Laser Processing Research Articles

Enhanced capillary pumping performance of flexible heat pipe device with multi cross-section ultra-thin wick

Copper mesh, with its excellent flexibility and thermal conductivity, is an ideal material for the wick of flexible heat pipe. In this paper, a structure optimization strategy of wick with multi cross-section is proposed to enhance its capillary pumping performance. The analytical solution models of single-section and multi cross-section wicks are established by the kinetic equation of capillary pumping. Numerical simulation is used to analyze the capillary pumping performance of the multi cross-section wicks, and the results confirm the multi cross-section enhancement mechanism with the infrared experimental results. Laser processing, sintering and molding, and super-hydrophilic modification are used to fabricate the multi cross-section wick. Laser removal of rectangular units can modulate the capillary pumping performance of the multi cross-section wick. The capillary height h of the multi cross-section wick is enhanced by 13.4 % when the size of the rectangular unit l × w = 40 mm × 1.5 mm and the number of removals N = 5. Compared with the heat transfer performance of the single cross-section flexible heat pipe, the evaporator temperature T and thermal resistance R of the multi cross-section flexible heat pipe decreased by 16.6 % and 77.4 %, respectively. The effective thermal conductivity Keff reaches 10,560 W/(m·K), which is 26 times higher than that of copper.

Influence of typical technological parameters on the processing quality of laser surface texturing technology for finger sealing

Abstract In recent years, to achieve favorable tribological characteristics, surface texture technology for friction reduction has been extensively studied, and its effectiveness has been successfully validated. The quality of surface texture processing directly impacts the tribological performance of finger seal friction pairs. To investigate the influence of the laser process parameters on the finger seal surface texture of the GH4169 and improve its processability and process predictability, a comparative experiment and analysis involving multiple processing parameters, including the laser power (P), laser frequency (F), scanning speed (V), and scanning times (N), were conducted. To evaluate the quality of laser surface texturing processing technology, four processing morphology parameters were established. Uniform experiments and regression analysis were employed to analyze the influence and synergistic effects of laser processing parameters on processing quality. The research results indicate that laser power, scanning times, and scanning speed are the main process parameters that significantly affect laser surface deformation. The outer diameter is directly proportional to the laser power and inversely proportional to the scanning speed; the bottom diameter ratio is directly proportional to both the laser power and scanning times; and the pit depth initially increases and then decreases with increasing laser power and scanning times. The suitable range of processing parameters is as follows: laser power (10~20%), speed range (400~700 mm/s), scanning times (8~18 times), and laser frequency (20~25 kHz). This research provides theoretical and experimental support for the precise control of surface texture prepared by laser processing of GH4169, laying the foundation for friction and wear tests of textured finger seals.

Hybrid Optical Sensor for Combined Thermal and Dimensional Monitoring in Laser Processing

Hybrid Optical Sensor for Combined Thermal and Dimensional Monitoring in Laser Processing

A Study on the Manufacture of CNT Composites Bipolar Plate for the Fuel Cell Using a Nanosecond Pulsed Laser

The channels of the graphite-based bipolar plate for hydrogen fuel cells were mainly manufactured through milling due to low forming elongation and processability. However, during the milling process, the machining precision is low due to tool wear and vibration, and there is a risk of breakage. Non-traditional laser processing can solve the problems of tool wear and vibration through non-contact processing. In this study, the interaction characteristics of the nanosecond pulsed laser and CNT composites were observed, and channels and bipolar plates were manufactured. The effect of scanning speed and pulse duration was observed for interaction characteristics. Defects were observed due to high thermal effects at low scanning speed and high pulse duration. Channels were created depending on parallel pitch distance [] and Number of scans (NOS). The channel was evaluated for depth, top width, bottom width, channel angle, material removal rate, and surface roughness, and significant changes were observed depending on . The chemical composition, surface resistance, and contact angle of the laser-processed channel were measured. The laser processed channel was oxidized, and the surface resistance and contact angle increased. Finally, the manufacturability of the CNT composites bipolar plate using laser was examined.

Modeling nanogratings erasure at high repetition rate in commercial optical glasses

Volume nanogratings (NGs) imprinted by infrared femtosecond laser in commercial optical glasses take the form of orientable subwavelength birefringent nanostructures, being composed of an assembly of nanopores. The existence of NGs strongly depends on the laser parameters and glass composition. Therefore, in this work, we tentatively model the erasure threshold of NGs in a pulse energy - repetition rate processing window. For this purpose, we combine i) a heat diffusion model to simulate the thermal treatment experienced by the glass upon laser irradiation, and ii) the Rayleigh-Plesset equation to take into account the evolution of a nanopore size during laser processing. We first determine a criterion for nanopores erasure, falling within a typical characteristic time of few tens of ns, in which the cooling of the last laser pulse absorbed by the material is progressively cooled. Then, considering a multiple pulse regime and the dependence of the deposited pulse numbers on the thermal treatment, the modeled NGs erasure threshold follows the experimental trend. Finally, considering a steady state regime for various repetition rates, and adjusting the energy deposition (absorption coefficient or beam waist) as a function of the pulse energy, the NGs existence window can perfectly match the experimental values.

Dual-laser powder bed fusion using 450 nm diode area melting and 1064 nm galvo-scanning fiber laser sources

This study introduces an innovative dual laser powder bed fusion (PBF-LB/D) system, which combines two distinct laser processing methods to enhance control over microstructural outcomes. Unlike conventional PBF-LB systems that employ a single laser type, this dual-laser setup integrates a traversing Diode Area Melting (DAM) laser head with multiple 450 nm diode lasers (4 W each) and a traditional high-power (200 W) 1064 nm fiber-laser. This unique configuration allows for significantly different melt pool solidification rates within the same layer. For the first time, Ti6Al4V feedstock was processed using both laser types within a single sample. A specific scanning strategy defined separate laser processing regions, including an overlap where both lasers interacted to fuse the feedstock and bridge the two regions. The fiber-laser melted (FLM) regions experienced much higher cooling rates (∼107 °C/s) than the DAM regions (∼600 °C/s), resulting in acicular ά/α phases. In contrast, DAM regions exhibited larger grains, with parent β grain sizes approximately 13 times larger than those in the FLM zone. This dual laser system investigation not only demonstrates microstructural in-situ spatial tailoring but also highlights variations in the laser-induced heat-affected zone, surface roughness, and mechanical properties across different regions within the fabricated Ti6Al4V samples.

Impact of repetitive, ultra-short soft X-ray pulses from processing of steel with ultrafast lasers on human cell cultures

Ultrafast lasers, with pulse durations below a few picoseconds, are of significant interest to the industry, offering a cutting-edge approach to enhancing manufacturing processes and enabling the fabrication of intricate components with unparalleled accuracy. When processing metals at irradiances exceeding the evaporation threshold of about 1010 W/cm² these processes can generate ultra-short, soft X-ray pulses with photon energies above 5 keV. This has prompted extensive discussions and regulatory measures on radiation safety. However, the impact of these ultra-short X-ray pulses on molecular pathways in the context of living cells, has not been investigated so far. This paper presents the first molecular characterization of epithelial cell responses to ultra-short soft X-ray pulses, generated during processing of steel with an ultrafast laser. The laser provided pulses of 6.7 ps with a pulse repetition rate of 300 kHz and an average power of 500 W. The irradiance was 1.95 ×1013 W/cm2. Ambient exposure of vitro human cell cultures, followed by imaging of the DNA damage response and fitting of the data to a calibrated model for the absorbed dose, revealed a linear increase in the DNA damage response relative to the exposure dose. This is in line with findings from work using continuous wave soft X-ray sources and suggests that the ultra-short X-ray pulses do not generate additional hazard. This research contributes valuable insights into the biological effects of ultrafast laser processes and their potential implications for user safety.

Microstructure Control and Hot Cracking Prevention During Laser Additive Manufacturing of Cobalt-Based Superalloy

Hot cracking is a frequent and severe defect that occurs during laser additive manufacturing of superalloys. In this work, a pulsed-wave (PW) laser modulation process was employed to control the solidification microstructure and reduce the hot cracking susceptibility of laser additive manufactured cobalt-based superalloy. The effects of continuous-wave (CW) and PW laser processing modes on the dendrite morphology, element segregation, eutectic phase, and hot cracking of fabricated Co-based superalloys were investigated. Optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to characterize the microstructural characteristics of samples. A two-color pyrometer was used to measure the molten pool temperature variation under different laser processing modes. The results show that coarse columnar dendrites, chain-like eutectic carbides, and hot cracks were observed in the CW sample. In contrast, the fine equiaxed crystals, discrete eutectic carbides, and low-level residual stresses were obtained to avoid hot cracks, owing to the high cooling rate and the periodic melting and solidification of the molten pool under the PW laser processing mode. This work provides a new method for controlling solidification structure and hot cracking of laser additive manufactured Co-based superalloy.

Numerical study of paste-bridge transfer process for laser induced high-viscosity silver paste

Laser-induced forward transfer (LIFT) is promising for solar-cell metallization and electronic printing due to its low dependence on paste viscosity and nozzle-free process. In this paper, the transfer process and morphological characteristics for LIFT of high-viscosity silver paste were studied through simulations and experiments. The shear-thinning rheological properties were considered using the fitted Carreau model. Variations of paste protrusion with single pulse energy and time were obtained from the high-speed imaging. The evolution of initial pressure that induces the paste protrusion was solved inversely and quantitatively expressed by a polynomial function. The internal pressure should be sufficiently larger than 40 MPa to induce the effective transfer. In the simulation, the induced bubble undergoes a non-spherical transition from mushroom to pea-pod and capsule shapes due to constraints from surrounding paste and substrate. The deposition morphology formed by the induced mushroom-shaped bubble shows high printing precision with thin width (<30 μm) and large height (∼10 μm). The simulated diameter and height of transferred single voxel agree with those from experimental measurement. It can gain insight into the transfer dynamics of high-viscosity pastes and provide process optimization for precision printing of voxels by LIFT.

Fabrication of micro holes with confined pitting corrosion by laser and electrochemical machining: pitting corrosion formation mechanisms and protection method

Laser and electrochemical hybrid machining (LECM) combines the advantages of high efficiency of laser processing and high surface quality of electrochemical machining and has been employed to process deep micro holes with high surface quality, high precision, and efficiency. However, surface pitting corrosion occurs around the entrance of the micro holes drilled by LECM, which deteriorates their surface quality and mechanical properties. This study revealed the mechanism of surface pitting corrosion formation mechanisms during LECM by characterizing surface micromorphology, chemical composition, microstructures, and surface stress. The difference between surface pitting corrosion area during LECM and the stray current corrosion during electrochemical machining was studied. Micro solid metal particles and inner microcavities were observed in micro pits. The depth of the micro pits was greater than that obtained using electrochemical machining. It has been concluded that in LECM, the surface pitting corrosion occurred owing to the enhanced stray current corrosion and the accumulation of solidified melt particles and cavitation microbubbles in the micro pits. Coaxial gas-assisted LECM was also proposed to restrict the surface pitting corrosion area. Experiments and simulations were conducted to verify the feasibility of minimizing the corrosion area using coaxial gas. The surface pitting corrosion area has been decreased by 85.1% at a coaxial gas pressure of 0.1MPa compared with that without coaxial gas assistance. Finally, the radial cooling holes with a diameter of 1.2mm and an aspect ratio of 125:1 in turbine blades with high surface quality were fabricated. This study provides a promising method to fabricate high-aspect-ratio micro-holes with high surface quality and high efficiency.

Morphology and Properties of the Laser-Irradiated Composition “Chrome Coating — Copper Substrate”

Introduction. During pulsed laser processing and modification of the surface of non-ferrous alloys and coatings based on them, several still unresolved issues arise. In particular, the extreme thermal deformation conditions of laser processing are not linked to the peculiarities of structure formation and formation of properties in irradiated “coating — copper substrate” compositions. A metal physical analysis of the possibility and reasons for increasing the adhesion strength of coatings to a metal (copper) substrate during high-speed laser processing is insufficiently substantiated and evidence-based. To make a reasonable choice of technological parameters for the surface hardening mode of non-ferrous alloy products, as well as for obtaining high-quality workable composite layers on their surface, it is necessary to solve the above issues and tasks. The aim of this article is to determine the possibility and conditions for increasing the adhesion strength of a chrome coating to a copper substrate under laser irradiation of the composition.Materials and Methods. Metal physical studies in the work were carried out on samples of non-ferrous alloys of the Cu–Zn system with a chrome electrochemical coating with a thickness of 20 μm. The “copper substrate — chrome coating” composition was irradiated at a Kvant-16 installation with a radiation power density of 70–250 MW/m2. Metallographic structural analysis, scanning probe microscopy, and durometric studies were used in the work.Results. It has been calculated that the dynamic and thermal stresses arising in the laser-irradiated compositions “chrome coating — copper substrate” were about 320 MPa. Metal physical studies revealed that, in extreme thermal deformation conditions of laser treatment, the effect of contact melting was manifested at the boundary of the coating with the copper base. Dynamic recrystallization occurred in the surface layers of the irradiated L62 copper alloy, resulting in the formation of grains with a size of 4.5–5.0 μm on the surface of the alloy with an initial grain size of 25 μm.Discussion and Conclusion. It has been found that the adhesion strength of a chrome coating to a copper alloy substrate increased laser irradiation at a radiation power density of 150 MW/m2. This was due to the formation of a transition region 2–4 μm deep in the contact zone with a structure consisting of sections of mutually insoluble solid solutions based on chromium and copper. Based on the analysis of the copper —chromium state diagram and the model of the temperature field under laser irradiation of the chromium coating, it was suggested that contact melting occurred in the transition zone from the coating to the copper substrate. It was shown that thermostrictive stresses, the calculated quantitative values of which were about 320 MPa, had an initiating effect on the observed processes of structure formation in the laser irradiation zones. It was found that such a level of stresses arising in copper alloys under laser irradiation was sufficient for plastic deformation and dynamic recrystallization of the metal and contributed to the formation of a fine-grained structure (4.5–5.0 μm) with an initial grain size of 25 μm. An analysis of the results of studies of irradiated compositions "coating — copper substrate" allowed us to conclude that they expanded the technological capabilities of the laser method of hardening materials and ensure guaranteed high performance of irradiated products with coatings

Mathematical modeling and investigation of intrinsic interaction mechanisms in CO2 laser processing of PMMA

Mathematical modeling and investigation of intrinsic interaction mechanisms in CO2 laser processing of PMMA

Development of highly sensitive and stable patterned PDMS flexible strain sensors for motion monitoring via laser direct writing

Flexible strain sensors have received widespread attention for their potential applications in wearables, human–computer interaction, and healthcare. However, achieving a good balance between sensitivity, stretchability, and stability remains challenging. Here, we report a cost-effective and scalable fabrication strategy that combines laser direct writing (LDW) with 3D printing (3DP) to prepare various patterned Polydimethylsiloxane (P-PDMS) flexible strain sensors. By varying the laser parameters and processing paths, different microstructured patterns can be obtained, which significantly influence the sensor’s performance. By introducing patterned composite microstructures, the sensitivity of the strain sensor was increased by 339 % compared to the sensor without surface structures. Additionally, the strain sensors exhibit high stability and durability, a fast response time (140 ms), low hysteresis (0.009), and an ultra-low detection limit (0.0125 % strain). Besides, the sensors demonstrate excellent electrical performance and thermal stability. Based on their superior performance, we demonstrated their capability for real-time monitoring of human physiological signals. These findings successfully illustrate the potential of laser processing in fabricating complex microstructures, enabling the development of high-sensitivity flexible strain sensors for applications such as wearable health monitoring and human–computer interaction.

Influence of wood modification on parameter settings and treatment results in CO2 laser structuring of beech veneers

In this study, the possible influences of thermal modification of wood on the quality of laser texturing of beech veneers are investigated by comparing native and thermally modified samples. By varying the process parameters of a CO2 laser, the surfaces of both types of veneer were textured and the resulting surface roughness and aspect ratios were analyzed in order to evaluate the efficiency of the laser texturing and the quality of the textures produced. The main results show that the thermal modification of the wood influences the cutting widths, the removal depths, and the surface roughness, with thermally modified veneers generally having larger cutting widths and different removal depths compared to native veneers, indicating the influence of the wood modifications on the material physical and chemical properties and their interaction with the laser processing. Furthermore, the study shows how the laser processing parameters—feed rate and laser power—influence the surface quality and structural dimensions of the engraved lines, and establishes that the moisture content of the wood has a significant influence on its thermal conductivity and thus on the laser cutting process. The research work highlights the complexity of laser texturing of wood and emphasizes the need to take into account the change in the intrinsic properties of the material as a result of thermal modification.

Nanosecond laser ablation of micro-pits in Ni60/WC coatings with coupled thermal-stress simulation and parameter optimization

In order to solve the problem of crack sprouting inside the micro-pit caused by improper design of laser ablation process parameters, this study establishes a thermal-stress coupling simulation model of nanosecond laser ablation of micro-pits on Ni60/WC coated surfaces. It researches the influence of laser process parameters (laser power, scanning speed, processing times) on the index parameters of micro-pit diameter, depth, and maximum residual stress. The weighting of diameter, depth and maximum residual stress sub-objectives in the comprehensive evaluation objectives of micro-pits are calculated. The response surface method of Central Composite Design (CCD) and regression analysis are used to fit the response surface functions of micro-pit diameter, depth, and maximum residual stress as a function of the variation of laser ablation process parameters. The Genetic Algorithm (GA) is used to minimize value of the maximum residual stress sub-objective function and to optimize the process parameters of laser ablation of micro-pits, using the values interval of the micro-pit diameter and depth functions as nonlinear constraints. The results show that the maximum residual stress varies quadratically with laser power and scanning speed, increases linearly with the processing times, and is coupled with the ablation process parameters. A design method for optimizing the parameters of nanosecond laser ablation by maximum residual stress is established, and the process parameters are optimized to meet the design parameters and quality requirements of micro-pits: laser power of 12 W, scanning speed of 276 mm/s, and 4 times of processing. The optimized process is provided for the parameter tuning nanosecond laser ablation of micro-pits on Ni60/WC coating surfaces.

Effect of laser surface melting on microstructure and hardness of Mg–4Y–2Zn–1Zr-0.6Ca alloy

To improve the performance of magnesium and enhance its mechanical properties and microstructure, a laboratory-scale Mg alloy with the composition Mg–4Y–2Zn–1Zr-0.6Ca was developed. Subsequently, the alloy was subjected to homogenization and extrusion processes to reduce casting defects and the microstructure refinement. Additionally, surface modification was performed using a pulsed Nd:YAG laser. The findings of the experiment indicate that by controlling the laser processing parameters, it was possible to attain a microstructure devoid of any defects. Moreover, an examination of the microstructure and secondary phases was conducted through the utilization of characterization techniques such as the Optical Microscope (OM), Field Emission Scanning Electron Microscope (FESEM) equipped with Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). Furthermore, the micro hardness of the samples was evaluated using the Vickers micro hardness testing method. Consequently, the microstructures of all specimens exhibited equiaxed grains, predominantly composed of (α-Mg), (Mg24Y5+α-Zr), and the W-phase (Mg3Y2Zn3). In addition, the laser-melted surface revealed a noteworthy refinement of the grain structure, with an evolution in grain morphology from the top to the bottom of the melted area. Equiaxed grains were present in the centerline, whereas columnar grains were observed in the fusion line. Additionally, as the scanning speed increased, a finer microstructure was observed. Due to the rapid heating and cooling involved in the laser surface melting (LSM) process, the secondary phase (Mg3Y2Zn3) dissolved in the microstructure, and the (Mg24Y5+α-Zr) phase was uniformly distributed throughout the LSMed area. Ultimately, the micro hardness showed a significant increase due to the dual influence of grain refinement and the homogeneous dispersion of the secondary phase.

Demonstration of a three-active-section DFB laser with photon-photon resonance and detuned loading effects to obtain enhanced bandwidth and maintained high output power

Enhancement of the modulation bandwidth of the directly modulated semiconductor laser has attracted tremendous attention for applications in optical fiber communication and optical interconnects. However, modulation bandwidth is enhanced by some special technology such as integrating the active region or passive region regularly, which lead to low power and complex fabrication. Here we design and demonstrate a monolithic integrated three-active-section distributed feedback (TAS-DFB) laser with enhanced bandwidth theoretically and experimentally. The laser includes three sections: the DFB section, feedback section and active phase section. The three sections share the same multiple quantum-well structure. To enhance the modulation bandwidth beyond the intrinsic modulation bandwidth, both photon-photon resonance (PPR) and detuned loading (DL) effects are utilized to achieve over 55 GHz. The active phase section shows promise in achieving high bandwidth with PPR and relatively high output power of ∼ 10 mW at 25 °C under continuous-wave (CW) operation simultaneously. The fabrication process of the TAS-DFB laser is simplified due to the conventional and identical active layer structure.

Influence of crystal orientation and incident plane on n-type 4H-SiC wafer slicing by using picosecond laser

Laser slicing has been considered as the most efficient technique for slicing SiC wafers with the advantages of small kerf width (loss) and crack, low roughness on cleaved surface, high quality and efficiency, etc. Here, laser slicing of n-type 4H-SiC was demonstrated by using a homemade 1064 nm picosecond laser combined with mechanical stretch stripping. The influence of laser processing along [11 2¯ 0] and [1 1¯ 00] crystal orientations on Si-face and C-face of n-type 4H-SiC, specifically on the internal laser ablation lines and cracks, the peeling tensile strength, and the surface roughness of the peeled surfaces was investigated. The semi-insulating 4H-SiC wafer laser slicing was conducted for comparison. Under the same laser conditions, laser slicing of semi-insulating 4H-SiC was easier than that of n-type. The laser modification quality along [1 1¯ 00] orientation was better than that along [11 2¯ 0] orientation for both the semi-insulating and n-type 4H-SiC and the reasons were explained. The results indicated that the optimal laser slicing scheme detailed laser scanning along [1 1¯ 00] orientation and incidence from the C-face. Finally, a 6-inch, 420.36 µm-thick n-type 4H-SiC wafer was successfully sliced.

Research progress on laser processing of carbon fiber composite materials

AbstractCarbon fiber reinforced polymer (CFRP) is a high‐performance composite material composed of carbon fibers embedded in a polymer matrix. CFRP is extensively used in various sectors such as aerospace, automotive, sports equipment, and construction due to its advantageous properties. Laser processing offers numerous advantages when working with carbon fiber‐reinforced composites, including its non‐contact nature, precision, efficiency, and controllability. However, disparities between carbon fibers and the polymer matrix can lead to challenges during laser processing, such as delamination, heat‐affected zones, and fiber pullout. Consequently, there is a substantial body of literature focusing on improving the quality and efficiency of laser processing for CFRP materials. This paper provides a comprehensive review of various studies investigating the impact of laser parameters (laser mode, pulse frequency, pulse width, and laser wavelength) on carbon fiber‐reinforced plastics. It discusses how different laser parameters affect the processing quality and performance of these materials. Additionally, drawing from recent research findings, the paper explores potential future trends in laser processing for carbon fiber‐reinforced plastics.Highlights The application of laser technology in CFRP, including laser cutting, drilling, welding, and surface treatment, has been extensively researched. A detailed discussion is held regarding the impact of laser mode, wavelength, frequency, and pulse width on the quality of machining. More auxiliary processing has evolved in CFRP manufacturing due to the ongoing advancements in laser technology. The goals of laser processing CFRP technology are increasingly focused on reducing carbon emissions, enhancing energy efficiency, and minimizing waste.

Picosecond pulsed flat-top beam in a mode-locking all-fiber laser.

Ow7ing to the flat center and steep edge, the flat-top beam is widely used in the fields of micromachining and optical image processing. Here, we propose an efficient scheme to generate a picosecond pulsed flat-top beam in a mode-locking all-fiber laser. After utilizing an orthogonal polarization method for complete incoherence and a high-precision all-fiber optical delay line (ODL) for rigorous time synchronization, the pulsed fundamental mode (LP01) and the pulsed vortex beam (VB) are superimposed to generate a pulsed flat-top beam. The pulsed flat-top beam has a duration of 6.10 ps, with a normalized root mean square (NRMS) variation of 0.049 and a steep degree value of 0.876, indicating an excellent beam quality. In addition, the effect of coherence between the two superimposed beams on the quality of the combined beam has also been investigated. This is the first, to the best of our knowledge, demonstration of a picosecond scale pulsed flat-top beam in the mode-locking all-fiber laser, which may greatly promote its application in laser processing and biomedicine.