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FLEXO Magazine : November 2009
48 FLEXO NOVEMBER 2009 www.flexography.org Laser cutting, a.k.a. digital die cutting, uses high-pow- ered lasers to vaporize materials in the lasers' beam path. The powering on and off of the laser beam and the way in which the beam path is directed toward the sub- strate effects the specific cuts that the artwork requires. Be- cause parts that are cut away are vaporized, the hand labor or complicated extraction methods otherwise needed for small part scrap removal is eliminated. These basic facts about laser cutting are as true today as they were when laser cutting systems were first put to practi- cal industrial uses in the 1980s. However, recent advances in laser cutting technology, and especially those that relate to the sophistication of the software engineering underlying laser cutting controls, have created dramatic improvements in the type of outputs that can be expected from laser cutters. This article continues the discussion of the difference between high-end and low-end laser die cutting systems. The first half of this article can be read in FLEXO's October issue, page 52. FALLACY OF THE DOUBLE SCAN HEAD ADVANTAGE Another area that can get confusing to those who do not understand the specifics of laser scan head design is the use of so-called double scan head systems, which are designed to accelerate cutting speed. These higher-priced double scan head laser cutters are, at times, no faster or even slower than single scan head laser cutters that use higher wattage lasers coupled with more sophisticated algorithms in the laser control software. Although it might sound good---i.e. the idea of using two lasers at once to double your production speed--- this creates significant quality issues. In addition, the physical constraints of putting two laser scan heads next to each other and the compromises that this forces one to make means it cannot truly double speed. When you are stitching two halves of the web width togeth- er, it is often possible to have more parts on one side of the web as compared to the other side, as shown in Figure 21. In such a scenario, with a double scan head machine you will lose web speed because of the laser on the overloaded side. To solve this problem, manufacturers of double scan head systems usually position the two laser scan heads as close together as possible across the web width to create the great- est possible overlap between their two cutting fields. However, for wider material there is always an interplay between the size of the scan heads, how closely they are po- sitioned together, the spot size that results, the extent to which there is overlap in the cutting area of the two scan heads, and the related stitching involved. If the scan heads are so large that they cannot be placed very close together, there will be less overlap in the cutting area and more need to stitch. This becomes a challenge to quality, as shown in Figure 22. Al- ternately, if small can heads are used and positioned closely together, there might be a greater overlap in cutting area, but the spot size would need to be much larger---as much as 280+ microns---which is also an eventual challenge to quality. A third option would be to use small scan heads positioned a distance apart for a smaller spot size, but again creating a need for stitching because there is a much smaller overlap in the cutting area, as in Figure 23. How to Match Today's Laser Cutting Technology to Application Requirements (Part II) By Markus Klemm • Higher-priced double scan head laser cutters are not always faster than single scan head laser cutters. • 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. • If a laser cutting system integrator is married to par- ticular components---whether they are lasers, scan heads, etc.---consider it a red flag. FIGURE 21. Unequal number of parts on each half of the material. TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009