Nanosecond Pulsed Fiber Laser Research Articles

Welding of Thin Tab and Battery Case for Lithium-ion Battery Cylindrical Cell Using Nanosecond Pulsed Fiber Laser

Welding of Thin Tab and Battery Case for Lithium-ion Battery Cylindrical Cell Using Nanosecond Pulsed Fiber Laser

Tribological and Vibration Studies of Textured Spur Gear Pairs under Fully Flooded and Starved Lubrication Conditions

The tribological and vibrational behaviors of conventional and textured spur gear pairs were experimentally explored under fully flooded and starved lubrication conditions at different operating parameters. Three different gear tooth profile textures were created by creating vertically oriented ellipsoid, horizontally oriented ellipsoid, and hemispherical dimples in zigzag patterns using a nanosecond pulsed fiber laser. Tribological parameters (contact resistance, temperature rise, and surface topography) and vibration (in time and frequency domains) were obtained, compared, and analyzed. The results revealed a reduction in vibration amplitudes, increase in contact resistance, decrease in temperature rise, and less damage of mating surfaces in the presence of textures. Moreover, the texture with vertically oriented ellipsoidal dimples yielded the best results.

The Characteristics of Laser Welding of a Thin Aluminum Tab and Steel Battery Case for Lithium-Ion Battery

During lithium-ion battery packing, joining between battery cases and tabs is challenging for manufacturers due to dissimilar materials of the battery case and the tab, as well as their thicknesses. Laser welding, which has proven to produce a good weld with high productivity and low electrical resistance, is introduced to weld these materials. The weld was conducted with nanosecond-pulsed fiber laser and the effect of laser powers on mechanical and electrical properties as well as microstructure of the joint is investigated. The weld bead at the low laser power exhibited several blowholes on the surface, while the formation of voids including centerline and root cavities was observed through the cross-section. Moreover, the phenomenon of upward penetration (UP) was observed in all laser powers and recoil pressure which was generated by metal evaporation was supposed to cause the formation of an upward flow of the lower material. A hardness test was performed on both horizontal and vertical directions through the fusion zone. Additionally, the increase of upward penetration (UP) resulted in higher strength and lower electrical resistance of the weld.

Wettability modification of laser textured copper surfaces applied to phase change heat transfer

Phase change heat transfer allows high heat transfer rates associated with small temperature variations. Given that this technique is employed in several energy and industry applications, such as automotive air-conditioning evaporators, pulsating heat pipes are used for aerospace thermal management and in semiconductor-manufacturing heat exchangers. Although phase change heat transfer has served mankind for more than two millennia, little progress has been made in the last 40 years regarding the basic performance of phase change heat transfer surfaces. However, laser texturing is expected to change this scenario through wettability modification of heat exchanger surfaces, which can lead to heat transfer improvement. In this context, surface texturing of electrolytic copper (a material commonly employed in phase change heat transfer applications) was performed using a nanosecond pulsed fiber laser source associated to a galvanometric scanner. A design of experiments was performed in order to correlate the parameters’ pulse overlapping, laser power, number of scanning repetitions, and pulse duration to their respective machining features. Machining depth and width were evaluated, as well as the surface integrity of the processed region. These analyses were performed by means of white light interferometry, optical microscopy, and scanning electron microscopy. The surface integrity analysis is especially important, since there is a lack of information regarding texturing effects on surface properties, as most studies focus almost exclusively on surface topography and not on the thermal effects that laser texturing can promote to the substrate material. After comprehending the parameter effects on the machining features, surface textures were manufactured and evaluated in order to define their effect over surface wettability, which influences the heat transfer performance. Copper oxide present on the laser generated textures granted them hydrophilicity so that most of the tested textures achieved contact angles of 0°. A cleaning process with H2SO4 was proposed to remove this oxide and decrease the wettability, also allowing hydrophobic surfaces with a contact angle up to 180° to be obtained.

Nanosecond laser fabrication of superhydrophobic Ti6Al4V surfaces assisted with different liquids

In this paper, the Ti6Al4V surface was textured in air, water, ethanol and saturated sodium bicarbonate solution respectively using a nanosecond pulse fiber laser, and the surfaces with different degrees of hydrophobicity were obtained. The morphology, chemical compositions and wettability of the surfaces textured in different environments were analyzed. The dynamic characteristic of laser ablation in liquid was also analyzed briefly. It is found that surfaces with different wettability can be obtained by liquid-assisted nanosecond laser etching. Especially in the ethanol environment, the water contact angle and the rolling angle are 154.9° and 9.8°, respectively, which indicates the superhydrophobicity of the textured surface. In addition, the surface textured in saturated sodium bicarbonate solution has strong adhesion to water. Due to the presence of the liquid layer on the surface, the debris and dust generated during the laser texturing process is significantly reduced. Furthermore, these surfaces maintain excellent hydrophobicity after being placed in the atmosphere.

Wetting angle stability of steel surface structures after laser treatment

In this work, we have used a nanosecond pulsed fiber laser to modify the wettability characteristics of AISI 430 steel. For this, various surface morphologies were created on the samples by laser irradiation with different overlapping and intensity parameters. Immediately upon laser treatment, all the structured samples acquired either hydrophilic or superhydrophilic wetting angles. All the samples were also analyzed with XRD. Then, laser-treated samples were kept in ambient air and/or low-temperature annealing was applied to reach hydrophobic surface properties. Interestingly, these surfaces returned back practically to their initial wetting state by cleaning in an ultrasonic bath. The obtained results are analyzed based on the existing wettability models.

Nanosecond pulsed fiber laser as a tool for laser micro welding

Laser micro welding is – due to its local and limited thermal input into the parts – a well suited joining technique for the contacting of battery cells, modules and packs for electrical vehicles. The most common laser micro welding processes employ a fiber laser emitting in the infra-red range in continuous wave mode. Recently however, it was shown that a nanosecond pulsed fiber laser, usually used for ablation applications, can be used for joining as well. The aim of this paper is to examine welding dissimilar materials with a nanosecond pulsed fiber laser.

Pulsed laser machining of high-performance engineering and biomedical alloys

The exceptional mechanical and thermal properties of high-performance engineering and biomedical alloys lead to difficulties in machining with conventional processes. This work explores nanosecond pulsed laser machining as a flexible alternative to overcome manufacturing-related limitations associated with Ni Hastelloy, Ti-6Al-4V titanium alloy and Stellite 6K. An extensive experimental campaign was performed with a 1064 nm nanosecond pulsed fibre laser, quantifying the ablation threshold, penetration depth and material removal rate as functions of average laser power (2 to 20 W), repetition rate (20 to 80 kHz), scanning velocity (100 to 2,000 mm/s) and number of laser passes (1 to 20). Optimum conditions for machining were achieved for all alloys with 20 W average power, 20 kHz repetition rate and 1,000 mm/s scanning velocity due to strong ejection of the liquid phase with high pulse fluence (71 J/cm2), good process stability and material removal rates in the range 0.08 to 0.17 mm3/s.

Laser finishing of polycrystalline diamond as strengthening mechanism

Abstract Polycrystalline diamonds are widely used in the cutting tool industry for machining of aluminium alloy and metal matrix composites as they exhibit superior wear resistance. However, their wear characteristics are dependent on their microstructural features (i.e. percentage of binder phase and size of grains) which are defined during the sintering process. Low-energy fibre laser process of polycrystalline diamond composites with different grain dimensions is proposed to promote microstructural changes, enhance their hardness, and retain surface finish. Specimens were processed with a nanosecond pulsed fibre laser (ytterbium-doped) at a wavelength of 1064 nm. Samples treated at various fluences, beam speeds and pulse durations were characterised via 3D interferometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and micro-indentation hardness test. At a fluence below the composite’s ablation threshold (i.e. 20 J cm2), the investigated finishing/polishing process for a coarse grain polycrystalline diamond resulted in a change of diamond grain size, a surface integrity of 140 nm and increased micro hardness (i.e. 240 GPa). The laser treatment caused plastic deformation of the grains, changing the intergranular boundaries area therefore impeding dislocation movements and enhancing hardness.

142 W高峰值功率窄线宽线偏振脉冲光纤激光器

An all fiber linearly polarized narrow-linewidth nanosecond pulsed fiber laser based on master oscillator power amplifier (MOPA) structure was reported. The pulsed seed was generated by modulating a single-frequency distributed feedback (DFB) fiber laser using an electro-optic intensity modulator. In order to suppress stimulated Brillouin scattering (SBS), the pulse width was set to be 3 ns and the linewidth of seed was broadened to be 2.9 GHz by a phase modulator. After amplifying by two stages polarization maintaining Yb3+ doped fiber amplifier chain, the output pulse laser was obtained with an average power of 142 W, a repetition rate of 1 MHz, a pulse duration of 2.88 ns, corresponding to peak power of 49.3 kW. At maximum output power, the laser beam quality M2 was ～ 1.15 and the polarization extinction ratio(PER) was >15.4 dB.

Ultra-flat supercontinuum from 1.95 to 2.65 µm in a nanosecond pulsed Thulium-doped fiber laser

Abstract We report on mid-IR supercontinuum generation in an all-silica nanosecond pulsed fiber laser. The laser topology is a master oscillator power amplifier which consists of a two stage Thulium-doped fiber amplifier seeded with a directly modulated semiconductor laser at 1952 nm. The supercontinuum performance is investigated for repetition rate frequencies between 35 kHz and 100 kHz and pulse widths between 6 ns and 21 ns. Supercontinuum average output powers greater than 1.5 W and spectra ranging from 1.95 µm to 2.65 µm are demonstrated.

Bright/dark switchable mode-locked fiber laser based on black phosphorus

Stable bright/dark switchable mode-locked nanosecond pulse fiber laser incorporating black phosphorus (BP) was demonstrated in the Yb-doped fiber ring cavity for the first time, to the best of our knowledge. The high-quality BP saturable absorber (SA) was fabricated by the modified electrochemical delamination exfoliation process. The states between bright and dark pulse could be switched by simply adjusting the intra-cavity polarization states, and close agreement with the cubic Ginzburg-Landau equation (CGLE) models is present.

Nanosecond pulsed fiber laser cleaning of natural marine micro-biofoulings from the surface of aluminum alloy

Abstract Herein, environmentally effective nanosecond (30 ns) pulsed fiber laser cleaning technology was innovatively used to remove natural marine micro-biofoulings with the thickness of 61.7 ± 26.5 μm from the surface of aluminum alloy. The morphologies and chemical compositions of the uncleaned and cleaned surfaces of the samples were examined and analyzed by field emission scanning electron microscopy (FESEM), electron microprobe (EPMA), atomic force microscopy (AFM), and energy dispersive spectroscopy (EDS). The wettability of cleaned surface was studied by contact angle analyser. Successful cleaning of the aluminum surfaces to remove marine micro-biofoulings can be achieved by using different laser fluences (1.38–5.52 J/cm2). The aluminum content of laser-cleaned surface was 88 wt% approximately, which reached up to 91.7% of that of the original substrate surface. Mechanism analysis indicated that laser-induced vaporization and ablation broke and eradicated of marine micro-biofoulings. The generated new surfaces were with free of damage and acceptable. At specific laser fluences (5.52 J/cm2), the surface even had additional superhydrophobicity which provides the feasibility of antifouling in the periodic service. This work offers fundamental research and practical guidance for laser cleaning of marine micro-biofoulings on the surface of aluminum alloy.

나노초 펄스 파이버 레이저를 이용한 CFRP 미세가공

CFRP (Carbon fiber reinforced plastic) has been widely used in different industries such as aerospace, automobile, sports and medical. Laser processing of CFRP has a great potential for industrial applications. In this paper researched the micro cutting and drilling of CFRP with 0.5 mm thickness using 1064 nm ytterbium nanosecond pulsed fiber laser. It also investigated machining characteristics of micro cutting and drilling according to laser power, frequency, scan speed and number of scan (or irradiation). Complete cutting and through-hole drilling were achieved with low frequency when the laser power was low and with low and middle frequency when the laser power increased. However, those were not achieved a frequency of 100 kHz. The cutting width increased when the power increased and decreased when the frequency and the scan speed increased. The hole size increased when the power and the number of irradiation increased and decreased when the frequency increased. In the case of micro hole array, the hole was blocked during the next hole machining when the hole spacing was narrow. The resin was melted by the heat thus blocking the pre-drilled hole. We devised the laser scan method, and the micro hole array with narrow hole spacing was fabricated successfully.

White marking inside the transparent plastic materials by 1.55 μm nanosecond pulse fiber laser

In this paper, the authors report that it is possible to create a white marking inside transparent plastic materials by heating them to a temperature close to the threshold of creating a void and using a fiber laser. Heating plastic materials and using a fiber laser enable the threshold to be in excess only in the focus position, and a white marking is created. The authors experimented with polycarbonate and polyethylene terephthalate as the transparent plastic materials, and a 1.55 μm nanosecond pulse fiber laser as the laser equipment. They irradiated laser in the sample inside while heating. As a result, when polycarbonate was heated to 150 °C and polyethylene terephthalate to 50 °C, a void was created at the focus position. Therefore, the authors successfully created a white marking inside the transparent plastic materials by heating them and using a fiber laser.In this paper, the authors report that it is possible to create a white marking inside transparent plastic materials by heating them to a temperature close to the threshold of creating a void and using a fiber laser. Heating plastic materials and using a fiber laser enable the threshold to be in excess only in the focus position, and a white marking is created. The authors experimented with polycarbonate and polyethylene terephthalate as the transparent plastic materials, and a 1.55 μm nanosecond pulse fiber laser as the laser equipment. They irradiated laser in the sample inside while heating. As a result, when polycarbonate was heated to 150 °C and polyethylene terephthalate to 50 °C, a void was created at the focus position. Therefore, the authors successfully created a white marking inside the transparent plastic materials by heating them and using a fiber laser.

Nanosecond laser texturing with hexagonal honeycomb micro-structure on Titanium for improved wettability and optical properties

Nanosecond laser provided an efficient and flexible solution for surface texturing on different metals. In this work, a hexagonal honeycomb model was designed on Titanium by laser processing. The surface texturing experiment was carried out by a nanosecond pulsed fiber laser with different scanning speeds. The Scanning Electron Microscopy and White Light Interferometer were used to characterize the surface morphology and roughness. Besides, the contact angle instrument and the Fourier Transform Infrared Spectrometer were used to obtain the effects of surface modification on wettability and optical properties of the Titanium. The wettability and optical reflectivity of the surface changed by controlling the side length of the hexagonal honeycomb model and the laser scanning parameters. The contact angle reached a maximum of 147.4°, the contact angle hysteresis was found to lie between 1.6° and 7.1°, and the optical reflectance for titanium surface decreased by more than 90% after laser processing. The approach presented in this study provided a feasible and efficient method to improve the wettability and optical absorption of titanium surface.

Micro-Welding of Stainless Steel and Copper Foils Using a Nano -Second Pulsed Fiber Laser

Joining of materials is an essential process step in manufacturing industry. The need to weld dissimilar thin materials is growing lately with applications in MEMS devices involving different materials. Welding of thin dissimilar materials is a challenging task in comparison to their bulk counterparts as they are quite susceptible to damage. This paper is concerned with the feasibility of welding extremely thin stainless- steel foil (AISI 304) with pure copper foil of thickness of tens of microns in lap joint configuration using a single mode nano-second pulsed fiber laser. Welds were made in “weld brazing” mode as well as in “full fusion” mode with linear heat inputs of 0.1 J/mm and 0.145 J/mm respectively. Optical microscopy and electronic microscopy were used to evaluate the weld microstructure, X-ray radiography was employed to evaluate the integrity of the weld, while tensile testing and micro-hardness measurements of the welds were carried out to ascertain the mechanical properties the weld. Welds could be made without any defects, e.g. lack of fusion, cracks and porosities. Welds made in “weld brazing” mode was found to be mechanically superior to the welds performed in “full fusion” mode. The decided advantage of the usage of nanosecond single mode laser for this application is also elucidated.

Removal of Surface Spatter and Recast layer by Chemical Cleaning

Abstract Laser microdrilling has various applications in aerospace and electrical industries in manufacturing components such as nozzle guide vanes, combustion chambers, cooling holes on turbine blades, etc. In this study, cleaning of laser micro-drilled holes has been carried out. These holes were drilled using nanosecond pulsed fiber laser. The holes produced were with defects like surface spatter and recast layer. Therefore defects were cleaned by chemical etching using HNO3+HCl as etchant by keeping workpiece in still solution and passing etchant through the holes using electric pump. Qualitative and quantitative analysis were done using optical microscope. Surface spatter was cleaned in a still etchant solution at room temperature and a good quality etched holes was obtained for 40%HNO3 + 10%HCL when etched for 6 minutes.

Pulsed laser ablation for enhanced liquid spreading

Nanosecond pulsed laser ablation is shown to be an effective method for enhancing liquid spreading on surfaces where the intrinsic droplet static contact angle is less than 60°. A simple theoretical model is developed to optimise the laser scanning strategy and maximise the resulting Wenzel roughness factor, r. Laser ablation experiments are then performed with a nanosecond pulsed fibre laser with emission wavelength of 1064 nm on stainless steel and aluminium alloy surfaces, with beam scanning based on model outcomes to achieve discrete ablation craters in the longitudinal and lateral directions. Adhesive, oil and ethanol droplets are deposited on untreated and laser-textured surfaces, with liquid spreading quantified via photography and image processing. Large increases in adhesive and oil droplet spreading area on laser-textured surfaces are accounted for in terms of a transition from Wenzel state to film regime, where liquid spreading is driven by a negative change in interfacial energy with progression of the imbibition front. By increasing r, laser ablation is found to increase the threshold contact angle below which transition to a film regime takes place. Further increases in r are found to further improve liquid spreading due to a larger negative interfacial energy gradient until the ablated volume becomes significant and liquid retention within the surface limits further gains. Eighteen- and seven-fold increases in spreading area are achieved for adhesive and oil, respectively, while no improvements are observed for ethanol due to immediate onset of a film state on untreated samples.

MODERN POLYMER COMPOSITE MATERIALS AND POSSIBILITIES OF THEIR LASER MACHINING

The widespread introduction of polymer composite materials in key sectors of modern industry such as wind and hydropower engineering, aircraft and machinery ones, etc. due to the high level of their strength properties, versatility and ability to provide the lowest weight of parts of products raises the problem of their processing. Traditional processing methods (mechanical and abrasive water jet machining) have some significant shortcomings: high tool wear, delamination due to vibration and shock loadings, limitations on the cutting contour and others. The paper deals with the polymer composites laser machining which is considered to be one of the promising solutions for elimination of conventional methods disadvantages due to a contact-free, flexible and high-performance processing method. As a result of analysis of theoretical and experimental domestic and foreign works, the use of industrial ytterbium fiber lasers are found to be a promising direction for high-quality and productive processing of polymer composite materials. The results of studies using the experimental technological setups on the basis of nanosecond pulsed and continuous ytterbium fiber lasers with a radiation power up to 1 kW and optical scanning systems based on the biaxial galvo scanners and focusing F-Theta lenses with beam travel speeds up to 20 m / s have shown that the laser multi-pass machining of polymer composite materials with layer-by-layer removal (ablation) of the material due to the evaporation mechanism allows for precise and high quality cutting and drilling of carbon and glass fiber reinforced plastics and carbon plastics with a thickness 1–3 mm.