By Bruce Morey, Manufacturing Engineering
When it comes to cutting, welding, drilling, and marking, lasers have proven their worth. New improvements are further driving down cost and expanding the list of laser choices available
Lasers first started making a significant impact for manufacturing in the early to mid 1970s. Since then, a number of advances, both evolutionary and revolutionary, have made lasers a common tool of choice for applications such as cutting, welding, drilling, brazing, and cladding. They are often easier to automate than many of their mechanical competitors. No moving part contacts the metal, so no tool wears out that needs replacement.
As the field has developed, there has been a proliferation in the number of choices available, from gas lasers to solid state to ultrashort pulse.
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In the Beginning CO2 and Nd:YAG
CO2 and solid-state lasers are now considered a mature technology, and they offer practical, cost-effective industrial material processing. The CO2 is a gas laser, with the gas acting as a lasing medium excited by electricity. For solid-state lasers, what emerged as the most common for industrial processing was a laser that dopes Neodymium in an yttrium-aluminum-garnet medium, or Nd:YAG. The solid core rod is ‘pumped’ with flash-lamps (or semiconductor diodes today) to create a lasing effect.
An important contrast between the two is that the CO2’s beam wavelength is about 10 µm, solid-state lasers like Nd:YAG about 1 µm. Engineers figured out how to deliver a 1-µm beam through a fiber-optic cable, an important convenience in machinery and around the shop floor. The 10-µm beam of the CO2 must rely on comparatively clunky mirrors and optics. The CO2 laser has a wall-plug efficiency of about 10–12% and the Nd:YAG about 3% or less. CO2 lasers have improved from 500-W versions to 6 kW (or more) versions today for roughly the same price, with commercially available powers up to 20 kW. Reliability for both has improved to the point that users see no reason to replace existing lasers for years to come.
Energy in each wavelength interacts with material at different efficiencies. Tuning the wavelength to the application is another important element in choice.
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The Nd:YAG laser can deliver high-frequency, modulated beams that have a very high peak power in pulses measured in micro and picoseconds. “This delivers very high peak power, for example 30-kW peak in a millisecond or less, even though the average power could be between 20–600 W,” explained Tracey Ryba, laser product manager for Trumpf (Plymouth, MI). Early CO2 lasers were modulated with spinning mirrors, but not at nearly the same frequency as modern CO2 lasers using high-frequency RF modulation in the kHz range. In addition, they do not achieve the high peak powers such as those seen in pulsed Nd:YAG.
Short and ultrashort-pulsed lasers are used for fine cutting, drilling, and ablation. For example, fuel injectors are drilled and heart stents cut with such devices. An example of an ultrashort-pulse device is the StarFemto released by Rofin-Sinar in March. With an average power of only 20 W, it delivers up to 200 MW of peak power and frequencies up to 2 MHz.
New Technology Advancements—Better Solid-State Lasers
Not content with the status quo, laser engineers continue to develop ways to improve lasers. Solid-state lasers like Nd:YAG experience thermal limitations, limiting efficiency and average power. As the lasing rods heat up during use, they lose efficiency through thermal lensing. If the lasing material is thinned out into a disk and pumped with diode lasers, the thin disk can be cooled better and kept at a uniform temperature, preventing thermal lensing. Enter disk lasers, a prime offering from Trumpf. These greatly improve efficiency and peak power for laser beams in the 1-µm wavelength, while offering higher power than Nd:YAG. The Trumpf disk lasers produce power up to 16 kW. High-beam quality means light cable diameters measure as small as 50 µm, making them easy to attach to robots and other common automation systems.
A related type of laser for industrial processing that is gaining market share fast is the fiber laser. Instead of a disk, diode lasers pump an optical fiber. This too provides excellent cooling with a simpler construction resulting in a more efficient laser than when using a Nd:YAG lasing rod.
SOURCE: Manufacturing Engineering
IPG Photonics (Oxford, MA) was a pioneer in the development of high-power fiber lasers. Offering a wide range of such lasers, their YLS series alone ranges from 500 W to 100 kW, operating in continuous wave or modulated up to 20 kHz with wall-plug efficiencies greater than 30%, according to information from the company. Fiber delivery cable diameters are as small as 50 µm, depending on the power delivered. Reflecting the growing importance of this class of laser, companies like Trumpf and Rofin-Sinar also offer versions of fiber lasers as well. Both fiber and disk solid-state lasers offer wall-plug efficiencies in the 30–35% range.
Both disk and fiber lasers are pumped by a semiconductor laser, the direct-diode laser. This begs a question—why not use that as a laser source? It boasts up to 40% wall-plug efficiency and is less complicated to use. Its downside is that it has poorer beam quality, limiting its use to applications that need less beam quality.
Trends and Predictions
“The CO2 laser is not going to go away anytime soon, but its market share will decrease,” predicts Chris Dackson, laser product manager for Rofin-Sinar (Plymouth, MI). The long 10-µm wavelength of the CO2 actually reacts less with most metals than the 1-µm beams, putting less energy into them.
Counterintuitively, that can be an advantage, especially in welding. “The CO2 beam spatters less and creates a cleaner looking weld,” said Dackson from Rofin-Sinar precisely because the 10-µm wavelength reacts less with metals. This makes it a better choice for high-volume automotive powertrain parts, where tiny bits of welding spatter could cause problems in precision gearing, for example. “It is also important for stainless steel welding where simple cosmetics are important, such as tubes used in appearance applications,” agreed Ryba from Trumpf.
SOURCE: Manufacturing Engineering
Another advantage for the CO2 laser is that it is ideal for nonmetallic processing, such as wood, fabric, glass, or plastics. “There is a huge market in low-power CO2 applications, less than 2 kW, for plastic welding and cutting, as an example,” explained Ryba, such as precision medical applications. He also said there are new applications for the old workhorse in making the next generation of computer chips. “CO2 is ideal in exciting another element to create a shorter wavelength, in the ultraviolet,” he said. As he describes it, the resulting extreme UV light is ideal for the next generation of chipmaking devices, allowing them to pack more transistors onto a chip. “It will be a niche market, but an important one,” said Ryba.
Make no mistake, both Ryba and Trumpf see the future in fiber and disk lasers. “This is because of their high efficiency and simple delivery through a fiber-optic cable. They are the preferred laser for most metal processing applications today,” said Ryba. He also sees direct-diode lasers as achieving the power and beam quality required for cutting and remote welding in the next couple of years.
Learning and Matching Is the Key to New Lasers
“We currently sell about 50% of our laser systems equipped with CO2 lasers and 50% with fiber lasers,” said Matt Garbarino, marketing manager for Cincinnati Inc. (Harrison, OH). “The fiber laser share is growing.” His company specializes in laser cutting systems featuring flying optics, where the material remains stationary and is cut by a moving beam. They purchase a laser source and integrate it into a platform. Incremental improvements in CO2, he said, have meant a slow evolution in improvement. “What is different is that fiber lasers are a revolution in technology, not an incremental step,” he said.
As with other new technologies, fiber lasers come with a higher purchase price. A 4-kW fiber laser will cost more to Cincinnati than a 4-kW CO2. “There are a variety of reasons for that, but against that we are seeing operating costs for fiber lasers that are 60–70% of that for a CO2, depending on the application,” he said. The choice is in the tradeoffs. “Fiber lasers excel in cutting thinner materials fast, in some cases up to twice as fast in thinner materials than an equivalent CO2,” he explained. Not so for thicker materials. “The breakpoint [for choosing a CO2] is approximately 10 gage or thicker,” he said, which is equivalent to about 4-mm thick. “Edge quality is better with a CO2 [in those thicker metals], that is why you do not see everyone buying fiber lasers,” he said. Garbarino related that applications like food industry equipment are well suited for fiber-laser cutting, while agricultural equipment and heavy-duty machinery are at present well suited for CO2. Thick versus thin.
Mazak Optonics (Elgin, IL) is another machine provider specializing in laser cutting applications for fabrication, both 2D and 3D as well as tube and pipe. “We make about 50 different models, and 60–70% of our systems currently use CO2,” explained Mark Mercurio applications and technical support manager for Mazak, with the balance using fiber lasers. He also sees a trend towards more fiber lasers in just the last few years. The key is tuning the laser to the application. “Our 4-kW fiber laser can now compete with a CO2 laser cutting ¾” {19.1-mm] mild steel plate,” stated Mercurio. “That will grab a wider segment of the cutting market.”
To better tune lasers to applications, Mazak developed a multifunction torch. “Its function is to make the process more consistent by removing the operator from the process, allowing the machine to do the setup rather than the operator,” he explained. Engineering the beam that the fiber laser delivers for optimal cutting is the key. Thick cutting requires a different beam shape than thinner material.
However, he also predicts CO2 remaining a viable solution for some time to come. His perspective is that both CO2 and fiber lasers cut materials in the ½–¾” thickness almost identically, with similar edge quality and speeds. “But the CO2 is quite a bit less expensive. If I am cutting 1/2″ [12.7-mm] thick material all day long, the CO2 is cost-effective,” he said. Where fiber lasers really become attractive is when they can cut faster, say in 20 gage material where the feed rate is 2400 ipm [61 m/min]. “The CO2 may only cut at 800 ipm [20.3 m/min] in that application,” he said, making the fiber laser the clear choice.
Mark Barry, vice president of sales and marketing, Prima Power Laserdyne (Champlin, MN) is direct in his enthusiasm for fiber lasers—they are increasingly the tool of choice today. His company also delivers turnkey laser systems for cutting, welding, and drilling. “A laser is like an electric motor, it is useless without a machine to enable it to do something,” he said. “From that perspective, the fiber laser is often a better engine. There are things I am doing today with a fiber laser that are vastly superior to what we were doing with a CO2 or an Nd:YAG.”
Further advancements will lie in controlling the laser beam rather than in choosing the laser itself. An example Barry pointed out is Laserdyne’s SmartRamp software recently installed in their controllers for consistent endpoint control during laser welding. SmartRamp controls laser parameters in conjunction with the motion of the beam to eliminate depressions at the end points of welds. Depressions are a common occurrence in laser welding because the power is ramped down at the end of welds after the start point has been overlapped. It is more than aesthetics, these can be leak points in hermetically sealed devices.
Future Developments—Direct Diodes
As convenient as fiber and disk lasers are, the technology to watch is direct-diode lasers. While still considered under development, there is evidence that direct diodes are gaining ground even now. They offer better efficiency, smaller footprint, and less complexity. “We are seeing the laser market for material processing increasing by 10%, but the business for our diode lasers increased by 25% last year and we are aiming for that in 2015 again,” said Wolfgang Todt vice president US operations for Laserline (Santa Clara, CA), a company that specializes in what it terms as fiber-coupled diode lasers.
Laserline’s LDF series of fiber-coupled diode lasers ranges from 3 to 25 kW in power, though the beam quality decreases as power increases. For example, the 3-kW version of Laserline’s LDF system has a beam parameter product (BPP) of 20 mm-mrad, the 6-kW version is only 40 mm-mrads, compared with single-digit BPPs for fiber or disk lasers. Note: a smaller BPP means finer beam quality.
Still, for a number of applications—especially outside of cutting—direct-diode lasers are often competitive. “There are a number of industries where we are seeing the same competitive situations pop-up time and again, with customers comparing disk lasers, fiber lasers, and direct diodes,” he said, where all three are competitive at some level. Todt shared that their prices have come down 10–15% in the last year as well, driven by higher production volumes and decreasing cost in components.
His company’s direct diodes are continually improving, now boasting a top power range of 40 kW with a 220 mm-mrad BPP first introduced in 2014. “This is aimed at high-speed cladding operations or deep welding,” he said. He said to look for a new product family announcement in 2015 that will reduce the physical size of their diode lasers with even better beam quality. The aim is to make direct-diode lasers competitive in applications where a brilliant beam quality matters.
This article was first published in the May 2015 edition of Manufacturing Engineering magazine. Click here for PDF.