At present, there are two main types of metal sheet metal cutting laser cutting machines in the sheet metal processing industry. One is the CO2 laser cutting machine that was transformed from an industrial laser into a product about 20 years ago, and the other is the optical fiber laser cutting machine that was formally transformed from an industrial laser into a product about 5 years ago. According to the number of laser cutting machines sold in China's sheet metal equipment market in recent years, CO2 laser cutting machines account for 40% and fiber laser cutting machines account for 60%. Although in 2007, almost 100% of the laser cutting machines sold in the market were CO2 laser cutting machines, we know that in recent years, the optical fiber laser cutting machines have a strong momentum, are constantly recognized by the market, and the sales volume is gradually expanding.

Basic differences between CO2 laser and fiber laser

Although the current market trend is to favor optical fiber laser cutting machine, is optical fiber laser cutting machine really the best choice? CO2 laser and fiber laser have different laser processing technologies due to their different physical characteristics. Of course, they actually have their own strengths and weaknesses. According to the different processing objects, they have their own advantages and disadvantages.

CO2 laser is a gas beam obtained by exciting carbon dioxide molecules, and its wavelength is 10.6 μ m； The fiber laser is a solid laser obtained by putting a crystal of Yb (ytterbium) compound as a medium into the fiber and irradiating the crystal with a beam of light. Its wavelength is 1.08 μ m。 The physical characteristics of different wavelengths have a great impact on the processing characteristics of both.

At first, the concept of optical fiber laser was recognized because it is a laser that can be transmitted through optical fiber. The reason why it can propagate through optical fiber is that its wavelength is 1.08 μ M wavelength can be transmitted through optical fiber. The advantage of using optical fiber for transmission is that its optical components have a long service life and high maintenance performance.

The CO2 laser cutting machine transmits the laser from the generator to the processing point by means of the mirror, generally in the optical path isolated from the outside air. Although the optical path is filled with air free of ordinary dust or foreign matter, the surface of the reflector will also be attached by dirt after a long time of use and needs to be cleaned. In addition, the reflector itself will also be lost due to absorbing a small amount of laser energy, which needs to be replaced. In addition, to spread the laser from the generator to the processing point, multiple mirrors need to be used to adjust the reflection angle of the laser for transmission. Therefore, to maintain normal operation, certain technical capabilities and management are required.

Comparison of CO2 and optical fiber processing speed

However, from the generator to the processing point of the optical fiber laser cutting machine, the laser propagates through one optical fiber. This fiber is generally called a light guide fiber. Since no optical components like reflectors are needed, and the laser is propagated in the light guide fiber isolated from the outside air, the laser will hardly be lost. But strictly speaking, the laser is propagated repeatedly around the light guide fiber, so the light guide fiber itself will be somewhat lost. However, the service life of this mirror is several times longer than that of the reflector in the CO2 laser cutting machine. In addition, if the propagation path is above the minimum curvature of the optical fiber, then the path can be determined freely, so it is very convenient to adjust and maintain.

In the process of laser generation (laser generator structure), the two are also different. The CO2 laser generator generates laser by placing the gas mixed with CO2 in the discharge space. In order to ensure the normal operation of the resonance length obtained from the laser output power, optical components are configured inside the generator, and the optical components inside the generator need to be cleaned and replaced regularly.

As mentioned just now, the optical fiber laser generator generates laser in the optical fiber, which is isolated from the outside air and has no optical components, so it is almost unnecessary to maintain it regularly.

The cleaning and other maintenance cycle of the CO2 laser generator is set at about 4000 hours, while the optical fiber laser generator is set at about 20000 hours. In terms of the service life and maintenance performance mentioned above, it can be said that the fiber laser cutter has great advantages.

In addition, we can also try to compare from the perspective of operating costs such as power consumption. The photoelectric conversion rate of CO2 laser generator is said to be about 10-15%, while that of fiber laser generator is about 35-40%. Due to the high photoelectric conversion rate, there is less electrical energy that can be converted into heat, so the optical fiber laser cutting machine can control the power consumption of cooling devices such as the cooler lower. Generally speaking, the generator of the optical fiber laser cutting machine requires higher accuracy for the cooling temperature management of the generator than the CO2 generator. However, under the same laser output power, the cooling capacity of the CO2 laser generator used for the generator of the optical fiber laser cutting machine is enough. Therefore, considering the power consumption of all devices of the laser cutting machine, the optical fiber laser cutting machine can operate under about 1/3 of the power consumption of the CO2 laser cutting machine, which can be said to be a very energy-saving laser cutting machine.

Differences between optical fiber cutting machine and processing characteristics

In the processing of CO2 laser and fiber laser, due to their different wavelengths, they are very different.

Comparison chart of processing speed of CO2 laser cutting machine and optical fiber laser cutting machine when processing stainless steel materials. The output power of the laser is 4kW. We can see that in the field of plate thickness less than 4.0mm, the optical fiber laser cutting machine can process at 2-3 times the cutting speed of the CO2 laser cutting machine.

Why is there such a big difference in processing speed even under the same output power? First of all, it can be said that there are great differences in the absorptivity of laser energy to metal materials. Not only metal materials, but also in all things in the world, due to the different physical properties of materials, the absorbance of light energy is different at different wavelengths of light. For example, the stainless steel material mentioned above has an absorption rate of about 12% for CO2 laser and about 35% for fiber laser, a difference of about three times. The so-called high absorptivity means that after the laser irradiates the metal material, the light energy is converted into heat energy and then the metal material is melted in a very short time, so the cutting process can be formed at a very fast processing speed.

If the quartz glass is to be cut with a laser cutter, the CO2 laser cutter can be used for cutting, but the optical fiber laser cutter cannot. This is due to the physical principle that quartz glass can absorb the wavelength of CO2 laser, but instead of absorbing the wavelength of fiber laser, it will penetrate. In addition, in the field of cutting highly reflective materials such as aluminum and copper, the optical fiber laser is more advantageous than the CO2 laser cutting machine, which is also due to the principle that metal materials can better absorb the wavelength of optical fiber laser.

When comparing the processing speed of stainless steel materials, we can see that in the area where the plate thickness exceeds 6.0mm, the processing speed of both is basically the same. From the perspective of cutting process, it is more important to refer to the coefficient of how to remove molten metal more efficiently than to refer to the coefficient of instantaneous molten metal. When cutting with laser, it is necessary to spray auxiliary gas (generally nitrogen, oxygen, etc.) to the processing point while irradiating the laser on the material, so as to get a good processing state. Different materials of cutting objects use different auxiliary gases. In addition, another major role of auxiliary gas is to isolate the molten metal from the bottom of the material. When the processing object is thick plate, in order to get a good cutting state, auxiliary gas is required to play a role in isolating the metal to be melted from the lower part of the material, which can finally achieve the effect of improving the processing speed.

However, from the perspective of processing field and cutting quality, it can be said that CO2 laser cutting machine is better. CO2 laser processing machine has experienced about 30 years since it was applied in the industry. Many characteristics of its processing technology have been thoroughly studied, so it can correspond to the processing field from thin plate to thick plate. In addition, the processing technology is also very mature, which can ensure a certain processing quality. It not only has the processing technology to cut various shapes, but also has the processing technology to ensure that the cutting surface reaches a certain roughness.

There are still some problems to be solved in the aspect of ensuring the cutting quality when cutting with optical fiber laser cutting machine. Especially in the field where the plate thickness exceeds 3.0mm, the products processed by optical fiber laser cutting machine will have some obvious small particles attached to the surface below the cutting surface, which are difficult to peel. These small particles are often referred to as scum. In addition, the cutting surface is also rougher than the CO2 laser cutting machine. This is the phenomenon caused by the above mentioned high absorption of metal materials. Laser processing is the process of reflecting the laser to the material surface, and then the metal is melted down. When the optical fiber laser is reflected on the metal surface with high absorptivity, it will cause reverse absorption to melt the metal on the cutting surface, resulting in the roughness of the cut section after cutting.

Sample display

Processed sample of CO2 laser cutting machine (stainless steel material 20mm)

Processing quality is one of the items that are difficult to be quantified, so many customers do not pay much attention when choosing laser cutting machines. However, the scum problem mentioned above is related to the processing quality. Even if the optical fiber laser cutting machine is used, the cost is controlled very low even if the speed is faster. If the subsequent processes such as removing scum need to be carried out after laser cutting, the total processing cost is similar to that of CO2 laser cutting machine. This means that we need to pay more attention to the processing quality of laser cutting machines.

Although I have compared the concepts of fiber laser and CO2 laser, is it enough to make such a comparison when selecting laser cutting machine? The concepts of optical fiber and CO2 are always the comparison of the generator, which is the constituent element of the laser cutting machine. There are also X, Y, Z drive shafts in the system of laser cutting machine, and the motion performance and control performance of this drive shaft are also a major component.

In addition to round holes, square holes and rectangles, the shapes processed by laser cutting machines also have complex appearance shapes such as special-shaped holes, wedges and concavoconvex shapes. Therefore, no matter how fast the machining speed is, if the motion performance of XY drive shaft that determines the machining shape is low, there is no hope to shorten the machining time. Assuming that the processing speed of optical fiber laser machine is 40m/min and that of CO2 laser cutting machine is 20m/min, the processing time of optical fiber laser machine will be twice as long as that of CO2 laser cutting machine. So when processing a certain shape, is the processing time half as long as that of CO2 laser cutting machine? If the machining shape is complex and the number of machining holes is large, the answer becomes NO. To obviously reflect the difference in processing speed, it is necessary to improve the kinematic performance of the drive shaft, especially the acceleration and deceleration capability during cutting.

Comprehensive capability of laser cutting machine

With high acceleration and deceleration performance, it also needs a strong and rigid frame that can withstand its sports performance. In order to maintain the processing accuracy of products, it is necessary to control the internal structure with high mobility. To maximize the laser processing capacity of the generator, it is necessary to improve the comprehensive capacity of the laser cutting machine including the drive shaft.

Because the components of the optical fiber laser cutting machine are relatively simple, when considering the design and manufacture of the laser cutting machine, there is no laser processing technology, and a certain quality optical fiber laser cutting machine can be manufactured. In addition, many components of the optical fiber laser cutting machine can be purchased in the market, and the cutting machine made by assembling these components is basically no inferior. This is one of the reasons why the manufacturers of optical fiber laser cutting machines are flooded recently.

However, in CO2 laser cutting machines, many processing technologies such as laser propagation are required, so it is easy to have differences in characteristics and performance between different cutting machine manufacturers. The manufacturers of real laser cutting machines should have mature technology, be able to design and manufacture CO2 laser cutting machines, and use the processing technology accumulated from the production of CO2 laser cutting machines to design and manufacture optical fiber laser cutting machines. The manufacturers with such processing technology will be needed in the future processing machine market.

Although it is difficult to express the machining accuracy and quality by numerical value, the laser cutting machine that can always maintain high machining accuracy and quality and has very high motion performance is the best choice. However, before making a decision, we need to make a calm judgment based on the processing content. If there are many thin plates in the processed materials, the production volume is large, and the processing cost is to be controlled, the optical fiber laser cutting machine is the best choice. However, CO2 laser cutting machine is more suitable if it is often necessary to process thick plates of more than 6.0mm or to achieve certain processing quality. Subsequent operations need to be carried out by other processes, and the total processing cost is very high if manual operation is used. When choosing a laser cutting machine, in addition to judging the laser processing process, please make a comprehensive judgment from the perspective of your products and manufacturing.