The difference between fiber laser and CO2 laser

Sales and trends of laser cutting machine

At present, there are two main types of metal sheet metal cutting laser cutting machines in the sheet metal processing industry. One is a CO2 laser cutting machine that was converted from an industrial laser to a product about 20 years ago, and the other is a formal Fiber laser cutting machine transformed from industrial laser to product. Judging from the number of sales of laser cutting machines in the Chinese 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, the laser cutting machines sold on the market were basically 100% CO2 laser cutting machines, but we know that in recent years, the momentum of fiber laser cutting machines has been fierce and is being continuously recognized by the market. 

The basic difference between CO2 laser and fiber laser

Although the current market trend is toward fiber laser cutting machines, is fiber laser cutting machines really the best choice? CO2 laser and fiber laser, because of the different physical characteristics of the laser, so the laser processing technology is also different. Of course, the two have their own strengths and weaknesses. Depending on the processing object, each has its own advantages and disadvantages.

The CO2 laser is a gas beam obtained by exciting carbon dioxide molecules, and its wavelength is 10.6 μm; and the fiber laser is a crystal of Yb (ytterbium) compound placed in the optical fiber as a medium, which is obtained by irradiating this crystal with a beam The solid laser has a wavelength of 1.08μm. The physical characteristics of different wavelengths have a great influence on the processing characteristics of them.

Initially, the concept of fiber laser was recognized because of the laser that can propagate through fiber. The reason why it can propagate through optical fiber lies in its wavelength. It is because of its 1.08μm wavelength that it can propagate through optical fiber. The advantage of using optical fiber for propagation is that its optical components have a longer service life and higher maintenance performance.

The CO2 laser cutting machine propagates the laser from the vibrator to the processing point by means of a reflector, generally in an optical path isolated from the outside air. Although the light path is filled with air without ordinary dust or foreign objects, the surface of the mirror will be attached to dirt after a long period of use and needs to be cleaned. In addition, the mirror itself will be lost due to the absorption of a small amount of laser energy and needs to be replaced. In addition, to propagate the laser from the vibrator to the processing point, it is necessary to use multiple mirrors to adjust the reflection angle of the laser to propagate, so to maintain normal operation requires certain technical capabilities and management.

However, in the fiber laser cutting machine, from the oscillator to the processing point, the laser is propagated through one fiber. This fiber is generally called a light guide fiber. Since no optical parts like mirrors are needed, the laser is propagated in the light-guiding optical fiber isolated from the outside air, so the laser is almost not lost. Therefore, the light guide fiber itself will be somewhat lost, but this is several times longer than the reflector in the CO2 laser cutting machine. In addition, if the propagation path is above the minimum curvature of the light guide fiber, then the path can be freely determined, so adjustment and maintenance are also very convenient.

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

The fiber laser oscillator, as just mentioned, generates laser light inside the fiber and is isolated from the outside air. There are no optical parts, so there is little need for regular maintenance.

The maintenance cycle for cleaning the CO2 laser oscillator is set at about 4,000 hours, while the fiber laser oscillator is set at about 20,000 hours. It can be said that the fiber laser cutting machine has great advantages in terms of service life and maintenance performance.

In addition, we can also try to compare from the perspective of operating costs such as power consumption. The photoelectric conversion rate of the CO2 laser oscillator is said to be about 10 to 15%, while the fiber laser oscillator is about 35 to 40%. Due to the high photoelectric conversion rate, the electrical energy converted into heat dissipation is reduced, and the fiber laser cutting machine can control the power consumed by cooling devices such as cooling machines to be lower. In general, the oscillator of the fiber laser cutting machine requires higher accuracy for the management of the cooling temperature of the oscillator than the CO2 oscillator. However, at the same laser output power, the vibration of the fiber laser cutting machine The cooling capacity of about 1/2 to 2/3 of the CO2 laser oscillator used for the device is sufficient. Therefore, considering the power consumption of all devices of the laser cutting machine, the fiber laser cutting machine can operate under the power consumption of about 1/3 of the CO2 laser cutting machine, which can be said to be a very energy-saving laser cutting machine.

Difference in processing characteristics

In the processing of CO2 laser and fiber laser, the wavelengths of the two are very different.

When processing stainless steel materials, a comparison chart of the processing speed of CO2 laser cutting machine and fiber laser cutting machine. The output power of the laser is 4kW. We can see that in the field of plate thickness below 4.0mm, the fiber laser cutting machine can be processed at 2 to 3 times the cutting speed of the CO2 laser cutting machine.

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

If you want to use a laser cutting machine to cut quartz glass, then you can use the CO2 laser cutting machine to cut, but you cannot use the fiber laser cutting machine to cut. This is due to the physical principle that quartz glass can absorb the wavelength of the CO2 laser, but does not absorb the wavelength of the fiber laser but will penetrate. In addition, the fiber laser that we usually talk about is more advantageous than the CO2 laser cutting machine in the field of cutting highly reflective materials such as aluminum and copper. It is also because the metal material can absorb the physical characteristic of the wavelength of the fiber laser more.

When comparing the processing speed of stainless steel materials, we can see that in the field of plate thickness exceeding 6.0mm, the processing speed of the two is basically the same. From the point of view of the cutting process, it is more important to refer to the coefficient of how to exclude the molten metal more efficiently than to refer to the coefficient of melting the metal instantaneously. When cutting with laser, it is necessary to spray auxiliary gas (generally refers to nitrogen, oxygen, etc.) to the processing point while irradiating the laser to the material, so as to obtain a good processing state. Different cutting objects use different auxiliary gases. In addition, another important role of the auxiliary gas is to isolate the molten metal from under the material. In the case where the processing object is a thick plate, in order to obtain a good cutting state, the auxiliary gas is required to function to isolate the metal to be melted from the lower part of the material, and finally the effect of increasing the processing speed can be achieved.

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

There are still some problems that cannot be solved in the guarantee of cutting quality with the fiber laser cutting machine. Especially in the field where the board thickness exceeds 3.0mm, the products processed by the fiber laser cutting machine will have some obvious small particles attached to the surface below the cutting surface that are difficult to peel off. These small particles are often referred to as scum. In addition, the cut surface is also rougher than the CO2 laser cutting machine. This is the phenomenon caused by the above-mentioned characteristic of high absorption of metal materials. Laser processing is the process of reflecting the laser light to the surface of the material, and then the metal is melted and falls. When the fiber laser is reflected on the metal surface with a relatively high absorption rate, it will cause the back absorption of the molten metal on the cutting surface, resulting in the roughness of the cutting section after cutting.

CO2 laser cutting machine processed samples (stainless steel material 20mm)

Processing quality is one of the items that is difficult to digitize, so many customers do not pay much attention when choosing a laser cutting machine. However, the problem of dross mentioned earlier is related to the quality of processing. Even if the speed of fiber laser cutting machine is faster, the cost control is very low. After laser cutting, if the subsequent processes such as scum removal are required, the total processing cost is similar to the cost of processing with CO2 laser cutting machine. This means that everyone needs to pay more attention to the processing quality of the laser cutting machine.

Movement performance of laser cutting machine

Although I have compared the concepts of fiber laser and CO2 laser, when choosing a laser cutting machine, can I just make such a comparison? The concepts of optical fiber and CO2 are always the comparison of the laser cutting machine's constituent elements-the oscillator. There are also drive shafts called X, Y, Z in the system of laser cutting machine. The motion performance and control performance of this drive shaft are also a big component.

In addition to round holes, square holes, and rectangles, the shapes processed by laser cutting machines also have complicated appearance shapes such as special-shaped holes, wedge shapes, and irregularities. So no matter how fast the processing speed is, if the motion performance of the XY drive shaft that determines the processing shape is low, shortening the processing time is hopeless. Assuming that the processing speed is 40m / min with a fiber laser machine, and the processing speed is 20m / min with a CO2 laser cutting machine, the processing time of the fiber laser machine will be because its speed is twice that of the CO2 laser cutting machine So when processing a certain shape, is the processing time 1/2 of the CO2 laser cutting machine? If the shape of the processing is complex and the number of holes is large, the answer becomes NO. To clearly show the difference in processing speed, it is necessary to improve the motion performance of the drive shaft, especially the acceleration and deceleration capabilities during cutting.

Comprehensive capabilities of laser cutting machines

With higher acceleration and deceleration performance, a tough, high-rigidity frame that can withstand its motion performance is also needed. In order to maintain the processing accuracy of the product, it is necessary to be able to control the internal structure of high mobility. To maximize the laser processing capability of the vibrator, it is necessary to improve the comprehensive capabilities of the laser cutting machine including the drive shaft.

Because the constituent elements of the fiber laser cutting machine are relatively simple, when considering the design and manufacture of the laser cutting machine, there can be a fiber laser cutting machine of a certain quality without laser processing technology. In addition, many components of the fiber laser cutting machine are commercially available, and the processing capability of the cutting machine made by assembling these components is basically not inferior. This is one of the reasons why manufacturers of optical fiber laser cutting machines are proliferating recently.

However, in the CO2 laser cutting machine, a lot of processing technologies such as laser propagation are required, so it is easy for different cutting machine manufacturers to have differences in characteristics and performance. Manufacturers of real laser cutting machines should have mature technology and the ability to design and manufacture CO2 laser cutting machines. They must also use the processing technology accumulated from the production of CO2 laser cutting machines to design and manufacture fiber laser cutting machines. Such a manufacturer of processing technology is what is needed in the processing machine market in the future.

Although the machining accuracy and processing quality are difficult to express with numerical values, the laser cutting machine that can always maintain a high machining accuracy and processing quality, and the movement performance is also very high is the best choice. However, it is necessary to make a calm judgment based on the processing content before making a decision. If there are many thin plates in the processed materials, the production volume is relatively large, and you want to control the processing cost, the fiber laser cutting machine is the best choice. However, if it is often necessary to process thick plates over 6.0mm, or to achieve a certain processing quality, the CO2 laser cutting machine is more suitable. Subsequent operations need to be carried out by another process, and if manpower is used to operate, the total processing cost is very high. When choosing a laser cutting machine, in addition to judging the laser processing process, please make a comprehensive judgment from the perspective of your product and manufacturing.