In laser beam cutting, the gas plays a major role in making the material to eject through the beam kerf path. Gas used in laser beam cutting is often named as “Assist gas”. Based on the application, sometimes reactive gas is used (Oxygen, O2) and sometimes non-reactive gas / inert gas is used (like Nitrogen (N2) / Argon (Ar)).
- Role of Assist gas
The functions of assist gas during laser cutting are as follows
To maintain the constant material removal by uniformly involving into the process
- To involve in the reaction if reactive gas is used (Exothermic reaction)
- To blow out the melt if inert gas is used (Fusion Cutting)
- Purpose of Compressed Air cutting
Compressed Air is a commonly used gas in any industry. So far, air has come across wide range of applications starting from loading and lifting to cleaning and dusting. To emphasize on the part of thermal cutting, still in plasma, compressed air is used in cutting mild steel. Though we have other options like oxygen / nitrogen for laser cutting, there are still customers chose to cut with compressed air. The major reason behind that is as follows
- This is available abundantly
- Cost of acquiring this is very low
- There is already a compressed air generator available in 99% of industries
- There is no waiting time and no supply chain involved
- There is Shortage of Oxygen and Nitrogen due to Pandemic and it is the major reason for all customers switching to Air cutting from Oxygen , Nitrogen cutting
- Properties of Air
Before we start using the Compressed Air, let us understand the basic properties of the air. Air is matter that is available in earth’s atmosphere. Air is a composition of Nitrogen (78%), Oxygen (21%), Argon (0.9%), Carbon dioxide (0.04%) and other gases (0.06%). This mixture also contains 1% of water vapour.
- Air preparation for laser cutting
The air preparation is the preliminary process before using the compressed air. The preparation setup consists of following items.
- Pipelines, Fittings, Valves & Pressure gauge
- Auto drain valve
- Compressed Air as Assist gas
Using compressed air in the laser cutting process has a mixture of reactive and fusion cutting, as the gas contains 78% of nitrogen which is non-reactive and 21% of oxygen which is reactive. Because the portion of inert in air is high it is possible to achieve speeds equal to nitrogen cutting. As well the major portion of remaining gas is oxygen, which is a reactive gas causing more heat in the cutting.
- Benefits of compressed air cutting
- It provides more economical solution
- Almost the speed of the nitrogen is achieved in air cutting
- Maintenance cost is low
- Post processing works are minimized for normal fabrication application
- Dependency on third party for gas is reduced or nil
- Limitations of compressed air cutting
- In case of Mild steel, there is a little dross but that is very low. The dross can be wiped. There is a black oxide layer formed on the cut surface.
- In case of Stainless steel, there is yellowish / blackish colour surface on the cut surface.
- During weld processing stainless steel after air cutting, the surface needs to be cleaned as the weld seam quality on the surface will not be proper.
- The major disadvantage is that the quality of air cutting depends on the laser power. The higher the laser power the speed and quality of the cutting can be improved. Also the thickness limitation is also based on the laser power.
- For certain application, the air cutting is undesired, as the oxidation on the surface is prolonged to react to its environment. Like aerospace, food processing, chemical tanks, vessels etc. where the surface is exposed to its environment. Because the cutting is done with air and oxidation is already on the surface, which continues to react and loses the original property of material (Corrosive resistance).
- It requires proper maintenance of air generation setup at periodical basis, else the optics in cutting head may fail quickly.
- Minimum setup or investment is required
It is one alternative way using assist gas in laser cutting process by which you gain competitive speeds in production and reduce cycle time. Thereby reducing cost of production. However, the speed and quality of cutting depends on the laser power. If the application of air cutting prevails, then it is a good alternative with proper setup.