Quality Of Laser Processing Research Articles

Rapid surface patterning to strengthen adhesive bonding of carbon fiber reinforced polymer by spatial shaping femtosecond laser

Carbon fiber reinforced polymer (CFRP) have become gradually important in the aerospace industry due to their outstanding strength-to-weight ratio. However, traditional mechanical surface treatment methods are challenging to apply to CFRP because of their anisotropic and nonhomogeneous properties. Femtosecond laser offers unique advantages for surface treatment, as it allows processing with very low thermal load due to the extremely short interaction time. This study investigates the effect of different surface structures resulting from surface treatment using a femtosecond laser on adhesive properties of CFRP. The experimental results show that: 1) beam shaping can be realized by using the plano-convex cylindrical mirror, which improves the quality of laser processing and greatly improves processing efficiency. It only takes 20 s to complete the laser processing of a 1 cm*1 cm area, which increases the work efficiency by 49 times. 2) pre-bonding surface treatment significantly enhances the tensile shear strength of the single lap joint, and the shear strength of samples with low spatial frequency LIPSS (LSFL) (14.57 ± 1.58 MPa) is 2.96 times higher than that of the untreated sample (US) (4.92 ± 1.34 MPa). 3) LSFL structure exhibits the best results, because the surface of CFRP with LSFL exhibits a relatively higher surface polarity and surface energy. This study provides an efficient, high-precision, and low-damage surface treatment method for preparing CFRP for adhesive bonding, which may promote the application of femtosecond laser technology in difficult-to-process composite materials and provide new methods and technical support for its application in aerospace, vehicle manufacturing, and other fields.

A Review of an Investigation of the Ultrafast Laser Processing of Brittle and Hard Materials.

Ultrafast laser technology has moved from ultrafast to ultra-strong due to the development of chirped pulse amplification technology. Ultrafast laser technology, such as femtosecond lasers and picosecond lasers, has quickly become a flexible tool for processing brittle and hard materials and complex micro-components, which are widely used in and developed for medical, aerospace, semiconductor applications and so on. However, the mechanisms of the interaction between an ultrafast laser and brittle and hard materials are still unclear. Meanwhile, the ultrafast laser processing of these materials is still a challenge. Additionally, highly efficient and high-precision manufacturing using ultrafast lasers needs to be developed. This review is focused on the common challenges and current status of the ultrafast laser processing of brittle and hard materials, such as nickel-based superalloys, thermal barrier ceramics, diamond, silicon dioxide, and silicon carbide composites. Firstly, different materials are distinguished according to their bandgap width, thermal conductivity and other characteristics in order to reveal the absorption mechanism of the laser energy during the ultrafast laser processing of brittle and hard materials. Secondly, the mechanism of laser energy transfer and transformation is investigated by analyzing the interaction between the photons and the electrons and ions in laser-induced plasma, as well as the interaction with the continuum of the materials. Thirdly, the relationship between key parameters and ultrafast laser processing quality is discussed. Finally, the methods for achieving highly efficient and high-precision manufacturing of complex three-dimensional micro-components are explored in detail.

Implementation of energy interaction between laser beam and keyhole wall based on algebraically reconstructing free surface: An experimentally validated numerical framework

The interaction of the laser beam with the material is critical for determining laser processing quality, with ray tracing methods mostly used in energy transfer research. These techniques generally rely on only the volume of fluid (VOF) method or level set (LS) function to track the molten pool free surface, resulting in either accuracy loss or difficulty in ensuring mass conservation of the interface. The few coupled algorithms are built on geometric notions that are difficult to understand while being limited to structural grids. In this paper, we have proposed a revised ray tracing framework, so-called ARCLS, to derive the exact intersections of the rays with the keyhole wall which is represented by a continuous LS surface algebraically rebuilt on top of the VOF interface. It is easy to code and convenient for unstructured meshes. This framework is tested through a V-groove case and a set of Ti6Al4V titanium alloy laser welding examples. The findings reveal that the reconstructed LS surface perfectly matches the VOF interface, and the predicted molten pool profile agrees with the actual data well. The keyhole morphology and molten flow patterns are also consistent with the physical truths. Spattering, porosity, necking, and swelling are observed in the developing keyhole, which are the possible reasons for the potential welding defects. Further investigation suggested that the ARCLS-based algorithm collected more laser rays at the keyhole bottom compared to the standard technique, achieving a deeper keyhole profile and a reflection pattern that was more optically logical. The work presents a reliable approach for estimating laser energy distribution, which can be effectively applied to the heat-fluid coupling simulation for laser manufacturing processes in order to forecast the dynamic behaviors of keyhole and molten pool.

Multi-objective optimization of fiber laser cutting quality characteristics of glass fiber reinforced plastic (GFRP) materials

Laser cutting can achieve ultra-precision cutting of materials by using appropriate parameters. In order to optimize processing parameters and obtain better processing quality, conducted experimental research on laser cutting of Glass fiber reinforced plastic (GFRP). In this study, the impact of four process parameters (laser power, cutting speed, assistant gas pressure and focus position) on quality characteristics (kerf width, kerf taper and kerf section roughness) was evaluated through analysis of variance (ANOVA), the regression relationship between laser processing parameters and quality characteristics was analyzed. And an integrative model for predicting and optimizing the quality characteristics of fiber laser cutting was constructed. In the proposed integrative model, Back-Propagation Neural Network (BPNN) was used to build a prediction model for quality characteristics. Through Non-dominated Sorting Genetic Algorithm (NSGAII) optimizes and outputs the complete optimal solution set of processing parameters, and finally realizes the nonlinear optimization of multi-objective parameters. The fitness value of BPNN model can reach 97.814%, and the maximum prediction relative error is 8.614%. And the set of suggested optimal solutions can be used as most of them are showing certain improvements in the quality characteristics. The results indicate that the integrative modeling strategy has the ability to predict and optimize laser cutting of composite materials.

Study on electron response to near-infrared, ultraviolet and extreme ultraviolet femtosecond laser by first-principle

The phenomenon of laser-induced electronic evolution in semiconductors is an essential issue in laser fabrication, which has been extensively investigated within the near-infrared and visible spectral ranges. However, electronic evolution at short wavelength laser has neither been systematically investigated. In this paper, time-dependent density functional theory is employed to investigate the response in silicon under laser irradiation of different wavelengths. The result shows that shorter wavelength induces the excitation of electrons to higher energy levels, consequently leading to increased impact ionization rates. Such a moderate excitation of energetic electrons even at low-medium intensity is considered as a distinctive feature of extreme ultraviolet light laser, which is expected to further enhance the quality of laser processing.

Numerical simulation and experimental study of femtosecond laser ablation of copper: A two-temperature model with temperature-dependent properties and multiple phase transitions

A fundamental study of the interaction between femtosecond laser and copper will be useful in optimizing laser parameters and processing quality in practice, and it faces challenges due to very short action time, complex energy transport and phase transition processes of this interaction. In this paper, A 2D two-temperature model was established and improved to include temperature-dependent optical and thermophysical properties and three phase transitions including melting, vaporization, and phase explosion. The temperature evolution of both the top surface and the sub-surface were simulated, thereafter, ablation experiments with different laser peak fluences were conducted using a femtosecond laser. It was found that the interface reflectivity would decrease rapidly, while the optical penetration depth and the ballistic electron penetration depth would increase significantly during laser irradiation. The temperature evolution of electron and lattice subsystems of the top surface could be divided into, respectively, 4 and 5 stages with different temperature trends in each stage. The variation of subsurface temperature was different from that of surface temperature and the temperature distribution showed that there was a temperature peak at near surface. A comparison of the experimental and simulation results showed that the simulated ablation depths were consistent with the experiment results.

Laser processing of silicon with GHz burst pumped third harmonics for precise microfabrication.

Femtosecond laser processing has proved to be a valuable tool for various microfabrication applications. In order to further increase the quality and efficiency of femtosecond laser processing, processing with GHz burst mode lasers has gained attention in recent years, where packets of high-repetition rate pulses are used instead of single pulses at the fundamental repetition rate. However, the use of burst-pulses has mainly been limited to the fundamental wavelength of powerful regenerative amplifier systems, often near 1 micrometer wavelength. In this study, we explore the characteristics and potential benefits of further wavelength conversion of burst-pulses emitted at the near-infrared to the ultraviolet region via direct third-harmonic generation. We construct an in-line process evaluation setup with a chromatic confocal sensor, and evaluate the ablation characteristics of the burst-pumped and non-burst processing of silicon. We observe that burst-mode processing has significantly reduced surface roughness and debris, resulting in high-quality laser processing. To demonstrate the utility of such burst-pumped UV processing, we show the successful milling of a spherical structure enabled by in-line surface profile feedback, while similar processing with non-burst conditions did not work. We believe such results show the strong potential of burst laser sources for use in accurate microfabrication of structures with micrometer-scale resolution.

Nanosecond laser processing and surface quality of SiC particle-reinforced AA2024 composite, homogeneous AA2024 aluminum alloy, and SiC: A comparative experimental study

This study performed comparative experiments on ablation behavior and surface quality obtained by nanosecond laser processing of silicon carbide (SiC) particle-reinforced 2024 aluminum alloy matrix composite (SiCp/AA2024), homogeneous SiC, and 2024 aluminum alloy. A nanosecond laser with a pulse fluence range of 0.68 ∼ 6.83 J/cm2 was used at irradiate samples of these materials, which were then ablated by various numbers of scanning passes (1 to 10) at a fluence of 6.83 J/cm2. The material melting could be achieved only for homogeneous AA2024. The ablation depth for SiC exceeded that of the composite, and the former could be ablated with a pulse fluence exceeding 3.42 J/cm2. The composite ablation threshold was higher than 4.10 J/cm2. Due to the thermal transition between the reinforcement and matrix, the melting threshold of the composite’s AA2024 matrix was lower than that of homogeneous AA2024 alloy. Moreover, the ablation threshold of SiC particles exceeded that of homogeneous SiC. The ablated surface roughness for the homogeneous material showed a sudden increase because of melting or oxidization, while that of the composite exhibited a gradual increase. For homogeneous SiC, oxidization accompanied by ablation and the accumulation of oxidization products on the surface deteriorated the laser pulse processing quality, especially in multipass scanning. In contrast, the dispersed distribution of SiC particles in the composite improved the composite’s machining feasibility.

Reliability study on the half-cutting PERC solar cell and module

In the photovoltaic industry, there are three critical parameters such as module power, cost and reliability. For increasing module power, half-cutting technology on the cell is one of the technologies because this can reduce the heating power by reducing the current. Therefore, laser scribing and mechanical cleaving (LSMC) technology have been implemented. As a result, the power of the module did not show any loss during standard test conditions when electrical luminescence and powers were monitored for the laser dicing process. However, in field conditions, the cut side of the cells with the laser process can cause cell breakage by wind or snow if the side has cracks. And then these crack cells can finally cause module power loss. Therefore, in this study, the laser process quality of the cell has been investigated by microscope image and scanning electron microscopy with laser process parameters such as laser power, frequency, and pulse width. In addition, cell strength was also checked by the four points of bending force to find the optimized laser process condition. The module power loss was analyzed with a static mechanical load test (MLT), which can represent snow or wind effect in the field. Our analyses show a strong correlation between crack width by laser, cell bending force, and module power loss. This correlation can explain the module power loss estimation, which can affect the reliability in the field without making module-level tests for the first time. In addition, the encapsulant thickness combination test and the mid-rail effect were also presented to reduce the power loss. As a result, the module power loss reached -1.34%. Finally, this study can contribute to the better reliability of the big wafer size products with LSMC technology.

Revealing the interaction mechanism of pulsed laser processing with the application of acoustic emission

The mechanisms of interaction between pulsed laser and materials are complex and indistinct, severely influencing the stability and quality of laser processing. This paper proposes an intelligent method based on the acoustic emission (AE) technique to monitor laser processing and explore the interaction mechanisms. The validation experiment is designed to perform nanosecond laser dotting on float glass. Processing parameters are set differently to generate various outcomes: ablated pits and irregular-shaped cracks. In the signal processing stage, we divide the AE signals into two bands, main and tail bands, according to the laser processing duration, to study the laser ablation and crack behavior, respectively. Characteristic parameters extracted by a method that combines framework and frame energy calculation of AE signals can effectively reveal the mechanisms of pulsed laser processing. The main band features evaluate the degree of laser ablation from the time and intensity scales, and the tail band characteristics demonstrate that the cracks occur after laser dotting. In addition, from the analysis of the parameters of the tail band very large cracks can be efficiently distinguished. The intelligent AE monitoring method was successfully applied in exploring the interaction mechanism of nanosecond laser dotting float glass and can be used in other pulsed laser processing fields.Graphical

A new method for laser grooving titanium alloy with the assist of a hybrid of gas jet and waterjet

High efficiency and low thermal damage grooving with a good surface quality is critical for the positioning and assembly of titanium alloy parts, which are widely used in aviation manufacturing and shipbuilding industry. In this paper, a new method of laser grooving by the assist of a hybrid of gas jet and waterjet was proposed, and Ti6Al4V titanium alloy was used as the specimen. The gas jet was applied co-axially to the laser, while the waterjet was applied off-axially. The effects of relative direction between the waterjet and laser traverse, the gas/water pressure, and the waterjet nozzle diameter on the groove characteristics and heat-affected zone were investigated. The surface macro morphology and microstructure were also examined, as well as the compositional change. Results show that larger grooves with a better quality can be fabricated and the range of heat-affected zone is still limited below 100 μm, when compared with other laser grooving methods. In addition, reverse-grooving creates a deeper and cleaner groove than the other two directions used in this study. The largest groove size can be obtained when the water pressure, gas pressure and nozzle diameter are 10 MPa, 0.1 MPa, and 0.4 mm, respectively. Moreover, the metallographic photo and spectrogram obtained by scanning electron microscope (SEM) indicate that fine acicular martensite and titanium oxidation can be formed near the groove. This work provides a new approach for improving the waterjet assisted laser processing quality and helps understand its mechanism. All the data sets supporting the results are included within the article.

Development of Laser Processing Carbon-Fiber-Reinforced Plastic.

Due to its exceptional advantages, such as high specific strength, high specific modulus, and good fatigue resistance, carbon-fiber-reinforced plastic (CFRP) is frequently utilized in aerospace, aviation, automotive, rail transportation, and other areas. Composite components typically need to be joined and integrated. In the equipment manufacturing industry, the most used methods for processing composite components are cutting, drilling, and surface treatment. The quality of CFRP is significantly impacted by traditional mechanical processing, causing flaws like delamination, burrs, and tears. Laser processing technology has emerged as a crucial method for processing CFRP for its high quality, non-contact, simple control, and automation features. The most recent research on the laser processing of CFRP is presented in this paper, supporting scientists and engineers who work in the field in using this unconventional manufacturing technique. This paper gives a general overview of the key features of laser processing technology and the numerous machining techniques available. The concepts and benefits of laser processing technology are discussed in terms of the material properties, mode of operation, and laser characteristics, as well as the methods to achieve high efficiency, low damage, and high precision. This paper reviews the research development of laser processing of carbon-fiber-reinforced plastics, and a summary of the factors affecting the quality of CFRP laser processing. Therefore, the research content of this article can be used as a theoretical basis for reducing thermal damage and improving the processing quality of laser-processed composite materials, while, on this basis, we analyze the development trend of CFRP laser processing technology.

Effect of SiC/SiC composites density on nanosecond-laser machining behaviors

For highly efficient processing technology of hard and brittle material such as SiC/SiC composites, laser machining has always been the focus of current research. In this work, the effect of composites density on the nanosecond pulse laser machining behaviors was systemically studied. The results revealed that the composites density will largely affect the morphology of laser machining, especially for the micro-hole inlet ablation condition and outlet circle degree. Besides, the roughness of the cutting surface is highly related with density, while the generated oxides and melting substances making the cutting surface smoother in high density samples. Finally, the laser machining induced products exhibited less relationship with density but high relationship with machining time. This paper provides a clear image that how intrinsic properties affects the laser machining behaviors and processing quality.

Organic solvent assisted laser processing of transparent polymer films based on the swelling and penetration behavior

The laser processing of polymer films has significant importance due to the wide applications in various fields. The problems in laser processing of transparent polymer films caused by the poor absorption and current doping methods have prevailed. In this paper, a simple, efficient, and low-cost doping and laser processing method based on polymers’ swelling and penetration behavior was applied to improve the laser processing of transparent polymer films: organic solvent assisted laser processing (SALP). In the SALP method, various common organic solvent molecules (Ethanol, Acetone, N, N-dimethylformamide, Chloroform) were introduced into transparent polydimethylsiloxane (PDMS) films through the swelling and penetration (SP) pretreatment and acted as the dopant to improve the efficiency, capability, and quality of laser processing. Experimental results showed that the SALP method performed higher efficiency and capability (kerf depth: 296.79 ± 11.98 μm, kerf width: 16.59 ± 1.46 μm, kerf aspect ratio: 18.02 ± 1.98) under the same processing conditions compared to the typical laser processing (TLP) method (kerf depth: 137.36 ± 6.47 μm, kerf width: 27.30 ± 1.11 μm, kerf aspect ratio: 5.04 ± 0.31). The roughness of the kerf inner surface and the debris and microcracks on the kerf surface were also significantly reduced. More importantly, this method hardly influenced the original properties of the native polymer films due to the removability of organic solvents. On the one hand, the introduction of organic solvent molecules improved the optical absorption of PDMS films and the heat transfer during laser processing. On the other hand, the excitation, ionization, and dissociation of organic solvent molecules under laser irradiation improved the decomposition process of PDMS, which improved photochemical reaction and promoted the complete and uniform decomposition in laser processing. The SALP method has enlightening significance for improving the laser processing of polymers and investigating the laser ablation mechanism.

A lens ultrasonic vibration-assisted laser machining system for laser polishing and laser drilling of 304 stainless steel

This paper proposes a novel lens ultrasonic vibration-assisted laser machining device which applies the ultrasonic vibration to the lens, thereby enhancing the quality of laser processing and retaining the flexibility of laser processing. The general analytical expression of the hollow ultrasonic transducer is derived by exploiting the electromechanical equivalent circuit and the four-terminal network methods. The finite element analysis method is used to optimize the design results, and the resonant frequency and ultrasonic vibration amplitude of the prototype are calibrated using testing equipment. The results show that the vibration form of the device at the mode of 23 meets the designed requirements, and the resonance frequency is 29703 Hz. Under the condition of 30000 Hz, the device reaches the maximum amplitude of 30 μm on the end face of the lens, and the corresponding input voltage is 346 V. The processing mechanism for lens ultrasonic vibration-assisted laser machining is proposed based on this study, which changes the laser energy density on the workpiece by adjusting the diameter of the spot. Furthermore, the initial experiment validation of the device shows that the ultrasonic vibration of the lens is attracting significant interest for improving the surface quality of laser polishing and reducing the taper angle of laser drilling, which is mainly caused by the change of laser energy density.

Recognition of laser defocusing distance based on the plasma charge voltage signal

It is known to all that the energy density of laser beam is depended on the laser focus size in laser processing. A stable laser focus size is important to the quality of product either in laser welding or in laser additive manufacturing. The laser focus size closely relates to the laser defocusing distance, and it is necessary to sensor the laser defocusing distance in order to ensure the stability of the laser focus size. But in the process of laser processing, the measurement accuracy of laser defocusing distance by optical and acoustic sensor is easy to be interfered by the laser manufacturing environment. The electrical signals in laser processing are less affected by environment, which can effectively improve the measurement accuracy. In this study, the plasma charge voltage signal in the laser processing is detected and processed to find out the relationship between the signal and the laser defocusing distance, and to identify the variation of laser defocusing distance in processing. The experiment results show that when the laser defocusing distance deviates, the plasma charge voltage fluctuates regularly with the variation of the deviation amount. This work reveal a regular mathematical relationship between laser defocusing distance and plasma charge voltage. The deviation of laser defocusing distance can be identified using this relation. The verification experimental results show that the maximum recognition error is less than 7.1% when the laser defocusing distance is within the range of 6–8 mm. This result provides the possibility for the application of laser plasma charge voltage signal in laser focusing distance recognition and controlling. Accordingly, higher measurement accuracy can be obtained for laser defocusing distance, which is conducive to more accurate control of laser defocusing distance and more stable laser processing quality.

Investigations on the ablation behavior of C/SiC under femtosecond laser

In this study, the femtosecond laser was used to process carbon fiber-reinforced silicon carbide (C/SiC), and the morphologies under different laser processing parameters were compared. The experimental process was photographed by a high-speed camera. It was found that the original surface roughness of C/SiC had a significant effect on the laser ablation morphology, and that the laser irradiation at different positions of the material surface could cause irregular morphology. A large amount of debris generated during the action of femtosecond laser pulse was ejected with the plasma at high speed and was deposited in the processing region. The reaction products CO and CO2 leaved the material, and the SiO2 particles covered the C/SiC surface to form an oxide layer. The research can help to understand the ablation mechanism of the femtosecond laser on C/SiC, and to provide basis for further optimizing the laser processing quality on silicon carbide ceramic matrix composites.

Influence of helix geometric parameters on surface quality during laser cutting of photovoltaic float glass

Influence of helix geometric parameters on surface quality is investigated in laser cutting of photovoltaic float glass. 110 square holes through the selected photovoltaic float glass of thickness 2.5 mm are processed by 532 nm nanosecond laser with different helix geometric parameters (width w and overlap ratio r). Three dropping modes can be summarized by 110 group experiments as smoothing drop, serrated crack, and snowflake crack. The To ensure the falling smoothly and stably of square glasses with smooth edge, optimization ranges of helix geometric parameters are 0.45 mm ≤ w ≤ 0.55 mm and 65 % ≤ r ≤ 80 %. Micro-profile evaluation of cutting cross section was more sensitive to r than that to w. Improving of overlap ratio is useful to decrease thermal gradient, microcrack and then form small sized chipping. Homogenous distribution of different elements was in granular zone, and inhomogeneous distribution was in block zone. It can be concluded that selecting an appropriate helix line parameter is helpful to stabilize laser process and surface quality of photovoltaic float glass.

Mathematical modeling of heat distribution on carbon fiber Poly(ether-ether-ketone) (PEEK) composite during laser ablation

Since large amounts of energy are transferred precisely to the material in a very short time, laser and material parameters strongly affect the laser process quality. Mathematical modeling of heat distribution during cavity formation on carbon fiber reinforced PEEK composite material was performed. The temperature distribution equation has been obtained by the Fourier method.At the first stage, 1 J energy laser beam was sent onto the material and the cavity on the composite material was obtained. The constants in the temperature distribution equation obtained by making measurements over the cavity were found. Then the cavities were created with 2, 3 and 4 J laser beams to prove its reliability of the model. The results obtained from the measurement on the cavities and calculated from the temperature distribution equation were compared.Since the unidirectional carbon fibers were used, the obtained cavities have an elliptical shape. Verification experiments were carried out using two different heat conduction constants for in direction along fibers and perpendicular to carbon fibers. Experimental results and the mathematical model are in good agreement.

Gas-powder laser cladding with slot nozzles

The topic of this research is the investigation of technological processes of gas-powder laser cladding with the help of high-power diode lasers with rectangular cross-section of laser beam, the mutual influence of technological parameters of gas-powder streams and focused laser beam on the properties of clad layer (dimensions, shape, etc.) in particular. The research stages included the following: It was established that the use of multi-channel gas-powder delivery nozzles significantly influences the productivity and quality of laser processing.