Size doesn't matter

July 1, 1998
A tiny package houses a powerhouse of a laser.

A tiny package houses a powerhouse of a laser.

Rofin Sinar Inc. recently introduced a 2 kW high-power diode laser with a compact welding head that weighs a mere five lb. Typical CO2 or Nd:YAG lasers of that power often weigh several thousand pounds and aren't as energy efficient or cost effective, claims the company.

A Rofin Sinar diode laser is comprised of stacks of diode bars that produce up to 2 kW of power. Because of these diode modules, the head of a DL system is extremely small—12X4X61 /2 in.—and solid-state, with no mirrors or output couplers to misalign or service.

The output power from a single bar can be 30 W or greater. The high output power and uniform line/beam profile make the diode laser particularly well-suited to a variety of cladding and heat-treating applications.

Imagine one guy picking up an industrial laser, typically a couple of thousand pounds, to carry across a shop floor. Sound impossible? It's not. Using the same diode technology that is found in CD players and laser pointers, Rofin Sinar Inc., Plymouth, Mich., has introduced a laser system whose smallest head weighs a mere five lb. Added bonuses, reports the company, the DL Series lasers are more efficient than a conventional CO2 or Nd:YAG system at come at significantly less capital cost.

Diode lasers have a number of advantages to conventional systems, says Richard Walker, Rofin Sinar's general manager. The most obvious is that diode arrays make for smaller, simpler packages. The head of one of the DL lasers, for example, measures roughly 12 34 3 6 1 /2 in. "This laser is small—it literally weighs just a few pounds—so you can put it on the end of a robot, move it around the shop floor, and so on. It has two power cables and two small water cables connected to the back of the laser head," he reports. As for the power supply, it's a 19-in., rack-mounted unit that provides low-voltage power for the diodes.

Another plus, says Walker, is that diode lasers are solid-state devices, with no mirrors or output couplers to misalign or service. "This, amongst other things, makes them more reliable than conventional systems and virtually maintenance-free."

In addition to these benefits, the DL has an energy efficiency of approximately 30%, compared to just 10% efficiency with a CO2 laser and only 4% with a Nd:YAG system. "To get this into perspective," says Walker, "Compare a 1-kW diode to a comparable Nd:YAG laser. The diode laser runs on 5 kW of power, and only requires a 2-kW chiller. With the Nd:YAG you need roughly 50 kW of power and a 55-kW chiller. These are significant improvements in terms of efficiency and will save companies a great deal of money."

Although diodes have been used in commercial applications, such as the aforementioned CD player, narrow bandwidth requirements and high costs limited their use in manufacturing. Rofin Sinar overcame these problems by applying new production techniques to make and cool the diode bars, which it stacks into modules.

This innovative module design produces power outputs as much as 2 kW for material processing applications at a relatively inexpensive cost.

"This is the first time that we've been able to take this type of power level and focus it down to a usable spot size," claims Walker. An extra benefit, he stresses, is that diodes have a lifetime of 10,000 hours or better. "If a laser is run on one shift, every day for a year—that's roughly 2,000 hours of up-time—then systems can easily last a minimum of five years."

According to Walker, an important and unique aspect of the Rofin DL is its efficient absorption by metals. The wavelength of the DL is between 800 and 1,000 nm, versus the 1,000 nm of the Nd:YAG and 10,000 nm of the CO2. "The shorter wavelength provides better absorption into metals," says Walker. In fact, at room temperatures, a CO2 laser provides between 10% and 12% absorption, a Nd:YAG approximately 25%, and a high-powered diode laser 30% absorption.

Jobs made for the DL
"Diode lasers provide a uniform output intensity in the form of a line, which is ideal for heat-treating, surfacing, and hardening," says Walker. They can also tackle jobs such as soldering or brazing of electronic or medical devices, plastic welding of automotive components, and some limited metal-welding applications involving wide weld beads, such as cosmetic welds.

The DL systems don't have the beam quality of conventional lasers, so cutting applications are out of the question for now. However, Rofin Sinar expects that they will soon have broader application in metal welding. "At the moment, we are limited by spot size: It's typically 1.4 33.5 mm, which is more of a line than spot. We're trying to make the beam even smaller and rounder, which would produce a higher power density, smaller spot. This advance would make the laser appropriate for other material processing applications," reports Walker.

Although the beam quality could be considered the DL's only drawback, it is also one of the system's major advantages. "Actu-ally, it's harder to uniformly heat-treat a metal surface with a conventional laser, which produces a small, round spot," explains Walker. "Often, you get hot spots in the beam, and you end up with melting or other problems, making it a difficult process to control."

The DL systems are now in a number of commercial facilities and development labs. Says Walker, "Basically anyone looking for a small, compact, efficient device that's not too expensive will be interested in this laser."

Comparison of three laser sources
Wavelength (nm) 10,600 1,064 800-1,000
Efficiency * (%) 5-10 1-4 30-40
Output power (kW) Up to 20 Up to 4 Up to 2
Laser head size (m 3 ) 1.0 0.1 10 -3
Power density (W/cm 2 ) 10 6...12 10 5...9 10 3...5
Absorption—metals (%) 10-12 25-30 30+
Maintenance intervals (hr) 2,000-4,000 500-800 maintenance-free
* Electrical excitation (pump) power/laser power

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