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FLEXO Magazine : October 2009
www.flexography.org OCTOBER 2009 FLEXO 55 the laser control software, which is adjusted accordingly. If a laser cutting machine does not integrate inputs from a cam- era system to the laser cutting controls it does not have a way to make needed corrections. Tight systems integration where one component (the camera) communicates with another (the scan head) is key to the higher quality output of today 's best- in-class laser cutters. The quality of the laser source itself will also have bear- ing on the cutting quality possible. Better lasers with smaller spot sizes (e.g. 210 microns) will facilitate crisp cuts, IF the control software uses advanced algorithms to move the better shaped and smaller sized beam along. Better quality lasers combined with advanced laser control software will also avoid the excess heat that can literally muck up the works in label applications where excess heat can melt adhesives onto release papers making it difficult to automatically remove la- bels from the release papers in subsequent production steps. The type of laser tube a system uses---open or closed---will also have bearing on how the laser can be controlled and how this affects cut quality. Although open, unsealed lasers are getting better in quality, they are still rarely up to the demands of many applications. There are several intrinsic problems with an open laser tube design. CO2 is usually one of several gases in a laser tube, with helium, nitrogen and hydrogen making up the balance. The proportion of each of these gases in the mixture will affect the laser power. This ratio is apt to shift in an open laser tube design. With open tube designs there is a requirement to frequently change one open laser tube CO2 tank for another. This makes it nearly impossible to save settings because there almost always is a difference in gas mixture ratios from one CO2 tank to another. These shifting ratios affect how the laser powers and the quality of its cut. To achieve the same quality cut, an opera- tor will need to fuss with adjustments every time he/she switches tanks, and even then, there will likely be variations. In contrast, the sealed laser tubes are not as likely to change in gas ratio composition and only require replacement every 10,000+ hours of operation. This translates into a much better ability to control cutting and to get a consistent result. CUTTING SPEED VS. WEB SPEED Today 's laser cutting systems are faster for a variety of reasons. One is that higher-powered lasers that cut faster are more affordable, such that most users of laser cutting technol- ogy today opt for 200-watt+ systems. Secondly, the more sophisticated algorithms used in today 's better quality laser cutting machines are able to shave milliseconds off of each cutting operation, which cumulatively result in faster cutting speeds. The third and most important reason why the better quality laser cutting machines of today are faster is that they are able to better optimize the cutting sequence resulting in much faster web speeds. To illustrate the impact of software that can optimize for web speed see the first example of the U.S. map shown in Figures 12 and 13. In each figure the blue dotted lines show where cutting has stopped while the laser repositions for a next cut. In Figure 12 a cutting sequence is shown where there is absolutely no optimization done by the software on how the cutting sequence should proceed. In such non- optimized cutting, the path follows the lines of how the vector drawn image was first created in Solidworks or equivalent software. This non-optimized cutting sequence is so slow that the web would only be able to advance intermittently. In Figure 13, we see a significant improvement in web speed that is done automatically by the sophisticated algorithms in the control software. This improved web speed is determined during the setup of the job, before it is run. A second step in the web speed optimization during job set up is shown in Figure 14 and 15, where the maximum web speed is 17 percent higher and is achieved by splitting the single image of the US map up into two separate images, and optimizing the web speed for the split image. This optimization is also done automatically by the software. In fact, the software can tell the operator whether it is best to cut the geometry as a single image, two images, four, etc. Today 's better laser cutting technology can seamlessly stitch these multiple images together, which is done in this case to maximize web speed, and in other cases FIGURE 8. Low frequency laser output. FIGURE 9. Lack of optimizing laser beam movement. FIGURE 10. Same as Figure 7 with cutting speed doubled. FIGURE 11. Optimized cutting. FIGURE 12. Lack of optimization during cutting. TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009