flexible dies
Flexible dies are becoming more widely accepted in the narrow web converting field. These products, less expensive than solid tooling, are manufactured of spring steel. They are mounted magnetically on specially designed cylinders and run in die stations in the customary manner.

One of the major manufacturers of flexible dies, Kocher + Beck of Germany, opened a US plant in Shawnee, KS, two years ago. “People have large libraries of solid dies,” says Rick Clark, regional sales manager. “Those who we have switched over to flexible dies see the benefits of reduced cost and delivery times. Those are two key factors.”

Flexible dies, he adds, are continuously undergoing improvements, and today can compete against solid dies on highly abrasive substrates and long runs. “The quality is getting much better,” says Clark. “We are able to cut films well. And we have the ability to laser-harden the cutting lines, raising the hardness level and not interfering with the flexibility of the die. We harden only those lines that come into contact with the substrate.” That hardening process, he notes, is proprietary.

“One of the biggest advantages of flexible dies is in repeat jobs, and also where the die has complex shapes, such as in the sticker industry. Flexible dies can have much more complex shapes than solid dies, and at a very much reduced cost.”

Many a converter employs punching tools for specific jobs. Punch units are available that have cylinders equipped with slots for inexpensive punch tools that can be replaced for very little money.

“Punching tools are an alternative to rotary dies,” says Peter Tupman, sales manager of Tools & Production Inc., Temple City, CA. “If you have 200,000 labels or tags to convert with a punched hole, you could probably manage with a rotary air eject tool to complete the run. But if you have 20 million labels to punch, the air eject tool isn’t going to do it. A punch unit is much more cost effective, can run at maximum press speed and has much better control of the waste after punching.

“A drop-in punch unit for punching EDP labels or tags can cost around $8,500 for a 10" flexo press die station, and the replacement punch pins are a matter of cents each to replace,” he adds. Punch units can be put into die stations, or they can be mounted onto platforms above the press. “There are restrictions when you want to go into a die station,” Tupman says, “such as the cylinder circumference on some presses. If a punch unit is installed onto a press platform, then a suitable circumference can be selected, without restriction.

“Everyone uses rotary dies, but punching is much more of a specific and custom type of requirement. It is not viewed as a competitor to a rotary die, but as an option dependent upon the amount of business that has to be converted. If you have a run of five million that will be repeated four or five times a year, it’s a good investment.”