First, let's take a look at the process of laser cutting: after passing through the lens, the laser generated by the oscillator will converge on a point to form a small spot. By accurately controlling the distance between the lens and the plate, the stability of the laser spot in the material thickness direction can be guaranteed. At this time, due to the convergence of the lens, the laser energy with very high power density is gathered at the site, and the power density can generally reach 106~109W/cm2. After absorbing the point energy, the material melts immediately, and the molten liquid is blown away from the material by using auxiliary gas to complete the cutting process.
In the whole cutting process, the main function of auxiliary gas is to form driving force to remove molten metal liquid from the material itself. In this process, different kinds of gases will have different effects on materials and sections:
1. Oxygen as auxiliary gas
While blowing away the molten metal, the oxidation reaction will promote the endothermic melting of metal, thus realizing the melting of thicker materials. This process will significantly improve the processing capability of the laser. However, due to the presence of oxygen, the cut part of the material will be obviously oxidized. And quenching effect will be produced on the material around the cutting part, which will improve the hardness of this part of the material and have a certain impact on the subsequent processing.
2. Nitrogen as auxiliary gas
A protective atmosphere will be formed around the molten metal liquid to prevent the material from being oxidized, thus ensuring the quality of the profile. But at the same time, because nitrogen has no oxidation capacity, it does not help to improve the cutting ability like oxygen. In addition, when nitrogen is used as auxiliary gas, nitrogen consumption is very large. Therefore, cutting costs are higher than other gases.
3. Air as auxiliary gas
Nitrogen accounts for about 78% of air and oxygen for about 21%. When air is used as the auxiliary gas for cutting, the oxidation reaction of the cutting part must occur due to the presence of oxygen. But at the same time, due to the presence of a large amount of nitrogen, the oxidation reaction caused by oxygen is not enough to enhance heat transfer, and the cutting ability will not be improved. Therefore, the effect of air cutting can be understood as between nitrogen cutting and oxygen cutting. The advantage is that the cost of air cutting is very low. All the costs are the power consumption caused by the air supplied by the air compressor and the consumption of the filter element in the air pipeline.