Laser Die Cutting: “Making the technology pay”; Converting Today (UK); November 12, 2008

More on Laser Cutting
By Tom O’Hara, President, Spartanics

Laser cutting, a.k.a. digital die cutting, uses high-powered 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 towards the substrate effects the specific cuts that the artwork requires. Because cut away parts 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 practical industrial uses in the ‘80s. 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. Today’s lower cost laser cutting systems made from less expensive components have far superior capabilities to the expensive systems that were designed and engineered only a few years ago. At the top end, state-of-art laser cutting systems are able to consistently cut far more intricate designs in a wider range of substrates and with tighter tolerances than ever before.

The challenge to those making investments in laser cutting technology is to source machines that are well-matched to application requirements. One can still find laser cutting systems in the marketplace that force compromises in quality or production output that should not be brooked in light of engineering advances in laser cutting technology. On the other hand, those with more straightforward application requirements are often well-served by lower cost models of laser cutting systems that are powerful and versatile enough for the jobs at hand.

Matching laser cutting technology to application requirements involves study of the difference between out-of-date technology, low-cost systems, and high-end systems, as summarized in Figure 1.

Laser cutting systems that were engineered just a few years ago were often not up to the challenges of cutting complex designs, especially when there were many sharp angles in the artwork geometry. One can still find inferior laser cutting systems being sold today that similarly are plagued by the quality problems usually evidenced by pinholes at the start and stop of cutting sequences or burn throughs.

Improved quality in today’s better quality laser cutting systems is seen not only in better edge quality but in the far more consistent cut-to-print accuracy afforded by the new level of systems integration in the best-in-class laser cutting machines. For example, earlier systems had no way to compensate for the rotation in the working field that can occur as the web moves through the laser cutting machines. Today’s best-in-class systems not only use high resolution cameras but also integrate the camera information with the laser software that is controlling cutting. This means that as the camera systems determine any X/Y offset values, they communicate these to the laser control software, which is adjusted accordingly. If a laser cutting machine does not integrate inputs from a camera 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 bearing 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 labels from the release papers in subsequent production steps.

The type of laser tube one 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 is 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 operator will need to fuss with adjustments every time they switch 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.

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 technology 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.

Optimizing for cutting speed alone can result in slower web speeds and buyers of laser cutting systems are well-advised to ignore manufacturers’ claims re: cutting speeds and instead focus in on demonstrations of the ability of the system software to optimize for web speed. These web speed optimizations are done automatically by the better quality laser cutting systems and do not require any operator training.

The extent of systems integration in one or another laser cutting system can largely determine how user-friendly they are to operate and has great bearing on the production outputs that can be achieved. For example, older systems required users to obtain a separate camera system, and required operators to additionally master the camera control software. In contrast, today’s better quality laser cutting systems come with cameras fully integrated with the laser software. Operators do not have to learn set up of a separate camera system, as this is now done directly from the laser control software, and in the best-in-class systems only takes three simple steps.

The best case scenario of comparative shopping would include use of laser cutting system manufacturers’ contract manufacturing services. These would provide not only proof of concept but would allow expert software integrators to fine tune operations to your exact application requirements.

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Tom O’Hara is President of Spartanics, which manufactures the family of Spartanics Fineprint Laser Cutting Systems as well as die cutting equipment, screen printing systems, and other equipment used by worldwide label converters.

 

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