Something in the Air:
Three Things You Should Know About Air-Assist Laser Cutting
By Robert Farrell, Owner of Farrell MarCom Services
Looking to squeeze more out of your laser cutting process and save some money along the way? Take a deep breath and relax -- the answer might literally be all around you.
If you laser cut metal for a living you are no doubt familiar with assist gas. You may know that nitrogen and oxygen are the most popular of these gasses; and you may have even heard that air is a cost-effective alternative gas. But how do you know if air-assist is right for you in your laser cutting operation? Here are three things that you should know about air-assist cutting.
How it Works
Neither fiber nor CO2 lasers rely strictly on a light beam for cutting metal. Rather the process includes the injection of an “assist” gas at the nozzle to supplement the process. This confluence initiates a process known as an exothermic reaction. That is, a chemical reaction that releases energy by light or heat. The introduction of nitrogen, oxygen or air helps transfer heat more effectively than the beam alone.
Initially oxygen was the most popular gas for the laser cutting process. Later it was discovered that nitrogen produced a cooler cut resulting in cleaner edges – perfect for industries where aesthetics and edge quality were critical. While nitrogen remains the most widely used laser cutting gas, air is today, for a growing number of fabricators, proving to be an effective and cost-saving alternative.
This is not to suggest that air assist cutting is a radical departure from nitrogen or oxygen. Air is, after all, approximately 80% nitrogen with remaining components consisting primarily of oxygen. The goal with air assist cutting is to utilize this high concentration of nitrogen while at the same time leveraging the added benefits of substituting slightly more deluded gas.
While relatively new to some, air-assist cutting has been around for nearly twenty years. An early pioneer is machine tool manufacturer CINCINNATI Incorporated (CI) who began researching and developing the process as early as 1998. Since that time the use of air as an assist gas has continued its steady growth in popularity among both fiber and CO2 laser users alike. “Mode quality was a major limitation when compressed air was first introduced for CO2 lasers,” explained Drew Schneider Product Applications Manager for CI. “However, laser mode quality has improved significantly and today air-assist is a very efficient and popular method for cutting a variety of materials. Many OEMs, job shops, and fabricators are using air-assist laser cutting with steel, stainless steel, and aluminum.”
Air carries with it a substantial return on investment for those employing fiber lasers or those cutting stainless steel. “Air is an especially good fit for fiber laser cutting,” said Schneider. “The intense heat of fiber lasers, combined with injected air, creates cuts without producing an oxide formation on the cut surface. This means that secondary clean-up operations are significantly reduced or even eliminated.”
As any fabricator using nitrogen will tell you, it is a costly gas. In some instances the cost of the gas alone can run as high as 90% of the total operating cost. Air is considerably less expensive than both nitrogen and oxygen. Another advantage of air is the faster cutting and increased throughput it delivers. CI and some of its customers have run cutting tests on the full range of materials and thickness. “For material above 10 gage we’ve found that nitrogen produces faster cuts,” Schneider stated. “However, in the mild steel range of 10 gage (.135”) and thinner air is roughly 3% faster than nitrogen. In the stainless steel range from 3/4" (.750”) down to 20 gage (.036”) air is about 22% faster; and in the aluminum range from .190" down to .032" air is approximately 14% faster.” The chart below shows a direct time and cost comparison between air and nitrogen.
When to use Air
Today businesses are scrutinizing all areas of the operation to cut costs and boost productivity; and for fabricators the shop floor is under a microscope. Something as common as air can deliver measurable improvements in each of these areas. While air is generally used to cut thin material, most stainless parts, especially those used in assemblies, are candidates for air-assist laser cutting.
While clearly not the best gas in all instances, generally speaking utilizing air as an assist gas produces a laser-cut edge quality that is at least comparable to parts cut with oxygen or nitrogen. “If one were to label nitrogen edge cut quality as a ten, then the edge quality resulting from an air-assist cut would be about an eight,” added Schneider. “For fabricators serving the majority of industries air-assist edge quality is more than satisfactory for most powder coatings to adhere, eliminating the need for secondary cleaning operations.”
Still there are times when nitrogen remains the best gas choice. Nitrogen produces a cleaner cut and those serving customers throughout the Food Processing and Aerospace industries for example should continue their use of the gas. Additionally, some cosmetic parts cannot show any blemish whatsoever – again these would not be candidates for air-assist cutting.
Doyle Equipment: Putting Air to Work
Doyle Equipment Manufacturing (Quincy, IL) serves the agricultural industry with dry fertilizer blending, conveying, tending, and spreading equipment. Primarily processing stainless steel, more than 90% of the parts are cut on lasers. For this both nitrogen and air are utilized with about 1/3 of all cutting (both mild and stainless steels) relying on air as the assist gas.
“Our main concern was the weld quality of the cut part. We need a nice, clean edge for a good weld, and thickness .105 and below cut on the fiber laser with air-assist weld perfectly,” said Doyle Production Manager, Stuart Rumple. “While we’ve successfully cut stainless material up to one-half inch using air, we generally find that thicker cuts are best suited for nitrogen. That said, we utilize air on a regular basis and have found the cost-savings to be immense. Air-assist allows us to run our machines at less than $4 per hour which equates to about a 90% savings over our CO2 laser and about 75% less cost than using nitrogen on the same machine.”
Is it for you?
So is air the best choice for you in your laser cutting operation? The short answer is of course… Maybe. It all depends on the industries you serve and how important edge quality is to you and your customers. CI’s Drew Schneider points out while OEMs have largely turned to air the smooth edge quality that nitrogen delivers makes it the best assist gas for some. The bottom line is that when edge quality is absolutely critical, nitrogen remains the best option. Nitrogen produces cooler cuts and is an inert gas meaning that there is no chemical reaction when cutting stainless steel. This prevents oxidization from occurring leaving a clean, shiny edge that eliminates secondary descaling operations.
What about set-up cost? Switching your laser cutting operation to air is relatively easy and cost-effective. Even most existing older model lasers can be adapted to cut with air. Although there is an initial investment for the proper equipment, tapping air as an assist gas will generate sustainable cost and time savings while boosting productivity.
While air is certainly not the optimum assist gas in all cases, it is an efficient and cost-effective alternative for many. Take a look at the parts you cut and investigate how much you are spending on assist gas. Run some tests and determine for yourself if the answer to increased productivity and profitability isn’t literally all around you.