Photo courtesy ESAB

Laser Welding

Combining the best of both worlds, lasers and gas metal arc-welding together are expanding possibilities for large gap welding applications.

Laser Welding Applications Expand Solid-state laser technology has matured, leading to development of new, cost-effective welding applications, such as hybrid welding Bruce Morey Contributing Editor

L

asers for welding have proven their worth in the last 35 years in select applications. Despite their high capital cost, the precise, intense heat source makes lasers the right choice where there are tight tolerances, close fit-ups, and thin materials. These

are applications where lasers produce less distortion, with their smaller heat-affected zone (HAZ) around the weld. That lack of distortion is critical in applications from medical devices to sheetmetal lap joints on automobile body parts, according to Ed Hansen, global product manager for ESAB (Florence, SC), the international welding company.

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Laser Welding He said that the laser has become more popular as solid-state lasers have come to dominate the field. Because of their operating wavelength in the near infrared, solid-state lasers deliver their beams along flexible fiber optics instead of the optics and mirrors required with older CO2 technology. “Fiber-delivered lasers are now useful on larger and higher-volume parts,” he said, noting that automated welding applications that do not currently use lasers should consider them given the advances. “Most of the things you need to do Photo courtesy Trumpf

for automated welding,” he said, “you will need to do to be successful at using a laser.” However, as an autogenous process with no filler material, laser-only welding has been limited to those thin-walled and tight-tolerance applications. Laser-only welding is currently limited to applications where joint tolerances allow no more

Scanner welding of an automotive car door using Trumpf’s

than about 0.1 mm of gap variation. In a number of ways that

programmable focusing optics PFO 3D. The yellow fiber

is changing. One way is with hybrid welding.

optic cable connects to a solid-state TruDisk laser.

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Laser Welding Companies like ESAB are using their expertise in gas metal arc welding (GMAW)—think MIG—combined with fiber-delivered laser energy to create the best of both in these hybrid Photo courtesy Laserline

systems. The addition of GMAW means using an arc to add-in filler material from a wire. Welds in thicker materials benefit from the precise, deep penetration heat source of lasers, and the combined system is faster and more forgiving. “With a filler metal added, this allows you to start applying laser welding to joint fit-ups and joint designs that are not optimal,” Hansen said. Modest gaps can be bridged. Certain amounts of surface contamination are tolerable and weld chemistry and mechanical properties can be manipulated. Designers can

A high power direct-diode laser from Laserline welding an aluminum deck lid. Aluminum is a particularly good application for direct-diodes, according to Laserline.

also add fillets and bead reinforcements for greater strength

cording to the company. Its wider bead bridges gaps that are

and to resist fatigue failures. “This means laser welding can

four times wider than a conventional laser-only process. Just

be applied in more conventional applications,” he said.

as importantly, an adaptive control system monitors the weld

ESAB’s Hybrio is such a hybrid system, combining a

joint in real time, adjusting for joint gaps and mismatches

solid-state laser with GMAW. It welds at 3–10 times the speed

and further broadening the process window to handle gaps

of conventional processes, with 80–90% less heat input, ac-

up to 1.5 mm. New applications now opened to laser welding

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include shipbuilding, construction, pipeline supplies (such as

Remote welding systems rapidly direct a laser beam over large

oil-country tubular goods), heavy equipment/off-highway, and

parts like automotive doors and closures. They weld a num-

railroad equipment.

ber of spots and short seams separated by distance, saving

In terms of hybrid welding, Jim Hurley, southeast regional

time over traditional spot-welding methods. In many cases, it

sales manager for Trumpf Inc. Laser Technology Center (Plymouth, MI), also pointed out that the laser not only saves time, but material as well. Many weld joints prepared for welding are Vgrooves, and a wide joint is needed for traditional GMAW to get heat energy to the bottom. With laser’s deep penetration, a smaller included angle is needed

#

and hence less filler material. Solid-State Lasers— Power and Multiplexing Hansen from ESAB noted that while

Productivity Gains

The specific geometry of the Multi-Carb was designed with a large, uneven flute count for a smoother cutting performance that increases tool life and positively impacts cycle times*

solid-state and fiber lasers now run up to many 10’s of kW in power, the

* SGS helped an aerospace company GAIN over 27 days of production while REDUCING the cost per part by nearly

practical limit of what they would use in hybrid welding is around 12 kW. Beam quality in terms of beam parameter product (BPP) need not be finer than 10–12 mm-mrads, in most welding applications. In fact, for “high power” welding applications, from hybrid to

78%.

remote scanning, 75% or more of most applications require lasers that provide power between 4–6 kW, according to

** The Multi-Carb accomplished a tool life of 25 parts with twice the axial engagement where the competitor only obtained 4 parts. This yielded a 625% improvement in tool life and 338% more material removal.

Hurley from Trumpf, with a BPP around 8 mm-mrad or better. For example, a common laser for welding is the Trumpf TruDisk 6002. It provides a near-IR beam at 6 kW with a BPP of 8 mmmrad. Another plus is that some models deliver their energy through up to six

DEFINING HIGH PERFORMANCE

individual fibers, enabling a single laser

MILLING

to power a number of independent

DRILLING

ROUTING

workcells, reducing capital cost. As important as the advent of hybrid welding is, Hurley also noted that remote

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laser welding remains important. Remote welding uses the unique standoff capability of lasers and scanning optics.

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Laser Welding produces a better weld, according to Hurley. Remote welding

separation cleanly and quickly is what you worry about. How-

started with far-IR beams from CO2 lasers delivered in flying op-

ever, for a successful weld you do not only worry about getting

tics. Today, he noted that solid-state lasers are now the choice.

things to ‘stick’ together but also what has to be done so that

This means that laser heads mounted on common six-axis

‘union’ will last in the long term. For laser welds you have to

articulated arm robots provide unprecedented mobility, combin-

be concerned about the chemistry of the base and weld met-

ing motion of the head with directed motion of the beam.

al, the resulting microstructure of the weld and the HAZ, and

With advancements like solid-state remote welding and hy-

the size.” He sees laser-welding growing, from remote welding

brid welding, Hurley believes there is plenty of room for growth

to creating tailor-welded blanks. Lincoln Electric supplies

for laser welding, especially in North America. “The Europeans

laser-welding systems, hybrid laser systems that combine

are leaders in developing and deploying it,” he said. They are

laser and GMAW, and hot wire cladding laser systems.

more comfortable with the technology, according to Hurley.

The key, as Denney sees it, is to think of laser welding as

“They are seeing the benefits,” he said. Those benefits will

a revolutionary, not an evolutionary, process, especially for the

grow on manufacturers in North America, he believes.

newer hybrid approaches. “You do not want to try and replace a resistance or arc-welding process one-for-one. For example,

The Foundation Elements for Growth

lasers want to give you a high aspect, deep penetration weld,

“Laser cutting is like a divorce, but laser welding is like

but if you look at the drawings from most companies they

a marriage,” said Paul Denney, senior laser applications

might specify an edge-lap joint or fillet-type joint,” he ex-

engineer of Lincoln Electric (Cleveland, OH). “For a cut getting

plained. Simply using a laser to weld the fillet they specify, you

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Laser Welding cannot get high enough deposition rates to justify the laser. “What you want to do is use a joint that works to the strength of the laser like a butt joint,” he said. Anecdotes like these speak to the need to introduce laser welding early in the design process, with design engineers involved as well as the manufacturing engineers on the factory floor. At that point, it is vital to explain the process in terms of economics. “You almost need to talk to the finance guys,” he said, explaining that with a rapid process like lasers, if the part is designed to the laser process, you can actually reduce the cost per part.

Precision & Repeatability for Challenging Workholding Applications

At the same time, manufacturers are necessarily cautious about adopting novel approaches to mainline products. “You need to ease into some novel areas and then, once it has proven itself, [manufacturers] can trust it and use it more broadly,” he said. “That has happened in transmissions and in car seats. Eight years ago, no one was really using laser remote welding for car seats and now almost all suppliers are doing it. Why? Because they trust it,” he said.

“For laser welds you have to be concerned about the chemistry of the base and weld metal, the resulting microstructure of the weld and the HAZ, and the size.” He also pointed out that for select industries and applications, laser welding has reached a certain maturity, like tailor-welded blanks, drive train, and medical components. Costs for lasers have decreased, but he sees that cost-curve flattening in the last couple of years. Nevertheless, he predicts both hybrid and remote welding applications will expand, replacing other welding methods. “Sweeping a laser beam from spot to spot is much faster than moving a resistance weld gun between spots even as the welds themselves take about

At Hydra-Lock, we continue to develop our workholding technologies, engineering industry’s best chucks and arbors while providing application support to meet the increasing demands of the high-tech aerospace industry. Among our many innovations are solid- and split- steel expanding sleeve designs, and the Conform-A® technology for the highest expansion and capability to hold thin-walled and out-of-round components, while averaging center, and without rounding.

the same,” he said. Therefore, for the same number of spot welds, that means faster cycle times and higher throughput. Machine Tool Approach to Laser Systems “Welding once was background noise compared to laser cutting, which is where the majority of systems were sold,” said Mark Barry, vice president sales & marketing of Prima

Originators and developers of Hydraulic Chucking

Power Laserdyne (Champlin, MN). “But about five years ago, we began to see an expansion in laser welding applications.”

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www.hydralock.com

Laser Welding From a negligible slice of their business, he has seen welding grow to about 25%. Laserdyne specializes in delivering turnkey class 1 laser installations that provide all of the stable movement and control of an accurate machine tool. Customers include turbine, high-precision medical device, and electronics device manufacturers. He attributes two reasons for the growth of laser welding: the nature of the parts and the availability of efficient and economical fiber lasers. “The parts we deal with today are more often near-net shape. We are joining finished parts together,” he said. These highly machined, high-value parts already have the tight fit-up needed Photo courtesy ESAB

for an autogenous process. They also need a process that minimizes distortion—ideal for laser welding. The fiber lasers Laserdyne incorporates into its machines are providing an ideal and convenient laser source to meet the needs for precision welding. The fiber delivery means an output beam Hybrid welding, combining GMAW with high-power lasers,

source that is evenly distributed as a top-hat (as opposed to a

is also suitable for automation, as shown here.

peak Gaussian distribution), with the advantage of low divergence.

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Even with the advent of fiber lasers, laser welding capital

mediate power source. The direct diode laser skips the interme-

expense costs can be relatively high but are offset by many

diate process. The trade-off is poorer beam quality but higher

advantages. As Barry found out from an extensive review with

efficiency. Laserline (Santa Clara, CA) is a supplier of high-power

existing customers, capital cost was not the most important

direct diodes used to create the laser beam used in welding, cut-

buying factor. The factors that matter include good process control; high-quality welds; robust operation with high uptime; and ease of use by operators not expert in lasers.

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“Fiber lasers when employed correctly are easy to use and easy to teach people to use,” he said. “They provide a large window of acceptable parameters.” Some customers prefer a lower

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average power with many pulses; others prefer high power with few pulses. Customers can obtain a variety of results from the same basic system. “The simple processes actually mean we can do more interesting welding,” he added. Laser Developments Another key development Barry is seeing is a single laser system tasked to do multiple operations, such as cutting, drilling, and welding. He attributes this to the newer quasi-continuous wave (QCW) fiber laser. “Before, manufacturers would cluster lasers in the same area, now they are distributing them into work cells because they can perform

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diode lasers, according to Hansen.

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Attributes he likes include lower cost, higher electrical efficiency and the small footprint or form factor. In fact, they are similar in size to current welding power.

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What are direct-diode lasers? Many solid-state lasers use diodes to excite a

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3:19 PM

Laser Welding ting, or brazing. “The wall plug efficiency of a direct-diode system

quality. Wall-plug efficiency is reduced and the beam

is between 40–48%,” said Wolfgang Todt of Laserline.

converter adds capital expense. Said Todt: “It is our answer

Laserline’s LDF series direct-diode lasers range from 3-20 kW power, though beam quality decreases as power

to fiber lasers in applications requiring higher-quality fiberoptic delivery of a beam.” ME

increases. For example, the Laserline’s LDF 3-kW version is 20 mm-mrad, the 6-kW version is only 40 mm-mrads, with standoff distances of 150 mm. These are better than they used to be and today there are a number of applications where this is sufficient beam quality, especially in aluminum welding, Todt said. Welding with direct diode lasers is not always autogenous. Audi uses LDF diodes to weld aluminum with aluminum-silicon wire filler, using 2–6kW LDF lasers. In other applications requiring higher quality, Laserline introduced a beam converter device for its LDF line of laser diodes. “For up to 4 kW, the beam converter provides 8 mmmrads of beam quality with a standoff distance of 500–650 mm,” Todt said. There are trade-offs for the enhanced Want More Information? ESAB Welding & Cutting Products Web site: www.esabna.com/ Hybrid Laser Microsite: www.esab.com/hlaw Ph: 843-669-4411 / 800-ESAB123 Laserdyne Ph: 763-433-3700 Web site: http://tinyurl.com/ laserdynesme Laserline Ph: 408-834-4660 Web site: www.laserline.de/t Lincoln Electric Ph: 888-935-3876 Web site: www.lincolnelectric.com/ en-us/ Trumpf Inc. Ph: 860-255-6000 Web site: www.us.trumpf.com/en

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