Laser cutting is to use the high power density of the laser beam to concentrate the laser on a small light spot, quickly heat the material, vaporize it to form a cavity after reaching the boiling point, and then move the laser beam to create a slit on the surface of the material to complete the cutting of the processed object.
Laser cutting is one of the thermal cutting methods, which can be divided into laser gasification cutting, laser melting cutting, laser oxygen assisted melting cutting and controlled fracture cutting.
Working principle of laser cutting
Compared with other cutting methods, laser cutting is characterized by fast cutting speed and high quality.
Specifically summarized as follows:
(1) Good cutting quality.
Due to the small laser spot, high energy density and fast cutting speed, laser cutting can obtain better cutting quality.
(2) The laser gas cutting incision is thin and narrow, the two sides of the cutting seam are parallel and have good perpendicularity with the surface.
(3) The cutting surface is smooth and beautiful, and it can even be used as the last processing procedure without machining, and the parts can be used directly.
(4) After laser cutting, the width of the heat affected zone is very small, and the performance of the material near the cutting seam is hardly affected, and the workpiece deformation is small, and the cutting accuracy is high.
The cutting speed comparison between laser cutting and other cutting methods is shown in the table below.
The cutting material is low carbon steel plate.
Comparison of cutting speed of several cutting methods:
|Cutting method||Laser cutting||Plasma cutting||Oxyacetylene cutting||Waterjet cutting|
|Cutting speed||Very fast||Fast||Slow||Very slow|
(5) Fast cutting speed, for example: 2500W laser cutting 1mm thick cold-rolled carbon steel plate, the cutting speed can reach 16-19m / min.
(6) For non-contact cutting, there is no contact between the nozzle and the workpiece during laser cutting, and there is no tool wear.
1. Laser cutting accounts for 39% of the laser equipment market
Although the laser market increased in 2020, the growth rate began to slow down compared with the previous two years.
The market sales revenue of laser equipment (including imports) in all fields was 69.2 billion yuan, an increase of 5.17% year-on-year.
Affected by the uncertainty of the global economic trend, it is estimated that the overall sales revenue of China’s laser equipment market will be 74.0 billion yuan in 2021, an increase of 6.94% year-on-year.
In the industrial laser equipment market, laser cutting is the most widely used, accounting for 39%.
Marking and welding rank second and third, accounting for 19% and 12% respectively.
2. Advance towards high power, high precision and large format
In recent years, domestic laser cutting machine technology has made a breakthrough development, and is moving towards the direction of high power, high precision and large format.
In the context of China’s intelligent manufacturing, the industrial sector has shown a trend of transformation from traditional processing to high-end manufacturing, and the market scale of China’s laser cutting sector will continue to maintain a trend of rapid development.
3. Application of compressed air in laser cutting
Laser cutting machine can meet the cutting requirements of various materials and complex shapes.
In addition to the need to provide high-energy lasers, auxiliary gas is an indispensable material to complete the cutting process.
The auxiliary gases used for laser cutting mainly include oxygen (O2), nitrogen (N2) and compressed air.
Compressed air is easier to obtain than oxygen and nitrogen, and the price is very cheap compared with oxygen and nitrogen.
It is very common to use compressed air as auxiliary gas for laser cutting.
The quality of compressed air has a very direct impact on the quality of metal laser cutting.
The size and stability of gas pressure will affect the cutting effect.
The selection of the size of the air compressor supporting the laser cutting machine as the auxiliary gas should be mainly determined according to the design of the laser cutting head used by the laser cutting machine, the auxiliary gas pressure and the nozzle size, so as to get the best match between the air compressor and the laser cutting machine.
4. Comparison of laser cutting with different auxiliary gases
During laser cutting, different cutting gases are selected according to different materials of cutting plates.
The choice of cutting gas and its pressure has a great influence on the quality of laser cutting.
The commonly used auxiliary gases for laser cutting include oxygen (O2), nitrogen (N2), compressed air, and sometimes argon (Ar).
According to the gas pressure, it can be divided into high-pressure gas and low-pressure gas.
The functions of laser cutting auxiliary gas mainly include: supporting combustion and heat dissipation, blowing off the molten stains produced by cutting in time, preventing the cutting molten stains from rebounding upward into the nozzle, protecting the focusing lens, etc.
According to the different materials to be cut and the power of the laser cutting machine, different laser cutting processes are selected, and the selection of auxiliary gas is also different.
The characteristics, uses and scope of application of different types of auxiliary gases are as follows:
(1) Oxygen (O2)
Oxygen is mainly used for cutting carbon steel materials.
The chemical reaction heat of oxygen and iron promotes the endothermic melting of metal, which can greatly improve the cutting efficiency, realize the cutting of thicker materials, and significantly improve the processing capacity of laser cutting machines.
But at the same time, due to the existence of oxygen, there will be an obvious oxide film on the end face of the cut, and it will produce a quenching effect on the materials around the cutting surface, improve the hardness of this part of the materials, and have a certain impact on the subsequent processing.
The cut end face of the material cut by oxygen is black or dark yellow. Generally, carbon steel plates are cut with oxygen, punched and cut with low pressure.
When nitrogen is used as auxiliary gas for cutting, nitrogen will form a protective atmosphere around the molten metal to prevent the material from being oxidized, avoid the formation of oxide film, and realize oxidation-free cutting.
But at the same time, because nitrogen does not react with metal, there is no reaction heat, the cutting ability is not as good as oxygen, and the nitrogen consumption of nitrogen cutting is several times larger than that of oxygen, and the cutting cost is higher than that of oxygen cutting.
The non oxidation cutting mask has the characteristics of direct welding, coating, strong corrosion resistance, etc., and the end face of the incision is white.
Generally, nitrogen is used to cut stainless steel, galvanized plate, aluminum and aluminum alloy plate, brass and other materials, with low-pressure perforation and high-pressure cutting.
During nitrogen cutting, the change of gas flow has a great impact on cutting.
Under the condition of ensuring the cutting gas pressure, we must ensure the sufficient gas flow.
(3) Compressed air
Compressed air can be directly provided by air compressor, which is easy to obtain and very cheap compared with oxygen and nitrogen.
Although the air contains only about 20% oxygen, and the cutting efficiency is far less than that of oxygen cutting, the cutting ability is close to that of nitrogen, and the efficiency of air cutting is slightly higher than that of nitrogen cutting.
The cut end face of air cutting is yellow.
When there is no strict requirement on the surface color of the material cut, it is the most economical and practical choice to cut with compressed air instead of nitrogen.
(4) Argon (Ar)
Argon is an inert gas, which can prevent oxidation and nitridation in laser cutting, and can also be used in welding.
However, the price of argon is higher than that of nitrogen.
Generally, argon is not cost-effective for ordinary laser cutting.
Argon cutting is mainly used for titanium and titanium alloys.
The cut end face of argon cutting is white.
At present, the liquid nitrogen on the market is about 1400 yuan / ton.
Dewar cans are required for liquid nitrogen used for laser cutting, generally 120kg a can, and the price of 1kg 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 can be seen that using compressed air instead of nitrogen cutting is very economical and practical.
In recent years, laser cutting machine technology has made a breakthrough development, and is moving towards the direction of high power, high precision and large format.
In the context of China’s intelligent manufacturing, the industrial field is showing a trend of transformation from traditional processing to high-end manufacturing.
The market scale of China’s laser cutting field will always maintain a trend of rapid development, which will bring great market growth space for laser air compressors.