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In Laser Welding, Power Needs Precision

Geoff Giordano
By Geoff Giordano Contributing Editor, SME Media

With greater laser power being used to weld sheet metal, tubes, copper and aluminum, operators must deliver that power with a precision that avoids defects.

Implementing laser welding can result in a process that is up to four times faster than traditional welding processes—for improved productivity and efficiency—while also increasing weld quality and repeatability. (Provided by Miller Electric)

With great power comes great responsibility, the saying goes. And with greater laser power being used to weld sheet metal, tubes, copper and aluminum, operators have a greater responsibility to deliver that power with a precision that avoids defects.

For instance, Trumpf’s BrightLine Weld technology lets users of its TruDisk lasers apportion power to the inner and outer cores of a two-in-one fiber to produce the ideal join.

And, multiple upgrades by IPG Photonics to its fiber laser portfolio refine welding through programmable adjustment of the output beam mode and monitoring technology that provides real-time feedback for crucial processing characteristics.

Likewise, Miller Electric is employing multiple beam modes to optimize welding of coated steels, aluminum and dissimilar materials. Meantime, Prima Power Laserdyne is expanding its welding repertoire with continuous wave and quasi-continuous wave options.

Boosting Weld Power and Speed

Since launching its BrightLine Weld technology in early 2018, Trumpf, Farmington, Conn., has caught the attention of the automotive, e-mobility and electronics industries, thanks to the technology’s ability to weld faster and at highest quality by adjusting the laser’s intensity distribution.

Trumpf has sold more than 120 lasers with BrightLine Weld functionality. The company presented details of the manufacturing improvements those systems have afforded OEMs at February’s Photonics West conference.

BrightLine Weld combines Trumpf’s standard TruDisk laser with a two-in-one fiber that has two fiber cores located coaxially, explained Stefanie Feuchtenbeiner, product manager for TruDisk lasers and BrightLine Weld. Users can program each core to deliver a percentage of the laser’s power—for instance, directing 40 percent to the inner fiber core and 60 percent to the outer core. Power can be adjusted in 1 percent increments.

In the case of automotive powertrain applications, Feuchtenbeiner said, “we can adjust power distribution in a manner that the process is almost free of spatter,” for instance when welding a gear wheel.

“Normally when you are welding with solid-state lasers, you are limited in your feed rate because at a feed rate of about 6 m/min, the process starts spattering,” she explained. With BrightLine Weld’s tailored power distribution, that feed rate soars to 15 m/min by using a 5 kW laser as opposed to the 3.4 kW laser setup that joins at a rate of 5 m/min.

Adding to BrightLine Weld’s flexibility is that it can be retrofitted to TruDisk lasers that have the proper beam quality. “Another big advantage for our customers is the fact that the two-in-one fiber is pluggable as it is standard for TruDisk lasers,” Feuchtenbeiner added. In case of fiber damage, users can simply plug in a replacement.

Copper welding, a vital process to produce hairpins for electric motors, is another application at which BrightLine Weld excels, she said, with significant prevention of spatter in deep-penetration keyhole welding of copper. For copper, BrightLine Weld also enlarges the process window toward lower speeds and higher penetration depths.

“We were able to produce high-quality weld seams with weld depth greater than 8 mm at a power level of 16 kW,” she said. “Furthermore, welding with beam shaping also supports reliable weld-depth monitoring using optical coherence topography (OCT). Until now, for copper welding the keyhole has been too unstable to measure.” With BrightLine Weld, “the keyhole and process are much more stable, so we are capable of applying OCT weld-depth measurement to copper samples.”

Trumpf began testing BrightLine Weld with partial penetration welding, she recalled, where reducing spatter on the top of the weld seam is the concern. The technology proved itself effective when joining mild and stainless steel, copper and aluminum. Those tests were followed by full-penetration welds, where spatter must be reduced on the top and bottom of the seam.

Tube and profile welding is another area BrightLine Weld is finding applicability, she noted.

“Typically you have tubes and profiles made from stainless steel that are welded in a continuous process at very high feed rates. At the moment, they still use CO2 lasers because with standard solid-state lasers you cannot weld fast enough at good quality. With BrightLine Weld, we are capable of full penetration welding of stainless steel sheets and also tubes and profiles with a very high feed rate at good quality, and we were able to reduce spatter on both sides.”

Thicknesses that BrightLine excelled at include 2 mm stainless steel sheet, welded at 12 m/min; for very thin sheet, that rate climbed to 30 m/min.

“Regarding the general TruDisk portfolio, we are working on increasing the maximum power out of a single disc from 6 kW to 8 kW,” Feuchtenbeiner confirmed. “Soon we will introduce a TruDisk 8001 with only one disk in a most compact housing with a footprint of less than one square meter and increased energy efficiency.”

To further expand its repertoire in copper welding for the automotive, electronics and consumer electronics industries, Trumpf introduced pulsed TruDisk lasers with green wavelength last year. Called TruDisk Pulse 221 and 421, they are being joined by a 1 kW continuous wave version called TruDisk 1020. “Due to its excellent absorption in copper, it is especially well-suited for heat conduction welding of copper foils and thin copper sheets and also for deep penetration welding with a weld depth of up to 1 mm.”

Fiber Refines Focus

IPG’s Adjustable Mode Beam enables programmable adjustment of the output beam mode to any combination of a small-spot, high-intensity bright core to a larger ring-shaped beam. (Provided by IPG)

Fiber laser giant IPG Photonics, Marlborough, Mass., recently launched several performance upgrades to its portfolio, including Adjustable Mode Beam (AMB) for its flagship YLS family of high-power CW lasers and an integrated high-power scan head with LDD weld monitoring technology.

AMB enables programmable adjustment of the output beam mode to any combination of a small-spot, high-intensity bright core to a larger ring-shaped beam, explained Applications Manager Vijay Kancharla. This reduces spatter at high weld speeds and also facilitates processing of zinc-coated metals. “These lasers are available at up to 25 kW of total output power, with the central core delivering up to 12 kW with IPG’s wall-plug efficiency of over 45 percent.”

By allowing power to be distributed between the core and the ring to suit a particular material, AMB achieves weld speeds in excess of 6 m/min in automotive steels and aluminum, he added. “The energy from the ring leading and trailing the central core beam can provide pre-heating and post-heating of the weld path, which enhances the overall results.”

LDD’s in-situ weld depth monitoring, completely integrated with IPG’s recently released high-power scanning heads and high-power lasers, “provides the most comprehensive and direct measurement of crucial processing characteristics, including weld depth, part fit-up, seam position, undercut, surface porosity and focal distance,” said Kancharla. “Integration of this technology within IPG’s high-power scan heads offers improved remote welding consistency and significant cost savings for applications such as medical, e-mobility, seating, powertrain and body-in-white applications.”

Meanwhile, IPG’s wobble welding heads and single-mode lasers “have allowed us to develop unique recipes for the welding of dissimilar metals such as copper and aluminum for electric vehicle battery manufacturing,” he said.

“Single-mode lasers that can be focused to a small spot can achieve a high power density and the ability to manipulate keyhole dynamics with optics and have resulted in production-ready solutions for an automotive customer,” he added. “Using this technology, we were able to minimize weld defects and keep intermetallic compounds to a minimum while achieving strong welds that make critical electrical contacts of individual cells to the sealing of the entire battery enclosure.”

IPG has been employing wobble welding—in which a galvo scan-head rapidly oscillates the focal spot of a high-quality beam—in two applications where pulsed YAG lasers have traditionally been used: the welding of aluminum microelectronic packages and 316 stainless parts.

“While both of these applications are typically welded with pulsed lasers, they are prone to weld cracking and defects,” Kancharla said. “Using wobble technology, we developed new process recipes using a CW laser, which resulted in improved throughput, yield and reduction of weld defects. Dynamic beam wobbling changes the melt pool dynamics and cooling rate of the weld, improving the overall process.”

Proving that its innovations are paying off, IPG also recently won accolades from Ford Motor Co. for dramatically reducing electrical consumption in Ford’s automatic transmission gear welding production. The automaker switched from CO2 lasers to IPG fiber lasers for its new generation of eight- and 10-speed automatic transmissions, improving energy efficiency by 300 percent and greatly reducing maintenance and downtime.

Laser vs. Arc

Also taking advantage of the combination of ring and center beams is Miller Electric Mfg. LLC, Appleton, Wis., which just installed an adjustable ring mode (ARM) laser from Coherent.

“This has improved the weldability of certain difficult materials,” said Erik Miller, laser product specialist. The ARM will improve the welding performance of coated steels, aluminum, and dissimilar materials, driven largely by requirements of the aerospace and automotive industries.

Miller also recently installed a PerformArc laser welding system for Pro Metal Works, “an end user that manufactures precision stainless steel sheet metal,” Miller explained. “They evaluated GTAW, plasma and laser welding. Laser won out due to performance and productivity benefits; laser was approximately four times faster than traditional welding processes.”

Laser can typically be a direct replacement for GTAW, he added, as “laser is more forgiving in variations in the contact-to-work distance, and it can improve weld access on complex geometries. The major barrier to adoption is capital cost and required volume.”

But using laser welding to replace GMAW “typically requires a change in part design,” he said. “Most parts welded today with GMAW rely on the filler material to create the weld. Laser welding can reach a one- to two-year ROI in either application if the volume is sufficient.”

Miller Electric operates two laser labs to help end users evaluate the process on their parts. The company offers a pre-engineered robotic laser welding work cell that is delivered pre-wired, pre-assembled and built to a common platform. “The system is rated as a Class 1 enclosure (that) has two part-loading stations with a single-point load/unload work area. The A and B stations have an additional servo motor for part position or rotation. The cell can be delivered with fiber or direct diode fiber-delivered lasers and with optional wire feed,” Miller said.

To Pulse or Not to Pulse

Since Prima Power Laserdyne, Champlin, Minn., began offering its SmartTechniques suite of technologies to facilitate more effective laser welding, “general interest in laser welding has gone up substantially,” according to Mark Barry, vice president of sales and marketing.

“We’re starting to see a lot of people” asking about switching from TIG or electrical discharge to put together multiple components. “We’re doing a lot of applications work trying to demonstrate the feasibility of laser welding. The number of systems that we would say are dedicated welders has grown substantially in the past three years.”

Barry explained that the company’s “sweet spot” is medium to heavier industrial applications in aerospace, turbine engines and medical, “so our systems are 1,000 W and above.”

The company’s repertoire of continuous wave fiber lasers extends up to 4 kW. “For people who want to do real finesse welding, we have a tendency to gravitate toward the QCW (quasi-continuous wave) lasers, which are the premier lasers for hole drilling but also give you extra control over power; you are able to do a lot of fine detail welding. A CW laser also has very good control, but I like that more for its speed and consistency in processing.”

IPG’s LDD in-situ weld depth monitoring is integrated with the company’s recently released high-power scanning heads. (Provided by IPG)

An example of an application ideal for QCW use would be welding a thin sheet metal cover on a turbine engine component, Barry explained. “You’re going to find that the QCW laser, with its power control, is going to allow you to do multiaxis contour welding much easier than a CW laser.”

That ability to control power delivery with pulsed beams contributes greatly to a growing need for joining dissimilar materials—a topic Laserdyne will be speaking to with a handful of conference presentations this year. That “finesse” welding of electronics and lithium-ion batteries, Barry explained, requires a system that allows exceptional ability to precisely manipulate energy and pulse formation.

Most recently, Laserdyne modified nozzle design and wire feed for its SmartTechniques portfolio to enhance processing control, Barry noted. With many customers buying laser welding systems for the first time, the onus is on laser machine suppliers to build smarter, more automated systems, he added.

“Laserdyne does something a little bit different than most people,” he explained. “We address the laser directly from our controller. In a conventional system, your controller will talk to the laser control, give it a series of commands, tell it how to develop the pulse, what the power should be, etc. It’s a closed-loop process between the laser controller and the laser, and the output is the output.

“But, if you want to do things very quickly and you want more control, our machine tool controller talks directly to the laser and by-passes the control,” he continued. “We get very fast response time. We’ve demonstrated changing laser conditions on a pulse-by-pulse basis at very high frequency.”

Such responsiveness should open new processes for welding, gaging hole depth and drilling, he added.

While fiber lasers continue to expand upon their position as the go-to laser for such operations, and with the industry keeping an eye on the potential for direct diode lasers, Barry offered some perspective.

“In conventional machining, people are not obsessed with the next thing,” he noted. “In laser processing, for years we’ve been obsessed with the next thing that’s really going to make the breakthrough.” Ultimately, success is determined by strict process control. “People aren’t looking to do the most unusual thing in the world; they need to be able to make their parts consistently.”

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