Special issue-Laser cleaning technology
2023, 52(2): 20230049.
doi: 10.3788/IRLA20230049
This paper introduces the main task of the fifth sub-topic project "Key Technologies in Laser Engineering and Cleaning Application" of the National Key Research and Development Project of the Ministry of Science and Technology (2017YFB0405100) from 2017 to 2021: the key technologies of quasi-continuous all-solid-state kilowatt level laser cleaner prototype. Laser cleaner prototype with three-dimensional large gantry frame forms laser cleaning industrial platform. A laser cleaning mechanism model for rail surface rust removal and aircraft composite skin paint removal is introduced. The methods of laser cleaning monitoring are introduced from sample identification, process monitoring and result detection. The laser cleaning parameters of 60 rail rust removal and aircraft aluminum skin depainting are obtained by author's research group, and the cleaning efficiency index passes the expert test. During the implementation of the project, developed prototypes are applied to more than 10 units such as China National Petroleum Corporation, Harbin Institute of Technology, Academy of Armored Force Engineering, Lianbo Heyi Technology Co., LTD. At the end of project execution, the project is awarded as the outstanding project of the key R&D plan of the Ministry of Science and Technology.
2023, 52(2): 20230073.
doi: 10.3788/IRLA20230073
High efficiency and quality is the main focus direction within the laser cleaning area, and also the key to realize the large-scale industrial application. The National Key Research and Development Program "Additive Manufacturing and Laser Manufacturing" Key Special Project "High Energy High Repetition Rate Pulsed Laser Intelligent Cleaning Technology and Equipment" (common key technologies) aims at the urgent demand for precision, green, intelligent and controllable new cleaning technology in aerospace equipment manufacturing and repair. This project is dedicated to understanding the multi-beam laser cleaning multi-field coupling mechanism, and breaking key technologies such as cooperative control of high energy high repetition rate nanosecond laser with multi-dimensional gain, residue location identification and path planning on complex surfaces, multi-beam splicing and energy control in ultra-wide format. At the same time, the research on high energy high frequency nanosecond pulsed laser, high efficient and high quality cleaning mechanisms and key technology, and ultra-wide format cleaning process and equipment are carried out. Finally, the research results will enable some typical applications for removing thermal control coatings from spacecraft surfaces and paint from aircraft radome surfaces.
2023, 52(2): 20220739.
doi: 10.3788/IRLA20220739
In high-power laser facilities, contaminants on the surface of optical components can reduce beam quality and even induce damage to optical components. For the contaminated large-aperture vacuum separator (430 mm×430 mm) coated with SiO2 sol-gel antireflection film in the facility, a Nd:YAG pulsed laser with a wavelength of 355 nm was performed in laser cleaning experiment. The experiment adopted a single-shot laser dry cleaning and a laser cleaning system assisted by an airflow replacement system. The influence of key characteristic parameters on in-situ laser cleaning was studied, and the process parameters that could be used for laser in-situ laser cleaning were obtained. The processing of optical elements was characterized by microscope, dark field imaging and image processing software analysis. The experimental results suggest that there is an optimal process window for laser in-situ cleaning of optical components. After the laser cleaning method assisted by airflow replacement, the laser cleaning ability is greatly improved compared with the simple single-shot dry laser cleaning. Therefore, the single-shot laser cleaning assisted by the airflow displacement system can effectively improve its cleaning ability and provide an effective means for the in-situ removal of contaminants on the surface of large-aperture optical components in high-power laser facilities.
2023, 52(2): 20220836.
doi: 10.3788/IRLA20220836
The light-gray erosion protection coating and anti-static finish coating on the surface of glass fiber-reinforced polymer composites were removed using a nanosecond laser with a wavelength of 1 064 nm employed in both pulsed and continuous-wave (CW) modes. The effect of the laser parameters at different laser modes on cleaning quality was investigated. SEM was used to observe micro morphology of material surface and cleaning products after processing. EDS and FTIR were used to detect the element content and chemical functional groups on the surface of materials before and after cleaning respectively. The temperature field during cleaning was analyzed by COMSOL Multiphysics. The results reveal that when removing the single anti-static coating, the pulsed laser can completely remove the top coating while just slightly harming the primer. When employing pulsed laser technology to remove the double paint, there is still a residual paint on the substrate's surface. The rainproof prime paint, resin and fiber layer of the substrate are also easily damaged. While the continuous laser can fully remove double paint and provide a clean surface. The pulsed laser removal process predominantly involves thermoelastic vibration effect, whereas the CW laser removal procedure is mostly thermal ablation. These results can serve as a guide for choosing the laser mode when removing paint from aeronautical composite surfaces.
2023, 52(2): 20220782.
doi: 10.3788/IRLA20220782
For the contamination problem of micro-particles on glass surface, the cleaning threshold of pulsed laser and its cleaning effect on particle contaminants are studied in this paper. The particle adsorption and deformation model was used to calculate the particle adsorption force. The relationship between thermal stress and laser energy density was analyzed, and the cleaning conditions and theoretical thresholds for particle contaminants were obtained. The cleaning effect of forward irradiation and back irradiation of particles on glass surface were compared in experiments, and the effect of parameters such as power density, scanning speed and cleaning times on the cleaning rate were studied. The results show that the back irradiation cleaning of large particles can be removed, and forward irradiation cleaning of small particles is more effective. The experiments of single-factor and three-factor show that the laser power density has a greater impact on the cleaning rate than the scanning speed, and the laser cleaning times have little impact.a greater impact on the cleaning rate than the scanning speed, and the laser cleaning times have little impact.
2023, 52(2): 20220821.
doi: 10.3788/IRLA20220821
The aging paint removal of aircraft skin is an important step in aircraft maintenance and repair. Compared with traditional chemical cleaning methods, laser cleaning has the advantages of high efficiency and low pollution, but the problem of substrate damage caused by excessive cleaning of high-energy laser exists, so it is very important to monitor the cleaning process in real time so as to give feedback to the laser in time. Aiming at this problem, a real-time monitoring method based on acousto-optic composite method is proposed, and the optical and acoustic signals are collected and analyzed respectively in the cleaning process. For the spectral detection method, the laser-induced breakdown spectrum is used to calibrate the different characteristic peaks of different elements in different paint layers to realize the inversion of different paint layers; The acoustic signal detection method is to determine the corresponding paint layer by comparing and analyzing the intensity and frequency of the acoustic signal generated by the laser ablation of different paint layers, and then the cleaning condition and removal effect of the paint layer can be deduced by comparing the two methods. The research shows that the acousto-optic composite method can achieve accurate real-time monitoring of the laser paint removal process.
2023, 52(2): 20220534.
doi: 10.3788/IRLA20220534
The processes, testing and application technology research were carried out for the welding synchronous laser cleaning of aluminum alloy for rail transit vehicle carbodies. The process window of laser cleaning for oxide film of aluminum alloy was obtained through the study of process. The prediction model of laser cleaning parameters before matching different welding speeds was established. And the effect of laser cleaning on the superficial oxide film of aluminum alloy was analyzed. According to the actual working conditions, an integrated laser cleaning and arc welding synchronous device was designed. And the pre-welding synchronous laser cleaning process verification was carried out. High-quality and high-efficiency removal of oxide film before welding was achieved. By analyzing the mechanical properties of welded joints, detecting weld defects and observing the microstructure of the cross-section of the welded joint, the quality of welding synchronous laser cleaning welds was evaluated. The research shows that with 200 W pulsed laser, the cleaning speed is adjustable from 0.5 to 1.1 m/min. Welding synchronous laser cleaning of oxide film with a line width of 45 mm can be effectively achieved. After laser cleaning, the primary oxide film is completely removed and the effect of regenerative oxide film can be avoided. The shear strength and strain of the welded joint after laser cleaning before welding increased by 26.4% and 9.98% compared with the untreated joint. The shear strength and strain of welded joints after laser cleaning increased by 3.53% and 1.43% respectively compared to those after manual grinding. And the central microstructure of the weld was mainly composed of α matrix and β (Mg2Al3) phase. The performance of the welding met the requirements of rail transit vehicle carbody manufacturing. Laser cleaning with welding can effectively replace manual grinding technology.
2023, 52(2): 20220779.
doi: 10.3788/IRLA20220779
In order to study the influence of laser parameters on the performance of laser cleaning based on thermal ablation effects, considering the working mechanism of thermally-induced ablation, Fourier heat conduction equation, and energy conservation theorem, a finite element analysis (FEA) software is used to establish a two-dimensional laser cleaning simulation model of dynamic energy conservation during the thermal ablation. In the simulation model, there is a mathematical relationship between the laser ablation intensity of the thin layer-base system and the normal velocity of the paint layer boundary, by using the virtual Robin boundary condition in the Fourier heat conduction equation. The simulation reflects the dynamic conservation of energy between the laser ablation energy and the latent heat consumption inside paint layers, which confirms the mathematical relationship between the mass loss and the energy consumption, and the simulation results become more precise and reliable. Such a simulation model is used to analyze the effects of the laser power, spot diameter, scanning speed, and scanning energy density on the cleaning performance. The simulation results show that the average residual thickness of a paint layer decreases with the increase of the laser power and scanning energy density, and the decrease tendency gradually slows down. When the laser power becomes too large, the metal base will be damaged. The average residual thickness of the paint layer increases with the spot diameter and scanning speed. However, reducing the spot diameter and scanning speed is harmful to enhance the cleaning efficiency. According to the relationship between the physical parameters of the paint layer and the scanning energy density, the optimization protocol of laser cleaning parameters has been proposed by considering both the cleaning performance and the cleaning efficiency. The simulation model is also used to analyze the cleaning performance of each scanning of an uneven surface paint layer by the uninterrupted multiple scanning. The study in this paper could be helpful for the design of laser cleaning devices as well as the optimization of laser parameters.
2023, 52(2): 20220155.
doi: 10.3788/IRLA20220155
In order to meet the requirements of removing rust on the surface of complex space materials in ship cabins, this paper adopts the pulsed fiber laser cleaning platform to carry out the optimization of laser cleaning process parameters and the experimental study on the surface properties of EH36 Marine steel plate after cleaning. Based on the macroscopic and microscopic morphology observation and surface chemical composition analysis, and combined with the derusting standard specification of the shipbuilding industry, the quality evaluation criterion of Marine steel laser rust removal is established, and the optimal process parameters of material laser rust removal are determined. On this basis, the surface quality, microhardness, roughness and comprehensive mechanical properties of the materials after laser derusting are tested and evaluated. The results show that, under the optimal derusting process parameters (average power 210 W, repetition frequency 250 kHz, pulse width 300 ns, scanning speed 4000 mm/s), the surface quality of Marine steel plate can reach Sa2.5 grade, and the mechanical properties remain basically unchanged, which can meet the requirements of derusting process on the surface of complex space materials in ship hold. It has excellent applicability in the field of surface rust removal of shipbuilding materials.
2023, 52(2): 20220164.
doi: 10.3788/IRLA20220164
A 200 W nanosecond pulsed fiber laser is used to study the laser cleaning of surface area carbon and oxide of GH3030 nickel base superalloy. The effects of laser spot overlapping rate on the cleaned surface morphology, element composition, phase composition, surface roughness and microhardness are analyzed. The results show that as the overlapping ratio of laser spot increases from 58.33% to 70.83%, the content of carbon and oxygen decreases first and then increases, the content of nickel increases first and then decreases, and the surface roughness decreases first and then increases. When the spot overlapping rate is 66.67%, the contents of carbon and oxygen decrease to the lowest value, which are 5.01 wt% and 1.40 wt% respectively. At the same time, the content of nickel reaches the peak, which is 72.96 wt%. The surface roughness Ra decreases to 0.229 μm and Rz reduces to 1.47 μm. The change of laser spot overlapping rate will not have a significant impact on the surface microhardness of GH3030 superalloy.
