Laser Cleaning Process Research Articles

Microstructure and mechanical properties of laser welded hot-press-formed steel with varying thicknesses of Al–Si coatings cleaned by nanosecond pulsed laser

The Al–Si coatings are commonly used for hot-press-forming (HPF) steel to prevent oxidation in the automobile industry. However, due to the presence of Al–Si coating, undesirable intermetallic compounds are easily formed in the welds of HPF steel. In this work, an environment-friendly and effective nanosecond pulsed laser cleaning process was used to remove the Al–Si coating, and HPF steel with varying thicknesses of coatings was prepared for laser welding. The microstructure and mechanical properties of laser welded HPF steel with different thicknesses of coatings were further investigated. The results showed that there was a threshold of power to remove the Al–Si coatings in the laser cleaning process. The reduced thickness of coatings not only could improve the stability of the welding process due to the diminishing of metal vapor generated by coating ablation, but also decrease the content of the Fe–Al phase in the welded joint, which is detrimental to weld performance. The tensile strength and cupping test pass rate of weld joints gradually increased with the decreasing thickness of coatings to 5 μm. After that, the Al–Si coating almost had no effect on the mechanical properties of the laser weld joints. The laser weld joint with 5 μm-thick of Al–Si coating showed, a tensile strength of 1435.05 MPa, a microhardness of 488.38 HV and a pass rate of 100% for the cupping test.

Convolution Neural Network with Laser-Induced Breakdown Spectroscopy as a Monitoring Tool for Laser Cleaning Process.

In this study, eight different painted stainless steel 304L specimens were laser-cleaned using different process parameters, such as laser power, scan speed, and the number of repetitions. Laser-induced breakdown spectroscopy (LIBS) was adopted as the monitoring tool for laser cleaning. Identification of LIBS spectra with similar chemical compositions is challenging. A convolutional neural network (CNN)-based deep learning method was developed for accurate and rapid analysis of LIBS spectra. By applying the LIBS-coupled CNN method, the classification CNN model accuracy of laser-cleaned specimens was 94.55%. Moreover, the LIBS spectrum analysis time was 0.09 s. The results verified the possibility of using the LIBS-coupled CNN method as an in-line tool for the laser cleaning process.

Towards low-temperature laser paint stripping by photochemical mechanism on CFRP substrates

Multilayer paint on the surfaces of carbon fiber-reinforced polymer (CFRP) composites was cleaned using an ultraviolet picosecond laser (λ = 355 nm) under different parameters. The surface morphology of the composite after paint removal was investigated by scanning electron microscopy (SEM), chemical composition and functional group detection by energy dispersive spectroscopy (EDS) and FT-IR, while the sample temperature was monitored by an infrared thermal imager during cleaning. Additionally, CFRP performances were evaluated before and after paint removal. These results demonstrated that after three cleaning cycles with 12 W laser power, the paint layers on CFRP is removed, the surface epoxy resin is retained, and the carbon fiber does not have any morphological damage. At the same time, the surface after de-painting also met the re-painting conditions, and the tensile strength was not degraded compared with the original sample. It is noteworthy that the UV picosecond laser shows “low temperature cleaning”, which completely removes the paint layer on the CFRP surface at a temperature below 80 °C. This means that the paint stripping process will not cause potential thermal damage or degradation of mechanical properties for CFRP. Mechanism analysis indicated that the photochemical action led to the breaking of the chemical bond of the paint, thus achieving paint removal. This study demonstrates the feasibility of a laser cleaning process for de-painting from resin-based composite surfaces and guides the repair and maintenance of commercial aircraft.

P‐5.5: Research of laser cleaning technique application for mini/micro‐led

This paper studies laser cleaning for mini & micro COG products. Research shows that laser cleaning has great advantages, which can realize accurate position cleaning and remove various pollution. The adjustment of laser cleaning process parameters can improve the adhesion of substrate surface and realize mass production application on the premise of ensuring low surface damage.

Laser-induced breakdown spectroscopy monitoring of aluminum alloys laser cleaning process

The paper considers an approach to monitoring the condition of the treated surface in real time based on the laser-induced breakdown spectroscopy technique. As a result of the study, the aluminum alloy was cleaned from the plimer coating, spectral analysis was carried out, the relationship between the processing modes and the thickness of the coating being removed was experimentally established, which allows removing the paint coating in one pass without damaging the underlying layers. The optimal spectral range for the control operation, the contrasting spectral lines of the elements that make up the coating, the optimal parameters of laser exposure are determined based on the monitoring data of the spectral signal recorded during laser processing

The Surface Properties of an Aviation Aluminum Alloy after Laser Cleaning

In this study, we explored the effects of a laser cleaning process on the surface properties of an aerospace aluminum alloy. We performed surface cleaning on an AA2024 aluminum alloy. Through SEM and EDS analyses on the surface of the aluminum alloy samples after cleaning, the cleaning effect on the aluminum alloy under different laser energy densities was studied. After laser cleaning, residual stress, hardness, friction, and wear tests were performed on the aluminum alloy samples. The experimental results demonstrated that the oxides on the surface of AA2024 could be effectively removed when the laser energy density was 10.5 J/cm2. With an increase in the laser energy density, the friction and wear properties of the AA2024 surface could be improved. Laser cleaning could also generate a new hardened layer and residual tensile stress on the surface of AA2024. This article provides a reference for applying laser cleaning in the aerospace field by studying the structure and mechanical properties of an aluminum alloy after laser cleaning.

Numerical and experimental analysis for morphology evolution of 6061 aluminum alloy during nanosecond pulsed laser cleaning

Laser cleaning technology has become an important method for surface cleaning of aluminum alloy oxide film . However, the heat and mass transfer mechanism during the laser cleaning process is still unclear, which hinders the precise control of surface morphology . In this work, a 3D heat transfer and flow coupling model of laser cleaning for aluminum alloy oxide film was established, and the dynamic evolution behavior of surface morphology with different average laser power ( P L ) was analyzed. The simulation morphology was agree with experimental results. There is no splashing for P L as 20 W, while a large amount of splash is generated as P L increased to 40 and 60 W. The morphology evolution is mainly attributed to the combined effects of recoil pressure, surface tension and gravity. The maximum flow velocity ( v ) is only 5 m/s for P L as 20 W, while v can reach 150 m/s for P L as 40 and 60 W. With increasing P L , the depth of molten pool reached 4.5, 5 and 8 μm for 20, 40 and 60 W, respectively. The strong heat effect caused by high P L can not only enhance the melting phenomenon, but also enhance the force effect, which plays an important role in the morphology evolution. • A 3D heat transfer and fluid flow coupling model for laser cleaning was developed. • Simulation results were in good agreement with the experimental results. • Transient distribution and evolution of temperature and flow field was analyzed. • Evolution mechanism of aluminum alloy surface morphology was expounded.

The Effect of Roughness Variation on Heat Absorption in Laser Cleaning Process to Remove Paint Layer on Aluminum Alloy

The Effect of Roughness Variation on Heat Absorption in Laser Cleaning Process to Remove Paint Layer on Aluminum Alloy

Optimization of Laser Cleaning Process Parameters for Petroleum Pipe Threads Based on Response Surface Method and Particle Swarm Algorithm

Optimization of Laser Cleaning Process Parameters for Petroleum Pipe Threads Based on Response Surface Method and Particle Swarm Algorithm

Effect of Laser Cleaning Process Parameters on Surface Quality of 7075 Aluminum Alloy Anodic Oxidation Film

Effect of Laser Cleaning Process Parameters on Surface Quality of 7075 Aluminum Alloy Anodic Oxidation Film

Research on surface integrity optimization of TC-4 alloy surface structure processed by picosecond laser

The fabrication of microstructure on metal surface by laser processing technology will damage the surface integrity. In this research, picosecond laser was used to fabricate microstructure on the surface of TC-4 alloy, and the surface integrity was protected by adjusting parameters. The results show that using 0.6W power, 100mm/s scanning speed, 700kHz pulse frequency and 0.1ms point engraving time can avoid the influence and remodeling of the structure when the laser removes the material. In addition, the surface integrity after material removal is improved by ultra-low power and ultra-high speed laser cleaning process.

Pulsed laser cleaning of resin-based surface coating on the titanium alloy substrate

In this work, the laser cleaning process of the surface coating for the Ti-6Al-4V titanium alloy was investigated using a pulsed laser, including cleaning time, laser power, and scanning speed. Meanwhile, the corresponding mechanism of laser cleaning was analyzed using the surface morphology, element content change, coating fracture cross section, and phase change. Results demonstrated that the quality of the coating removed by laser cleaning increased first and then decreased with the increase in the three key process parameters of laser cleaning time, laser power, and scanning speed, respectively. The superior laser cleaning efficiency was achieved when the laser power was 15 W, the cleaning time was 8, and the scanning speed was 400 mm/s. It is concluded that the removal of the titanium alloy surface coating is the result of the coupling of the cleaning mechanisms such as ablation and thermal expansion.

Hybrid laser cleaning characteristic of marine barnacles fouling attached on Al alloys

In previous papers, the nanosecond laser has been proven to be an effective tool for removing the settlement of soft-fouling microorganisms (biofilm, microbial film, and microbiofoulings). This work is a continued study on laser cleaning of marine biofouling. The authors attempt to develop a hybrid laser treatment method to control the hard-shelled barnacles attached to Al alloys. Morphologies of the laser-cleaned surfaces were evaluated by a digital camera, 3D optical microscopy, and scanning electron microscopy. Furthermore, a high-speed camera and fiber optic spectrometer were used to capture the specific laser cleaning dynamic behaviors and characterize the chemical compositions of laser-induced plasma, respectively. The shell structures of the barnacles cannot be removed by a nanosecond fiber laser but continuous CO2 laser, while for the base plates of the barnacles the result is the opposite. Hence, a step-by-step CO2/nanosecond hybrid laser cleaning process is proposed to conquer the attached barnacles fouling. The cleaning strategy follows a top-down principle of the barnacles’ structures. In the first step, the CO2 laser is utilized to heat the external shell; thus, the upper parietal shell and the main body are entirely peeled off. In the second step, the nanosecond laser is employed to remove the lower remaining base plate, cement layer, and biofilm. Laser cleaning mechanisms of barnacles included heating, stripping, and ablation.

Finite element simulation of temperature field in laser cleaning of TA15 titanium alloy oxide film

<p indent=0mm>Laser cleaning is a noncontact cleaning method that uses a short-pulse high power density laser to irradiate an object. The pollutants are removed by the complex physical and chemical interactions between the laser and the object to be cleaned. The mechanism of laser cleaning is very complex, including photodegradation, photodetachment, and photovibration, which are closely related to the temperature distribution in the laser-cleaning process. In this study, the finite element simulation model of laser cleaning of TA15 titanium alloy oxide film is established by using Comsol Multiphysics commercial simulation software. The influence of spot shape, laser energy, loading mode, and pulse width on the titanium alloy oxide film temperature field is analyzed. The results showed that the substrate was severely damaged by a millisecond pulse laser. The shorter the pulse width, the smaller the surface thermal diffusion. The square flat-top spot was more evenly heated than the Gaussian spot, and the rectangular pulse was less damaged than the Gaussian spot. The laser-cleaning effect of titanium alloy oxide film was the best when the square flat-top laser was loaded in a rectangular pulse.

Nanosecond Laser Cleaning Method to Reduce the Surface Inert Layer and Activate the Garnet Electrolyte for a Solid-State Li Metal Battery.

The garnet-type electrolyte Li6.4La3Zr1.4Ta0.6O12 (LLZTO) has been widely researched for its high ionic conductivity and excellent stability against the Li anode. However, the garnet electrolyte is susceptible to CO2 and H2O in air to form a Li2CO3 insulating layer leading to poor wettability with the Li anode, which hinders its practical application. Herein, we introduced a simple method to effectively reduce the Li2CO3 layer on the garnet electrolyte surface by laser cleaning and made the garnet surface back with lithiophilicity. The resulting Li/garnet interfacial resistance decreased to 76.4 Ω·cm2 at 30 °C and 3.1 Ω·cm2 at 80 °C. The assembled Li symmetric cell with the as-laser-treated electrolyte steadily cycled for 300 h under 0.1 and 0.2 mA·cm-2 at 80 °C. The solid-state battery coupled with the composite LiFePO4 cathode and the Li anode exhibited stable long-term cycling performance for over 100 cycles with a capacity retention of 84.8%. This work provided a novel method to reduce the surface inert layer and make the garnet electrolyte reveal the intrinsic lithiophilicity by laser cleaning process with high efficiency, which helped address the challenges for the application of garnet-based solid-state batteries.

In-Process Monitoring of Laser Surface Modification

The laser cleaning process has the potential to become an alternative to the existing chemical-based cleaning process if integrated with an effective in-process monitoring system that could serve as a control mechanism over surface damages or contaminants through which the desired surface cleanliness could be achieved. This paper presents results of an investigation into the characteristics and viability of utilizing probe beam reflection (PBR) and laser plume-emission spectroscopy (PES) as respective integrated monitoring systems during and after cleaning of titanium alloy sheets using a frequency-tripled Nd:YAG laser. The results present the probe beam reflection as a better system with the ability to differentiate between cleaned and un-cleaned surfaces for both small and large surface areas.

Investigation of the laser cleaning process for IBS grids in optical coating technology

The ion-beam sputtering (IBS) grid laser cleaning process is described as an alternative to manual cleaning and sandblasting in terms of surface morphology, roughness, and speed. It has been demonstrated that nanosecond fiber laser processing can be successfully used for controlled cleaning of complex grid surfaces at high speed and low surface impact, which is important for increasing the life of expensive parts. Under optimal conditions for single-pass processing, the scanning speed in the focal plane of a 160 mm F-Theta lens was 8 m/s at a laser pulse energy of 300 μJ, a pulse width of 120 ns, and a repetition rate of 100 kHz.

A study on the application of laser cleaning process in shipbuilding industries using 100 W fiber laser

To address the limitations of existing surface cleaning technologies in shipyards, various studies are underway to apply the laser cleaning process, which uses a laser as a heat source, to pretreatment for painting and welding. Accordingly, this study conducted a cleaning experiment that uses a low power Q-switching fiber laser to remove the primer and oxide layer from the surface of steel for shipbuilding. To enhance the field applicability, this study derived the optimal laser cleaning process parameters that satisfy pretreatment standards. The main process parameters include scan speed and energy density. The most thoroughly cleaned surface was obtained at a scan speed corresponding to laser beam overlap rate of 20 % and an energy density of 10.5 J/cm2, and the working time was also significantly reduced. Therefore, this study is expected to be highly useful as important data for applying laser cleaning technology, which is receiving greater attention across many industries in addition to the shipbuilding and marine industry.

Cleaning of Graphite Particles Embedded in the Surface of Ductile Iron by Using a Novel Method

Ductile iron has unique mechanical property and has been widely used in many industrial applications, e.g., engine cylinder covers, crank axles, and machine tool beds and cams. The welding performance of ductile iron is normally influenced by graphite particles in the surface of ductile iron, which needs to be removed before welding. In this article, laser cleaning technique was developed to remove graphite particles implanted in the surface of ductile iron. Laser cleaning parameters and the damage threshold value of the substrate were investigated by using a pulsed Nd: YAG laser. The optimized laser cleaning parameters were obtained to achieve high-quality cleaning effect and avoid the formation of the oxide layer. Surface morphologies and elemental compositions of specimens before and after laser cleaning were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Results indicated that graphite particles implanted in the surface of ductile iron were removed completely and efficiently by using the pulsed laser without the protection of inert gas atmosphere, and surface oxidation was not observed during the laser cleaning process.

Off-line programming of robot on laser cleaning for large complex components

Laser cleaning path planning is great for significance to the cleaning effect of component surface. In view of the fact that the cleaning head must keep a fixed focal length with the workpiece surface and keep a vertical angle with the workpiece surface at all times in the laser cleaning process, this paper introduces the numerical model of large components into the general off-line programming software, and according to the relevant laser cleaning process and setting specific parameters in the software, obtains the automatically planned machine. The human trajectory program is introduced into the robot to realize the surface cleaning of large and complex components. Finally, according to the actual cleaning effect in the field, the laser focal length deviation is controlled within ± 2mm, and the application of off-line programming of industrial robots in complex surfaces is summarized and prospected.