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Beam shaping helps fiber lasers cut thin and thick metal parts

Jun 19, 2023

Fiber lasers are starting to use a beam shaping technology that changes the beam's energy profile to match the cutting needs of the application. Mazak Optonics

Metal fabricators who’ve been in the business for a while can be sentimental about the CO2 laser. Sure, machine maintenance wasn't simple, but a finely tuned system, with the beam centered in the nozzle and a beam path free of debris, could deliver buttery smooth, dross-free edges. For most of the past 10 years, fabricators who wanted edge quality (especially on plate) chose a CO2 system, while those who needed speed chose the fiber laser. This calculus, however, is starting to change.

"Brute strength of total fiber laser power isn't the answer."

So said Al Bohlen, president of Mazak Optonics, during a late April open house at the company's Elgin, Ill., facility, an event where the company formally introduced its OPTIPLEX 3015 NEO 15-kW fiber laser cutting machine.

In recent years laser machine vendors have introduced innovations that alter the beam characteristics with the aim to expand the fiber laser's capabilities to effectively cut a range of material grades and thicknesses—not just thin sheet. At its April event, Mazak Optonics described its approach to making the fiber laser more flexible.

As Bohlen explained, the system uses more than the "brute strength" of high fiber laser power. Its nLight fiber laser source uses beam shaping technology that, together with a Mazak cutting head, can create different heat profiles as well as different beam diameters and focal lengths to produce high edge quality in both thin and thick material.

Rather than being delivered through a single-core fiber cable, the laser travels through a multicore cable. In essence, the technology controls how power is distributed over the multiple cores of the fiber. "We can proportion how much laser power goes through each core," Bohlen said. "This allows us to create a cooler core of the beam and concentrate more energy on the outer edges. We’re moving the heat of the fiber laser through different elements of the core, and in doing so, we create different modes."

Historically, most fiber laser cutting machines have been sold with lasers having a single beam profile, with high power density in the center and low power density on the edges. "This creates a shape with heat in the center, like a point of a spear. With great power density comes incredible capability to cut very fast in thin material," Bohlen said. But as material thickness increases, cutting with such a beam power profile becomes more challenging. "The assist gas has to work very hard to get molten material out of the cut," Bohlen said. "It's fighting its way through the cutting process." As material gets thicker, the gas flow attempts to reverse direction, and the cut gets slag, dross, and heavy striation.

Over the years optics have been able to increase the fiber laser beam diameter, but using the same heat profile—high in the center, low around the edges. Altering the beam profile at the source, before the light reaches the cutting head, creates a beam-energy distribution with more energy around the edges and less in the center.

"With all this, you still need an intelligent cutting head that can take this beam and do something with it," Bohlen explained. A new Mazak cutting head has optics that can accommodate the larger beam diameter emitted from the multicore fiber and send it through the center of a small nozzle orifice. "We can take that doughnut mode and now make it smaller and control its diameter. The [cutting head] remains an important ingredient to the recipe."

High energy on the outside of the laser beam also helps smooth the striations and eliminate taper, especially when cutting very thick plate. That taper is created as molten metal struggles to evacuate down the narrow kerf, with a beam energy profile that's relatively cool on the edges and hot in the center. Waterjet and plasma systems can tilt the torch to eliminate taper. Now, with fiber laser cutting using beam mode and diameter control, "I can cut a 1-in.-thick part, dead straight," Bohlen said.

Such beam shaping technology isn't entirely new. Mazak Optonics introduced its OPTIPLEX S series with beam shaping technology four years ago (the "S" stands for beam shaping), including a 4- and 7-kW system. The April event unveiled the technology in a 15-kW system.

The cutting speed for many materials rises faster than the cutting power. For 0.25-in.-thick mild steel, nitrogen cutting speed moving from a 10 kW to a 15 kW can double. "It's double the speed, but not double the power," Bohlen said. "That's because it's not just power but also mode control that gives you a clean, dross-free part. It's not just brute force."

Bohlen described nozzle technologies that reduce loss of nitrogen assist gas and improve assist-gas flow through the kerf. He discussed advances in nitrogen generation, and the newfound capabilities of gas mixtures as well as air cutting. "With higher power, we can cut a greater range of material and a greater range of thicknesses with air," Bohlen said, "not with nitrogen." He added that lasers do need clean, ultra-dry, high-pressure air (400 PSI) produced by specialized systems—far different from standard shop air. "But for many operations, once you invest in such systems, you will be able to cut most anything you need to cut with air."

Bohlen also described new control technology that can manage changing beam profiles on the fly—this includes using one beam profile for piercing and another for cutting. It also offers so-called "camera nesting," where an overhead camera identifies available space on a sheet available for cutting, then draw from available parts to fill it. Operators can allow the controller to populate the space, or they can place the parts manually.

A new upper panel on the machine control can handle various aspects of scheduling and production control, which can be particularly critical for systems integrated with automation. The rise of automation in laser cutting has been hard to ignore, especially over the past three years. According to Bohlen, while many operations among Mazak's customer base still buy stand-alone lasers, most don't remain that way.

"About 50%, about every other machine we sell, has automation on it from the beginning," Bohlen said. "If we include stand-alone machines that have automation added to them within a two-year window, that number jumps to 70%. That number was 30% just five years ago."