Today’s lasers can cut sheet metal, even thick plate, and achieve high-quality edges, meaning secondary deburring operations are not required. “Laser cutting has replaced many punching and plasma operations because of that far superior edge quality,” says Dustin Diehl, laser product manager, Amada America Inc.
In the mode
Fiber lasers produce edges in thinner material very similar to the high-quality edges CO2 lasers produce, but as material thickness increases, edge quality can decline.
A newer technology, however, changes the beam properties of the fiber laser, allowing it to cut thick material with the same high-quality edges as CO2. And that technology has to do with the purity of the beam delivery system.
One of the benefits of a fiber laser is it has a TEM 00 beam mode that has very high spot density so all of the power is focused into a very small area. This allows fiber lasers to cut material at high speeds. But while the small beam diameter can evaporate the material out of the cut in thin material, in thick plate that beam doesn’t provide enough room to allow that material to be removed.
Amada’s ENSIS fiber laser technology changes the beam mode to efficiently process thin-to-thick materials without additional machine setup. The technology uses a variable beam control unit that allows the mode to change from a TEM 00 to the TEM 01* mode that provides a wider, flatter beam distribution, which provides good edge quality in material 1/4 in. and thicker. This is done with Amada’s own fiber engine design.
Amada’s ENSIS technology allows a 2-kW fiber laser to cut thick material.
“With this technology, we have the ability to truly change that mode and open up the beam to make it like a CO2 laser, and that gives us more room to remove that material,” Diehl says. “This allows us to duplicate the high-quality edges CO2 lasers produce on thick material with a fiber laser.”
The ENSIS technology also allows a 2-kW fiber laser to provide 4-kW CO2 cutting capabilities. This makes it more cost effective to cut the thick material.
“Amada is showing you don’t need all that power for good edge quality,” Diehl says. “Those higher wattages run at a higher cost of operation and a larger initial investment. We’re cutting 1-in. plate on a 2-kW laser, and we’re getting a great edge quality.”
Other technologies, on both CO2 and fiber lasers, are available to produce high-quality edges. Improved cutting times and repeatable edge quality are possible through Amada’s process monitoring capabilities.
A 1-in.-thick part cut on Amada’s ENSIS 3015 AJ fiber laser cutter.
A laser can’t attain good edge quality without a good pierce. With pierce monitoring, the laser only starts cutting after detecting the beam has pierced through the material.
“There are different pierce routines per the application,” Diehl says. “In 1/4-in. and thinner material, no technique is involved. You just bring the cutting head down to the material, blast a hole through it and start to cut.”
But a different technique is needed with thick material. “You need to allow some of that material to be removed as you are ramping up power,” Diehl says. Amada has pierce routines with the desired height much further above the material before starting the drilling or pecking process. Different amounts of power are introduced as the head is coming down to the desired cut height. By the time it gets to the desired height, there is enough of a hole to make one clean out blast and then start cutting. All of this is done in a matter of seconds.
A side blow feature causes the molten material on top of the plate, which can affect edge quality, to be removed as the beam is coming down and creating the hole. Also, a quick blast of oil may be used. This allows any of the molten material to bead up and then the side blow feature moves those beads away from the nozzle so it doesn’t become contaminated and affect edge quality.
Amada’s ENSIS fiber laser technology uses a variable beam control unit that automatically adjusts the laser beam’s properties to process a range of material thicknesses.
Cut process monitoring is another feature “that detects if the laser machine is starting to struggle when cutting,” Diehl says. This feature provides good edge quality through auto-plasma detection, which is used when cutting steel and aluminum with nitrogen as the assist gas. As the laser melts the steel and the nitrogen removes the molten material from the hole, if the laser is going too fast or the focus is off, the nitrogen and molten material create a plasma.
“You’ll start to get sort of a blue plasma plume on top of the material,” Diehl says. “When that is detected, the machine slows down, gets through that difficult spot of material and then when it stops detecting that plasma, it picks back up and resumes cutting at the commanded speed, producing clean edges.”
To absorb heat generated in thick plate cutting, a water-assist cutting system (WACS) cools the material during laser cutting, allowing thick material to be efficiently processed and parts to be closely nested. The system puts a fine water mist on the material during cutting that absorbs into it and helps keep it cool. With reduced heat buildup, the laser can cut closely nested parts increasing material utilization and eliminate the need of traversing to different areas of the material. This heat dissipation technique requires extra machine travel time.
Cut process monitoring, pierce monitoring and WACS work together to allow a range of materials to be processed without operator setup or intervention.
“With mild steel plate up to approximately 1/2 in. or 5/8 in., sometimes we’ll just do a side blow as we’re doing a quick peck pierce,” Diehl says. “Anything above 5/8-in. mild steel plate, we’ll definitely use the water-assisted cutting, as well. We have different levels of techniques and technologies to get through the full range of cutting up to 1-in. plate.”
The nozzle and assist gas also affect edge quality. The most common assist gases for fiber and CO2 laser cutting are oxygen and nitrogen and they are selected based on the type of material, its thickness and the edge quality required. Nitrogen is used with stainless steel, aluminum and thinner mild steels. Oxygen is used with thicker mild steels, in most cases. Shop air also can be used when cutting thinner mild steel and aluminum.
Also for aluminum, Amada offers a gas mixer that introduces small amounts of oxygen mixed with nitrogen for good edge quality and dross-free cutting.
It is best to use a specific nozzle per application and, therefore, some machines are equipped with automatic nozzle changers. “You change nozzles per material thickness, and material thickness corresponds with the amount of pressure you’re going to use to get through the material,” Diehl says.
Even within the nozzles, there’s a lot of new technology whether it’s with a standard single nozzle or a double or coaxial nozzle, which has internal venturies that help mix the gas around the beam and help regulate gas flow, Diehl notes.
Also, nitrogen requires a high gas flow to cut thick material, so a large-diameter nozzle is required to attain good edge quality.
Amada’s cut process monitoring feature makes adjustments to the laser cutter when it detects plasma is present.
The right edge
The operator himself does have some control over edge quality by setting up the machine properly and performing the basics, such as checking the consumables. This includes cleaning the lens at the beginning of every shift or at least once daily and making sure he has a good nozzle and good nozzle center. He can also adjust power, frequency, duty, gas pressure, feed rates and the focal position to try and obtain good edge quality. With the AMNC 3i control, different user levels can be defined. This allows full access to more experienced operators and limited access to certain features of the control to newer or entry-level operators.
To absorb heat generated in thick plate cutting, Amada’s WACS feature applies a fine water mist on the material during laser cutting.
Edge quality is, of course, subjective. “It is up to the end user to find what edge quality fits the desired application,” Diehl concludes. “If they know the part is going to be welded all around and don’t mind a little bit of a burr, they can speed the laser up and cut a little faster. With pushing the machine faster and faster, the edge quality is one of the first things to be sacrificed.
“Amada provides what we call premium edge quality,” he adds. “Our machines are going to start at the highest level, regardless of if it is necessary or not. It is up to the end user to decide about the edge quality.”