Nanosecond Pulsed Fiber Laser Research Articles

Effect of Swing-Spiral-Trajectory on pulsed fiber laser welding stainless steel/Copper dissimilar metals

The dissimilar metal combinations of SUS303 stainless steel and C19210 pure copper with a thickness of 0.2 mm by utilizing a nanosecond pulsed fiber laser was performed in lap welding with swing-spiral-trajectory. The weld effect was evaluated by means of microstructural and mechanical examinations. The influence of pulse frequency, speed and swing frequency as well as pulse waveform on mechanical properties and microstructure was clarified. The metallurgical behavior and weld penetration inside the fusion zone were observed with microscopic inspection of the welded joints and the welded surface. Part of molten pool materials inserted into copper plate formed an intertwined nails for enhancing the interfacial bonding strength was observed in the cross-section of the weldment. Additionally, the presence of a thin intertwined transition layer with solid solutions accomplished by the copper and liquid stainless steel mutual diffusion at the fusion line, indicated that the swing spiral welding pattern can strengthen the interface fusion. Some defects, such as porosities and microcracks, were also found in the welded joints. They were mainly due to the significantly different linear expansion coefficients of copper and steel. Energy dispersive spectroscopy (EDS) analysis confirmed that the interdiffusion and dissolution of copper and stainless steel occurred inside the molten pool, and the surface composition of the weld pool was dominated by iron. The microhardness (MH) study showed that the heat-affected zone (HAZ) was harder than the fusion zone on the stainless steel side, and the fusion interface microhardness much variation indicated microstructural change alongside the weld interface. The tensile test results revealed that the fracture location was in the molten pool on the stainless steel side, the fracture was protruded and the fracture mode was intergranular brittle fracture.

Fabrication of metallic patterns on ordinary polymer substrates by laser direct activation and electroless plating

In recent years, the fabrication of metallic patterns on polymer substrates has been given increasing attention because of its wide and important applications in many fields. This paper reported a selective metallization technology on ordinary polymer substrates basing on laser direct activation of copper hydroxyl phosphate [Cu2(OH)PO4] and electroless deposition of copper. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the interaction mechanism between nanosecond-pulsed fiber laser (1064 nm wavelength) and Cu2(OH)PO4. It was found that after laser modification and activation by appropriate parameters, the special surface microstructure (e.g., porous sponge-like) appeared and explained the good adhesion strength (the highest grade of 5B) between the copper layer and substrate. At the same time, Cu+ was generated from the Cu2(OH)PO4, adsorbed on the microstructure, and acted as catalytic active centers to realize the selective copper deposition in the laser-activated zone. In addition, the copper layer possessed good selectivity (< 3% error of line space and width) and electrical conductivity (10−6 Ω·cm volume electrical resistivity). By comparison with laser direct structuring (LDS) technology and with palladium chloride as laser sensitive material, this was a more universal and less-cost technical pathway to fabricate planar and/or three dimensional (3D) metallic patterns on more kinds of ordinary polymer substrates.

Nanosecond pulse fiber laser patterning of bilayer molybdenum thin film on 2-sq inch soda-lime glass substrate for CIGS thin film solar cell applications

Nanosecond pulse fiber laser patterning of bilayer molybdenum thin film on 2-sq inch soda-lime glass substrate for CIGS thin film solar cell applications

Laser fabrication and evaluation of holographic intrinsic physical unclonable functions

Optical Physical Unclonable Functions (PUFs) are well established as the most powerful anticounterfeiting tool. Despite the merits of optical PUFs, widespread use is hindered by existing implementations that are complicated and expensive. On top, the overwhelming majority of optical PUFs refer to extrinsic implementations. Here we overcome these limitations to demonstrate for the first time strong intrinsic optical PUFs with exceptional security characteristics. In doing so, we use Computer-Generated Holograms (CGHs) as optical, intrinsic, and image-based PUFs. The required randomness is offered by the non-deterministic fabrication process achieved with industrial friendly, nanosecond pulsed fiber lasers. Adding to simplicity and low cost, the digital fingerprint is derived by a setup which is designed to be adjustable in a production line. In addition, we propose a novel signature encoding and authentication mechanism that exploits manifold learning techniques to efficiently differentiate data reconstruction-related variation from counterfeit attacks. The proposed method is applied experimentally on silver plates. The robustness of the fabricated intrinsic optical PUFs is evaluated over time. The results have shown exceptional values for robustness and a probability of cloning up to 10^{-14}, which exceeds the standard acceptance rate in security applications.

Superhydrophobic graphene/ceramic templates for the preparation of particulate drugs

This paper proposes the use of superhydrophobic graphene/ceramic templates fabricated through laser texturing and patterning for the preparation of particulate drugs. A nanosecond pulse fiber laser was used to texture a graphene film coated on ceramic substrates for obtaining a superhydrophobic surface. Then, laser patterning was conducted on the laser-textured surface to define the diameter of the prepared particulate drugs. Laser-textured graphene/ceramic substrates with a laser areal fluence of 17.51 J/cm 2 and a hatch distance of 0.01 mm exhibited a maximum water contact angle of 151.5°. This result was obtained because the laser-textured graphene films contained coral reef structures with nanoscale pores. Raman analyses indicated that the intensities of the G and 2D bands gradually decreased after the laser texturing and patterning processes. Moreover, the sheet resistance of the laser-textured and laser-patterned graphene films was larger than that of untextured ones because the thickness of the graphene films was reduced through laser thinning. The maximum heating temperature of the graphene-based heater was 140 °C for an input direct current voltage of 36 V. In addition, graphene-based self-heating devices were developed and successfully used to dry liquid roflumilast.

Enhancing laser-based contacting of aluminum current collector foils for the production of lithium-ion batteries using a nanosecond pulsed fiber laser

Cost reduction is a major aim for innovations in lithium-ion battery production. A promising approach to meet the high economic requirements is using high-speed manufacturing technologies like laser beam welding. This process can be applied to electrically connect the pre-stacked electrode sheets at the uncoated part of the current collectors. However, laser beam welding of the aluminum current collector foils is particularly challenging due to emerging seam defects such as cracks.In order to eliminate cracks occurring between the seam and the base material, this paper presents investigations on joining aluminum foil stacks using a nanosecond pulsed laser. Forty aluminum foils were welded with an arrester tab in a lap joint. This work examined the influence of several process parameters on the seam characteristics. A detachment of the seam from the foils was prevented, and promising results regarding the mechanical and electrical seam properties were achieved.

Unconventional milling of zirconia-based bioceramic material with nanosecond pulsed laser

Fabrication of dental restorations made of zirconia-based biomaterials with enhanced mechanical and tribological properties together with customized surface topography and microstructure for promoting enamel adhesion and cell proliferation while hindering bacterial spreading is a very challenging task to accomplish through conventional machining operations. In fact, traditional milling processes of sintered ceramics are typically labor-intensive, therefore expensive and time-consuming, and these aspects can be further exasperated when microsized features are required. On the other hand, unconventional techniques such as laser milling can represent a suitable solution to produce miniaturized individualized structures on advanced ceramics since it is a non-contact thermal process that ensures the elimination of cutting forces and allows hard and brittle materials to be machined without the need for special equipment which requires high investments and long processing times. In this context, this study aims to investigate the capability of a nanosecond pulsed fiber laser to machine samples made of yttria-stabilized zirconia through a systematic experimental approach in order to identify the most suitable process operational parameters combinations that ensure the obtainment of specific surface topographies while minimizing the machining time. The milling process is carried out by using a 30 W Q-switched Yb:YAG fiber laser by controlling laser beam scan speed, scan strategy and hatch distance and following a multi-level factorial design-based experimentation. The adoption of the laser technology to machine yttria-stabilized zirconia results in a high-repeatable, accurate and time-saving process allowing easy control of the process outcomes.

Laser micro welding with fiber lasers for battery and fuel cell based electromobility

New challenges are arising within the joining processes in the field of electromobility. Joining highly reflective metals and dissimilar materials such as copper and aluminum – often encountered in battery electrical vehicles – is viewed as a challenging task. Additionally, the use of thin sheets of stainless steel is gaining importance in applications with PEM fuel cells, where the welding length is sometimes up to and even more than five meters long, yet the process speed remains limited.Laser micro welding offers in comparison to conventional joining methods several advantages regarding process speed, parts accessibility, potential of automation, and particularly localized heat input. There are different types of lasers available on the market ranging from the visible to the infrared range, yet choosing the right laser depending on the task can be challenging. Several characteristics are considered when comparing weld quality such as surface finish, reproducibility and mechanical stability. Recently, the possibility of tuning the parameters of a nanosecond pulsed fiber laser to achieve welding is being examined. On another topic, using a novel welding strategy with spatial power modulation – by applying a new geometry – is also being investigated. In this paper, the welding process with the nanosecond pulsed fiber laser is evaluated based on mechanical stability and surface finish, which allows further insight into the suitability of such a method for welding particularly copper and aluminum materials. Additionally, some initial results from the here introduced spatial power modulation technique – used to weld stainless steel sheets – are presented.

Laser-assisted removal of weld heat tints from stainless steel surface

The heat generated during the welding of stainless steel results in the oxidation of the surface that, apart from aesthetics, adversely affects its corrosion property too. This communication reports the successful removal of heat tint generated by the gas tungsten arc welding process off a stainless steel surface in addition to an improvement in its pitting corrosion resistance by exposure to the emission of a nanosecond pulsed fiber laser. The laser cleaning experiments, conducted with six different laser pulses having different temporal shapes and duration that varied from 20 to 1020 ns, revealed that removal of the weld heat tint was possible in all conditions provided the effective laser fluence exceeded a definite threshold value. This threshold value, in turn, was found to increase with an increase in pulse duration. The laser cleaned specimens were subsequently analyzed for surface morphology, roughness, and pitting corrosion resistance. The pitting corrosion resistance of the laser-treated specimens was compared with the as-welded specimens and welded specimens with heat tint removed using conventional methods like wire brush cleaning and chemical pickling. The superior quality of tint removal, improved pitting corrosion resistance, and the ease of noncontact operation indicates the significant potential of the fiber laser-based weld tint removal method to substitute the conventional mechanical or chemical cleaning methods currently in use in the manufacturing industry.

Reducing scatter in bent angle by a laser shock peening pretreatment

Laser shock peening is a surface treatment technology, which modifies the residual stress state of metal parts. When forming thin sheet metal parts with thicknesses ≤1 mm, locally varying residual stress states are, according to the literature, the main reason for the scatter in the bent angle. Forming processes, such as bending, are often used to manufacture thin sheet metal. Thin sheets are formed in quantities of several hundreds of millions per year. Even scrap rates that are in the ppm range, caused by the scatter in the bent angle, lead to considerable manufacturing costs. To ensure a robust forming process, it is hypothesized that the laser shock peening process can reproducibly change the residual stress state in thin sheet metal parts in such a way that scatter in the bent angle can substantially be reduced. Annealed and 1 mm thick sheet metal made of X5CrNi18-10 were processed with a nanosecond pulsed fiber laser. The influence of laser peening without coating (LPwC) on the bent angle was investigated using bottom bending with a nominal bending angle of 90°. It was revealed that the standard deviation of the bent angle, i.e., the scatter, is reduced by a factor of 2 from ±0.14° down to ±0.07° compared to the initial sheet state. Hence, the possibility to use LPwC as a pretreatment to decrease the scatter in the bent angle for thin sheets is demonstrated.

Study on Laser Decontamination Technology for Metal Scraps with Radioactively Contaminated Surfaces

In order to apply the laser decontamination technology to the clearance or recycling of metal scraps with radioactively contaminated surfaces, this study builds a laser decontamination experimental setup based on the 350 W nanosecond pulsed fiber laser. Then, this study conducts a series of experiments for the key parameters of the laser ablation and decontamination technology, including laser power, pulse duration, frequency, line spacing and scanning speed. According to these experimental results, the rule and the optimum parameters corresponding to different decontamination depths for the laser decontamination technology are obtained. This study in turn conducts verification test of this technology by applying it to the storage rack baseplate of the control rod pool for a nuclear power plant (NPP). The test results show that after the laser decontamination technology is used and the decontamination depth reaches 10 μm, the contamination level of the surface radioactively contaminated by β rays of the sample is reduced to less than 0.8 Bq/cm2, and can meet the clearance level.

On the seam welding of ultra-thin commercially pure (CP) grade-2 titanium foils

ABSTRACT This communication reports a comparative study on the seam welding of CP grade-2 Ti foils with thicknesses of 10 µm, 50 µm and 100 µm using a repetitive nanosecond pulsed fibre laser and a lamp-pumped pulsed Nd-YAG laser. The welding was accomplished in a lap joint configuration. A fine acicular microstructure was observed in the welds made by the nano second fibre laser, whilst a coarse basket weave microstructure was observed in the welds made by the Nd-YAG laser. The tensile properties of the welds carried out by the nano-second fibre laser was found to be superior with respect to the welds carried out by the pulsed Nd-YAG laser. Welds made by the nano-second fibre laser could withstand ~17% more load, whereas elongation before fracture was almost double to that of the welds made by the Nd-YAG laser. This variation is comprehensible on the basis of the finer weld microstructure evolved in nanosecond laser welding due to the very low heat input and high cooling rate associated with this process. This study established with certitude that nanosecond duration pulsed fibre lasers are a better choice for welding thin titanium foils in comparison to long pulsed Nd-YAG lasers.

Tribodynamic studies of textured gearsets lubricated with fresh and MoS2 blended greases

The synergistic effects of surface texture and Molybdenum disulphide (MoS2) blended grease have been explored on the tribodynamic performance of spur gearsets. A texture involving ellipsoidal dimples on the face and flank of pinions’ teeth was fabricated using nanosecond pulsed fiber laser. The experiments were performed at different applied torques and a pitch line velocity of 4 m/s keeping in mind the practical application of the results. Contact resistance, vibrations, temperature rise and surface topographies have been measured and analyzed. Substantial increase (about 300%) in contact resistance and reduction (40% approximately) in vibration amplitudes at gear mesh frequency were found in the presence of texture. Reduction in interfacial temperature rise and less damage to teeth surface were also observed.

High-power single-frequency pulsed fiber MOPA via SPM suppression based on a triangular pulse

In this work, we demonstrate a high-power single-frequency nanosecond fiber master oscillator power amplifier (MOPA) at 1 μm with near transform-limited narrow spectral linewidth. The seed laser pulses were shaped to triangle for the purpose of suppressing the linewidth broadening induced by self-phase modulation (SPM). A tapered Yb-doped active fiber was used to enhance the stimulated Brillouin scattering (SBS) threshold. A high peak power of 31.4 kW with a narrow linewidth of 63 MHz, which was near the transform limit of the 8-ns triangle-shaped pulse, was achieved at a pulse repetition frequency of 20 kHz. No evident pulse distortion was observed at high-power levels. The results show that the triangle-shaped pulse is a promising technique for high-power single-frequency nanosecond pulsed fiber lasers with narrow spectral linewidth.

Effect of Au-Coating on the Laser Spot Cutting on Spring Contact Probe (SCP) for Semi-Conductor Inspection.

Spring contact probes (SCPs) are used to make contact with various test points on printed circuit boards (PCBs), wire harnesses, and connectors. Moreover, they can consist of the test interface between the PCBs and the semiconductor devices. For mass production of SCPs, ultra-small precision components have been manufactured by conventional cutting methods. However, these cutting methods adversely affect the performance of components due to tool wear and extreme shear stress at the contact point. To solve this problem, laser spot cutting is applied to Au-coated SCP specimens as an alternative technique. A 20 W nano-second pulsed Ytterbium fiber laser is used, and the experimental variables are different laser parameters including the pulse duration and repetition rate. After the spot cutting experiments, the heat-affected zone (HAZ) and material removal zone (MRZ) formed by different total irradiated energy (Etotal) was observed by using a scanning electron microscope (SEM). Then, the size of HAZ, top and bottom parts of MRZ, and roundness were measured. Furthermore, the change rate of HAZ and MRZ on Au-coated and non-coated specimens was analyzed with regard to different pulse durations. Based on these results, the effect of Au-coating on the SCP was evaluated through the comparison with the non-coated specimen. Consequently, in the Au-coated specimen, hole penetration was observed at a low pulse duration and low total energy due to the higher thermal conductivity of Au. From this study, the applicability of laser spot cutting to Au-coated SCP is investigated.

A Comparative Study on the Wettability of Unstructured and Structured LiFePO4 with Nanosecond Pulsed Fiber Laser.

The wettability of electrodes increases the power and energy densities of the cells of lithium-ion batteries, which is vital to improving their electrochemical performance. Numerous studies in the past have attempted to explain the effect of electrolyte and calendering on wettability. In this work, the wettability behavior of structured and unstructured LiFePO4 electrodes was studied. Firstly, the wettability morphology of the structured electrode was analyzed, and the electrode geometry was quantified in terms of ablation top and bottom width, ablation depth, and aspect ratio. From the result of the geometry analysis, the minimum measured values of aspect ratio and ablation depth were used as structured electrodes. Laser structuring with pitch distances of 112 μm, 224 μm, and 448 μm was applied. Secondly, the wettability of the electrodes was measured mainly by total wetting time and electrolyte spreading area. This study demonstrates that the laser-based structuring of the electrode increases the electrochemically active surface area of the electrode. The electrode structured with 112 μm pitch distance exhibited the fastest wetting at a time of 13.5 s. However, the unstructured electrode exhibited full wetting at a time of 84 s.

Nanosecond pulsed fiber laser irradiation for enhanced zirconia crown adhesion: Morphological, chemical, thermal and mechanical analysis

The increasing demand for aesthetics, together with advancements in technology, have contributed to the rise in popularity of all-ceramic restorations. In the last two decades, the continuous progression in ceramic materials science for dental applications has permitted the fabrication of high-strength materials. Amongst these, zirconia-based ceramics have improved in terms of fracture resistance and long-term viability in comparison with other silica-based materials.Unfortunately, while bonding of resin cement–silica ceramics can be strengthened through creation of a porous surface by applying hydrofluoric acid (5%–9.5%) and a subsequent silane coupling agent, the glass-free polycrystalline microstructure of zirconia ceramics does not allow such a reaction.The aim of the present in vitro study was to observe the effect of 1070 nm fiber nanosecond pulse laser irradiation on zirconia samples through morphological analysis (profilometry, SEM), thermal recording with Fiber Bragg Gratings (FBGs), elemental composition analysis (EDX) and bond strength testing (mechanical tests) in order to evaluate the possible advantages of this kind of treatment on zirconia surfaces, as well as to show the potential side effects and changes in chemical composition.Despite laser irradiation with a 1070 nm wavelength fiber laser and correct process parameters demonstrating suitable outcomes in terms of improved surface roughness and minimal thermal damage, comparison between irradiated and unirradiated samples did not exhibit statistically significant differences in terms of bonding strength.

The quality improvement of laser rubber removal for laminated metal valves

This paper utilizes a nanosecond pulse fiber laser to conduct rubber removal experiments on rubber laminated metal valves. The influence on surface roughness, metallographic structure and hardness of samples before and after different laser cleaning conditions are analyzed. Experimental results show that the laser has no significant effect on the substrate situation of the rubber laminated valves when it is immersed in water or sprayed with water. Through thermal simulation, the surface temperature when using wet-type laser cleaning is lower than that of using dry-type laser cleaning, and there is no significant effect on the substrate. Therefore, wet-type laser cleaning is appropriate for rubber laminated metal valves.

A Study of Fiber Laser Micro-Grooving of 316L Stainless Steel at Different Temperatures

The present article deals with the generation of micro-grooves on 316L stainless steel (SS) by a nanosecond pulsed fiber laser system. Fabrication of micro-grooves on 316L SS has immensely contributed to the biomedical and automotive industries through improving the mechanical, lubrication, and corrosion resistance properties. In the present work, the considered process parameters are the preheating temperature (100°C and 200°C), along with the room temperature (24°C), cutting speed, sawing angle, pulse frequency, and laser power. The ranges of cutting speed and sawing angle are 0.1–1.1 mm s−1 and 0.1°–1°, respectively. Besides, pulse frequency and laser power vary from 55 kHz to 85 kHz and from 15 W to 45 W, respectively. The constant parameters are the pulse width of 99% and assist air pressure of 6 kgf cm−2. The variable parameters for the analysis are cut width and heat-affected zone (HAZ) width. The article aims to showcase a comprehensive study of fiber laser process parameters at different temperatures (preheated condition and room temperature) with variable sawing angles to produce better process control and bring about each considered process parameter’s critical value. The experimental results show that higher dimensions of cut width and HAZ width are observed at 200°C with the increment of sawing angle and laser power, compared to other temperatures. With the increment of cutting speed and laser power, the HAZ width tends to rise sharply. A significant drop in cut width and HAZ width dimensions is observed with the increment in pulse frequency for any temperature.

Process Optimization for 100 W Nanosecond Pulsed Fiber Laser Engraving of 316L Grade Stainless Steel

High average power (&gt;50 W) nanosecond pulsed fiber lasers are now routinely available owing to the demand for high throughput laser applications. However, in some applications, scale-up in average power has a detrimental effect on process quality due to laser-induced thermal accumulation in the workpiece. To understand the laser–material interactions in this power regime, and how best to optimize process performance and quality, we investigated the influence of laser parameters such as pulse duration, energy dose (i.e., total energy deposited per unit area), and pulse repetition frequency (PRF) on engraving 316L stainless steel. Two different laser beam scanning strategies, namely, sequential method (SM) and interlacing method (IM), were examined. For each set of parameters, the material removal rate (MRR) and average surface roughness (Sa) were measured using an Alicona 3D surface profilometer. A phenomenological model has been used to help identify the best combination of laser parameters for engraving. Specifically, this study has found that (i) the model serves as a quick way to streamline parameters for area engraving (ii) increasing the pulse duration and energy dose at certain PRF results in a high MRR, albeit with an associated increase in Sa, and (iii) the IM offers 84% reduction in surface roughness at a higher MRR compared to SM. Ultimately, high quality at high throughput engraving is demonstrated using optimized process parameters.