More research reveals more can be done using shop air in laser cutting
March 13, 2007
Fabricators are increasingly using compressed air in laser cutting, instead of relying on laser assist gases such as oxygen and nitrogen. Recent findings reveal that shop air can be used on more material types and thicknesses, including parts on which the edge quality is visible.
Oxygen and nitrogen, two standard assist gases used in laser cutting, create two different reactions at the laser head. Oxygen produces an exothermic reaction, and the laser burns the metal. Nitrogen fosters a melting process, and the laser heats the metal without a chemical reaction, with the nitrogen gas pushing the molten puddle through the kerf. During air cutting, the combination of the laser energy being forced through a tight focal point and the presence of compressed air creates a plasma ball at the surface of the material, which then cuts the metal.
Editor's Note: This is an update of "A breath of fresh air."
In the summer of 2006, industry reports were made public regarding the initial study results on the benefits of laser cutting parts using compressed air instead of oxygen or nitrogen as an assist gas. Cutting with compressed shop air showed considerable benefits, including a significant cost savings and speed increases over nitrogen and oxygen assist cutting. As with any emerging technology, additional research has been conducted and new findings have emerged about the capabilities and limitations of compressed-air cutting.
A previous article, "A breath of fresh air," advised fabricators to use the compressed-air cutting technique for parts that would be coated, bent on a press brake, or not otherwise visible when the manufactured product was complete. Recent findings make it possible to expand this recommendation to more material types and thicknesses, including parts on which the edge quality is visible. Compressed-air cutting is now possible on 0.074-inch steel and thinner, 0.120-in. stainless steel and thinner, and 0.25-in. aluminum and thinner.
Additionally, compressed air can be used as an assist gas with thicker material. The maximum thickness has increased for aluminum to 0.50 in. thick. Previously cutting 0.180-in. stainless steel and carbon steel with compressed air required a laser cutting machine with a 6,000-W resonator. Now it can be cut reliably using 4,000-W and higher laser resonators.
New research has also taught us that different laser resonator styles perform differently in each material and thickness. For example, a diffusion-cooled resonator creates very good edge quality on materials 0.080 in. and thinner, while a 4,000-W, fast-axial-flow resonator cuts well on 0.135-in. material. Meanwhile, 5,000- and 6,000-W, fast-axial-flow resonators using compressed air cut 0.250-in. aluminum with the same edge quality and speed as nitrogen-assisted cutting.
In "A breath of fresh air," the compressed-air pressure figures presented were limited to standard shop air pressures. Since the article was published, laser technology specialists have successfully tested the capabilities of cutting with higher pressures and conducted analyses that make it possible to justify the financial investment necessary to upgrade laser machine compressors to cut thicker material.
For example, increasing pressure enables users of 4,000-W machines to cut 0.375-in. to 0.5-in. aluminum. Using higher than typical shop air pressures (105 pounds per square inch) may mean a small investment for some users, while other users already will be capable of these pressures.
Technical advances are continually made to laser cutting machines and the techniques that enhance them. Fabricators should be on the lookout for more examples of operational improvements in laser cutting sheet metal and plate.
Erin Chasse is the sales engineer for laser cutting machines, and Mickey Lawson is an applications engineer at TRUMPF Inc.