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FLEXO Magazine : November 2009
www.flexography.org NOVEMBER 2009 FLEXO 51 applications, this also allows for much better control of the heat transmitted to the release paper on the back of labels. Inferior laser sources with larger spot sizes often make it difficult to remove the cut labels because melted adhesives cause the labels and release paper to stick together. If a laser cutting system presents burn-throughs, it usually reflects both a poorer quality of software and an inferior laser source with a large spot size. The soft marking capabilities of today 's better quality laser cutters should be considered as a non-negotiable feature, whether a system is high-priced or low-priced. There are systems at all price levels that can and cannot achieve this level of quality and thorough investigation is required. The wattage of the laser should be carefully considered. Many of the commercially available lasers have the best laser beam quality with full power. For lasers of that type, if you end up using only 10 percent or less of the laser power from your laser source, you can expect significantly diminished laser beam quality. For example, a converter making kisscuts with easy-to-cut materials that has a 300 watt laser in its cutting system may be using only a small portion of available laser power and would be better suited by a lower watt laser. A converter making many throughcuts, including more difficult- to-cut release paper, which also wants to achieve high cutting speeds, would need that 300 watt laser. The smaller maximum working areas require a laser with a smaller spot size. This will lead to better cuts, because the energy is concentrated and less laser power is needed to achieve the same depth of cut. In addition, less heat is transferred to the material being cut is always the desired scenario. One of the differences you will find in lower-priced systems is that they sometimes use lower cost air cooling for lower power lasers, as opposed to the more costly water cooled lasers. The edge quality that a particular laser cutting system delivers will vary with the spot size of the laser. In systems with smaller working fields (e.g. 200mm by 200mm), this is not as much an issue and one can expect both the high-end and low-end systems to have a 210 micron spot size. If the working field is larger, however (e.g. 300mm by 300 mm) one needs to be able to make due with a 280 micron spot size when considering the lower-priced system. As an example, label converters might be well-served by a system with such larger spot sizes, but those involved in RFID applications might need the greater precision in cutting edge quality. Smaller spot sizes also have a bearing on cutting speed. It is very important to verify that a system can maintain the desired edge quality and cut-to-print accuracy at the maxi- mum cutting speed of the system. Some of the more poorly designed laser cutting systems cannot maintain cut-to-print accuracy over time. The lower cost laser cutting systems may use sensors for registration, or in more demanding applica- tions use the sophisticated camera technology to deliver the very tight tolerances in cut-to-print registration that are typical of high-end systems. If these camera systems are fully integrated with the laser scan heads they are able to apply the offset values to keep cuts to a precise registration. Here too, it is not only the quality of the camera but the underlying software engineering that has great bearing on the toler- ances that are achieved at varying speeds. Features that bear on user friendliness and ease of opera- tion are found in machines of all quality levels. Smart stop systems, job simulation software, automatic image splitting and optimization for web speed, variable job stop criteria, and one step job setups of all operating parameters make these systems straightforward, even for lightly skilled workers. Because the software is handling most operations behind the scenes---registration, web control, laser powering, laminating, slitting---and because there is full communication between dif- ferent system modules, the operator 's work is relatively simple; the software does the difficult jobs automatically. Obsolete technology does not have these features. Some out-of-date designs do not even give operators the capability to change job settings while the machine is operating, nor directly on the machine. These type of systems, which force operators to stop cutting operations entirely and reload a job from scratch, saddle users with unnecessary drags on production that today's better quality laser systems bypass altogether by giving operators numerous ways to amend job parameters without shutting down the production line. SUGGESTED METHOD FOR SOURCING To begin sourcing the best laser cutting technology for your operation, you must first determine your application require- ments in terms of: complexity of geometries to be cut; produc- tion rates required; sheet versus web; type of materials (PET, ABS, polycarbonate, etc.). One is best served by contacting several manufacturers that build laser cutting systems to request that samples be run on your materials using a few of your part configurations. The manufacturers should then be able to recommend the model of their laser cutting systems that will be correct for cutting your parts from your materials. TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009