It has now been four years since Koenig & Bauer first showcased a rotary die-cutter for folding car-ton production at drupa. In the meantime, countless advances have been made. The Rapida RDC 106 has evolved into a highly automated folding carton die-cutter characterised by exceptional productivity. The Report team spoke to Johannes Naumann, head of design at Koenig & Bauer Sheetfed, about this alternative to classic fltbed die-cutters.

Report:

When did Koenig & Bauer first start developing rotary die-cutters? And what motivated it to do so?

Johannes Naumann:

Interest was first expressed by IML printers several years ago. Production in this segment is generally a continuous process on narrow webs. An emerging trend to production in wider formats in sheetfed offset, however, left no alternative to finishing on fltbed die-cutters, which are rather slow for such substrates. Consequently, users began to ask about die-cutters which could run at higher speeds.

Report:

What makes the Rapida press platform suitable for rotary die-cutting?

Johannes Naumann:

The Rapidas can be used universally and, thanks to the double-size cylinder system in the sheet travel, are particularly well suited to a wide range of substrates. Rotary presses have continuous sheet travel, which is the prerequisite for high output. Flatbed die-cutters, on the other hand, operate discontinuously and are therefore limited in their sheet travel capacity. What is more, many subassemblies of the Rapida presses can be transferred to the web press. This starts with the feeder, extends to the infeed, in which the sheet is aligned just as precisely as during printing, and extends to the operation, which is identical in many details to that of sheetfed offset presses. This means that die-cutters can also be integrated into a sheetfed offset press line.

Report:

What were the principal steps in the development process?

Johannes Naumann:

First of all, we swapped the plate cylinder for a magnetic cylinder, and added replaceable jackets on the impression cylinder. Another challenge was to guarantee the torsional rigidity and stability of the die-cutter units. Heat-related deformation also needed to be brought under control. Just one degree of temperature difference can result in a 7.5µm (0.3thou) deviation in the cut. This is why the die-cutting units operate with temperature compensation. In other words, they are equipped with temperature control systems. The punching units are equipped with a very sensitive motorised punching depth adjustment that allows setting steps of 1 µm.

Report:

And the time scale?

Johannes Naumann:

Four years ago, we were offering the Rapida RDC 106 as an IML die-cutter, and showcased a folding carton version at drupa. The next step was then to find users for the first industrial trials. The Edelmann Group received one of the first machines with creasing and die-cutting units, as well as a stripping station. The great advantage of this machine is that each process step is performed in its own unit, which means that they can also be configured separately. The compromises that combination dies make necessary are thereby eliminated. Two years ago, we launched development of an automatic blanker. At the same time, optimisation of the die-cutting, creasing and embossing units continued, as did work to further improve the tooling. drupa visitors can now look forward to a Rapida RDC 106 for high-performance automatic folding carton production at speeds up to 15,000sph.

Report:

How do things stand today?

Johannes Naumann:

The RDC can be supplied both as a label die-cutter, and for industrial fold-ing carton production. It has been developed to cater for these two applications, though further improvements and optimisations are, of course, possible in future. The following process steps are available for the folding carton market: embossing, creasing, die-cutting, stripping and blanking. Depending on the particular job, the machine achieves a throughput of up to 15,000sph. At the same time, with an eye to one-pass production, die-cutting units can also be integrated into a Rapida 105/106 sheetfed offset press.

Report:

Where is the Rapida RDC 106 being used? And for which products?

Johannes Naumann:

We have already placed a significant number of machines on the market, for example in Germany, Denmark, Belgium, France and Poland, but also in Brazil and Australia. The applications range from 55µm (2.17thou) label substrates to folding cartons in thicknesses up to 0.6mm (0.024in). The different properties of the individual substrates are reflected in an assortment of special accessory equipment that has been developed for label and folding carton production. Typical products are inmould labels and folding cartons for the pharmaceutical and food sectors.

Report:

Flatbed or rotary die-cutters: What do you recommend to users?

Johannes Naumann:

JBoth types have their specific strengths. Rotary die-cutters achieve higher outputs; they are, however, subject to certain limitations in terms of the range of substrates that can be processed. The die-cutting principle is different. Users must rethink the production process, and take the special physics of rotary die-cutting into account. The cutting forces are much lower than those of a fltbed die-cutter. Rotary die-cutters do not require special foundations. They run as quietly and smoothly as a printing press. If the properties of the two machine types are cleverly combined to cater to a company’s individual product spectrum, very high productivity can be achieved with both technologies.

The process units of the rotary die-cutter are based on the established Rapida system

Report:

Can you name a few performance parameters of the RDC?

Johannes Naumann:

Users have found that the output of the Rapida RDC 106 is around 25 per cent higher than that of fltbed die-cutters. The average speeds of 12–13,000sph play a major role in this. The RDC is also much faster in makeready. Repeat jobs in folding carton production, with the typical die-cutting, creasing and stripping processes, can be set up in 15 minutes. For new jobs, we reckon with about 25 minutes. The precise figures do, of course, depend on the job in question. This makes it possible to plan a large number of makeready processes in a single day, ensuring the machine is suitable for both short and long runs.

Report:

How do the costs for consumables compare to those for a fltbed die-cutter?

Johannes Naumann:

There are hardly any differences. The tooling costs for a rotary die-cutter are comparable to the costs for high-quality fltbed dies. Separating the processes means that separate tools are needed for the rotary machine. The different dies are produced by specialists. We work with Wink for die-cutting and creasing dies, and with hinderer & mühlich for embossing tools. Other tool suppliers are also possible. Stripping tools are produced on a plotter using flexible letterpress or coating plates. This is usually done by the folding carton producers themselves.

Report:

What lies ahead?

Johannes Naumann:

Rotary die-cutters are becoming established in the high-performance folding carton segment. Their die-cutting and embossing quality is, for all intents and purposes, equal to that of a fltbed machine. Where it is technically feasible, and assuming that it makes sense for a certain application, integrating die-cutting and creasing units into a printing press is also conceivable. As with the digital VariJET 106, for example.

Report:

Mr Naumann, thank you for the interview.

Martin Dänhardt

Background photo: Johannes Naumann with a cutting die from cooperation partner Wink