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

Laser processing of diamond has become an important technique for fabricating next generation microelectronic and quantum devices. However, the realization of low taper, high aspect ratio structures in diamond remains a challenge. We demonstrate the effects of pulse energy, pulse number and irradiation profile on the achievable aspect ratio with 532 nm nanosecond laser machining. Strong and gentle ablation regimes were observed using percussion hole drilling of type Ib HPHT diamond. Under percussion hole drilling a maximum aspect ratio of 22:1 was achieved with 10,000 pulses. To reach aspect ratios on average 40:1 and up to 66:1, rotary assisted drilling was employed using > 2 M pulse accumulations. We additionally demonstrate methods of obtaining 0.1° taper angles via ramped pulse energy machining in 10:1 aspect ratio tubes. Finally, effects of laser induced damage are studied using confocal Raman spectroscopy with observation of up to 36% increase in tensile strain following strong laser irradiation. However, we report that upon application of 600 °C heat treatment, induced strain is reduced by up to ~ 50% with considerable homogenization of observed strain.

High power ultrashort pulsed lasers are an ultimate manufacturing tool for a large variety of materials and provide outstanding properties for high precision manufacturing with almost no thermal effects and numerous new processing possibilities. However, using high power ultrashort pulsed lasers with high pulse repetition frequencies in the MHz region can cause thermal issues like overheating, melt generation and low ablation quality. High ablation quality only can be achieved, if all process parameters are carefully matched, which requires a deep understanding of the process, intensive simulation for selecting processing strategies and innovative system components. Beside ultra high speed scanning using polygon scanners the use of multiple laser beams provide the best and most versatile high power ablation solution. With switchable single beams using parallel acoustooptic and phase modulating beam steering systems together with diffractive optical beam splitter, high ablation rates can be achieved while maintaining the high processing quality. However, using multiple laser beams each single beam can influence the adjacent beam either by heat accumulation or by plasma and vapour emission. Distance of the single beams, pulse repetition frequency and scanning strategy have to be matched to the material and ablation geometry. With a careful adaption of all parameters highly accurate and fast processing can be achieved. With this approach a next step up to an all optical manufacturing system can be provided. DOI: 10.2961/jlmn.2019.02.0003 Keywords: ultrafast laser processing, multi beam processing, diffractive optical elements, beam splitting, high speed scanning, laser ablation, laser drilling, simulation

Commercial cutter blades are widely used as disposable industrial tools, generating large material consumption and waste. Extending blade lifetime through simple post-processing could therefore contribute to improved resource efficiency. In this study, we demonstrate the feasibility of improving the abrasion resistance of mass-produced cutter blades using underwater laser peening with a 5-ns pulsed laser. The cutting performance was quantitatively evaluated using a sharpness tester under constant load conditions. Compared with untreated blades, laser-processed blades exhibited an approximately twofold increase in the maximum cumulative cutting distance, although a slight reduction in initial sharpness was observed immediately after processing. Vickers hardness measurements showed an increase from approximately 600 HV0.5 to 820 HV0.5, indicating surface hardening induced by laser peening. The sharpness tester was found to provide a practical and reproducible metric for evaluating abrasion resistance in laser-processed cutting tools. Although the present study does not aim at systematic parameter optimization or detailed microstructural analysis, the results demonstrate the practical potential of underwater laser peening as a simple post-processing technique for extending blade lifetime and highlight the applicability of sharpness testing as a quantitative evaluation tool.

Materials processing with ultrashort laser pulses is one of the most important approaches when it comes to machining with very high accuracy. High pulse repetition rates and high average laser power can be used to attain high productivity. By tightly focusing the laser beam, the irradiances on the workpiece can exceed 1013 W/cm2, and thus cause usually unwanted X-ray emission. Pulsed laser processing of micro holes exhibits two typical features: a gradual increase in the irradiated surface within the hole and, with this, a decrease in the local irradiance. This and the shielding by the surrounding material diminishes the amount of ionizing radiation emitted from the process; therefore, both effects lead to a reduction in the potential X-ray exposure of an operator or any nearby person. The present study was performed to quantify this self-shielding of the X-ray emission from laser-drilled micro holes. Percussion drilling in standard air atmosphere was investigated using a laser with a wavelength of 800 nm a pulse duration of 1 ps, a repetition rate of 1 kHz, and with irradiances of up to 1.1·1014 W/cm. The X-ray emission was measured by means of a spectrometer. In addition to the experimental results, we present a model to predict the expected X-ray emission at different angles to the surface. These calculations are based on raytracing simulations to obtain the local irradiance, from which the local X-ray emission inside the holes can be calculated. It was found that the X-ray exposure measured in the surroundings strongly depends on the geometry of the hole and the measuring direction, as predicted by the theoretical model.

Laser processing with galvanometric scanners and servo platforms has been prosperous in the industry recently, and researches in this field have been evolved from step-and-scan methods to on-the-fly methods. However, the major on-the-fly methods only consider the high dynamic performance of the scanner and waste the characteristic of the scanner working area. This study proposes a new method that utilizes both above to improve efficiency conspicuously without loss of accuracy, aiming at continuous large-scale trajectories. In this method, the decomposed trajectories for the platform are derived from the target trajectories geometrically, and interpolation for the scanner trajectories is implemented through vector subtraction of positions. The experimental results with the given patterns indicate that the total processing time of the proposed method is shortened by 67.3% compared with the traditional step-and-scan method and 51.4% compared with the major on-the-fly method. Meanwhile, motion performance is better, fewer defects appear, and all detected errors satisfy the requirement. In conclusion, the proposed on-the-fly method combines efficiency and quality, thus perfectly suiting industrial laser processing applications.

Because of the high hardness, brittleness, and anisotropy of reaction-bonded silicon carbide composites (RB-SiC), it is challenging to process high-quality textures on their surfaces. With the advantages of high processing accuracy and low processing damage, femtosecond laser processing is the preferred technology for the precision processing of difficult-to-process materials. The present work used a femtosecond laser with a linear scanning path and a spot diameter of 18 µm to process microgrooves on RB-SiC. The influence of different processing parameters on the microgroove profile, dimensions, and ablation rate (AR) was investigated. The ablation width Wa and average ablation depth Da of microgrooves were evaluated, and the various patterns of varying processing parameters were obtained. A model for Wa prediction was developed based on the laser fluence within the finite length (FL). As a result, the experimental values were distributed near the prediction curve with a maximum error of 20.4%, showing an upward trend of gradually decreasing increments. For a single pass, the AR value was mainly determined by the laser energy, which could reach the scale of 106 μm3/s when the laser energy was greater than 50 μJ. For multiple passes, the AR value decreased as the number of passes increased and it finally stabilized. The above research will provide theoretical and experimental support for the high-quality and efficient processing of RB-SiC surface textures.

Many additive manufacturing technologies involve the deposition of particles onto a surface followed by selective, targeted, laser heating. This paper develops a modular computational framework which combines the various steps within this overall process. Specifically, the framework synthesizes the following: particle dynamics , which primarily entails: (a) the movement of the particles induced by contact with the surface, (b) particle-to-particle contact forces and (c) near-field interaction and external electromagnetic fields. laser-input , which primarily entails: (a) absorption of laser energy input and (b) beam interference (attenuation) from particles and particle thermodynamics, which primarily entails: (a) heat transfer between particles in contact by conduction and (b) subsequent thermal softening of the particles. Numerical examples are provided and extensions are also addressed for two advanced processing scenarios involving solid-liquid-gas phase transformations.

At present, the use of microstructure to change the optical properties and wetting properties of the material itself has become the main means to improve the utilization rate of materials in the manufacturing industry. Due to the hydrophilicity of the material surface can achieve underwater self-cleaning, directional transportation function, it becomes an indispensable part of surface modification. Water jet-guide laser processing can significantly reduce the formation of the heat-affected zone and crack, and can clearly ablate the material, with higher precision and resolution. In this experiment, the effects of scan spacing, laser output power and channel aspect ratio are examined and processing conditions for achieving near superhydrophilicity are provided. Owing to the anaerobic processing environment, the surface chemical composition of the material does not change, and the hydrophilicity is increased by 8% to 43% compared with that before. Increasing the aspect ratio can increase the wettability, when the aspect ratio is more than 1.63, the wettability begins to rebound, and the wettability becomes worse. Using small laser power and multiple scanning processing scheme can make the surface covered with tiny small pillars of micro-nano particles layer beneficial to increase the droplet adhesion, and the minimum contact angle can reach 37.2°.

In recent years, superhydrophobic surfaces have attracted significant attention due to their promising applications, especially in ice prevention, reduction in air resistance, and self-cleaning. This study utilizes femtosecond laser processing technology to prepare different surface microstructures on polytetrafluoroethylene (PTFE) surfaces. Through experiments, it investigates the relationship between the solid–liquid contact ratio and surface hydrophobicity. The shape of water droplets on different microstructure surfaces is simulated using ANSYS, and the relationship between surface microstructures and hydrophobicity is explored in the theoretical model. A superhydrophobic surface with a contact angle of up to 166° was obtained by machining grooves with different spacings in polytetrafluoroethylene sheets with femtosecond laser technology. Due to the micro- and nanostructures on the surface, the oleophobicity of the processed oleophilic PTFE surface is enhanced.