Laser cutting with nitrogen is intended for applications where oxidation is not wanted. For example, an oxide layer can cause paint to adhere less strongly on non-alloy steel. If non-alloy steel is painted after cutting, the cutting gas should be nitrogen.
Weldable steel components laser cut with oxygen will not pass the bending test. Stainless steel loses its corrosion resistance when cut with oxygen, and aluminum pieces cut with oxygen have an uneven and burred cut surface.
When nitrogen is used as the cutting gas, the laser beam melts the material, and the nitrogen blows away the molten material from the cutting groove. Since no exothermic reaction takes place, the cutting speed is much slower than when cutting with oxygen. To ensure a burr-free cut edge, the laser beam must usually be focused on the bottom surface of the plate.
Guideline values for cutting – actual values may vary from equipment to equipment
Material
thickness
mm | Laser
power*
W | Focal
distance | Cutting
nozzle size
mm | Cutting
nitrogen
pressure**) | Cutting
speed
m/min ***) |
| 2 | 1500 | 5" | 1,4 | 10 | 4,0-2,0 |
| 4 | 1500 | 7.5" | 1,7 | 15 | 1,2-1,0 |
| 12 | 3000 | 7.5" | 2,5 | 19 | 0,4-0,3 |
*) more powerful laser usually cuts faster
**) cutting nitrogen pressure is measured at the cutting head
***) speed in quality cutting
The values above create a high-quality, burr-free cut surface. The cutting gas pressure is much higher than when cutting with oxygen. The thicker the piece to be cut, the higher the nitrogen pressure needed to transport the molten metal away efficiently. When using nitrogen, the focal point is on the bottom surface of the plate, whereas when cutting with oxygen, the focal point is on the top surface. Nitrogen needs a larger nozzle than oxygen, which results in a much higher gas consumption than when using oxygen.
When cutting stainless steel, nitrogen must be as pure as possible, since even a trace amount of oxygen in the cutting nitrogen can destroy the corrosion resistance of steel.
Even a slight discoloration on the cut surface indicates that oxygen has reacted with the cut surface. An expensive additional treatment is needed to re-establish the corrosion resistance.
By cutting high-alloy steels with AGA LASERLINE® laser cutting nitrogen, you can ensure a burr-free, clear cut surface that can be processed further straight away.