Assisting Gas Mixing to Promote the Development of Fiber Laser Technology

Just ten years ago, fiber laser cutting machines were considered experts in thin plates. The stores quickly realized that they had to invest in them to compete, at least by reducing their instrument materials. For high-quality sheet metal cutting, CO2 laser is still the way to go. Of course, fiber lasers can cut thicker blanks, but the quality is not very good, and their speed advantage almost disappears when cutting very thick sheets. Today, the world has undergone changes.

Assisted gas technology has made significant progress in just a few years and is one of the important contributors to the rapidly changing field of laser cutting. The lens material and its design have been improved, and the cutting head and nozzle have also been improved. It can be seen that modern fiber laser beam transmission systems are calmly dealing with enormous photon power. 20. Ultra high power lasers of 30 or even 50 kW can now quickly and cleanly slice thick plates.

"Clean" is an effective word here. The economic significance of lasers can be attributed to the cost of each component. Nowadays, high-power lasers are flourishing in the field of precision sheet metal cutting. If a part used to be plasma cut and then burrs or precision machined on a milling machine, it may now be able to be completed on a fiber laser.

Auxiliary gas mixing helps achieve all of this. Even the thickest sheet metal today is not processed with oxygen, but with a mixture of nitrogen and oxygen. The auxiliary airflow is still mainly composed of nitrogen gas, which is an inert gas that can expel molten metal from the incision, but a small amount of oxygen provides chemical reactions, helping to bring the incision to the bottom to obtain a slag free edge.

The bracket between the surface and nozzle has been reduced to almost non-existent, all in order to allow the laminar flow of auxiliary gas through the incision, so that the nitrogen oxygen mixture can work as expected. In the field of precision sheet metal cutting, excessive auxiliary gas turbulence is the enemy of clean laser cutting.

The early application of gas mixing appeared more than a decade ago, not for thick steel, but for slag free cutting of aluminum. Liberty Systems, headquartered in Pewoki, Wisconsin, is a nitrogen generation and gas mixing supplier. Steve Albrecht, the president of the company, recalled that in the early 2010s, when nitrogen oxygen mixtures were used, they were not for fiber lasers, but for cutting 0.125 inch thick aluminum in a 4 kW CO2 system.

"There is an oxide layer on the top of aluminum," Albrecht said. "You need to burn it to prevent any slag or burrs. As application engineers have discovered, nitrogen assisted airflow containing a certain amount of oxygen helps eliminate the difficult to remove scum on the edges of laser cut aluminum.".

"As a softer material, aluminum has some unique features in laser cutting," said David Bell, President of Witt Gas Control in Alphalita, Georgia. "Gas mixing is very helpful. If you cut aluminum with oxygen, you will burn it. If you cut it with nitrogen, you will get edge stripes. Mixing the two for cutting will give you a cleaner cut.".

As fiber lasers begin to dominate the market and the available power continues to grow, auxiliary gas strategies continue to evolve. Application engineers began experimenting with different combinations of nitrogen and oxygen.
As Albrecht recalled, when engineers began to achieve good results when the oxygen content approached 20%, it opened the door to using ultra dry air for cutting. This has saved manufacturers a lot of money, especially considering the amount of auxiliary gas consumed by early fiber lasers.

"When the first batch of 6 kW and 8 kW optical fibers were introduced," Albrecht said, "that was when ultra dry air cutting truly began to take off.".

However, with the continuous increase of fiber laser power, the auxiliary gas strategy has changed. The cutting conditions for the highest power fiber laser are established around a precise nitrogen oxygen mixture with low oxygen content.

Original equipment manufacturers of laser cutting machines are beginning to experiment with different nozzles and methods to achieve smooth laminar flow of auxiliary gas around stronger beams. Optimized nozzle design. Some nozzle geometries capture gas at the top of the metal. Other technologies use air curtains around the auxiliary gas column. As Albrecht explained, these methods depend on the machine manufacturer, but everyone is moving towards the same goal: achieving optimal cutting quality with the lowest single piece cost. This includes auxiliary gas utilization, especially finding the optimal mixture to improve cutting quality and speed.

Source: Laser Net