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Laser welding thick with dynamic beam shaping technology

May 15, 2023

This concept illustration shows a dynamic beam laser welding 70-mm-thick plate in a single pass.

At FABTECH 2022 in Atlanta, attendees could sit at a workstation in Civan Lasers’ booth, click a few points on a screen, and customize a laser welding beam energy profile and depth of focus, made possible by what Civan is calling dynamic beam laser, or DBL, technology.

DBL has led to some eyebrow-raising accomplishments, the most recent one announced on Feb. 9, when the company said it completed a single-pass weld that's 70 mm deep, accomplished at atmospheric pressure—no vacuum required.

The Israeli company doesn't manipulate its laser mechanically, relying on galvo mirrors that wobble the beam spot. Instead, the manipulation happens inside the laser itself.

"We have more than 30 fibers, and the goal is to control the diffraction pattern. With this, you can design any power distribution that you want on the workpiece."

That was Ami Spira, Civan's marketing manager, describing the basics behind the company's coherent beam combining (CBC) and optical phased array (OPA) technology, the two building blocks behind DBL. "This allows the user to do many applications that previously haven't been possible with a laser."

At the booth, attendees could click on a grid pattern to define a beam profile in free-form style. "That's the shape, but we can also control the density," Spira explained. "For example, say I want to create more energy in this area." He pointed to an area slightly off-center within the beam profile. "I can just add a click here, and now I have much more energy in that area."

Another parameter of control involves the diffraction pattern. "It has to do with the way we generate the laser," he said. "Our optical head has multiple beams that emit light, and they overlap to generate that diffraction pattern. And by controlling the phases of each laser, we can [change characteristics of the beam] in the X, Y, and Z direction."

The Z axis is especially critical because it gives new levels of control to the beam's depth of focus. "For example, using a focal length of 1.5 m, we could have a depth of focus of almost 30 mm. And if we have 3 m [focal length], then the depth of focus would be more than double."

Such depth of focus, combined with other beam parameter refinements, have pushed Civan into novel applications. One of the most recent involves the single-pass welding of extremely thick material in a butt joint configuration. Helping make this possible is a partnership between Civan and AMET, a company in Rexburg, Idaho, specializing in automated welding systems, including those involving very thick weld joints.

"[Civan] was looking for a partner in the U.S. to provide integrated systems," said Don Schwemmer, AMET president, during an interview at FABTECH. "We had been wanting to work with a laser provider [and] developer. And the control side is really our strength. With being able to manipulate the beam shape and focal lengths on the laser, we can add that to our [control] package. We’ve now got a huge toolbox to work with, instead of just a couple of wrenches. It's really a good fit."

The dynamic beam laser uses coherent beam combining and optical phase array technology (shown here) to create a beam tailored for the application.

At FABTECH, Civan exhibited work samples that showed the DBL's ability to produce strong welds in crack-sensitive material, reduced pores and spatter thanks to beam shapes that stabilize the keyhole, and the ability to control properties of dissimilar materials.

According to a Civan white paper, DBL technology alters the beam characteristics in four ways. First is through beam shaping, where users design a specific shape to match a specific application. This gives engineers the ability to test "multiple shapes to optimize the best shape for the specific weld. For example, when welding dissimilar metals, DBL would allow for the use of two laser spots moving at the same time (imagine the movement of a kitchen mixer) to provide the homogenous weld."

Another variable is shape frequency, or the ability to create the shape at different intervals. The greater the frequency, the closer to "static" the beam behaves. "Fast frequencies like 50 MHz, for example, are so fast that the beam behaves in a quasi-static shape," the white paper stated, adding that such a fast frequency produces completely different results than frequencies in the hertz or kilohertz range.

The third parameter is beam sequencing, which allows the laser to switch between beam shapes as fast as a microsecond. "This means you can create a series of different shapes and program the laser to run through them in order, at different speeds, at intervals of your choice."

The fourth parameter is focus steering. Again, according to the white paper, "this means you can change the focal position on the Z axis within the material at any time and at any speed during the process. Focus steering is especially beneficial when welding thicker materials, allowing for a smoother and more consistent weld."

Such focus steering is being utilized by AMET and others for single-pass, thick-plate welding. It's also how Civan achieved that single-pass weld in 70-mm-thick material in the application announced earlier this year.

Thick-plate welding is just one application area the company has tackled in recent years. At the other end of the thickness spectrum, the company has been involved with the Eureka Project at Fraunhofer Institute for Laser Technology in Germany, working on ultrahigh-feed-rate welding of bipolar plates in fuel cells—a project involving sheet just 0.1 mm thick and welding speeds of 1,500 mm/second.

For this project, researchers shaped the beam in such a way to combine high-intensity points with additional areas of lower-energy intensity, an arrangement that allowed an ever-so-brief preheat and postheat of the material. This helped control how the melt pool formed and solidified. They also changed the shape of the beam (which can occur mid-process) to an oval to reduce the melt pool's flow velocity behind the keyhole. This allowed researchers to increase welding speed without creating defects.

Although Civan has focused heavily on laser welding, it's also delved into other industrial laser processes. For instance, the company has partnered with Smart Move GmbH in Germany to develop new laser welding and laser powder bed fusion technology for additive manufacturing.

The company also has published a few papers detailing test results from a laser cutting application that exemplifies the benefits of focus steering. Specifically, the company cut 15-mm-thick 304L stainless steel with an 8-kW, single-mode, high-depth-focus laser. The beam was shaped into a spiral with two points in a vertical orientation. According to the paper, the focus steering occurred with the points "positioned at the middle of the material and steered up and down at ±8 mm through the Z axis. The focus steering frequency was set to 5.4 to 16 Hz at a feed rate of 15 to 18 mm/second … the focus steering improves control over the molten material and enables smoother roughness with less dross."

An interface at FABTECH allowed attendees to click and customize a beam profile.

Beyond this, Civan partnered with SLTL (Sahajanand Laser Technology Limited), an Indian company, to create a machine that performs both 3D laser welding and cutting. According to a Civan press release, "This project will create a complete end-to-end system with dynamic beam-shaping lasers."

Civan's technology might be a harbinger. The industrial laser beam is no longer static. It's evolved into a true Swiss Army knife of metal manufacturing, able to be shaped, sequenced, and focused in multiple ways and frequencies, all optimized for the application at hand.

Civan's dynamic beam laser can be customized with profiles to match a specific application.