Text/Shenzhen Jiepute Optoelectronics Co., Ltd
As an efficient and environmentally friendly cleaning method, laser cleaning technology is gradually replacing traditional chemical cleaning and mechanical cleaning methods. With the increasingly strict national requirements for environmental protection, as well as the continuous pursuit of cleaning quality and efficiency in the field of industrial manufacturing, the market demand for laser cleaning technology is growing rapidly. As a big manufacturing country, China has a huge industrial base, which provides a broad space for the wide application of laser cleaning technology. In aerospace, rail transit, automobile manufacturing, mold manufacturing and other industries, laser cleaning technology has been widely used, and is gradually expanding to other industries.
Workpiece surface cleaning technology has a wide range of applications in many fields, the traditional cleaning method is often contact cleaning, there is a mechanical force on the surface of the cleaning object, the surface of the object is damaged or the cleaning medium is attached to the surface of the object to be cleaned, which cannot be removed, resulting in secondary pollution. Nowadays, the country advocates the development of green and environmentally friendly emerging industries, and laser cleaning is the best choice. The abrasiveness and non-contact nature of laser cleaning solves these problems. Laser cleaning equipment is suitable for cleaning objects of various materials and is considered to be the most reliable and effective cleaning method.
Principle of laser cleaning
Laser cleaning is to irradiate a high energy density laser beam to the part of the object to be cleaned, so that the laser is absorbed by the polluted layer and the substrate, through the process of light peeling, gasification and other processes, to overcome the adhesion between the pollutant and the substrate, so that the pollutant leaves the surface of the object, and then achieves the purpose of cleaning, and does not damage the object itself.
Figure 1: Schematic diagram of laser cleaning.
In the field of laser cleaning, fiber lasers have become the winners of laser cleaning light sources due to their ultra-high photoelectric conversion efficiency, excellent beam quality, stable performance and sustainable development. Fiber lasers are represented by pulsed fiber lasers and CW fiber lasers, which occupy the leading position in the market for macro material processing and precision material processing, respectively.
Figure 2: MOPA pulsed fiber laser construction.
MOPA pulsed fiber laser vs. CW fiber laser cleaning application comparison
For the emerging laser cleaning applications, many people may be a little confused when facing pulsed lasers and CW lasers on the market: whether to choose pulsed fiber laser or CW fiber laser?
The test models were CL-300-10-A MOPA pulsed fiber laser and CW-R-B-W-2000L CW fiber laser, respectively, as shown in Figure 3.
Figure 3: CL-300-10-A MOPA pulsed fiber laser (top) and CW-R-B-W-2000L CW fiber laser (bottom).
The test results are shown in Figure 4 and Figure 5. Through microscopic observation, the sheet metal is processed by a high-power CW fiber laser, and the phenomenon of remelting occurs. After the steel is processed by the MOPA pulsed fiber laser, the substrate is slightly damaged and the texture of the substrate is maintained, and after the continuous fiber laser processing, serious damage and molten material are generated.
MOPA pulsed fiber laser (left) CW fiber laser (right)
Figure 4: Comparison of the surface effect (top) and microscopic (bottom) of a sheet metal surface after stripping using a MOPA pulsed fiber laser (left) and a CW fiber laser (right).
MOPA pulsed fiber laser (left) CW fiber laser (right)
Figure 5: Comparison of the surface effect (top) and microscopic (bottom) of steel after rust removal using a MOPA pulsed fiber laser (left) and a CW fiber laser (right).
Through the above comparison, it can be seen that CW fiber laser is easy to cause discoloration and deformation of the substrate due to its large heat input, and this type of laser can be used as the light source when the substrate damage is not high and the thickness of the material cleaning is thin. MOPA pulsed fiber laser acts on the material by means of high peak energy and high repetition frequency pulse, and peels off the cleaned object through instantaneous vaporization and vibration, which has the characteristics of small thermal effect, high compatibility and high precision, and can not damage the substrate.
It is concluded that in the face of high precision, it is necessary to strictly control the temperature rise of the substrate, and the application scenarios that require the substrate to be non-destructive, such as painted aluminum and die steel, it is recommended to choose MOPA pulsed fiber laser;
The principle and application difference between single-mode and multi-mode lasers
(1) Introduction to the principle of single-mode and multi-mode lasers
Figure 6: Singlemode (left) and multimode (right).
Single
Single-mode refers to the single distribution mode of laser energy in the two-dimensional plane, and also refers to the transverse mode of the laser beam, that is, there is only one mode in the cross-section, which is in the shape of a peak, and the energy density from the center to the outer edge decreases sequentially, and the energy distribution is in the form of a Gaussian curve, also known as Gaussian light.
Multimode
Multimode refers to the spatial energy distribution mode formed by the superposition of multiple distribution modes, and also refers to the transverse mode of the laser beam, that is, there are many energy points on the cross section, and the more modes, the more flat-top distribution the energy, also known as flat-top light.
With the accumulation of technological innovation and experience in the field of core light source, JPT company has independently developed the CL series laser in the power range of MOPA 100~2000W for laser cleaning applications (see Figure 7), which has the advantage of lightweight casing and output head design, and has a series of light sources of single-mode and multi-mode beam types for selection, and will continue to develop and upgrade the CL series in the future.
Figure 7: CL-2000-100-W multimode fiber laser (top) and CL2-200-1&5-A single-mode fiber laser (bottom).
(2) Comparison of spot morphology of single-mode and multi-mode laser processing
According to Figure 8a-c, it can be seen that the CL-1 series spot effect shows a "deep pit" shape, the CL-5 series spot effect shows a flat-topped "arc" shape, and the CL-10 series spot has a deep inside, like an outer volcanic crater.
Figure 8a: CL-1 series spot map, singlemode.
Figure 8b: CL-5 series spot map, multimode. Figure 8c: CL-10 series spot map, multimode.
(3) The difference between single-mode and multi-mode applications
The difference between multimode and single-mode: single-mode emits a typical Gaussian beam, the energy is very concentrated, similar to a steep mountain peak (see Figure 6 left), the beam quality is also better than multimode, multimode is equivalent to a combination of multiple Gaussian beams, so the energy distribution is similar to an inverted cup (see Figure 6 right), relatively average, of course, the beam quality is worse than that of single-mode.
For example, in the application of paint removal, rust removal, degreasing and texturing, if the cleaned object has a certain thickness or rust penetrates into the inner layer of the material, it is more appropriate to use a single-mode laser for cleaning;
Laser cleaning experiments
(1) Stainless steel paint removal and cleaning experiment
Figure 9: Cleaning effect of CL-1/-5/-10/-15 at different energy densities.
Under different energy densities, it can be seen from the microscopic diagram of the material (see Fig. 9) that most of the substrate texture of the CL-1 series is damaged, while the CL-5/-10/-15 series does not damage the substrate and retains the texture of the substrate.
(2) Carbon steel substrate rust removal and cleaning experiment
Figure 10: Carbon steel cleaning results obtained with CL-1000-15 (left) and CL-1000-50 (right).
Through the carbon steel substrate derusting and cleaning experiment (see Fig. 10), the surface of the CL-50 series macro effect is smoother, and the surface roughness value will be smaller, because the spot spot of CL-50 is larger than that of CL-15, and compared with the single mode, the multi-mode flat top light can use energy more efficiently, and the damage to the cleaning substrate can be minimized, which is suitable for working conditions with high requirements for the substrate.
(3) Elemental analysis test
JCM-7000 scanning electron microscope was used to analyze the surface element content, and the specific results are shown in Table 1.
Table 1: Analysis of surface element content
Fig. 11: (a) Uncleaned material (b) CL-10 series cleaning effect (c) CL-1 series cleaning effect
As can be seen from Table 1, the content of SiO2 and SO3 on the surface of the material decreased by 0.21% and 3.1% after cleaning with CL-10 series lasers, and all surface elements were completely cleaned off after cleaning with CL-1 series lasers.
Through the analysis of elemental data, under the fixed number of cleanings, there is still residual oxide on the surface after multi-mode cleaning, and after single-mode cleaning, the impurities on the surface are basically removed, and the efficiency is better than that of multi-mode.
In summary, the above experiments verify the difference between the principle and application effect of single-mode and multi-mode. CL-1 series lasers can thoroughly clean the surface rust, but it is easy to cause texture damage on the surface of the substrate; CL-5/-10/-15 series can remove the coating or paint surface while having almost no effect on the substrate, which can effectively retain the original texture of the substrate; CL-50 series focused spot is larger than CL-15 series, which has more advantages in macro effect.
Both single-mode and multi-mode lasers can remove the surface oxide layer macroscopically, and the single-mode laser is more thorough after cleaning, and the damage to the material substrate is greater. After multi-mode cleaning, the surface roughness is lower, and the damage to the material substrate is smaller, but the substance in the inner layer of the material cannot be cleaned, and the cleaning effect of multi-mode will be better under the same parameters.
For applications such as laser rust removal, anode stripping, pre- and post-weld treatment, hand-held marking, etc., the CL-1/5/10 series cleaning laser developed by JPT is more effective, if the material needs to be cleaned with high efficiency, it is more suitable to process the material with a flat top light with a larger spot, such as the CL-10/15/50 series cleaning laser, and if the application that requires paint removal, deplating, and rust removal without damaging the substrate, the CL-50/100 series laser can be used.
In addition to the CL series, JPT has also developed the M7 series light source in the 200~1000W power range, which is also a single-mode laser, and the M7 series uses an isolator output, which has a better processing effect on high-reflective materials, and the beam quality is better than that of the CL series, and the processing shading is more delicate. The M7 series is suitable for applications such as laser rust removal, surface treatment, sheet cutting, welding, engraving, drilling, stripcoating, and more.
In laser cleaning, the material needs to be considered to ensure that the cleaning needs are met while minimizing damage to the substrate. Depending on the actual operating situation, it is important to choose the right laser light source.
If laser cleaning wants to enter the large-scale application, it is inseparable from the innovation of new technologies and new processes, and JPT will continue to adhere to the positioning of laser +, control the pace of development steadily, and strive to deepen the upstream core laser light source technology, focusing on solving the key problems of key laser materials and components, and providing a source of power for advanced manufacturing.
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