Hand-held laser welding—to code

A hand-held laser welding torch, demonstrated here at last year’s FABTECH show, has a wire feed that helps govern the travel speed. Butler Photography

Two decades ago, few would have thought about wielding a torch that emits a laser with enough power and energy density to weld. Today, hand-held laser welding (HHLW) is gaining significant popularity.

Most HHLW performed now isn’t for code-level work. Popular applications simply haven’t demanded it. This, however, is starting to change. Some prominent manufacturers, including SpaceX, have started to employ HHLW in significant ways.

Standards-making organizations are taking note. The Canadian Welding Bureau has issued statements recognizing HHLW as a viable process to use under certain CWB standards. The American Society of Mechanical Engineers has recognized the process and the use of certain machinery in Section IX of the Boiler and Pressure Vessel Code.

Finally, the American Welding Society is working to update its standards and recommended practices to incorporate specifics about hand-held laser welding. These include the laser welding standard AWS C7.4, Process Specification and Operator Qualification for Laser Beam Welding, as well as AWS C7.2, Recommended Practices for Laser Beam Welding, Cutting, and Drilling.

The devil is in the details, of course, especially since the very foundation of laser welding is so unlike processes that weld with an electrical arc. What are the essential variables deemed critical for producing a weld with the required properties (and hence, if changed, require a requalification)? What are the nonessential variables, those that the welder can adjust without having to requalify a procedure? Many are spelled out in AWS C7.4, but they’re tailored for mechanized and robotic laser welding—not the hand-held process. Future code updates aim to change this.

Meanwhile, HHLW continues to proliferate, and the technology’s advocates continue to educate those with an interest to learn.

Tate Patterson, an Idaho-based welding engineer at Next Level Results, serves as chair of the AWS C7C subcommittee on laser welding, which is working on the C7.4 update. He explained that as a first step, the committee has been working to define the technology using the terminology framework of other AWS standards. “The industry commonly calls the process hand-held laser welding, but it will likely fall into subcategories, depending on whether wire is fed into the weld.”

Other AWS codes classify traditional welding processes as either manual welding or semiautomatic welding. In manual welding, the welder controls the entire process by hand. Shielded metal arc welding, also known as manual metal arc welding or stick welding, is the classic example. In semiautomatic welding, the electrode (usually a wire) feeds automatically into the arc, as is the case with gas metal arc welding (GMAW).

Current codes define “welders” as those who manipulate the welding gun or torch, while a “welding operator” operates adaptive controls, automatic, and robotic systems. Tate added that robotic welding processes today include instances in which welding torches are mounted on the end of cobot arms—including the hand-held laser welding torch.

“If you mount the laser torch on the end of a cobot arm, it’s still fully robotic and would be qualified as a robotic laser welding process. You might program it collaboratively, but once you’re done, you perform the entire weld through the push of a button.”

At THG Automation’s booth at last year’s FABTECH, an HHLW torch is mounted to a cobot arm. Tim Heston

HHLW can create an autogenous weld, without filler metal, but it often incorporates a wire that’s fed automatically into the melt pool. In fact, the wire feed itself helps the welder control the process in ways that are very different from the semiautomatic arc welding processes defined by existing codes.

“I think the biggest limiting factors for hand-held laser welding’s adoption is the lack of knowledge.”

That was Rex Alexandre, president and principal engineer at The Handheld Laser Institute in Seattle and an applicant of the AWS C7C subcommittee. Before striking out on his own, Alexandre helped build SpaceX’s hand-held laser welding program. Today, he offers training, research and development, and consulting to companies looking to adopt the technology. “It really is such a powerful technology that’s often misunderstood in the industry.”

When Alexandre sees someone perform hand-held laser welding for the first time, he can spot the veteran welders immediately. “I often see guys who have TIG [GTAW] or MIG [GMAW] welded for years trying to float the [laser welding] torch tip above the part. Really, you want the torch to rest on your part so it can propel itself down the joint. The wire is resting on the workpiece, and your focus position is in control.”

The wire also helps the welder maintain a consistent standoff and focus spot, while the wire feed governs the travel. Look at hand-held laser welding in action and you’ll notice the welder pulling the torch toward him. In reality, the welder isn’t “pulling” the torch but instead is just keeping the torch angle steady, parallel to the workpiece, as the feeding wire propels the torch toward him. The feeling is unique—again, very different from traditional arc processes, which is why experienced welders sometimes have trouble adapting.

“You’re manipulating the torch, but not like you would a TIG torch. Especially if you’re feeding a wire, the torch almost manipulates you.” So said Frank Rupp, a weld process specialist at Airgas, Schuylkill Haven Pa. The certified welding inspector and certified welding educator serves as a contributor to the AWS C7C subcommittee.

“I’m a welder, and throughout my career, when TIG welding, I learned to manipulate the weld pool with the torch. With laser welding, I had to let go all of that. With wire-fed hand-held laser welding, you just hold the torch steady. You can’t see the puddle and you’re not looking at it. When you set up the machine, you dial in the depth of penetration and your travel speed for the material and joint design you’re working with. When you initiate that torch, the wire starts feeding. From there, you just hold the torch and let it feed itself.”

“This is really what trips up welders experienced with other processes,” Alexandre said, “but it’s also what makes hand-held laser welding so easy and repeatable for people with no prior experience. The wire feed actually commences the torch’s motion, establishing your travel speed.”

As Rupp explained, even with autogenous HHLW, the welder never pushes the gun forward. “You always want to have the torch in front of you and having it move back toward you, never away from you.”

As Alexandre explained, depending on the machine manufacturer, the torch itself uses either a collet or tube to control the focus position, which the welder might adjust if a certain weld requires a defocused spot. And again, if the process uses a wire, the distance between the material surface and laser optics remains consistent.

A hand-held laser welding torch handle is designed to be kept parallel to the weld surface. Butler Photography

The idea is to keep the torch angle as consistent as possible. Changing the angle slightly doesn’t change the focus significantly, Alexandre explained, but it can change the depth of penetration. “Even this is fairly straightforward,” he said. “You want the torch handle to be parallel to the part you’re welding.”

As a consultant, Alexandre has helped clients qualify certain hand-held laser beam welding procedures using existing codes. The existing AWS C7.4 standard wasn’t written with hand-held laser welding in mind. So, he combines the essential variables from AWS B2.1, Specification for Welding Procedure and Performance Qualification, with essential variables from AWS C7.4.

He then uses these to draft the WPS, supported by test welds recorded on the procedure qualification record (PQR), detailing the results of bend tests, pull tests, and other destructive techniques. All this creates a bedrock of documentation practices Alexandre’s clients can use for qualification acceptance criteria as detailed in sector-specific codes, be it structural (like AWS D1.1), aerospace (AWS D17.1), or anything else.

Alexandre added that nearly all the procedures he’s written involve a filler wire, which helps keep the standoff between the laser and workpiece surface consistent. He’s only worked to qualify a few autogenous HHLW procedures, and in most, the welding torch is fixed and the workpiece moves. Again, the added wire puts the travel speed under the welding equipment’s control.

Alexandre reiterated that what is deemed acceptable depends on the ultimate engineering authority’s requirements for a job. Most of the qualification work he’s done has involved customers using HHLW for stainless steel or aluminum handrail fabrication. Having a welding code that specifically details HHLW’s use will help broaden the technology’s acceptance—hence the importance of the C7C subcommittee’s work.

The C7.4 standard begins with a chart detailing how the WPS is written, supported by test results in the PQR, with the process performed by someone with an up-to-date welding operator PQR. At the bottom of that chart is a detail that has spurred some debates at recent committee meetings: the equipment qualification record.

In the past, if a manufacturer with a large automated laser welding system needed to qualify a process to a code, the company likely invested in a beam profiler, which would periodically measure the beam and check its quality. “For hand-held laser welding, though, the laser welding equipment is actually less expensive than the beam profiler,” Alexandre said. “So, the question becomes, how do I know that my equipment is performing adequately?”

Some equipment comes precalibrated from the factory, Alexandre said, with special collimating lens systems actually adapting to any focal position change that could occur. For equipment validation purposes, Alexandre has suggested the use of precalibrated machinery. Even so, the standards-writing committee is considering solutions for the various machines now on the market. Possible approaches to equipment qualification, Alexandre said, are still being discussed.

Last year, Patterson started serving on a committee organized by the International Institute of Welding (IIW). “IIW has put together a committee to produce a set of documents or procedures about [HHLW] safety,” he said, adding that it’s too soon to say what exactly the IIW committee will produce. That said, the IIW meetings do signify the importance of addressing safety around the new process.

Though C7.4 is not a safety standard, it does provide safety guidance and references ANSI Z136.1, Safe Use of Lasers, and ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes.

People in metal fabrication view HHLW’s safety in various ways. Some don’t think about it at all; others are so concerned that they don’t even consider adopting the technology.

The concerns abound, and for good reason. Videos across the internet show HHLW taking place behind welding curtains or even in the middle of the factory floor. The operator might be protected by laser safety glasses, but how about everyone else in the shop? The fact that the fiber laser’s 1-µm wavelength is invisible to the human eye makes the lack of safeguarding even more concerning.ANSI Z136.1 requires that any fabricator operating a Class 4 laser designate and train a laser safety officer (LSO). “The LSO needs to maintain employee records for safety training,” Rupp said. “And before operating the laser, companies need a light-safe enclosure. They need proper signage and safety interlocks on the entryways. If someone opens the door, the system will shut down the laser and make it inoperable until the interlock is connected again.”

Rupp added that the LSO “needs to know about the parameters of the laser that they will be using in their facility. The PPE needs to account for the laser wavelength and other variables, so the eye protection and other clothing protects workers against those wavelengths.”

Rupp, who is an LSO, also incorporates safety into HHLW technique. The welding torch is designed so that the welder holds it from behind. And unlike with GTAW or GMAW, the welder cannot see the weld pool directly. That’s by design. “With GTAW, you’ll often be in front of the torch, so you can see your puddle and your wire. If you were behind the torch, you couldn’t see anything,” Rupp said. “With laser welding, it’s totally opposite. You never want to be in front of the laser torch. You need to be aware of your direction of travel. And before you initiate that torch, you need to be aware of where that beam can go. You need to be aware of your body position and other people in the enclosure with you. If they’re in there with you, they’ll have on PPE, but you also need to make sure they’re behind you and behind the welding torch.”

Any fabricator with a fiber laser cutting machine has experience designating and training an LSO, but for many small weld shops, HHLW might be their first foray into industrial laser processing. The technology is too attractive to ignore, though, especially considering the weld quality produced by those who’ve never welded before—hence the need to spread the word about best safety practices.

Sources emphasized that detailed laser safety strategies are outside the scope of the C7C laser subcommittee. Again, the code refers to widely accepted laser safety standards like ANSI Z136.1. Regardless, initiatives at the IIW and elsewhere are showing that the industry can’t ignore the unique safety considerations HHLW presents. Laser welding isn’t arc welding, and traditional welding curtains don’t protect against laser light.

Not too long ago, HHLW was seen as a novelty, with a handful of smaller vendors selling it in the U.S. Today, the major welding players are selling hand-held laser welding systems of their own. And now, standards-writing organizations are helping to develop a technical foundation for what’s become a rapidly maturing process.

Many questions remain, but code-writing committees continue their work toward answering as many as they can. At this writing, a timeline for the AWS C7.4 update hasn’t been released. The aim is to identify best practices and give the industry a framework for quality. Supported by qualified equipment, processes, and people, HHLW should help fabricators create welds as close to perfect as possible.