Better Lasers, Better Machining

HANK HOGAN, CONTRIBUTING EDITOR, hank.hogan@photonics.com

When it’s time to cut, weld, ablate, mark or otherwise machine materials, manufacturers are increasingly turning to lasers. Falling system costs and better resulting product quality are two reasons why. Still, the need exists to further lower the cost of laser machining while expanding the range of materials that can be handled. For that, there’s progress in fiber and other laser technologies from greater power, more precise processing and new wavelengths.

An illustration of these trends can be found at Mazak Optonics Corp. The company, which has its North American headquarters in Elgin, Ill., does not make laser engines but does incorporate those supplied by well-known vendors to make laser-cutting equipment used at large companies and independent job shops.

Fiber lasers, like the one shown here cutting an automotive part, are increasingly used for cutting and other machining. Courtesy of Coherent.

Mazak Optonics has seen a significant change in laser machining technology over the past few years, according to Marc Lobit, general manager of sales support operations. “Laser-cutting technology is still shifting to fiber [lasers], with about 75 percent of our machines sold in 2015 being fiber,” he said.

Lobit noted that five or so years ago a majority of the company’s products used CO₂ lasers. Fiber’s higher reliability and uptime, along with its associated decrease in maintenance costs as compared to CO₂ lasers, have driven the change.

A big reason for this is the beam delivery system, which is straightforward for fiber lasers. In contrast, CO₂ lasers employ mirrors to get the beam to the business end of the cutting machine, which leads to relatively high upkeep.

“[CO₂ lasers] were very labor-intensive and expensive to maintain.” Lobit said. “Mirrors would become damaged. They would wear out over time from the heat that’s reflecting off of [them].”

The transition to fiber laser technology brought about other advantages, he added. The ytterbium fiber lasers output a beam at 1070-nm wavelength, about a 10th of that of a CO₂ laser. The result of this difference, the greater uptime, and other differences was faster cutting using a fiber laser, and better results, particularly when it came to edge quality. Consequently, a single fiber laser cutting machine can replace two to three of the older systems.

The global fiber laser market was valued at $1.05 billion in 2014 and is expected to reach $2.22 billion in 2019, growing at a compound annual growth rate of 16.20% during the forecast period, according to Technavio. Courtesy of Technavio.

Laser machining does not completely replace and often is complementary to the traditional, mechanical approach, Lobit noted. Mazak Optonics is part of Japan’s Yamazaki Mazak Corp., a manufacturer of laser and mechanical machine tools and systems. The company’s customers may use lasers to cut but may go the traditional route for machining shapes or adding fine detailing.

As for the future of laser machining, more power is on its way. Today, Mazak Optonics has products ranging up to 6 kW. “Higher power is starting to hit the market. This enables thicker cutting, but probably the most important benefit will be faster cutting for 1/4- to 1/2-in. thicknesses,” Lobit said.

Laser manufacturers are also coming out with new wavelengths. This is important because not all materials react the same way to a given wavelength, pointed out Tracey Ryba, product manager for laser systems and OEM lasers at Trumpf Inc. The laser manufacturer has its U.S. headquarters in Farmington, Conn.

By doubling frequency to the green portion of the spectrum, lasers can weld copper, even thin layers, without damage to ceramic material lying below. Courtesy of Trumpf.

For instance, CO₂ lasers are good for producing perforated holes for easy separation of food packaging plastic bags. As for metals, a wavelength around 1000 nm generally works well. However, copper is highly reflective at that wavelength. So, Trumpf developed a frequency doubled, pulsed green disk laser for welding copper, Ryba said.

High precision = less processing

As for the future of laser machining, it’s instructive to look at the past. According to Ryba, fiber and disk lasers have largely replaced CO₂ lasers because they are more reliable and easier to maintain.

Both fiber and disk lasers depend upon a diode to pump the lasing material. Today, the beam quality or power (or both) of a diode laser makes it unsuitable for many machining applications, but Trumpf expects continued progress will change that. The push will be to simplify the laser system and go the direct diode laser approach, Ryba said.

CO laser separation after laser surface scribe of a borosilicate glass. Courtesy of Laser Zentrum Hannover eV.

This is because when it comes to laser versus traditional machining, ongoing cost cutting changes the balance and favors the laser approach, he added. Over the past seven or eight years laser systems have come down about threefold in cost per delivered watt. That drop in price cannot continue — unless the system can be further simplified. Going to a diode laser instead of a diode-pumped laser could do that.

It also could be that even without additional cost cutting that laser machining is more cost-effective than other approaches, due to the elimination of manufacturing steps.

“Part of the advantage of laser welding is you don’t have to do so much post processing typically,” Ryba said. “Compared to traditional machining, the laser is high precision.”

For another example illustrating trends and developments in laser machining, consider Boeing. The Chicago-based aerospace giant has been laser cutting materials for over a quarter-century, said William Schell, Boeing associate technical fellow. Today, the company uses laser machining to fabricate the ducting system for its airplanes, replacing conventional milling, band saw and shear/nibbling equipment.

“The lasers offer exceptional speed and accuracy over other cutting processes, particularly on nickel-cobalt alloy materials, which are difficult to cut,” Schell said.

He added that the company’s technology research organization designed, implemented and patented a laser trim machine for trimming duct details. With it, a mechanic scribes a mark, puts it in the field of view of a camera, and then a laser rotates around the stationary part, cutting off the excess to the scribe mark.

Boeing’s laser trim machine addresses process limitations with conventional cutting methods and the safety issues brought about by trying to manually handle duct trimming. Schell noted that the use of a laser was particularly beneficial when an increase in the thickness of the duct walls was needed to meet design requirements. The thicker walls began to damage the conventional cutting equipment. Asked about issues associated with laser machining, Schell mentioned one that impacts all manufacturing operations. “While lasers offer unique advantages over traditional methods, they also come with their own set of safety challenges. Being able to cost-effectively and safely implement the use of lasers in a factory environment — a production work cell — can be challenging,” he said.

When looking at the future of laser machining, Frank Gaebler, director of marketing at Coherent Inc. of Santa Clara, Calif., points to several trends. One is the emergence of increasingly powerful fiber lasers. Due to their nature they are inherently more reliable and cost less to operate than the old laser machining workhorse, the CO₂ laser.

However, the old standby is still best when working with very thick materials. “The shipyard business and these places where you have to cut plates instead of sheets, then the CO₂ laser might still be the best choice,” Gaebler said.

Another important development is the advent of affordable ultrafast lasers. With pulse widths in the femto- and picoseconds, such lasers enable machining on a microscopic scale, something that can’t be easily done, if at all, using traditional methods. Because the pulse widths are so short, the heat-affected zone in the material is negligible, and that gives laser processing an advantage.

For instance, ultrafast lasers are used to precisely drill holes of differing shapes and sizes in fuel injector nozzles. This buys better combustion of fuel, leading to greater efficiency, more power, or some combination of both.

A gasoline injector nozzle drilled by a Coherent Monaco Laser through 250-µm-thick stainless steel. Courtesy of Coherent.

Another example are stents and other medical devices that go into the body. These are made of biocompatible polymers and other materials that have to be finely machined, presenting challenges to manufacturing methods not based on ultrafast lasers.

A third trend is the development of new wavelengths. Coherent, for instance, has come up with a CO laser that produces a 5-µm wavelength output. Because it is half the wavelength of a 10-µm CO₂ laser beam, it can be focused to half the spot size, which ups the intensity fourfold.

As to why a new wavelength might be needed, Gaebler noted that some materials do not work well with current lasers.

Pigment-free polyethylene films, for example, have in the past not been processed well with lasers due to limited material absorption, too low a beam intensity, or both.

“But at 5 µm it works pretty well. They can cut it with high reliability and very little heat-affected zone,” Gaebler said.