Lasers equipped with dual-focus lenses and advanced shielding gases help fab shops cope with rapid growth while boosting quality.

Charles Caristan, Elisabeth Ferenz, and Jason Legrand, Air Liquide Industrial U.S. LP, edited by Ron Lucas, managing editor

According to Air Liquide Industrial U.S. L.P., there's been a dramatic increase in the number of industrial lasers used in the U.S. in recent years. The company attibutes the increase to the laser's greater flexibility and its cost-effectiveness compared to traditional metal cutting and welding.

With Bifocal technology, the outer part of the laser beam sees a focusing lens of focal length f, while the inner part of the same laser beam sees a focusing lens of focal length f+df.

Bifocal lenses have a wide spread Δz of high-power density along the pointing direction of the laser beam. This translates into a large focus position tolerance that makes the system user-friendly and a high-power density near the top surface of the workpiece that boosts cutting speed.

The width of the horizontal bars illustrate focus position tolerances. Bifocal technology speeds cutting and its large focus position tolerances ensure higher repeatability.

Irving Tool operates three Mazak laser cutting machines running two 10-hr shifts per day. By changing to Bifocal technology, the firm saw production speeds rise more than 30% on metals.

Tim Meade, VP operations, AW Mercer, tested Bifocal technology on his Bystronic 3500W laser and averaged a 20% increase in production speed.

With pure helium, the density of the shielding gas — and consequently the helium concentration above the keyhole — are diluted and contaminated by oxygen from the surrounding atmosphere. This decreases shielding efficiency.

Shops installing lasers are always looking to improve efficiency, productivity, and quality. That's the goal of a special laser technology that features a lens with dual-focusing capabilities. Compared to standard lenses, the system can increase production cutting speeds as much as 20% when cutting stainless and galvanized steel, aluminum sheets, plates, and tubes. To further boost quality and efficiency, shops can pair the laser system with a proprietary shielding gas instead of pure helium. Such a move can slash costs as much as 30%.

Bifocal laser cutting
Bifocal technology employs dual-focus lenses with two focusing points along the beam-pointing direction. A bifocal lens is made of the same material and coating as a standard lens. However, the outer part of the laser beam sees a focusing lens of focal length f, while the inner part of the same laser beam sees a focusing lens of focal length f+df.

During cutting, the top focusing point, obtained from the greater convergence angle, is positioned near the top surface of the material. The second focusing point, obtained from the smaller convergence angle, is positioned near the underside of the material. The focus point located near the underside of the workpiece works to avoid dross formation, while the other focus point, located near the upper surface, produces a high enough power density near the top surface to boost cutting speeds.

Cutting speeds also increase dramatically when Bifocal lenses are coupled with nitrogen or argon assist gas, particularly when laser-cutting stainless and galvanized steels, aluminum, and titanium.

Positioning a high-power-density focus near the bottom of the workpiece reduces dross formation. Bifocal lenses result in a wider spread Δz of high-power density along the pointing direction of the laser beam. This translates into a larger focus-position tolerance for improved user-friendliness and much higher power density near the top surface of the workpiece. This translates into substantially higher cutting speeds.

For production, laser cutting speeds must be repeatable and reproducible with at least ±0.020-in. focus-position tolerance. Bifocal technology can do the job hitting these speeds along with providing larger focus-position tolerances for good repeatability.

A number of laser jobshops are already using the technology. Tim Meade, vice president operations, AW Mercer, Boyertown, Pa., tested Bifocal technology on his Bystronic 3500W laser and averaged a 20% production speed increase. Likewise, Steve Gustlin, general manager, Serra Laser Center, Anaheim, Calif., says, "We tested Bifocal on our Mitsubishi 3,500 W laser cutting machine and found it cut thick aluminum and stainless steel better than ever."

Irving Tool and Manufacturing Co., Garland, Tex., operates three Mazak laser-cutting machines in two 10-hr shifts each day. "After more than six months of production with Bifocal technology, we improved our throughput with real production speed increases of more than 30% for some of the metals that we laser cut as well as reductions in downtime," says Harold Stringer, president.

Irving Tool also tackles CO2 laser welding of steel components for the electronic and telecom industry. The firm had used pure helium, which has high ionization potential, as a shielding gas for those applications. However, helium's light atomic weight flow characteristics deliver a highly diluted gas above the weld keyhole. This means it is easily contaminated with surrounding atmospheric oxygen because of a turbulenceenhanced Venturi effect.

That's not the case with custom mixes. By switching to a customized Lasal Mix advanced shielding gas developed and produced by Air Liquide Industrial U.S. L.P., the firm's shielding gas costs fell 30%, and the plasma shielding became far more efficient thanks to improved flow dynamics. The increase in shielding efficiency enabled double-digit increases in production welding speeds.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Gas mixes boost efficiency

High-power-density focused laser beams create surface metallic plasma, which absorbs a laser's power before it reaches a workpiece. Less power at the workpiece results in poorer performance and quality. A high-ionization-potential shield gas can be injected to reduce surface metallic plasma, but it also can become ionized by the focused beam and ignite to form a surrounding atmosphere plasma.	A high-speed-camera visible spectrum comparison of plasma plumes formed by He, Ar, and N2 shielding gases reveals He has 24.5 eV ionization potential, whereas Ar, and atomic N have 15.7 eV and 15.5 eV ionization potentials. However, to ionize atomic N, additional energy is necessary to break the bond of the N2 molecule first, thus making N2 a better shielding gas than Ar. Surface metallic plasma plumes are visible in all three views. Surrounding atmosphere plasma above the surface metallic plasma is most evidenced with argon shielding gas. The visible surrounding atmosphere plasma plume is much smaller with N2 than with Ar.
Pure helium creates a turbulent and highly diverging expansion flow. In contrast, a customized mixture provides a less turbulent gas dynamic flow and less diluted flow mixture at the workpiece.	Customized mixtures like Air Liquide's Lasal Mix can be delivered using on-site mixing equipment or in compressed cylinder form. Irving Tool gained add-on efficiency for leaner manufacturing from Air Liquide's Lasal-branded gas cylinder packaging. It features a safe permanent Scandina cap that protects the regulator at all times during operation — no caps to screw and unscrew and pileup on the facility floor. Each Lasal cylinder is dedicated to a single gas or mixture of gas product, and each has a chromed residual pressure valve. The valve ensures a minimum positive pressure of 20 to 30 psi at all times, preventing contamination by ambient atmosphere in the facility or at the refill plant. A shrink-wrap keeps valves clean and allows operators to easily identify unused cylinders from a distance.

 

About the authors

Mr. Caristan is business development manager, Advanced Fabrication Technologies, Air Liquide Industrial U.S. L.P., Houston. Mr. Legrand is the group's business development specialist, and Ms. Ferenz is Allex engineer. For more information call (713) 624-8000, or visit www.us.airliquide.com