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Laser Technology
Wednesday | 30 April, 2014 | 2:01 pm

An evolution in fiber cutting technology

By Jason Hillebrand

Above: Amada debuted the ENSIS-3015AJ at Fabtech 2013 in Chicago.

Advancements in technology result in fiber lasers that can also make the thick cut

April 2014 - For nearly a decade, fiber lasers have been making their way into the mainstream of the fabrication industry. During that time, manufacturers have seen a change in the number of machine tool builders using fiber technology, varying motion systems and increases in wattages.

Still, the continued rub against fiber technology has been the inability to adequately cover a full range of materials effectively, without compromising quality associated with that of CO2 production. Many end users have a certain comfort level with CO2 lasers and the edge quality they can provide in thick materials. CO2 lasers have a specific mode structure, or shape, that allows for greater heat distribution. This characteristic of CO2 lasers is one of the reasons why the edge quality of thick plate looks so smooth and clean.

Fiber lasers gaining traction 

The idea that fiber lasers cannot cut thick materials is, however, a misconception.  Fibers can and have been able to cut 1⁄2-inch, 5⁄8-inch, and even 1-inch mild steel. One of the problems has been that the mode or shape of the fiber laser has not been conducive to good edge quality in these thicknesses, when compared to CO2.

It begs the question, “Are fiber lasers going to replace CO2 lasers?” While there’s no definitive answer just yet, some laser companies are making great strides in developing technology that can be considered a true, all-purpose laser cutting system. At the 2013 Fabtech show in Chicago, Amada unveiled the ENSIS 2,000-watt fiber laser machine. Developed in partnership with Milpitas, Calif.-based JDSU, this system allows the fiber laser to manipulate laser beam properties, giving it the unique qualities needed for cutting thin material at high speeds and cutting thick material with CO2 quality and speed.

Comparing the two technologies, a 4,000-watt CO2 laser will have approximately 65 million watts per inch squared of power at its point of focus. That is the point where the laser beam is focused to the material to perform the cutting, or the “business end” of all that power. A 2,000-watt fiber laser will have approximately 100 million watts per inch squared of power at its point of focus. Why so much more? The beam properties of the fiber allow for a smaller focal spot, condensing the power, thus creating a narrow kerf and more wattage per inch squared. This is excellent for vaporizing material quickly and cutting at high speeds. When put into action, this is what is going on when fibers cut thin material and why a 2 kilowatt fiber can cut three times faster than a 4 kilowatt CO2 in thin materials. The faster you vaporize material, the faster the cutting head can go.

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Challenges persist

However, there is a shift as material begins to get thicker. That same narrow kerf now prohibits the assist gas from entering into the cut and helping with the overall cut process. Specifically in mild steels, O2 is necessary to help in the burning process of thick plate. When that O2 is choked off due to a narrow kerf, the cut speed must be reduced to allow the gas to “catch up.” This creates additional heat. Combined with other factors, the results can be heavy striations and dross.

Companies have found ways to manipulate the laser beam, extending depth of field (length of focal spot) and adjusting spot density, but this alone does not give the same edge quality and speeds of CO2 machines. It should be noted that edge quality is subjective, so this is not to say it is unacceptable edge quality, but for the general nature of this article and basic customer feedback, it simply did not compare to CO2.

For many shops, the preferred machine lineup has been to have both a high-powered CO2 and a fiber laser on their floor. Not considered ideal, it would be preferable to have a single technology that could achieve the extremely high cut speeds in thin materials and cut the thick materials with excellent quality, all in one machine; a machine that consumed a quarter of the power of CO2 and had none of the maintenance that CO2 requires.

Until Fabtech, Amada had been able to emulate a change in the mode on a fiber laser by using a specific optical setup in the cutting head. This forced the laser beam to convert to more of a CO2 style laser beam, resulting in an excellent cut in material up to 1-inch plate on a 4,000-watt fiber machine. While this was an alternative, there were a few items this could not resolve. First, it still required a lens change. This is a quick procedure, taking seconds to do, but just another manual intervention that manufacturers want to eradicate. Second, it could not change the beam properties enough so that it could still cut at the same speeds as its 4,000-watt CO2 counterpart.

Fabtech 2013 offered a glimpse into the future of fiber laser processing, with systems on display that are taking on that evolutionary challenge of making thick materials a true fiber application. For Amada, the ENSIS 2,000-watt fiber laser can cut thick plate, up to 1 inch, with the same cut quality and similar speeds as a 4,000-watt CO2 laser. Through continued research and development, a proprietary design can now change specific beam properties on the fly to allow for a different beam for every material thickness. In the past, this was not adjustable for either a CO2 or fiber laser. The new technology allows for continuously variable beam quality, meaning it automatically changes based on the material being processed. The other major factor is that this works without the need for any sort of lens change or additional setup. 

Weighing productivity needs, cost

What does this mean for the future of laser cutting technology? There are still several things an end user must evaluate before this question is answered. To quote a customer who purchased a fiber laser several years ago, when asked if he purchased the fiber because of the cheap operating expenses, he responded, “You don’t buy a machine because of the money it saves you. You buy it because of the money it makes you.” This statement has been validated over and over again when comparing the cost of making a part on a CO2 or a fiber laser. Operating costs are a very small portion of the cost per part breakdown. 

Productivity should ultimately drive the decision towards a specific machine or model. Generally speaking, when a fiber is cutting thin material (for a traditional 4 kilowatt fiber this may be considered less than 1⁄4 inch) it will outperform the CO2 because N2 assist gas can be used, allowing for maximum power output. This performance is a major factor in reducing the cost per part making the fiber a good choice. However, when the 1⁄4-inch threshold is reached, the assist gas will often change to O2, immediately putting the CO2 in a better position than the traditional fiber for speed and edge quality. In doing so, the process time advantage has gone to the CO2, making its cost-per-part less than the fiber, and the logical choice in this range of materials. Again, machine wattages and material types will impact these results, but for the more common conversation we can use this criteria. In addition to this, the clean cutting of thicker stainless steel has been of significantly less quality than that of CO2. 

With the advent of the new technologies debuted late 2013, some of these concerns and setbacks for fiber look to be changing. A 5,000-watt disk using new technology is able to process up to 1-inch thick stainless, while taking a leap towards edge quality closer to what CO2 can produce. A 2,000-watt fiber using new technology is cutting 1-inch thick mild steel with the same quality and near the speeds of 4 kilowatt CO2. The gap is closing. As with any technology, it is the natural evolution of development. The question of edge quality is subjective and can only be answered by the end user. Whether or not fiber will replace CO2 should not be the question. The question remains the same one it has been for decades, “What is the right machine for my company?” Ask that question first. The technology will answer the rest. MM

Jason Hillebrand is Laser Project Manager for Amada America Inc.

 

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