Gas up the laser

When it comes to deciding on the right type of laser cutting system, fiber lasers have been capturing recent headlines due to their speed advantages. However, CO² lasers have been supplying much of the laser cutting capacity in North America. The fact of the matter is CO² lasers have a stronghold in the manufacturing industry because of their longevity. They simply have been around for a lot longer than the fiber laser systems and continue to be a popular choice for customers searching for the right system for their specific applications.

“There is an install base of about 50 to 1 of CO² lasers versus fiber lasers,” says Mike Millette, laser product manager for Prima Power. One of the reasons is because CO² lasers can cut varying materials and thicknesses without challenge—cutting up to one inch thick stainless steel. Shops that focus on custom fabrication, the CO² laser offers the most flexibility.

What is the fundamental difference? When it comes to laser systems, the difference is found in the way the beam is created and the wavelength that is emitted. “CO² lasers create the beam using a gas as a gain medium, and the beam produced is of a 10.6 micron wavelength,” says Brett Thompson, sales engineer for TRUMPF Inc.

The energy represents what we commonly refer to as heat or infrared radiation. “It is transmitted from the laser to the processing head via line-of-sight copper mirrors enclosed in an external beam delivery system,” explains Bob Kloczkowski, regional sales manager for Rofin-Sinar, Inc. CO² lasers convert electric power into heat energy with approximately 10 per cent becoming the actual laser beam.

The transportation of the beam to the focusing lens also changes depending on the type of system that is used. The fiber laser uses “a fiber to transport the laser beam to the cutting head, where the CO² laser uses optics configured in a special way so they don’t suffer from beam divergency,” says Stefan Colle, laser product sales manager for LVD Strippit.

All CO² lasers are not created the same. In the fabricating industry, there are two designs that are generally used: Fast axial flow (FAF) and diffusion-cooled slab lasers. The methods of excitation and cooling of the carbon dioxide laser gas mixture is what categorizes these two different options, according to Kloczkowski. Although there are differences in the construction of the beam, the wavelength still remains at 10 micron.

At 10 micron, the laser beam wavelength is readily absorbed by most metals, making it a flexible option for most industrial metal cutting and welding applications. Because of its absorption characteristics, it provides a more forgiving parameter window for most metal applications. However, Kloczkowski explains that the CO² laser cannot be used with highly conductive metals such as brass, copper and aluminum.

This type of laser, though, is able to work with a large variety of metals as well as non-metals, including wood and plastic, making up for its limitations. The wavelength of a fiber laser is unable to cut these types of materials. This allows for more offerings when it comes to customers’ requests.

Setting aside some material exceptions, there are many advantages to choosing a CO² laser system for a manufacturing facility or job shop. “The primary advantage of a CO² over a fiber laser is its ability to cut thicker stainless steel with smoother edge quality than what a fiber can do,” says Jason Hillenbrand, laser product manager for Amada America Inc. From Amada’s stand point the real advantage is the fact that the CO² option can cut thick mild steel with a bit better edge quality as well as its speed.

Solid state, fiber laser systems are best suited for up to six millimetre thick material. Millette explains that this is where you get the speed differential and therefore the payback on the cost of the machines. He uses the example of a company that makes rail cars or something similar in nature, where a good edge quality is needed in half-inch, three-quarter inch or one inch material, this is where the CO2 laser has the advantage.

“As you get into thicker material the cut speeds become closer and closer together. One thing that is a detriment to fiber is when cutting thick material, the beam is so small that it is difficult to get parts out of the skeleton. All of the time you would gain, potentially, with more speed in the processing, you would lose getting the parts out of the nest,” says Millette.

The initial investment cost of the CO² laser system tends to be lower than the fiber option, and those working with a wide variety of materials generally see this as a reasonable choice. In addition, the overall performance and quality of the results tend to be higher compared to solid-state laser cutting,” says Thompson, who adds, “When processing stainless steel the CO² laser produces a substantially more cosmetically appealing edge.

Processing stainless steel with a solid-state laser produces a more striated edge and the stainless steel has a lower burr limit.

Fabricators who process high quantities of stainless steel, or who are especially concerned with the edge quality, would be more inclined to install a CO² laser system.”

Another area of concern when purchasing a new machine comes with operating costs. Even if the machine investment is the right price, a high operating cost can soon eclipse the initial savings. “The electrical efficiency of the CO² is approximately 10 to 12 per cent… [whereas] the electrical efficiency is 30 per cent for a fiber laser,” says Frank Arteaga, head of product marketing, NAFTA region, for Bystronic Inc.

What this means is that fiber laser requires less electricity to create the laser beam than its counterpart. This can equate to overall costs savings. However, another factor in operating costs is cutting material and thickness. When dealing with mild steels, the fiber laser has a lower operating cost, generally as low as $5-13/hour, whereas the CO² costs $9-15/hour. However, it is cutting stainless steels and aluminum where the cost differential is minimal.

“They get closer together [in cost] because [CO²] use nitrogen in the cutting and with fiber you have to use more nitrogen pressure and volume to accomplish the same [result]…so you would spend a bit more on the nitrogen cover gases than you would on a CO² . Both systems can be up to 25 dollars to cut aluminium or Stainless steels,” says Millette.

Overall, the decision to purchase or use one system over the other is predicated on a shop’s general applications. There is no fast and hard rule for choosing one over the other. The fiber laser system, the more modern of the two, offers many cost-effective solutions. However, “For a smaller job shop it is very difficult to make up a hundred grand in operating costs to the initial purchase price of the machine where you are only running the machine maybe 30 to 40 hours a week,” explains Millette.

The strength of the CO² machine comes in its usefulness. “CO² remains the most flexible laser cutting technology,” said Colle. Being able to cut various materials and thicknesses gives this machine an advantage. However, having both fiber and CO² lasers in the shop is a sure fire way to maximize the features of both machines.