Adapting Metal Cutting to Higher Power, Higher-Speed Lasers
Article From: October 2019 Manufacturing Engineering, Bruce Morey, Senior Technical Editor
Increasing power is easy, but what effect does that have on peripherals, beam delivery, cutting gas delivery, and automation?
Using lasers to cut metal, especially sheet metal or tubes, continues to show its value. The market is becoming dominated by the newer solid-state fiber laser over its CO2 gas rival. Fiber’s advantages in ease of operation, packaging and efficiency are clear.
New higher-power, faster lasers are making a big impact on the market. Dustin Diehl, laser division product manager for Amada America Inc., Buena Park, Calif. noted that speed is what people are typically after with their desire for higher power lasers, especially thicknesses below 1″ (25.4 mm). “We’re cutting quarter-inch mild steel three to four times faster than we were just a few years ago when CO2 was still a preferred tool,” he said.
Another point Diehl made is that higher powered machines can allow you to replace multiple machines with one purchase. “We are seeing customers replacing older, lower powered systems with fewer higher powered systems and regaining floor space, sometimes replacing three or four older generation systems [with one],” he said.
A particular care he noted is how much assist gas these higher power systems can consume, a comment made by others interviewed for this article. While it is true that higher power allows using nitrogen, eliminating worries about oxides, pure nitrogen still needs to be purchased and can be expensive.
“There has been a lot of development at Amada in nozzle technology, and in mixing different types of cutting gases,” he explained. Their nozzles mix a small amount of oxygen with nitrogen, lowering the amount of nitrogen needed, improving cut speeds while maintaining edge quality, according to Diehl. “Advancements in the gas mixing and the nozzles has helped reduce those costs.”
Faster Lasers, Faster Automation
Diehl also observed that faster cutting speeds affect the entire system, including downstream automation. “When a machine is putting out three or four times more work, that is going to create a bottleneck in, say, bending operations, which we at Amada have adapted to as well, with robotic bending solutions,” he said.
Another key trend is the ease-of-use fiber lasers has brought to the art and science of cutting metals with lasers. Both delivery via an optical cable and the general trend in CNC controls now operated with touch screens and icons means operators do not need to be as skilled today to run complex laser cutting operations. “It’s all touch screen; operators view different windows and they can enhance, zoom, spin, rotate the part to get a different look at it,” said Diehl. “It has come a long way.”
A good example is Amada’s ENSIS line of automated fiber laser machines, available in powers up to 9 kW. It also features automatic beam adjustment, enabling continuous processing of thin-to-thick materials with no lens changes.
When customers use high power to get faster cutting, he agreed that now the problem becomes having automation systems that can keep up with the higher speeds. “Companies that don’t put in automation, they don’t get nearly the throughput. They just can’t keep up with the machine,” said Jeff Hahn national product specialist for MC Machinery Systems Inc., Elk Grove Village, Illinois.
Recognizing the continued importance of automation, Mitsubishi Electric Corp. (the parent company of MC Machinery) purchased the Swiss automation specialists ASTES4 in 2018. “They specialize in part removal [and sorting] from sheet automation, something that will be demonstrated this year by us,” said Hahn. “The challenge our customers are seeing, even with automation, is sorting the parts. When you buy a high-speed machine, even with high-speed material handling, somebody still has to physically go through and sort out and de-nest the parts.”
That starts to create a bottleneck, which the latest MC Machinery automation system developed by ASTES4 is designed to alleviate. It is a pick-and-sort system with four pick-up arms, so it can remove four parts at once. “And while that system is picking up four parts at a time, we can still be cutting on the machine and going to conveyors with sheets,” he said. Sending those parts that need sorting and de-nesting down conveyors creates multiple de-nesting points throughout the system.
Lot sizes are growing smaller as well, as customers respond to a market that wants mass customization. As lot sizes becomes smaller, the planning process starts to become the bottleneck. “So, we are automating that as well,” he said. That leads into the general notion that programming needs to be more intelligent. “We have a feature called M-cut with our cut-planning software that allows cutting grid patterns without shutting the beam off,” he said, though it is limited to 16 gauge thickness or less.
The company’s Advance 800 Series EX-F fiber laser is a good example of how these trends come together. It comes standard with Mitsubishi’s all-in-one Zoom head, which uses beam mode manipulation to process a full range of materials automatically without any setup, according to the company.
Higher Power Complications
As noted in the discussion of automation above, higher power and higher speeds can create issues with parts production. Laser users need to understand how fiber lasers well above 6 kW—and in some cases up to 12 kW—operate and how to use them effectively.
“In [the U.S.] we are seeing many of our customers wanting increased wattages,” said Jeff Tyl North American sales manager–fabrication for Murata Machinery USA Inc., Charlotte, N.C. “We are offering 2.5, 4, 6, and now 8 kW machines,” he said. “And, we are testing 10 and 12 kW machines.”
Does Tyl think higher power is a good thing? “It depends. When someone asks about 6 kW or higher, I always ask them what they are cutting,” he answered. Ideally, high wattage means high speed. But he noted that high power offers more speed advantages in thinner gauges, especially in thicknesses from 0.25-0.75″ (6.35-19 mm).
A distinct advantage of solid-state lasers over CO2 is the ability to deliver a beam along an optical cable. (Another is their ability to cut more reflective materials.) Murata Machinery offers different diameters of cables, including smaller 50 and 80 µm diameters as well as the more standard 100 µm. The 50-µm diameter cable is offered on lasers up to 2.5 kW, 80 µm up to 6 kW and 100 µm above 6 kW. The smaller the beam, the better the cutting performance, according to Tyl. “For example, our 50 µm beam at 2.5 kW will outperform a 100 µm at 6 kW, in any [material] of 0.25″ (6.35 mm) or below,” he said.
Peripheral Equipment Matters
There is more to cutting than power. Other considerations include the cutting heads, nozzles that deliver the assist gas, the drives that move the cutting head, and dust collectors. “They all make a huge difference,” said Tyl. “One of the biggest things to consider is the dust collector. Higher powers mean creating more potentially flammable substances, and if undersized, the efficiency of the laser suffers.”
Is there a limit to the effectiveness of higher powers? Perhaps. “I tend to think that 8 kW is the magic number at the moment. There are diminishing returns when it comes to cost and what is being cut,” said Tyl.
“What people are looking for is not necessarily higher power, but faster and less expensive parts,” said Brett Thompson, sales engineer-TruLaser for Trumpf Inc., Farmington, Conn. “The power question is just a byproduct of that.” He also noted that powers up to 6 kW continue to be big sellers.
Trumpf produces multiple solid-state laser formats, including fiber, rod, and disk. For 2D flat cutting, Trumpf uses the disk format for its robustness and stability. “The disk laser is unique in being able to maintain a consistency within one percent of its original laser power over the life of the laser; you buy a 10 kW TruDisk laser today, it’s still a 10 kW TruDisk laser five years from now,” said Thompson. “This is the major advantage of the disk architecture. There’s not the continual loss of power that can frustrate the cutting process.”
There are other processing technologies that can help improve cutting efficiency. Two Trumpf innovations Thompson especially noted are the company’s BrightLine fiber and high-speed ECO technologies.
The BrightLine fiber allows users to switch both beam size and beam mode via a co-axial optical cable. “We can deliver the beam in both a 100 µm core or a 400 µm core, giving a much greater beam diameter range,” explained Thompson.
At first, this may seem confusing. Finer beams mean higher energy density and therefore a finer kerf and a faster cut. “Finer beams become a problem as materials get thicker,” explained Thompson. “The cut speed relative to thickness gets so fast it is necessary to push a lot of gas through the kerf to eject the melt. At a point, quality, speed and consistency suffer. That is why the much larger beam produced by the 400-µm core is important for thicker materials.”
According to the company, BrightLine fiber can be used to cut all material types, increasing process stability, part quality and material thickness capacity, from mild steel to stainless steel, as well as reflective materials such as aluminum in thicknesses from 0.040-1.00″ (1-25.4 mm).
Trumpf‘s Highspeed Eco nozzle is aimed at reducing cutting gas consumption. Trumpf designed a nozzle with a flexibly mounted sleeve. Most nozzles ride above the cutting surface, allowing some of the assist gas to flow around the nozzle as well as into the cut. The Eco nozzle’s sleeve directs the assist gas solely into the kerf, providing up to 70 percent lower assist gas consumption while improving edge quality and speed by as much as 100 percent, according to the company.
Nitrogen Gas, Better Cuts
While users may face some challenges adapting to higher power lasers, the trend is clearly continuing, and some see even faster adoption. “There is a race,” said Dave Cotton, flat sheet laser business development manager for BLM Group USA, Novi, Mich. “Various types of assist gas—nitrogen, compressed dry air and gas mixers—are producing significant advantages with increased wattage, leading to new and improved benefits in dross-free cutting, better edge quality, and higher cutting speeds. Where high-wattage fiber also shows advantages is in its ability to cut over 1″ (25.4 mm) aluminum and stainless.”
This output advantage is gained across the board, with the notable exception of cutting mild steel using oxygen. Cutting mild steel currently maxes out at 1″ (25.4 mm) in a production environment, according to Cotton. When using oxygen, speed output is not increased above 6 kW due to mild steel’s molecular structure, according to Cotton. A secondary disadvantage to using oxygen is that it oxidizes the surface of the cut. If the cut part requires painting or welding, the oxidation must be removed, an expensive secondary operation.
“Nitrogen is the preferred method of cutting because it is inert—it’s a cold cutting process,” he explained. “Higher-power lasers mean cutting the same thickness [using nitrogen] but without an oxidized surface. It’s ready for welding or powder coating right from the machine.”
Oxygen is a heat accelerant with the heat providing additional power. Nitrogen being a cold cut requires additional wattage and gas flow, according to Cotton. Cutting 1″ (25.4 mm) mild steel with oxygen means using at minimum a 5 kW laser. Using nitrogen with a 5 kW laser limits the thickness to 5/16″ (7.9 mm). “That is a big difference,” he said. That is why higher wattage becomes important when cutting with nitrogen.
Cotton also agreed that all the peripherals such as gas and beam delivery, nozzles, and automation contribute to faster and less expensive cutting as well as better quality cuts. As an example, the BLM Group’s LS5 Flat Sheet Laser and LC5 Combo machines are currently available in wattages up to 8 kW. The solid-state fiber laser makes it appropriate for cutting reflective materials (copper, brass, aluminum and stainless) as well as mild and galvanized steels.
With the development of new cutting nozzles for the reduction of gas flow and improved edge quality, it is imperative users monitor nozzle quality. In 2018, BLM introduced an automatic nozzle monitoring and changing function to its LS5 product line. This feature automatically monitors, via a camera, the wear of the cutting nozzle and swaps it out from a choice of 18 available nozzles based upon the conditions set within the controller. This feature is critical to maintaining consistent edge quality and the ability to run unattended (lights out) operations.
Lasers as Machine Tools
One of the other advances in laser—3D cutting—requires a different approach, according to Carl Bryant, sales and marketing manager for Prima Power North America Inc., Arlington Heights, Illinois. Three-dimensional lasers cut formed parts such as stamped automotive pieces used in car body structures. “In the 3D world, we rarely get above 4 kW, but we are playing around with 6 kW and we see some advantage,” said Bryant, unlike in the flat-sheet world where he sees 10 kW is becoming standard.
Prima Power North America offers both 2D and 3D laser cutting machines. As Bryant himself noted, there are many similarities, including the use of high-speed linear motors to move the cutting heads. “Everybody wants to go fast,” he said. “When solid-state lasers like the fiber laser was introduced, suddenly we had to reinvent the machine tool because now the machine tool was the pacing item to the process.” That is when linear motors entered the picture, to provide those motion platforms with high dynamics to match the speed of the laser.
One difference from 2D is that 3D uses higher pressure assist gases, with Prima Power North America primarily using air at 15 to 16 bar. “Some [3D] customers use nitrogen, but there is a price premium for that,” he said. The nozzle to deliver that gas had to evolve as well. “In the 3D world, nozzle tips are consumable. They cost about $4.00 and operators will change them out two or three times in 24 hours,” he said.
That mirrors the evolution of laser cutters during Bryant’s career, becoming today a mature commodity. A good example is Prima Power North America’s Laser Next series of laser cutters, which are designed for stamped metal parts manufacturers in different industrial sectors, including job shops, press shops, aerospace, agricultural and automotive. Laser Next is a machine run by operators that need to know little about how lasers work. “To our customers, an operator is a person that loads a part and pushes a button,” he said.