Laser Welding Applications Expand L - sme. · PDF fileCompanies like ESAB are using their...

March 2014 | ManufacturingEngineeringMedia.com 81

Lasers 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 applica-

tions from medical devices to sheetmetal lap joints on

automobile body parts, according to Ed Hansen, global

product manager for ESAB (Florence, SC), the interna-

tional welding company.

Combining the best of both worlds, lasers and

gas metal arc-welding together are expanding

possibilities for large gap welding applications.

Laser Welding Applications ExpandSolid-state laser technology has matured, leading to development of new, cost-effective welding applications, such as hybrid welding

Bruce MoreyContributing Editor

Laser Welding

Photo courtesy ESAB

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

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

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

is changing. One way is with hybrid welding.

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82 ManufacturingEngineeringMedia.com | March 2014

Laser Welding

Scanner welding of an automotive car door using Trumpf’s

programmable focusing optics PFO 3D. The yellow fiber

optic cable connects to a solid-state TruDisk laser.

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Companies like ESAB are using their expertise in gas metal

arc welding (GMAW)—think MIG—combined with fiber-de-

livered laser energy to create the best of both in these hybrid

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

also add fillets and bead reinforcements for greater strength

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

be applied in more conventional applications,” he said.

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

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

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

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

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

as importantly, an adaptive control system monitors the weld

joint in real time, adjusting for joint gaps and mismatches

and further broadening the process window to handle gaps

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


Laser Welding

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.

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rline

include shipbuilding, construction, pipeline supplies (such as

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

railroad equipment.

In terms of hybrid welding, Jim Hurley, southeast regional

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 V-

grooves, and a wide joint is needed for

traditional GMAW to get heat energy to

the bottom. With laser’s deep penetra-

tion, a smaller included angle is needed

and hence less filler material.

Solid-State Lasers—

Power and Multiplexing

Hansen from ESAB noted that while

solid-state and fiber lasers now run

up to many 10’s of kW in power, the

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

remote scanning, 75% or more of most

applications require lasers that provide

power between 4–6 kW, according to

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 mm-

mrad. Another plus is that some models

deliver their energy through up to six

individual fibers, enabling a single laser

to power a number of independent

workcells, reducing capital cost.

As important as the advent of hybrid

welding is, Hurley also noted that remote

laser welding remains important. Re-

mote welding uses the unique standoff

capability of lasers and scanning optics.

Remote welding systems rapidly direct a laser beam over large

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

ber of spots and short seams separated by distance, saving

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

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produces a better weld, according to Hurley. Remote welding

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

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

This means that laser heads mounted on common six-axis

articulated arm robots provide unprecedented mobility, combin-

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

With advancements like solid-state remote welding and hy-

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

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

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

more comfortable with the technology, according to Hurley.

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

grow on manufacturers in North America, he believes.

The Foundation Elements for Growth

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

a marriage,” said Paul Denney, senior laser applications

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

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

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

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

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

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

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

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

to creating tailor-welded blanks. Lincoln Electric supplies

laser-welding systems, hybrid laser systems that combine

laser and GMAW, and hot wire cladding laser systems.

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

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

newer hybrid approaches. “You do not want to try and replace

a resistance or arc-welding process one-for-one. For example,

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

but if you look at the drawings from most companies they

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

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.

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 ap-

plications, 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, re-

placing 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

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

Power Laserdyne (Champlin, MN). “But about five years ago,

we began to see an expansion in laser welding applications.”

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Laser Welding

From a negligible slice of their business, he has seen weld-

ing 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. Cus-

tomers 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 ma-

chined, high-value parts already have the tight fit-up needed

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

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

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

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Laser Welding

Hybrid welding, combining GMAW with high-power lasers,

is also suitable for automation, as shown here.

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B

Even with the advent of fiber lasers, laser welding capital

expense costs can be relatively high but are offset by many

advantages. As Barry found out from an extensive review with

existing customers, capital cost was not the most important

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.

“Fiber lasers when employed cor-

rectly are easy to use and easy to teach

people to use,” he said. “They provide

a large window of acceptable param-

eters.” Some customers prefer a lower

average power with many pulses; others

prefer high power with few pulses.

Customers can obtain a variety of re-

sults 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, manufactur-

ers would cluster lasers in the same

area, now they are distributing them into

work cells because they can perform

multiple operations and they do not

need specialized operators who are

experts with lasers,” he explained.

The next big jump in development

may very well be high-brightness direct

diode lasers, according to Hansen.

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.

What are direct-diode lasers? Many

solid-state lasers use diodes to excite a

lasing material. Therefore, disk-lasers or

fiber-lasers use diode lasers as an inter-

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

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

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

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

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

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

Laserline’s LDF series direct-diode lasers range from

3-20 kW power, though beam quality decreases as power

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 mm-

mrads of beam quality with a standoff

distance of 500–650 mm,” Todt said.

There are trade-offs for the enhanced

quality. Wall-plug efficiency is reduced and the beam

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

to fiber lasers in applications requiring higher-quality fiber-

optic delivery of a beam.” ME


Laser Welding

ESAB Welding & Cutting ProductsWeb site: www.esabna.com/

Hybrid Laser Microsite: www.esab.com/hlaw

Ph: 843-669-4411 / 800-ESAB123

LaserdynePh: 763-433-3700

Web site: http://tinyurl.com/ laserdynesme

LaserlinePh: 408-834-4660

Web site: www.laserline.de/t

Lincoln ElectricPh: 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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