Spot Overlap Ratio Research Articles

Exploring the potential of laser-textured metal alloys: Fine-tuning vascular cells responses through in vitro and ex vivo analysis

Medical stents are vital for treating vascular complications and restoring blood flow in millions of patients. Despite its widespread effectiveness, restenosis, driven by the complex interplay of cellular responses, remains a concern. This study investigated the reactions of vascular cells to nano/microscale wrinkle (nano-W and micro-W) patterns created on laser-textured nitinol (NiTi) surfaces by adjusting laser processing parameters, such as spot overlap ratio and line overlap ratio. Evaluation of topographical effects on endothelial and smooth muscle cells (SMCs) revealed diverse morphologies, proliferation rates, and gene expressions. Notably, microscale wrinkle patterns exhibited reduced monocyte adhesion and inflammation-related gene expression, demonstrating their potential applications in mitigating vascular complications after stent insertion. Additionally, an ex vivo metatarsal assay was utilized to bridge the gap between in vitro and in vivo studies, demonstrating enhanced angiogenesis on laser-textured NiTi surfaces. Laser-textured NiTi exhibits a guided formation process, emphasizing their potential to promote swift endothelialization. These findings underscore the efficacy of laser texturing for tailored cellular interactions on metallic surfaces and offer valuable insights into optimizing biocompatibility and controlling cellular responses, which may pave the way for innovative advances in vascular care and contribute to the ongoing improvement of stent insertion.

Laser cleaning of paint layers on white marble surface based on cooperative use of laser-induced breakdown spectroscopy and image binarization

The key to precisely removing paint layers sprayed onto stone surfaces using laser cleaning without damaging the stone substrate is to select the optimized laser parameters based on the online monitoring methods. In this paper, a pulsed laser beam with a high-pulse repetition frequency of 100 kHz, a pulse width of 200 ns, and a wavelength of 1064 nm was used to clean 39 µm- and 31 µm- thick of gold and silver paint layers off of white marble surfaces. The optimized average laser power for removing the paint layers was determined to be 40 W using laser-induced breakdown spectroscopy (LIBS) method and an image binarization method. Under the optimized average laser power of 40 W, the optimized spot overlap ratios for cleaning the layers of gold and silver paint were determined to be 10% and 30% respectively, using the image binarization method. The corresponding optimized number of cleaning shots was 5 and 4, respectively. The laser cleaning efficiency for both the gold and silver paint layers exceeded 95%. It was thereby demonstrated that this research protocol based on the cooperative use of two online monitoring methods to determine the optimized laser parameters in sequence (average laser power → spot overlap ratio → number of cleaning shots) not only optimizes the laser cleaning efficiency for different paint layers but does so without causing any damage to the white marble substrate.

Influence of laser parameters on corrosion resistance of laser melting layer on C45E4 steel surface

The key to further improve the corrosion resistance of the laser melting layer on steel surface is to select appropriate laser parameters. In this paper, a single factor laser melting experiment on C45E4 steel surface by using a pulsed laser beam at a wavelength of 1064 nm and electrochemical analysis were conducted to explore the influences of laser parameters including single pulse energy density, spot overlap ratio and number of laser scans on the corrosion resistance of the laser melting layers. The optimal laser parameter combination was obtained: single-pulse energy density of 3.82 J·cm−2, spot overlap rate of 80 % and 4 number of laser scans. The thickness of the optimal laser melting layer prepared with the optimal laser parameters was only 10.85 μm, and it had a maximum self-corrosion potential of 1.031 V, a minimum corrosion current of 3.451 × 10−9 A·cm−2 and a maximum charge transfer resistance of 1541.2 Ω·cm−2. During the salt spray corrosion test, the corrosion rate of the optimal laser melting layer was only one third of that of the traditional hot alkaline blackened layer with a thickness of 12.04 μm. The results showed that the corrosion resistance of the optimal laser melted layer was significantly improved compared to that of the conventional thermally alkaline blackened layer. The main reason was that the determination of the optimal single-pulse energy density, spot overlap ratio and number of laser scans in turn, made the optimal laser melting layer had a stable Fe3O4-FeO corrosion resistance structure, effectively reduced the surface roughness, microcrack density and oxidation leakage point, and prevented the C45E4 steel surface from being over-oxidized.

Effects of Scanning Speed on the Polished Surface Quality of Mold Steel by Dual-Beam Coupling Nanosecond Laser

In this paper, a novel dual-beam coupled nanosecond laser was used to polish S136D mold steel. The effects of scanning speed, total fluence, spot overlap ratio, and SPSN on surface quality were analyzed. The polished surface roughness Ra without ultrasonic cleaning is too large due to slag, splash, and dust produced by laser polishing. When scanning speed is 1250 mm/min, surface roughness Ra with ultrasonic cleaning is reduced from the original surface 1.92 μm to 0.72 μm, and the surface roughness Ra is reduced by 62.50%. When the Ftot is 35.38 J/cm2, the minimum value of surface roughness Ra is 0.72 μm. If the total fluence is higher or lower, it is not conducive to reducing the surface roughness, the total fluence is higher, and there is a polished surface with SOM phenomenon. The polished surface with spot overlap ratio of 98.55% has a smooth morphology, and a minimum value of surface roughness Ra of 0.41 μm. When the specimen is inclined at a certain angle, the high-magnification camera captures color on the polished surface. It is found that the microscopic texture of molten material flow trace and polishing scanning track is obvious. Polished surface is mainly distributed with Fe, Cr, C, and O elements. The surface material processing speed per unit time is low, and the polishing surface quality is improved less. The maximum surface roughness Ra is 1.98 μm. The minimum Ra of polished surface with smoother morphology is 0.41 μm, and surface profile height is basically the same. The research results show that the new dual-beam coupled nanosecond laser polishing technology can improve surface quality of materials. This research work provides process guidance for laser polishing effect analysis and mechanism innovation.

A composite strategy for high-quality and high-efficiency milling of alumina ceramic via femtosecond laser burst-mode

Industrial alumina ceramics require high surface accuracy when assembled to critical components of devices, for which high-quality milling has become an integral process. To achieve high-quality milling of alumina ceramics efficiently, this paper introduced a composite strategy based on the sequence of roughing and finishing via the femtosecond laser burst-mode. Firstly, the effects of laser parameters in the single-pulse mode such as energy fluence, spot overlap ratio, and scanning spacing on the milling quality and efficiency of alumina ceramics were investigated to provide a basis of the parameter selection for the subsequent composite strategy study. Then, the influence of the burst-mode on the optimization of the milling results was discussed, and the advantages of this mode over the single-pulse mode were revealed. Finally, a comparative investigation on the processing performance between the composite strategy and the single strategy was carried out. The results showed that milling the same structure, the roughness of the groove was reduced by 10.69% compared to the optimal processing results in a single process. At the same time, the processing efficiency was maximized with an increase of 49.91%.

Surface Quality of Silicon Carbide Ceramics Polished by Coupled Laser Based on Bidirectional Spot Overlap Ratio Regulation

Surface Quality of Silicon Carbide Ceramics Polished by Coupled Laser Based on Bidirectional Spot Overlap Ratio Regulation

Numerical simulation and experimental analysis of machining morphology with pulsed laser

In this study, simulation and experimental studies are used to evaluate the temperature field distribution and process law for the pulsed laser processing of stainless steel. The numerical simulation is based on the theory of heat transfer. The temperature field distribution and change process of the stainless steel surface under the influence of laser is explained subjectively, and the morphology evolution law of stainless steel during the entire process is studied. The influence of insufficient laser spot overlap ratio and the variation of laser power on the machining quality is analyzed by comparing with the experimental results. The evolution law of machining morphology and size with the laser incident angle, scanning speed, repetition frequency, and laser power are evaluated. The results provide theoretical support for determining the high-quality processing of stainless steel by a pulsed laser, which can be used for the parameter optimization of laser processing, such as metal material cutting, surface microstructure preparation, and two-dimensional code marking.

Effect of laser pulse energy deposition method on nanosecond laser scanning ablation of SiCp/AA2024 composites

The control of the thermal stress and heat accumulation is major issue faced in the laser precision machining, and plays a key role in the laser machining of composite materials. In this pursuit, the present study envisaged the effect of pulse energy deposition method on the processing of particulate reinforced aluminum alloy matrix composites SiCp/AA2024. Specifically, by modulating the combination of the spot overlap ratio (SOR) and the area scanning passes, a variety of pulse energy deposition methods with the same number of received pulses per unit area were designed and applied on a target. The influence of the pulse energy deposition on processing was evaluated by measuring and comparing the ablation depth and surface roughness. The results showed that by using multiple scanning passes with small spot overlap ratios led to a good processing with a high ablation depth. Furthermore, the influence of SOR and scanning passes on the machining was studied using the control variable method. The influence of energy deposition method was studied from the aspect of nanosecond laser ablation mechanism, Fresnel reflection effect and heat accumulation.

Nanosecond pulsed laser cleaning of titanium alloy oxide films: Modeling and experiments

Nanosecond pulsed laser cleaning is an indispensable green technology. A three-dimensional (3-D) finite element model (FEM) was used to predict the surface temperature during laser cleaning. Then, the macroscopic morphology of the FEM that was obtained was verified using digital ultra-depth-of-field microscopy (OM). Finally, the variation in the surface morphology with the maximum power density (F), x-axis spot overlap ratio (Ux), and y-axis spot overlap ratio (Uy) was determined using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The change in surface composition was analysed using X-ray photoelectron spectroscopy (XPS), and optical emission spectroscopy (OES) was used to monitor laser cleaning. Transmission electron microscopy (TEM) was used to analyse the surface secondary oxidation thickness. The original surface consisted of titanium oxides (Ti4+ and Ti3+) and organics. The Ti0 peak was enhanced, and the O content was reduced after laser cleaning. Therefore, the laser-cleaning effect was clear. The surface was smooth without cracks when the maximum power density and the spot overlap ratio were set to 31.85 MW/cm2 and 80 %, respectively. A dense and uniformity oxide film, 29 nm thickness, was formed on the surface of TA15 titanium alloy after laser cleaning. Changes in F, Ux, and Uy caused noticeable changes in the Ti I and Ti II peaks in the OES spectra, which were used to monitor laser cleaning.

Process Research on the Microgroove Depth Uniformity of Bursting Discs Using Femtosecond Lasers

This study proposes an ultrafast laser ablation method for improving the depth uniformity of microgrooves in bursting discs. Under a lower laser fluence, the influence of the spot overlap rate on the depth uniformity of microgrooves was studied. The results show that 80% of the spot overlap ratio has good performance in ablation efficiency and depth uniformity of microgrooves. On this basis, the relationship between the number of laser scanning layers and the depth of microgrooves was studied, and the number of scanning layers needed to ablate 70 µm microgrooves was obtained. Based on the combination of the process parameters and the optimization of the laser scanning path, laser ablation of bursting disc microgrooves with a specific shape was realized. The depth uniformity of microgrooves in different sections of the bursting disc was not worse than 4 µm. The preliminary bursting test shows that the bursting pressure between the discs was no more than 0.06 Mpa. Compared with the results of the traditional processing method, the microgroove depth uniformity of bursting discs was greatly improved. Therefore, femtosecond laser ablation technology provides an advanced manufacturing method for bursting disc microgroove machining.

Optimization of the processing parameters in laser sharpening of bronze-bonded diamond grinding wheels

In this paper a new contribution to the optimization of processing parameters in the process of laser sharpening grinding wheels is presented. In the establishment of the three-dimensional heat conduction model, the laser heat source model is improved and the temperature field of the pulsed laser ablation material is obtained. The effects of laser power, laser line spot overlap ratio and laser scanning track overlap ratio on the sharpening efficiency and accuracy have been studied through the established numerical model. Like what happened in the actual machining process, the morphology of the bond material surface after laser sharpening was obtained by the simulation. The results show that the optimal values of laser power, laser line spot overlap ratio and laser scanning track overlap ratio are 20 W, 70%, and 70%, respectively. The simulation results have been verified and compared with the experimental results, revealing a good correlation between the simulation and experimental data. In a word, the numerical model established in this paper can be conveniently used in the optimization of the process parameters in the laser sharpening grinding wheel.

Numerical study on laser shock peening of TC4 titanium alloy based on the plate and blade model

The compressive residual stresses and grain refinement induced by laser shock peening (LSP) are two very important surface strengthening mechanisms that are responsible for the significant improvements of the mechanical property and fatigue performance of metallic materials. A computation framework linking the dislocation-mechanism-based constitutive model with the dislocation density evolution model was developed and implemented into ABAQUS/Explicit code for numerical simulations of the residual stresses and grain refinement induced by LSP of TC4 titanium alloy. Two kinds of three-dimensional finite element models involving the plate model and TC4 blade model were respectively created to simulate the multi-LSP processes, and the effect of laser spot overlap ratio was accordingly investigated in detail. The obtained results show that with the increase of laser spot overlap ratio, the depths of both the compressive residual stresses and grain refinement increase, and with respect to the same depth, the compressive residual stresses increase and the refined cell size decreases. An attempt was made to employ the artificial neural networks (ANNs) to estimate the residual stresses and grain refinement induced by LSP of the whole TC4 blade model, and the ANNs-estimation approach presents the excellent efficiency in predicting the multi-LSPed results with inexpensive cost of numerical computation.

Effect of laser spot overlap ratio on surface characteristics and adhesive bonding strength of an Al alloy processed by nanosecond pulsed laser

• Nanosecond laser ablation treatment enhances adhesive bonding strength for Al alloy. • Laser-induced surface physiochemical modifications increase with overlap ratio. • Excessive overlap ratio of laser spots reduces the strength of laser-treated joints. • Micropores in adhesive layer caused by insufficient wetting reduce joint strength. • Corrosion resistance of laser-treated substrate drops with increasing overlap ratio. The laser ablation treatment has been validated to be an effective surface treatment method in improving adhesive bonding performance for metal or composite materials. This study was further conducted to investigate the effect of laser spot overlap ratio on surface characteristics and resultant adhesive bonding strength for AA6022-T4 Al alloy. The laser spot overlap ratio was changed by varying the laser processing speed and line spacing between laser scanning lines. Surface characteristics analyses show that the laser ablation treatment at higher overlap ratio produces rougher surface morphology and thicker aluminum oxide layer on substrate surface, which are considered to be more favorable for adhesive bonding strength. Lap-shear strength results show that the laser ablation treatment at overlap ratio of -49 % (corresponding with separated laser spots) improves the joint strength by 6.8 % and 17.1 % before and after water soak exposure compared to as-received condition. Meanwhile, the desired cohesive fracture mode is also achieved which indicates that the joint strength reaches to the saturated value depending on mechanical performance of adhesive. This explains that the continuous increase of laser spot overlap ratio from -49 % to 63 % exhibits negligible improvement on joint strength. Nevertheless, although inducing a higher degree of surface physicochemical modifications on Al substrates, the laser ablation treatment with an overlap ratio beyond 63 % decreases the joint strength. Detailed studies of SEM micrographs verified that the decreased joint strength is attributed to insufficient wetting of adhesive on the rough surfaces of laser-treated substrates resulting in entrapment of air between substrate and adhesive layer, which forms micropores defects in the adhesive layer and consequently weakens the adhesive-bonding joints. In addition, the improved corrosion resistance of adhesive-bonded Al joints by laser ablation treatment is attributed to the barrier effect of laser-produced rough surface morphology to water diffusion along bonding interface.

Strengthening characteristics in TC17 titanium alloy treated during LSP

The objective was to address the strengthening characteristics in TC17 titanium alloy treated during laser shock processing (LSP) by simulation and experiment. A simulation model with the size of 4 mm × 4 mm×2 mm during LSP was established by ANSYS/LS-DYNA. The propagation characteristics of stress waves and residual stresses were simulated, and the residual stresses were also measured by an X-ray stress. The influence rules of different spot overlap ratios on the residual stresses were analyzed, and the distribution laws of residual stresses on the model surface were obtained in uniaxial direction. Further, the impact effect was discussed when the spot overlap ratio was 60 % by experimental test and fractographic observation. Simulation and experimental results explained that the plastic deformation layer on the model surface became more even with the increase of spot overlap ratio, and impact unevenness was greatly reduced. Especially, the residual compressive stress was greatly increased when adopting 60 % overlap ratio, the maximum residual compressive stress could be reached 691 MPa, and a stable plastic deformation layer was formed on the model surface.

Femtosecond laser micromachining in combination with ICP etching for 4H–SiC pressure sensor membranes

4H–SiC is one of the most promising materials for pressure sensing in harsh environments. A Yb:KGW femtosecond laser was employed to fabricate 4H–SiC sensor membranes with size of Φ1200 × 80 μm. The optimal parameter combination under 15 μJ single pulse energy was obtained with the laps of 16, the scanning speed of 130 mm/s, the scanning line interval of 2 μm and the repetition rate of 100 kHz. High size accuracy (±1%) and steep sidewall (87.4°) were achieved. Wet cleaning and inductively coupled plasma (ICP) etching can obviously improve the membrane bottom surface morphology. The surface roughness Ra in X direction was reduced from 0.82 μm to 0.15 μm, and that in Y direction was reduced from 1.32 μm to 0.16 μm. Pinhole defect was related to the nonuniform distribution of laser fluence. This defect can be avoided by reducing the laser spot overlap ratio. Energy-Dispersive X-ray Spectroscopy (EDS) and Raman spectrum were adopted to analyse the changes of material properties after laser processing. The analysis indicated that the crystal properties of the membrane bottom and the thin epitaxial layers on the front side of membrane are not damaged by the integrating micromachining. The results indicate the potential of utilizing the femtosecond laser combined with ICP etching to fabricate 4H–SiC sensor membranes.

Laser-dressing topography and quality of resin-bonded diamond grinding wheels

Laser dressing technology has shown extremely outstanding advantages and broad application prospects in dressing of superabrasive grinding wheels. However, this technology is currently facing bottlenecks that the generation mechanism of the metamorphic layer on the surface of the grinding wheel is unclear, and the influence rule of the heat accumulation effect on the removal threshold of the grain is not mastered. In this paper, the laser cutting experiment of single diamond grain, and the laser ablation experiment and dressing experiment of resin-bonded diamond grinding wheels were systematically carried out, and the effects of process parameters on the topography and quality of nanosecond laser dressing were comprehensively explored by means of SEM, Raman, EDS, XRD and other detection methods. The mechanism of generation and removal of the graphite layer on the surface of diamond grains during profiling was revealed. It was found for the first time that there was a clear interface between the graphite layer and diamond, and the increase of the finishing time was beneficial to reduce the degree of graphitization of profiled diamond grains. The influence rule of the heat accumulation effect on the removal energy threshold of diamond grain during the sharpening process was first clarified. It was found that the removal energy threshold of diamond grain decreased first and then stabilized with the increase of the spot overlap ratio. The pyrolysis process and phase transformation of resin bond during laser dressing were innovatively explored. It was found that the proportion of C element increased and the proportion of O element decreased in the bond, while the composition and content of the auxiliary materials in the bond changed little. Finally, the comprehensive optimization of laser dressing parameters was completed, and low damage and ultra-precision dressing of resin-bonded diamond grinding wheels were achieved.

The effect of spot overlap ratio on femtosecond laser planarization processing of SiC ceramics

Silicon carbide ceramics are widely used in many fields owing to their excellent mechanical properties such as good wear resistance, thermal stability, and chemical corrosion resistance. The laser planarization processing can effectively achieve the functional, practical, and engineering process, satisfying the demands of the assembly precision. Therefore, different spot overlap ratios were utilized to investigate the effect of femtosecond laser planarization processing on silicon carbide ceramic samples. Various scanning speeds and laser repetition frequencies were matched to achieve different spot overlap ratios under the premise of fixed laser incident angle and single pulse energy. Under different parameters, the ablation depth, surface roughness, surface morphology, oxidation, and residual stress were compared. The result showed that at the same spot overlap ratio, the ablation depth and surface roughness are basically maintained at a stable value despite the difference in the scanning speed and repetition rate. The surface oxidation phenomenon remarkably decreased at the spot overlap ratio less than 90%. The decrease in the overlap ratio leads to the transition of the low frequency nano-ripple and the high frequency nano-ripple, and the surface residual stress converted from tensile stress to compressive stress. Combining processing requirements with ablation quality, the parameters are divided into three parts to fit three processes based on the spot overlap ratios. The variation in the spot overlap ratios as the guidelines had good potential in guiding the parameter range selection.

Effect of single pulsed picosecond and 100 nanosecond laser cleaning on surface morphology and welding quality of aluminium alloy

Removing the oxide film and dirt on the surface of the aluminium alloy can improve the welding quality of the aluminium alloy. In this paper, the characteristics of picosecond and 100 nanosecond pulsed laser cleaning aluminium alloys are explored by changing the average laser power, spot overlap ratio and scanning trajectory overlap rate. The results show that the oxide laser removal depth and diameter are related to the average power. As the average laser power increases, the depth and diameter of the ablation pit increase. At the same average power, the nanosecond laser ablation depth is greater than the picosecond laser. To achieve good surface quality, the nanosecond laser requires a higher overlap rate than the picosecond laser. The high overlap rate results in a nanosecond laser cleaning efficiency that is much lower than that of a picosecond laser. More importantly, the surface quality obtained by picosecond laser cleaning is much better than nanosecond laser cleaning. In addition, the welding experiment shows that the laser cleaning pre-treatment can effectively improve the welding quality.

Effect of process parameters on the microstructure evolution of laser surface quenched Ni-Al bronze

Laser surface quenching technology was used to modify the surface microstructure of as-cast Ni-Al bronze (NAB). The modified microstructure was studied by scanning electron microscopy (SEM), and the effect of laser process parameters on microstructure evolution was investigated. It was found that a fine-grained zone with fully [Formula: see text] phase microstructure formed on the surface of NAB. The depth of the fine-grained zone increased with the increase of laser power, and surface melting occurred when the power reached a threshold value. Laser scanning at a low rate caused the coarsening of grain boundary, while too high rate led to incomplete quenching. Spot overlap ratio determined the microstructure of the superimposed area, and unsuitable ratio would cause bulky [Formula: see text] precipitation at the grain boundary or incomplete transformation from [Formula: see text] phase to [Formula: see text] phase.

Dislocation density-based study of grain refinement induced by laser shock peening

Laser shock peening (LSP) is an innovative surface processing technique. Grain refinement induced by LSP has been proved to be feasible to improve the surface properties of materials and prolong the service life of metallic components. The three-dimensional finite element model, which incorporates a dislocation density-based constitutive model and the temporal-spatial distribution of laser shock wave, was adopted to simulate the process of grain refinement induced by LSP. The predicted dislocation cell sizes, dimple fabrications induced by the repetitive LSP of copper are in good agreement with experimental results, which confirms the validity of the dislocation density-based three-dimensional finite element model. The effects of laser spot overlap ratio and laser power density (peak laser shock wave pressure) on LSP-induced grain refinement were investigated in detail based on the numerical simulations of multiple LSP of copper and CP-Ti.