First of all, let's understand the process of laser cutting: after the laser generated by the oscillator passes through the lens, it is concentrated at a point to form a very small spot. By precisely controlling the distance between the lens and the plate, the laser spot is guaranteed to be stable in the material thickness direction At a certain position, due to the converging effect of the lens, the laser energy with a very high power density is gathered at the spot, and the power density can usually reach 106-109W/cm2. After the material absorbs the spot energy, it melts instantly. The liquid blows off the material to complete the cutting process.
In the whole cutting process, the main function of the auxiliary gas is to form a driving force to remove the molten metal liquid from the material itself. In this process, different types of gas have different effects on the material and section:
01. When oxygen is used as auxiliary gas
While blowing away the molten metal liquid, an oxidation reaction will also occur to promote the endothermic melting of the metal, thereby enabling the melting of thicker materials, a process that significantly improves the processing capability of the laser. But at the same time, due to the presence of oxygen, the cut surface of the material will be significantly oxidized, and the material around the cut surface will be quenched, which will increase the hardness of this part of the material and have a certain impact on subsequent processing.
02. When nitrogen is used as auxiliary gas
A protective atmosphere is formed around the molten metal liquid to prevent the material from being oxidized, thereby ensuring the quality of the cut surface. But at the same time, because nitrogen has no oxidizing ability and cannot enhance heat transfer, it will not help improve cutting ability as oxygen does. In addition, when nitrogen is used as an auxiliary gas, the consumption of nitrogen is very large, resulting in a higher cutting cost than when other gases are used.
03. In the constituent gas of air
Nitrogen accounts for about 78% and oxygen accounts for about 21%. When air is used as an auxiliary gas for cutting, the cutting section will inevitably undergo oxidation reaction due to the presence of oxygen, but at the same time, due to the existence of a large amount of nitrogen, the oxidation reaction caused by oxygen is insufficient. In order to enhance the heat transfer, the cutting ability will not increase, so the air cutting effect can be understood as between nitrogen cutting and oxygen cutting, and the advantage is that the cost of air cutting is very low, all the cost is the air compressor to provide air. The resulting power consumption, as well as the consumption of the filter element in the air line.