Welding With Laser

As more original equipment manufacturers (OEMs) and job shops "warm up" to the idea of laser welding, many have turned their attention to four specific technologies:

More job shops are taking the plunge and acquiring laser welding systems—generally when suitable applications come through their door or when seeking to replace MIG and TIG welding.

"People are really jumping into laser head first these days," said Wes Wheeler, sales manager of Alpha Laser, Meadville, Pa. "Laser welding has traditionally been driven by repair processes, such as tooling repair and high-value repairs. As lasers become more efficient, people are starting to use them for production welding."

But with all the choices on the market, it can potentially be "more confusing now than it was three years ago," said Tracey Ryba, senior product manager of high-power OEM lasers for Trumpf Inc., Farmington, Conn. That said, he noted a slew of OEM projects in development and getting ready to launch—testament to the inroads laser welding technology is making. "I think we’re just starting to scratch the surface of the potential."

A major benefit of laser welding is the ability to eliminate post-processing steps like grinding and finishing.

Ultimately, having patience in studying the options and learning what they can do pays off big, according to Dan Belz, FLW product manager for Amada America Inc., Buena Park, Calif. "If you take the time to understand what it does and what it can do, it's phenomenal. There are some parts you can look at and not be sure if they were formed or welded."

Adapting the library of preprogrammed routines from its ENSIS laser cutting systems, Amada America now employs that technology for welding.

In the past six years, a team of three technicians including Belz has been perfecting the company's sheet metal welding system, ideal for joining thicknesses of up to ¼" (6.35 mm). The platform is available in two 3-kW options: M3, with 15' (4.57-m) table, and M5, featuring two 18' (5.49-m) shuttle tables.

On these systems, Amada's ENSIS technology starts users with five basic welding conditions that adjust the beam from an ultrathin shape for thicker steel and deep penetration to a flatter doughnut shape for bridging wider gaps. Using the flatter shape also facilitates wobble welding.

"We have quite a few customers who weld up to ¼" steel," Belz noted. "That's right in the wheelhouse of the unit—and with our technology, 3,000 W of power is more than enough. We’re geared for sheet metal, even as thin as 0.020" [0.51 mm], and can also apply filler wire if needed."

Amada's platform also excels at joining dissimilar materials: copper to stainless, copper to mild steel, copper to Inconel, and Inconel to stainless. Belz and his team also perfected joins with a feed of titanium wire for a specialized project.

"We’re still experimenting, although we don't always get as much chance to experiment as much as we used to because we’re getting a lot of projects—customers sending us parts and asking us to weld them and teach them how to laser weld." Being so busy, he added, means Amada has had to temporarily shelve its attempts to weld aluminum to stainless.

To prevent porosity, Amada provides two types of nozzles, both with primary and secondary flow so shield gas is always close to the laser beam. "As material cools, it's still covered by the gas, so you’re eliminating porosity," Belz explained.

Furthermore, "because of the wavelength we’re using, as well as the speed, the heat-affected zone is almost nonexistent," he added. "Most of our parts can be handled without gloves right after they are welded."

Meanwhile, Trumpf provides its OEM customers about 40 recipes for its beam-in-beam technology through its BrightLine Professional software. "That gives them a starting point for most common materials," Ryba noted. "From there, customers can build a library and experiment on which variations work better." The software includes settings for multiple materials, thicknesses and weld styles.

A relatively new concept continuing to gain traction is the range of beam-in-beam laser processing systems. Trumpf, a pioneer of the technology, offers two such solutions: BrightLine Weld from its laser technology division, and FusionLine from its machine tool business. The ring technology and single fiber are available for use on the TruLaser Weld 5000, introduced about three years ago.

Ryba noted that by using the inner core and outer ring beams simultaneously, spatter is greatly reduced. This increases longevity of tooling and fixtures and reduces the need for cleaning of protective cover slides—meaning more uptime. More importantly, welding speed and quality are increased, especially for aluminum and copper.

On copper, the outer ring acts like a preheating effect, allowing better coupling of the core beam. This provides a stable welding process, especially at slower speeds, allowing deep penetrating welds and a spatter reduction of 70–85 percent. By preheating copper before the weld, BrightLine is about 10 times faster than a single-spot beam, he said. With aluminum, spatter can be greatly reduced—and speed increased. "I can raise power to 5 kW and increase welding almost 7X to approximately 35 meters a minute" depending on aluminum grade, said Ryba. "Press fits and butt welds work well, and on steel you can weld three times faster with the same amount of power. On aluminum to copper you get a much better quality weld."

BrightLine's cores are adjustable in one percent power increments, Ryba explained, up to a maximum of 90 percent for one beam and 10 percent for the other. Operators can also switch from core to core at 100 percent strength. All power distribution adjustments are made in a window in the TruControl software.

On Trumpf's fiber lasers, available inner-outer core diameters are 50-200 μm, 100-400 μm and 200-700 μm.

In the TruDisk version of Brightline, an optical wedge adjusts power distribution between the two cores with a stepper motor. "We’ve found 30-70 or 60-40 tends to be the best power distribution," Ryba said.

The quality difference between single and dual beams is clear, he added.

"With a traditional single core laser weld, you use a flat top or rounded bullet shape beam—common when doing overlap welding with a larger spot," Ryba explained. "As you try to weld faster, the keyhole becomes unstable and the escaping metal vapor is blocked, having to push through the melt pool, and expelling some of that melt in the form of spatter. BrightLine, provides a semi-Gaussian center and a ring around the outer edge. That ring keeps the keyhole open and stable. The dual core beam profile and weld cross section resemble a wood screw shape, where the outer ring front side acts as a preheat, or premelt, to improve coupling efficiency of the core and the backside stabilizes the keyhole to keep it open. Stabilization of the keyhole allows the metal vapor to escape without blockage, reducing spatter by 70 to 97 percent. This process also helps prevent hot cracking by slowing the cooling process, and also smooths the weld a bit."

When the technology is used in Trumpf's FusionLine package, shops are able to use this doughnut-shaped pattern to retain original part designs, added Masoud Harooni, laser welding product manager. In those cases, users concentrate more power on the outside core instead of into the weld gap.

Trumpf further assists shops with its turnkey TruLaser Weld 5000, Harooni continued. Those customers are "counting on us to help them and provide process parameters to ramp up production."

The system is offered in multiple configurations based on part size and quantity, primarily for sheet metal applications. With a rotational changer table, operators can load and unload material while another workpiece is welded.

"Especially in the food industry, there are lots of benefits because the amount of post processing required for parts to be visible is enormous," Harooni said. "Most of our potential or current customers use MIG welding and want to change to laser. They weld 20 minutes with MIG then spend 35 to 40 minutes grinding. With laser welding, whatever they take from our cell can be sent to coating or another process without touching it."

Based on power and application, he added, the system can achieve speeds of 250 to 300 ipm. With thicker structural parts, the benefits are in preprocessing—for instance, eliminating edges from thick plate to prepare parts for MIG welding.

For shops doing repairs and production work, the flexibility of pulsed welding has been attractive thanks to its ability to limit heat input. Pulsed welding "is a forgiving process," explained Alpha Laser's Wheeler. "Traditionally, a continuous wave laser wants to get penetration; a pulsed laser can still get penetration but can also be used to get almost no penetration." Alpha Laser systems—including its ALFlak series—range in pulse time from 1 to 20 ms, with the normal range being 5 to 7 ms.

Alpha Lasers says its pulsed fiber and YAG lasers excel at providing low penetration levels and low dilution rates—the mix between base material and added filler. In one example comparing pulsed laser to a TIG process, Wheeler noted, the laser performed a 0.055" (1.40-mm) weld deposit with a heat affected zone of only 0.008" (0.20 mm) below the weld, and a weld dilution zone of about 0.006" (0.15 mm). "This was a test for a customer who didn't understand when I explained that laser had lower heat input," he recalled. "They asked what was wrong with TIG welding, and I said, ‘Let me explain what you’re doing to your base metal.’ "

In terms of expanding fabricators’ appreciation of the benefits of pulsed welding, Wheeler emphasizes material flexibility. "We’ve done everything from copper to stainless joining," he explained. With a beryllium copper base, "we put stainless steel on it all the time. We’ve worked with all the high-end metals, superalloys like Inconel and Stellites, and cast iron. The normal world for us is traditionally tool steels. One of the big applications we see is working with any kind of stainless, especially 300 series stainless, which is easy to warp and works really well with a laser."

In terms of replacing TIG welding setups, a recent Alpha Laser system that was sold to a major company's switch and control division has dramatically decreased scrap rates, from 15 to 3 percent, Wheeler added. That rate "should be even lower if we can get it perfect. It's going to provide a ton of value, with less work before and after—no preheating or postprocessing—and should decrease overall cycle time significantly." Another application in the paper industry is welding a component 30' (9.14-m) long with 6,000 tubes inside. There is even some talk of a single pulsed laser system being able to replace a pair of brazing lines.

When the rubber hits the road—or more precisely, when the beam hits the metal—some shops are building an impressive laser welding repertoire.

About 10 years ago, Phoenix Laser, Meadville, Pa., settled on using Germany's Alpha Lasers and created Alpha Laser U.S. to serve as the company's North American dealer. From there, Phoenix has expanded from its tool and die roots to perform laser cladding and hardening. Meadville was once the tool and die capital of the world, Wheeler noted, with about 300 shops in a 50-mile radius of Phoenix headquarters. Now, Phoenix has four locations, including in Kansas City, Cuyahoga Falls, Ohio, and Brookville, Ind., with more than 20 laser welding systems spread among them.

Tool and die repair with lasers is "super accurate, with super low heat input thanks no preheating or postheating," Wheeler said. "We can have a part done in 10 minutes."

Phoenix recently performed a trial run on some large containers, using pulsed welding on the seams. Since the walls were particularly thin, there was concern about too much heat input from TIG or CW laser joining. One of Alpha Laser's most dedicated users is Chicago Welding and Fabrication, which recently purchased a 300-W unit. Chicago Welding began its foray into laser welding about 15 years ago, recalled COO Gary Wealther, but machines of the day tended to be somewhat unreliable. Beginning with mold and die repair, the business added medical and production welding to its repertoire.

The initial attraction to laser welding was the limited heat-affected zone and lack of "collateral damage," he noted—ultimately, "being able to do things that you could not do otherwise." That said, he noted that some projects require a combination of TIG to start with and laser welding for delicate areas.

After initially experiencing a steep learning curve with older systems, Wealther recalled, he favors companies like Alpha Laser that "help you do everything." Because of the precision parts Chicago Welding processes, "we’re welding under microscopes" and even have a micro processing room. Thanks to the versatility and precision of pulsed YAG lasers, his company can process things like demanding medical parts featuring specialized stainless steels that would warp with TIG welding.

And while laser welding is slower, he added, "you’re getting no distortion, no heat." So as jobs come in, finding the right fit for the laser's capability is critical to offer customers the fastest, most economical and best solution. And when the job is right, his 300-W Alpha Laser does the job. "We absolutely love that machine," he said.

Having spent an intensive period refining and pushing the limits of Amada's sheet welding systems, Belz is keen to advise smaller shops how to make to a process work for them. "We figured from the onset that 99 percent of our customers would be OEMs," he recalled. However, it turns out that "most of our customers are job shops that do a lot of welding"—although the next few installations on his list were for OEMs. "The OEMs took a little longer to adapt to it but [now] see the benefit."

Among the ranks of fabricators, he notes two types: welding shops and shops that weld.

The former "are probably welding 90 percent of their product line. They’ve got welders, they understand welding, they are the ones who are easy to work with because they’ll see what we’re doing—they’ll understand it. We come in, install, give them some training, then they’ll kick us out and say, ‘We’ll call you when we need you.’"

But for shops that weld, "that's an area of pain for them because they can't get the welders or they spend too much time on post-processing." To get those customers comfortable with welding, "we look at their parts and look at their CADs and make some modifications for a tighter, better fit."

That redesign step is critical to success, Belz continued. "We’ve got a lot of customers who want to learn how to design to optimize laser welding. Others have existing product lines and we look to see what part or parts are giving the biggest pain. They usually have quite a few."

After a welding process has been drafted, tested, proven and installed, virtually all postprocessing is eliminated. Parts can go "right to the paint booth: no more grinding the welds." In the end, "some customers want to use it for specific parts and nothing else, while others want to use it for everything. You’ve got to triage it."

It is worth noting that last year, the National Institute of Standards and Technology revealed its three-year project to gather data on the most fundamental aspects of laser welding. That data is being used by computer modelers to create laser welding simulations aimed at giving manufacturers more control over the process.

The project illustrates a key point: laser welding—particularly in regards to controlling spatter, cracking and porosity while maximizing throughput—is a work in progress despite its great strides in many industries.

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