Laser cutting involves using a high-power density laser beam to concentrate light onto a small spot, rapidly heating the material until it reaches its boiling point and vaporizes to form a cavity. The laser beam then moves along the surface of the material, creating a cut and completing the processing of the object.
Laser cutting is a type of thermal cutting method, which can be further divided into four categories: laser gasification cutting, laser melting cutting, laser oxygen-assisted melting cutting, and controlled fracture cutting.
Working principle of laser cutting
Compared to other cutting methods, laser cutting stands out for its fast cutting speed and high-quality results.
The benefits of laser cutting include:
- Excellent cutting quality: The small laser spot, high energy density, and fast cutting speed result in better cutting quality.
- Thin and narrow incisions: The incisions made through laser gas cutting are thin and narrow, with parallel sides and good perpendicularity to the surface.
- Smooth and attractive surfaces: The cutting surfaces are smooth and visually appealing, and in some cases, they can be used as the final processing step without the need for additional machining.
- Minimal impact on material properties: The width of the heat-affected zone is small after laser cutting, which means the material properties near the cut are hardly affected. Additionally, there is minimal workpiece deformation, ensuring high cutting accuracy.
A comparison of cutting speed between laser cutting and other cutting methods for low carbon steel plates is shown in the table below.
Comparison of cutting speed of several cutting methods:
- High cutting speed: For instance, a 2500W laser can cut a 1mm thick cold-rolled carbon steel plate at a speed of 16-19 meters per minute.
- Non-contact cutting: Laser cutting is a non-contact process, meaning there is no physical contact between the nozzle and the workpiece, which eliminates the need to worry about tool wear.
1. Laser cutting accounts for 39% of the laser equipment market
The laser market experienced growth in 2020, but the rate of increase slowed down compared to the previous two years. The market sales revenue of laser equipment (including imports) across all industries was 69.2 billion yuan, which represents a year-on-year increase of 5.17%.
Due to the uncertain global economic trend, it is projected that the total sales revenue of China’s laser equipment market will be 74.0 billion yuan in 2021, with a year-on-year increase of 6.94%.
In the industrial laser equipment market, laser cutting is the most commonly used application, accounting for 39% of the market. Marking and welding come in second and third place, accounting for 19% and 12% of the market, respectively.
2. Advance towards high power, high precision and large format
In recent years, domestic laser cutting machine technology has experienced significant advancements and is now moving towards higher power, higher precision, and larger format capabilities.
In line with China’s push towards intelligent manufacturing, the industrial sector is undergoing a transformation from traditional processing to high-end manufacturing. As a result, the market scale of China’s laser cutting sector is expected to continue its rapid growth trajectory.
3. Application of compressed air in laser cutting
Laser cutting machines are capable of meeting the cutting requirements of a wide range of materials and complex shapes. Along with a high-energy laser, auxiliary gases are also necessary to complete the cutting process.
The commonly used auxiliary gases for laser cutting include oxygen (O2), nitrogen (N2), and compressed air. Compressed air is the most accessible and affordable option compared to oxygen and nitrogen. It is frequently used as an auxiliary gas for laser cutting.
The quality of the compressed air has a direct impact on the quality of metal laser cutting. Factors such as gas pressure size and stability can affect the cutting outcome.
When selecting the size of the air compressor used for supporting the laser cutting machine, it is important to take into consideration the design of the laser cutting head, the required auxiliary gas pressure, and the nozzle size to ensure the best match between the air compressor and the laser cutting machine.
4. Comparison of laser cutting with different auxiliary gases
When performing laser cutting, the choice of cutting gas depends on the type of material being cut. The selection of the cutting gas and its pressure can significantly impact the quality of the laser cutting process.
The most commonly used auxiliary gases for laser cutting include oxygen (O2), nitrogen (N2), compressed air, and in some cases, argon (Ar).
The cutting gas can be categorized into high-pressure gas and low-pressure gas based on its pressure.
The main functions of laser cutting auxiliary gases include supporting combustion and heat dissipation, removing the molten residue generated during cutting, preventing the molten residue from rebounding back into the nozzle, and protecting the focusing lens.
The choice of laser cutting process and auxiliary gas depends on the material being cut and the power of the laser cutting machine.
The following is a summary of the characteristics, uses, and scope of application of different types of auxiliary gases:
(1) Oxygen (O2)
Oxygen is primarily utilized for cutting carbon steel materials. The heat generated from the chemical reaction between oxygen and iron enhances the endothermic melting of the metal, thereby improving cutting efficiency and allowing for the cutting of thicker materials. This significantly increases the processing capacity of laser cutting machines.
However, the presence of oxygen results in the formation of an oxide film on the cut surface, causing a quenching effect on the surrounding material and increasing its hardness. This can impact subsequent processing.
The cut surface of carbon steel plates cut with oxygen is typically black or dark yellow. These plates are usually cut with low-pressure oxygen and then punched.
When nitrogen is used as an auxiliary gas for cutting, it creates a protective atmosphere around the molten metal, preventing oxidation and avoiding the formation of an oxide film. This results in oxidation-free cutting.
However, nitrogen does not react with metal, leading to a lack of reaction heat and weaker cutting ability compared to oxygen. Additionally, nitrogen consumption during nitrogen cutting is several times higher than oxygen, resulting in higher cutting costs.
The benefits of non-oxidative cutting include direct welding, coating, and strong resistance to corrosion. The cut surface is white in color.
Nitrogen is typically used for cutting stainless steel, galvanized plates, aluminum and aluminum alloy plates, brass, and other materials. Both low-pressure perforation and high-pressure cutting methods can be used.
The flow of gas has a significant impact on cutting during nitrogen cutting. To ensure optimal cutting, it is important to maintain a sufficient gas flow while ensuring the cutting gas pressure.
(3) Compressed air
Compressed air can be easily obtained and is much cheaper than oxygen and nitrogen, as it can be directly provided by an air compressor.
Although air contains only around 20% oxygen, leading to a lower cutting efficiency compared to oxygen cutting, its cutting ability is similar to that of nitrogen and slightly higher than nitrogen cutting.
The cut surface of air cutting is yellow in color.
When there is no strict requirement for the cut material’s surface color, using compressed air for cutting is the most economical and practical option compared to using nitrogen.
(4) Argon (Ar)
Argon is an inert gas that is commonly used in laser cutting to prevent oxidation and nitrification. It can also be utilized in welding processes. However, it should be noted that the cost of argon is higher compared to nitrogen, making it less cost-effective for typical laser cutting applications.
Argon cutting is mainly utilized for cutting titanium and titanium alloys, and the end face of the cut produced by argon cutting is white in color.
Currently, the market price for liquid nitrogen is approximately 1400 yuan per ton. When using liquid nitrogen for laser cutting, Dewar cans are required, with a typical can holding 120kg. The cost of 1kg of liquid nitrogen is more than 3 yuan.
Let’s calculate at 1400 yuan / ton.
120×1.4=168 yuan, and the specific gravity of nitrogen in standard state is 1.25kg/m3, so the maximum usage of liquid nitrogen in a Dewar tank is about 120 / 1.25=96Nm3, which is converted into nitrogen cost per nm: 168/96=1.75 yuan /Nm3.
If a domestic brand air compressor is used to provide 16bar compressed air, providing 1.27m3 per minute, the full load input power of this type of air compressor is 13.4kw.
If the industrial electricity charge is calculated at 1.0 yuan / kWh, the air cost per m3 is 13.4×1.0/ (1.27×60) =0.176 yuan / m3.
If the actual consumption of 0.5m3 gas per minute and the laser cutting machine works for 8 hours per day, the daily cost saved by using air cutting compared with nitrogen cutting is: (1.75-0.176) x8x60x0.5=378 yuan.
If the laser cutting machine works for 300 days a year, the gas cost saved in a year is: 378×300=113400 yuan.
It is clear that using compressed air instead of nitrogen for cutting is a more economical and practical option. In recent years, laser cutting technology has experienced significant advancements, with a focus on high power, high precision, and large format capabilities.
As China moves towards intelligent manufacturing, the industrial sector is undergoing a transformation from traditional processing to high-end manufacturing.
The market for laser cutting in China is expected to continue its rapid growth, offering ample market opportunities for laser air compressors.
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