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Laser Technology

Laser light

By Sue Roberts

Laser resonators, the heart and soul of each laser cutting machine, are constantly under pressure to improve. What do users want? They want greater efficiency, reduced downtime, easier maintenance, longer-life optics, increased speed and closer tolerances. All of which combined are a big order.

Each time an engineering department meets a development objective, the goals move forward. New and improved has become the norm rather than the exception.

Innovations come in many forms, from lightweight and directly cooled mirrors to dust collectors that all but eliminate contaminants within the laser cabinet itself to software that monitors and reports optic performance.

FFJournal talks to manufacturers about the ongoing efforts taking place to increase efficiency in using the power of light.

Built for speed
Maximum productivity built into the Syncrono Laser introduced by Prima last year demanded the advantages of lightweight components. Smaller linear drives, lightweight titanium components and thinner optics reduced overall weight.

The cutting head, a "machine within a machine" according to the company's Web site, has two small, linear-driven parallel kinematic axes on the moving gantry. This design, coupled with lightweight components, allows acceleration of up to 6 g, enabling the Syncrono to cut more than 1,000 holes per min.

Pieter Schwarzenbach, vice president of laser technology at Prima North America, explains. "The optics on the Syncrono machine are built very lightweight in order to reduce the moving mass and increase the dynamics of the machine," he says. "If you move around a small hole or a small radius corner, you get very high acceleration. One axis has to stop and the other has to be accelerated to full speed. That is why you want to have little mass to be accelerated and decelerated."

Titanium, which Schwarzenbach touts as having a notably better strength-to-weight ratio than alumunum, is the material of choice for components holding the mirrors within the cutting head. The mirrors themselves, constructed from silicon, are thinner and weigh about 90 percent less than their copper predecessors.

An added bonus from the lighter accelerated mass, says Schwarzenbach, is the substantially reduced electrical consumption.

Eliminating miniscule particles
Optics within the laser cavity must be clean to maintain beam mode, cut quality and speed. Cleaning or replacing the internal optics is no easy task and can take a laser cutting machine tool down for half a day or more.

Dirt comes from a variety of places, beginning with the laser gases that might be 99.999 percent but not 100 percent pure. Contaminants can sneak in when changing gas supplies if proper purging procedures are not followed. Seals within the system deteriorate over time, contributing particles, and in systems where quartz tubes are used, the glassware also deteriorates, adding miniscule glass powder contaminants to the resonator atmosphere. These particles can settle on the mirrors and lens.

Amada addressed this critical issue by including a centrifugal dust collector inside the laser cabinet itself. Jason Hillenbrand, Amada's laser product manager, says, "Our method takes the laser gas and circulates out the dust and contaminants. It collects and actually evaporates them inside the laser cavity. This is done before contaminants get to the mirrors themselves." An 80 percent increase in the life of the mirrors has been reported.

Further improvements can be made on the output mirror to minimize dirt on the outside of the optic that can cause deformation from overheating and lead to pre-focusing and a poor cut.

"We're doing everything we can to protect that mirror inside the cavity, but because the mirror also faces the beam delivery path that is outside the laser cavity, there have been advancements in making certain that no dust or dirt can settle on that optic on the outside," adds Hillenbrand. "Advancements in that facet have dramatically increased life on that mirror and decreased maintenance so the laser is able to keep running longer."

Keeping cool
Cooling of optics, how the cooling circuit effectively removes heat from the mirrors and mounts, becomes particularly critical with higher-power resonators where more heat is generated by the beam.
Bystronic addressed the heat exchange issue in its high-power Bylaser models by moving from a diffusion process to a direct-cooled process. Water flows through a cavity in the mirror, immediately absorbing the heat. This method helps maintain the integrity of the surface and the coatings, eliminating deformation and maintaining the stability of the beam.
"We have water cooling directly into the mirrors. We have in-ports and out-ports on the mirrors," says Frank Arteaga, laser product manager at Bystronic. "Water flows directly into the mirrors, creating a much better cooling efficiency. The mirrors stay flat and don't deform because of the heat."

Another change for the Bylaser resonators is the solid-state power supply. Arteaga says, "Basically, we have a transistor-type power supply versus the vacuum-tube power supply. It's more compact, more electrically efficient and is basically a wear-less power supply, reducing the replacement of expensive high-voltage components."

Arteaga elaborates, "All the components for the high voltage are actually located in the bottom portion of the resonator. Any time you switch to transistor-type technology, you miniaturize everything. Everything becomes more compact."

A diamond advantage
Finn-Power uses both types of resonators, DC-excited laser resonators on the L6 stand-alone flying optics systems and slab systems on the punch/laser equipment, the Laser Punch and Laser Brilliance series. Mike Palmer, Finn-Power laser product manager, reports considerable improvements in two areas.

The use of adaptive optics has created more stability and speed since being incorporated into the flying optics systems about four years ago. Cutting speeds and consistencies have increased by 20 percent. Yet another advancement is extended life of the turbine. Palmer remarks, "We're seeing in the neighborhood of 35,000 hrs. to 40,000 hrs. before the turbine needs to be replaced."

On the slab lasers used in the LP and LB models, Finn-Power has replaced the former output couplers with diamond windows. The thermal conductivity of the diamond material dissipates the heat better than other standard optics, allowing higher power outputs.

Palmer adds, "With the new configuration you don't have the power loss. The beam quality is exceptional." Regarding maintenance, he says, "The diamond window has a lower thermal lensing, making it much more resistant to damage as it separates the vacuum from the external atmosphere. Overall, it's a lot less troublesome than a standard output coupler."

Lenses for productivity
Lou Derango, 2-D laser product manager at Mazak Optonics, anticipates savings for laser users as BiFocal lenses become more practical. Although these lenses, a product of Air Liquide, have been available for a few years, he bases the delay in their acceptance on the lack of efficient tool changing capabilities within the machine tools.

"Our timing and the optic timing were a little off in that we weren't coming out with our tool change machine yet to utilize these kinds of optics," he says. "Now that we and other companies are doing automatic tool change on lasers, I'm hoping that these lenses come back so that we can see increased speed rates using the same amount of power."

Until then, Mazak's HyperTurbo-X provides the user the option of having a different-sized lens in each of six automatically changed torches. The program calls up the proper lens for each material type, providing higher feed rates without increasing resonator power. Derango says, "The lenses seem to complement our tool change capabilities very well by providing increased cutting speeds without increasing run costs. It's up to the user to take advantage of the products available."

Mazak resonators have also changed from a ring-type to a stinger-type electrode with nearly double the life span. Resonator optic maintenance is reduced because of the stinger's smaller surface area.

"After so many hours of running, the electrodes deteriorate and make deposits within the glass tubes of the resonator,"explains Derango. "So having a stinger is an improvement."

Overall Performance
Mitsubishi's patented resonators have a cross-flow design. Four low-speed blowers re-circulate the gas through an open design. Power is generated along with savings on laser gases.

Jeff Hahn, senior product manager at Mitsubishi, says that the company's resonators have the same basic makeup and structure as they did when introduced three years ago in the CFX Series; however, improvements are always being made. "Design changes in configuration have pulled a lot of the contaminants out of the resonator."

Mitsubishi, a full systems manufacturer, strongly recommends that only its optics be used in its laser systems. Bernardo Olguin, regional sales manager, consumables, points out that using a different brand of consumables in the lasers can greatly affect overall performance. A small variation in specifications makes a huge difference in speed, cut quality and overall machine performance.

Monitoring the environment
A large part of systems development has been in the automatic monitoring and preventative arena. Systems and software have been created to detect optics problems in time to make changes and avoid bad cuts, scrap or catastrophic failures of mirrors or lenses.

Elizabeth Kautzmann, Salvagnini's laser product manager for North America, refers to the company's goals as "giving the machine some intuition." This intuition is built in primarily through thermal monitoring systems, with some options that check the wavelength, the plume of the cut and the level of laser energy. If these are not within the proper parameters, the software can communicate any problems via the machine's visual alert system with an e-mail or phone call to a designated person, or it can simply pause the machine.

"An optic can be divided into quadrants," Kautzmann says. "If one quadrant is not the same average temperature as the other three, the suspect area may have a contaminant or other concern. The ability to have the unit monitor the process, updating checks of the laser energy and delivery optics, examining the resulting plume or other surface feedback while cutting live and delivering a response or adjustment in time to make a valuable correction, is the objective."

Laser manufacturers share an excitement for the future and a committment to continual development. Kautzmann explains this dedication to advancing lasers' capabilities. "Light is so wonderful, so predictable. If we set up the conditions or environment to have it perform in a certain way, light is going to do it. Light has its laws. All we have to do is learn those principles and prepare accordingly." FFJ

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AIR FILTRATION

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Camfil APC - Equipment Trilogy Machinery Inc. Metamation Inc. Admiral Steel
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STEEL

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WATERJET

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SAWING

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Osborn

METAL FORMING

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WELDING

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