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2009 Laser Technology FSEA Editorial

 

 

Trends in Laser Cutting Applications
Written By Tom Hrutky for FSEA Magazine
May-June, 2009


Much has changed since the introduction of lasers as a tool for paper cutting nearly thirty-five years ago. Advances in laser technology and paper handling have combined to lower equipment costs and increase both speed and capacity. And now that more is generally understood about the advantages and applications of this process, it rapidly is becoming the tool of choice for many diecutting operations where extremely detailed work is required. Laser cutting is a process that becomes essential when, for a variety of reasons, the requirements of a job exceed the capability of a blade cut.

Until recently, companies producing most of the laser application work were outside of the realm of printers and finishers. This primarily was because of the infrastructure required to support high-powered laser systems. But as history has indicated, technology tends to become more accessible with time. Now, equipment is available that requires less specialized engineering expertise to maintain and can be installed easily within a conventional printing environment. If this trend continues and equipment costs come down, laser cutting soon could be on the list of in-house services for many finishing shops. When used appropriately, laser cutting can be successfully combined with many other finishing processes with spectacular results. It remains true, however, that if a project can be cut with a conventional die, that is typically the most cost effective way to go for the present.

How the Process Works

In simplest terms, laser cutters use a focused beam of light to scan art onto, or completely through, material. No physical cutting tools make contact with the stock. Therefore, the level of detail possible in a laser-cut design is primarily limited by the durability required of the finished piece. Designs are created by moving the target sheet under a stationary beam, moving a beam over a stationary target sheet, or by a hybrid system utilizing a combination of both actions.

The first method described is called a XY cutter and the target sheet is typically held on a vacuum table that is moved orthogonally under a perpendicular and stationary laser source. On some equipment, several stationary laser sources exist so that multiple identical pieces are cut simultaneously. This style of cutter is what is used most often for cutting wood, plastics, and other thick materials. The moving target table can be quite large—in some systems measuring ten feet or more. In certain applications, the laser can be used to cut through a stack of material yielding multiple copies per cutting beam. However, the cut quality often is degraded proportionately to the thickness of the stack.

The second style of cutting moves the laser beam over a stationary target sheet. This can be accomplished in two ways. The beam can be reflected through two 45-degree mirrors that move parallel to the target sheet in a manner similar to the target table of the XY cutter. These mirrors reflect a horizontal beam downward, perpendicular to the sheet. Gantry-style cutters can be designed with a wide range of laser power and potential scan area and have the bonus of providing a constantly perpendicular cutting beam. These systems often are faster than XY systems as the mirrors can be moved more rapidly than a large vacuum table. The speed is limited only by material thickness and how quickly the mirrors can be moved over the target area. Frequently, gantry cutters are preferred over XY cutters for thinner materials such as paper and Mylar. This also is the cutting method used by some of the smaller portable or desktop laser systems. Because these small machines operate at relatively low power levels, the beam can be modulated off and on quickly, giving the machine a pulse-like effect that can render some remarkable results. These are typically hand-fed systems, and though the quality can be excellent for cutting prototypes or limited quantities, they are relatively slow for production purposes.

Another method is called a Galvo and has two XY mirrors, driven by small devices called galvanometers, which remain in one position over a stationary target sheet and steer the beam by changing its angles. Because the mirrors remain in the same location over the target sheet, the angle of the beam becomes increasingly oblique as the cut area’s diameter becomes larger. A Galvo’s beam can follow a vectored path faster than the eye can follow because its movement is only limited by the inertia of the small lightweight mirrors directing it. The angular change in the cutting beam unfortunately does limit the material thickness that can be successfully cut and also the size of the overall scan area. Galvo systems are extremely fast when the art being cut is a continuous vector, but it must power down the beam at the end of each cut and power up again after it moves to the next target cut. So, the complexity of the cut art, total length of the cut, and number of holes being cut determine the production speed.

The previously described systems are vector-driven and cut a narrow path that would typically be anywhere from .004” to .006” in width. That would be determined by the diameter of the laser beam. In many cases, they also have the ability to turn down the laser power or speed up the scan to achieve a cut that only goes partially through the stock. This ‘kiss-cut’ can act like a conventional cut score or create beautiful effects on printed or duplex stock. Being a single narrow cut, all these systems leave pieces of scrap when they cut completely around an element of a design. These scrap pieces are typically removed after cutting by a vacuum device.

Presently, the most effective high-volume laser cutter in the industry is a unique hybrid system that moves the target stock through the machine in the Y direction, much the same as a conventional offset press, while the laser scans across the sheet continuously with an overlapping pattern in the X direction. The cut image is defined by interrupting the laser’s path with a reflective copper template that has the art etched through it. This is produced using a process similar to that used to etch electronic circuit boards. This style of cutter can cut up to 3,000 sheets an hour and leaves no scrap to vacuum away. That is because the faster-style scan completely covers the area to be removed and vaporizes it. With this system, the laser scan area, not the complexity of the design, determines both speed and cost. Because its sheet-fed system utilizes conventional paper handling methods, it is naturally compatible with other offline processes such as foil and emboss.

These hybrid systems utilize 4,000-watt lasers. To put that into perspective, a typical XY, Gantry, or Galvo system can use 200- to 400-watt lasers if their mirrors are liquid-cooled— 200 watts would be the upper limit otherwise, and desktop cutters are not often over 100 watts. It is the hybrid’s ability to accurately utilize this level of power that makes its high production speed possible.

There are of course, other types of equipment, including some continuous web cutters that utilize a Galvo and even a hybrid system that uses a template in a step-and-repeat fashion, but the XY, Galvo, and the hybrid template machines are presently the major systems used for laser cutting paper.

Paper Choice

Choosing a paper stock for a laser cut project is extremely important as most stocks are produced for qualities other than laser compatibility. Most are formulated for an ability to be embossed, diecut, or scored cleanly, in addition to handling the specific requirements of whatever printing will be used.

Because of the nature of a laser cut, there can be some discoloration immediately adjacent to the beam’s path on the target side of the sheet. This effect can be worked around by printing a neutral color on the target side, designing the piece so the target side is not seen, or utilizing the discoloration as a part of the design, such as an “antique” look to a lace pattern. However the best solution to this potential issue is choosing a stock that cuts cleanly in the early design stages. Discoloration is most often found on stocks having a relatively high percentage of recycled material, perhaps more than forty percent. This discoloration can become progressively more noticeable with time. Archival and 100 percent cotton papers are typically without any discoloration and remain that way for years. Discoloration also is affected by the thickness of the stock. A thick stock exhibits the effect more than a thin one because more material has been vaporized.

Getting the stock test-cut is the best way to avoid quality surprises later on. This should ordinarily be a free service and encouraged by laser cutters as a part of every job where an unfamiliar stock is being used. Also, laser cutters will be able to recommend stocks with which they have had good results in the past.

The Future of Laser Cutting

Laser cutting, as a graphic art medium, still is relatively in its infancy. Though it has been used successfully by most greeting card companies for over 20 years, it is just now beginning to find much wider use in other markets such as party accessories, stationery products, insert ads, and direct mailings. It is no longer a high-priced novelty medium reserved for limited quantities and high-end applications.

Within the last couple of years, one of the most rapidly growing uses of laser cutting has been in packaging. The unique qualities of laser cut surfaces add elegance to food and cosmetic packaging that would be difficult to achieve in any other way. Cut openings can have a delicate visual quality and offer a subtle peek at the product or allow customers to sample scented products. The tactile quality of cut paper also creates an additional level of interest. In the highly competitive field of packaging, laser cutting has given manufacturers a new tool with which to differentiate their products. Increased demand, lower equipment costs, and higher volume capabilities suggest there are lasers in the future for many finishing shops.