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Laser Technology

Spatter matters

By Tom Klemens

How a simple, sophisticated add-on is boosting productivity and controlling costs

July/August 2013 - When Michael McCarthy came to work at his father’s fabrication shop in 1978, the equipment was a lot different than it is today. Just as it was back then, Metko Inc., New Holstein, Wis., is a family-owned job shop fabricating a variety of metal parts, although it now includes a division that makes hydraulic tanks. 

“I came into the business when it was mechanical machines. CNC did not yet exist,” says McCarthy, who now is CEO and president. He and his wife have owned and operated the company, which employs about 50, since purchasing it from his father in 2006.

New technology

“Dad started the company in 1971 with hole saws, but that’s something I didn’t see,” McCarthy says. “By the time I arrived, it was all Unipunch. Through the years, everything has gone to CNC and programming done offline.” Working through the adoption of new technology has given McCarthy plenty of experience in troubleshooting, built on a good foundation of traditional metalworking. “I’m glad I started when it was mechanical and I got to see how that was,” he says.

Metko purchased its first laser cutter in 1989. “We were one of the first to get a laser,” McCarthy says. “It was 1,500 W, which was a big one. Most were 500 or 1,000, so it just started from there.” The company continued adding equipment, sometimes bringing in new technology and sometimes duplicating existing processes but with newer FFJ-0708-laser-image1machines. “The latest thing is our fiber laser, and it has been a great machine,” he says. But it, too, has taken some troubleshooting to get to that point.

Most of the metal Metko works with is 1⁄4 in. or thinner. The company owns several laser cutters, one of which has the capacity to cut 1-in. material. In 2009, when it installed its newest CO2 laser, a 6,000-W Amada unit, Metko also invested in a nitrogen generation system to produce the necessary assist gas.

“That’s another one that took a while to get all the parts to fall into the right spaces, but it has worked out well,” McCarthy says. As a result, when Metko purchased a new Amada FOL-AJ fiber laser in 2012, it was set up to cut with nitrogen as the assist gas. “With the fiber technology, you also can cut with oxygen. But if you do, you’re not getting the full benefit out of the machine.”

However, cutting with nitrogen also dictated using a 7 1⁄2-in. (190 mm) lens, and the company immediately noticed spatter accumulating on the bottom of it. “That was quite surprising because the previous machine [from four years earlier] also used a 7 1⁄2-in. lens and had little or no issues,” McCarthy says. “But of course that was a CO2 system and the new system is a fiber laser.”

Although he couldn’t pinpoint the cause of the problem, McCarthy soon realized the spatter accumulation was causing each lens to last only a few weeks. “That was getting costly,” he says. “For a while we didn’t know if it was the process or the laser. But after a few months it was repeating every few weeks, so we knew we had to take a closer look at it.”

Years earlier, Metko had tried using protective salt lenses on its early CO2 laser, but with mixed results. The lenses were brittle, sensitive to humidity and caused a significant drop in laser power delivery. “We were trying to have the laser lens last as long as possible, but finally gave up and lived with spatter on the lens,” McCarthy says. Fortunately, when the fiber laser spatter issue came up, he remembered seeing a magazine ad for Lens Savers and soon a solution was in the works.

Economical protection

The focusing lenses for laser cutting machines are very expensive, says Robert Herpst, owner of International Crystal Laboratories, Garfield, N.J. Its Lens Savers have been protecting CO2 and YAG laser cutting and welding optics since the 1980s, and the company has been providing other optics and spectroscopy supplies and accessories since 1962.

“Our CO2 laser Lens Saver is an inexpensive, infrared-transmitting window with a low refractive index, which means it doesn’t need an anti-reflective coating and keeps costs down,” Herpst says.

FFJ-0708-laser-image2

Zinc selenide lenses for CO2 lasers have gotten less expensive over time because of the amount of material being sold to the industry. Fiber laser lenses, which are silica, are still very expensive—typically $1,000 or more—which makes a protective device worth considering. Lens Savers for fiber lasers, which are near-infrared, are made from a material with a higher refractive index that requires an anti-reflective coating. However, the window material is less expensive to coat and they remain far less expensive than new lenses. 

When Metko contacted ICL about its fiber lens spatter problem, Herpst jumped right in. “Laser manufacturers frequently change the way they mount their lenses, so we’re always facing new lens mount situations,” Herpst says, and that was part of the challenge at Metko. Amada had just introduced its new fiber laser, so Herpst says he again was starting from scratch. 

“Most of our engineering issues are how to shoehorn a protective window into an existing system that was not designed to accept it,” Herpst says. “We’re always trying to figure out ways to get one of these windows in front of a lens in a little, narrow compartment that somebody designed without any intention of having a window in front of it.”

ICL most often develops its custom mounts and adapters in cooperation with laser owners who provide the necessary field data. Developing a new solution for Metko required sending a mix of data and actual parts.

“At first he asked us to take dimensions,” McCarthy says. “He would send sketches and we tried that, but it didn’t seem to be the best path.” Eventually the company scheduled downtimes for the machine and sent ICL parts of the head for short periods of time. “That way he not only could get his own dimensions, but he also could grab it and look at it.”

FFJ-0708-laser-image3Because the machine can be used with three different lenses, Herpst developed shield holders for all three. One holder works for both the 7 1⁄2-in. and 10-in. lenses, using the same drop-in device, and a separate holder accommodates the 5-in. lens. Unlike its CO2 protective windows, which ICL makes with sodium chloride and potassium chloride crystals, the windows for fiber lasers are made of fused silica. “The fused silica is coated, unlike the other material, which is uncoated. But the windows are still much cheaper than the lenses.”

Passing the test

With the fiber laser mounting finalized, Metko installed the Lens Saver. “We put it in and it lasted for four months,” McCarthy says. As anticipated, there was very little loss of power in the beam. He says there have been two pleasant surprises, as well. “One was the shield lasting as long as the lens. The other is that the shield is virtually spatter free.”

Herpst says part of what makes the protective windows perform so well is ICL’s patented technology for dealing with the assist gas and cooling the window. “In these systems the lens is a pressure barrier,” he says. “An assist gas is forced through the nozzle in the laser head to make the cutting more efficient but also to deal with spatter on the lens.” He says the Lens Saver design creates a pressure-neutral environment around the window and circulates air to head off any build-up of pressure or temperature. The result is reliable performance and lens protection.

“As a manufacturer, you get involved with different things at different times and there just aren’t a lot of ready-made answers,” McCarthy says. “You have to go out and find your own. I happened to be lucky on this one. We found a vendor that helped solve our issue and was great to work with. It worked out, and that’s great.” FFJ

Interested in purchasing reprints of this article? Click here

Sources

  • International Crystal Laboratories
    Garfield, N.J.
    phone: 973/478-8944
    fax: 973/478-4201
    www.lenssavers.com
  • Metko Inc.
    New Holstein, Wis.
    phone: 920/898-4221
    fax: 920/898-1389
    www.metko.com


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