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Laser Welding Advances Fuel New Applications

Geoff Giordano
By Geoff Giordano Contributing Editor, SME Media

From producing lithium-ion batteries to processing sheetmetal, new laser welding systems are “pushing the envelope” of light absorption, beam control, speed and programming flexibility.

Prima Power Laserdyne’s SmartShield nozzle assembly protects the lens coverslide using clean compressed air while supplying shield gas to protect welds from oxidation.

With electric vehicles in increasing demand, the blue laser is coming to the fore in performing vital welding operations with copper and aluminum that infrared (IR) fiber lasers cannot handle. These batteries, as well as advanced consumer electronics, also require the joining of dissimilar metals with novel processes.

Industrial lasers continue to increase in power in the kilowatt (kW) range, and suppliers are increasingly aware of the need to more seamlessly integrate these devices into Industry 4.0 production operations with more user-friendly functionality.

Blue Light Special

Offering a breakthrough in metals processing, particularly the welding of copper, Nuburu’s blue laser systems have quickly been recognized for surpassing the relatively less effective joining ability of low-absorbing IR lasers, according to the company. Lithium-ion batteries are one of Nuburu’s specialties, but its blue lasers are tackling traditional materials processing.

Nuburu Inc. (Centennial, CO) was launched in April 2015 and unveiled its first product, the AO-150, in late 2017. The 150-W, 450 nm direct-diode laser has been nominated for SPIE’s Prism Award for photonics innovation for super processing speeds as well as weld and beam quality.

Demonstrating processing speeds two to 10 times faster than IR fiber lasers, Nuburu’s units execute cleaner welds in copper because it absorbs 65% of the blue wavelength compared with only about 5% of IR light. The unit also exhibits from three to 20 times more absorptivity across the spectrum of materials from stainless steel, nickel, titanium, aluminum, brass and gold, according to the company. “All metals absorb a lot more in the blue,” explained Jean-Michel Pelaprat, co-founder and chief marketing and sales officer. “You need much less power because you couple the wavelength much more effectively, so you have very strong heat transfer. We can weld those metals spatter free, meaning there is no porosity and no defect in the weld.”

Executing keyhole welds with IR lasers requires high peak power, producing vaporization—hence bubbling and porosity—inside the welds and weakening their mechanical strength and electrical performance. Nuburu has produced clean welds at powers up to 600 W, Pelaprat said. The blue laser’s continuous wave semiconductor power is fiber coupled and fiber delivered, with wall plug efficiency of roughly 25% dictated by the efficiency of the gallium nitride semiconductor, and is on pace to eventually exceed the efficiency of fiber lasers, according to Pelaprat.

Lithium-ion batteries require numerous conduction and keyhole welds of copper to copper, aluminum or stainless steel, as well as welding of copper and aluminum foils for cathodes and anodes, respectively, which IR lasers would simply cut through. By producing welds with no porosity or other defects, blue laser production means lower resistance and less heat dissipation inside the battery—and no dangerous hot spots. Blue laser also allows the use of thinner metals, which improves a battery’s energy exchange and energy density.

Nuburu’s 150-W AO-150 blue laser light is absorbed by copper at the rate of 65%; copper only absorbs 5% of IR light.

Nuburu’s lasers are finding use beyond energy-storage applications in automotive, aerospace, consumer electronics and health care. They have the ability to cut, braze, clad and even “print” blown powder to additively manufacture aerospace components or hip and knee implants. The company plans to release the AO-500, a 500-W version of the AO-150, later this year.

Also joining the blue laser trend is Germany’s Laserline, which displayed a prototype of a 450-nm unit at Photonics West. The LDM 500-60blue is rated at 500 W. The company will work with customers on proof of concept of projects in advance of the planned sale of systems beginning later this year or early in 2019, according to Oleg Raykis, sales manager.

Expanding the Toolbox

Laserline, known among other things for the diode laser systems it supplies for automotive brazing, also displayed its 19″ (483 mm) rack-mountable 6-kW fiber-delivered unit, “the most compact on the market as far as we know,” Raykis said. Based on the company’s LDM platform, the system performs the classic repertoire of conduction welding, hardening and mobile repair.

About two years ago, he noted, automakers began switching from electrogalvanized steel to hot-dip galvanized—introducing spatter and rough weld seams when using their conventional brazing methods. Laserline’s answer is a multi-spot module that combines two small beams and a larger spot. In production, the two small beams ablate zinc from the material surface before copper-silicon wire is laid in and melted with the larger beam. The power and distance between beams is adjustable, and the unit can be retrofitted to typical Laserline laser systems.

Further exploration revealed that the multi-spot module and Laserline’s standard OTS-5 optic could work together to move the two smaller beams of the triple spot within the larger beam to improve aluminum welds by using aluminum-manganese wire instead of aluminum-silicon wire. “This increases the hardness of the weld seam and gives you about a 20% increase in process speed,” Raykis said. The first systems are in testing at OEMs.

The company has also found a new use for its hybrid laser, which allows three modes: diode, converter and combined use of a converter source and a diode source. Generally used for blending cutting and annealing or softening processes, the beams can be superimposed on one another to weld aluminum quickly with a smoother weld seam.

Nanosecond pulsed welding, pioneered about three years ago by Trumpf-owned SPI Lasers, is another way to join dissimilar metals for electronics. “The melting temperature and properties of these metals are very different,” noted Richard Hendel, SPI’s vice president of sales, at Photonics West. “Using this process, you don’t create a conventional weld pool that can suffer from brittle intermetallics.”

Combining high peak powers and relatively short pulses creates mechanical adhesion and electrical contact in small joins between, for instance, copper and aluminum. While consumer electronics is a significant user of SPI’s method, electric vehicles are an up-and-coming opportunity, Hendel said. The process starts with a low power fiber laser (e.g., 70 W). “If you tried the same weld with a CW laser, you would need 500 or 1000 W.” SPI has released a 200-W system to cut already short cycle times in half.

“Our redENERGY lasers can pulse down to 3 nanoseconds and up to 2 microseconds,” added Colin Nolan, Eastern regional manager, US and Brazil. “If it can be done with a 1064 nanometer beam, we can do it.”

Applications previously performed with green or UV lasers can be done with SPI’s lasers. “I was micromachining on kapton last year—that has always been a green or UV application. Because I could pulse down to three nanoseconds, I had no problem machining it. There are things we’re learning that could not be done before, such as processing polymeric materials.”

Minding the Gap

In the quest to improve heat conduction and deep weld penetration in sheet metal applications, Trumpf (Ditzingen, Germany and Farmington, CT) launched its FusionLine welding system in North America around mid-2017, and “we are still discovering uses for the system,” said Brett Thompson, sales engineer.

This beam-delivery option for Trumpf’s disk lasers allows manufacturers to close gaps larger than typically allowed for laser welding. By combining two beam-diameter ranges—one normal, one large—and wire when needed, FusionLine helps OEMs bridge another gap—between traditional and laser welding technology.

“We have our normal welding beam diameter, and then a secondary beam diameter,” Thompson said of the process. “We’re getting creative with the delivery of the beam so we can make a spot size substantially bigger than the normal welding beam.” In a case where a weld is failing in a gap between materials and the part is being burned, FusionLine allows the user to either flow the materials together with the large beam or inject wire at a very hot point in the beam.

“It’s not just a large beam, which would become problematic because energy densities become lower,” Thompson said. “You lose welding speed, especially when you have to melt the wire, and that will transfer heat to the part,” leading to brittleness and distortion. FusionLine creates a hot center that rapidly melts the necessary joining wire without inhibiting weld speed.

The goal is to allow sheet metal manufacturers to transition directly from TIG or MIG welding to laser welding, “without having to do a lot of development work,” he said. FusionLine facilitates immediate transitioning of tolerances from, say, 0.004 to 0.01″ (0.1016– to 254 mm).

“You don’t have to use wire with FusionLine,” Thompson said. “You can bridge a much larger gap without wire than you could using only the normal beam diameter. We can make a beam that is substantially bigger to flow material together.”

Using a heat conduction process without wire on, for example, 2-mm-thick material, “you can achieve much higher welding speeds than TIG while achieving a more cosmetic weld, which doesn’t require any rework.” The focus is above the sheet, and the heat conducts from the top of the metal to the bottom, causing a radius to form.” Meanwhile, by employing a more aggressive deep penetration process, “you can be looking at speeds of 150–200 ipm [3810–5080 mm/min].”

Furthermore, with parts being subjected to less heat, OEMs can use higher-carbon and higher-strength steels to reduce material thicknesses. A manufacturer using a higher-grade steel that is perhaps 10% more expensive than a lower grade steel like A36 could use material that is 40% thinner.

Manufacturers in industries with high aesthetic requirements are likely to reap these benefits—for instance, makers of high-end kitchen equipment. With a top-of-the-line range, “the customer has a certain expectation for quality, and it can be difficult to manually grind down a TIG weld and make the radius look consistent.” Laser welding ensures a repeatable process with identical results.

The ultimate value proposition for OEMs and job shops is adopting a more efficient tool “without having to spend a lot of time redesigning their product to make it work for the traditional constraints of laser welding,” Thompson said. The change of the beam condition afforded by FusionLine, “is totally integrated and seamless,” and can be programmed to turn on and off in nanoseconds.

The new redENERGY 200 W air-cooled fiber laser by SPI Lasers, and samples of dissimilar metal welding capable with SPI’s nanosecond pulsed method. Each metal strap (0.3 mm) is welded to a stainless steel disk (1.2 mm).

Feel the Power

Higher power lasers offer new approaches to laser welding. According to Mohammed Naeem, senior manager of applications engineering and technology development for Prima Power Laserdyne LLC (Champlin, MN), multikilowatt laser welding “is one of the fastest growing applications for industrial laser materials processing. It is replacing traditional welding processes and enabling new designs of components that have been designed around the capability of laser welding. The main challenge is to develop robust processes that make use of high-power lasers.”

To that end, Laserdyne is developing gas shielding, plume reduction and beam shaping methods, as well as welding techniques with scanning heads and filler materials. The company’s suite of SmartTechniques solutions—especially SmartRamp and SmartShield—enhances the capabilities of its 2D and 3D systems.

More specifically, SmartTechniques are “exclusive processing techniques enabled through recent hardware and software developments allowing advanced, integrated control of laser, motion, process gas and process sensors within the Laserdyne S94P control,” Naeem explained.

To prevent weld defects, Laserdyne’s SmartRamp Weld Profile Control “minimizes post-process inspection triggered by weld endpoint defects—depression/weld bead undercut, porosity—and eliminates manual rework at the end of the weld,” he said. This is vital for critical components, particularly in aerospace engines, for which weld underfill or undercut are unacceptable.

Meanwhile, the SmartShield Laser Weld and Focusing Optics Protection module “includes a nozzle assembly with cross-jet that uses compressed shop air to protect the lens-protecting cover slide, while supplying shield gas such as nitrogen or argon to protect the weld from oxidation.”

Unlike other cross-jet welding heads, Naeem says, “there is no intermixing of the gases used for the cross-jet and for weld protection” with SmartShield. “The cross-jet nozzle can be used with the entire range of shield gas delivery devices, including welding shoe and coaxial gas nozzle tip. The focusing lens and shield gas assemblies can be changed quickly to vary the focused spot size. This allows welding of materials that are difficult to shield, such as nickel and titanium alloys for aerospace applications.”

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