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A Guide to Laser Cutting Technology, Part 1

(April 2009) posted on Tue Apr 21, 2009

Laser cutters have evolved from prototyping tools to highly-productive finishing systems. Read on to learn about developments in lasers, control software, and other facets of the technology that make laser cutting systems a viable option for any shop currently using conventional, tool-based cutting machines.

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By Markus Klemm

To demonstrate how cutting speed potentially affects quality, consider Figures 4A-4D showing the laser cutting of a small folding box. In Figure 4A, the frequency of the laser output is 10 kHz, which is so slow that the single pulses of the laser give the cut the appearance of a dotted line rather than the continuous line cut that is desired.

Figure 4B shows results from a laser cutter without algorithms for optimizing the laser movement relative to the design geometry when the cutter is operating at a high speed. Here the cutting speed is too fast, and the scan-head mirrors cannot follow the contours of the artwork in a synchronized way, leading to inexact results. Contours that should be sharp are rounded. In this example, the mass of the device’s scan-head mirrors and what it takes to move this mass are not adequately handled by the control software. These problems are even more pronounced when the cutting speed is doubled as shown in Figure 4C.

In contrast, the result of using a laser cutter that can match the cutting speed to the part geometry and optimize the powering on and off of lasers accordingly is shown in the greatly improved quality output in Figure 4D. Here, the algorithms the laser cutting software is using can match the speed of cutting to the design geometry in an optimized fashion.

Improved performance in today’s laser cutting technology is seen not only in better edge quality but also in far more consistent cut-to-print accuracy. 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 unit. Today’s high-quality 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 adjusts the laser 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 in which one component (the camera) communicates with another (the scan head) is key to the higher quality output of today’s most capable laser cutters.

The quality of the laser source itself also will have bearing on the cutting quality possible. Better lasers with smaller spot sizes will facilitate crisp cuts if the control software uses advanced algorithms to move the 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 such heat can melt adhesives onto release papers, making it difficult to remove the labels.

Whether the system uses an open or closed laser tube also affects how the laser can be controlled and the quality of the cut it can provide. Although open lasers are getting better in quality, they are still rarely up to the demands of many applications. Open laser tube design has several intrinsic problems. 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, users must frequently change one open 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 tank to another. These shifting ratios affect laser power and cut quality. To achieve the same cut quality, an operator will need to fuss with adjustments every time tanks are switched, and, even then, there likely will be variations.

In contrast, 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 much better ability to control cutting and get consistent results.

This article continues in A Guide to Laser Cutting Technology, Part 2.


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