Laser cutting is a popular technique for cutting metal profiles, especially for stainless steel, due to the faster cutting speed and superior quality. This process uses a focused laser beam and coaxial assist gas to remove excess molten metal for cutting. Different gases can be used according to their characteristics and how they affect the cutting quality. Commonly used auxiliary gases are nitrogen, oxygen and air.
Nitrogen and compressed air are used as auxiliary gases, and a 3kW fiber laser is used to test 5mm thick stainless steel (grade 316). When cutting with air, the presence of oxygen will produce an exothermic chemical reaction, which releases heat, causing the cutting speed to increase, but the edges will turn brown. On the contrary, when using nitrogen as the auxiliary gas, no chemical reaction occurs at the cutting edge. On the contrary, the auxiliary gas will shield the metal edges, resulting in shiny edges.
It should also be noted that the cutting speed varies between these auxiliary gas tests. Compared with nitrogen, the use of air as an auxiliary gas can produce a higher cutting speed. The results obtained show that the production horizontal cutting speed using air is 3.6 m/min, and the cutting speed using nitrogen assist gas is 2.8 m/min. In addition, the compressed air auxiliary device requires only 10 bar of air, while nitrogen is 16 bar.
Although the use of oxygen can provide a higher cutting speed, the final cutting edge will be severely oxidized and usually requires post-processing.
Overall, compared with compressed air, nitrogen assist gas can provide cleaner cutting edges, but at a slower speed.