Picosecond Laser Machining Research Articles

Fabrication of polycrystalline diamond micro-milling cutter with different grain sizes by picosecond laser

Polycrystalline diamond (PCD) is an excellent material for machining micro-tools due to its high hardness and wear resistance. However, the diameter of micro-milling tools is generally required to be less than 500 μm. When preparing micro-milling tools with a large aspect ratio, the processing load introduced by traditional grinding methods is easy to cause tool fracture. Therefore, a composite structure of carbide tool holder and diamond tool head is proposed in this paper. A technique of picosecond laser machining PCD micro-milling tool was studied, and the overall manufacturing process of tool blank preparation, nanosecond laser roughing and picosecond laser finishing was formed. A two-dimensional ablation mathematical model for tangential machining of PCD with a multi-pulse picosecond laser was established, and experiments verified the reliability of the mathematical model. In addition, the effects of picosecond laser pulse pitch, pulse energy, and track spacing on the surface quality of PCD materials with different particle sizes and cutting edge radius were studied by orthogonal experiments. The results showed that after picosecond laser processing, the surface roughness (Sa) of PCD with a particle size of 2 μm was the best, which can reach 0.33 μm, and the cutting edge radius of PCD micro-milling tool with a particle size of 25 μm was the smallest, which can get 1.67 μm. Using the optimized picosecond laser parameters, the high-sharpness single-edge micro-milling cutters with different particle sizes PCD with a diameter of 100 μm, aspect ratio greater than 3, and a cutting edge radius less than 3 μm were successfully fabricated.

Investigating surface integrity of laser-machined polycrystalline diamond using a 300 W picosecond laser

Polycrystalline diamond (PCD) is an important material in the tool industry due to its superior wear resistance and strength. Picosecond laser machining enables accurate cutting, geometric profiling, and precise dimensional features to be produced on PCD. The industrialisation of this manufacturing process necessitates the development of laser systems and process strategies that facilitate high throughput and quality. This paper investigates the feasibility of using a 300 W picosecond laser to machine PCD. It examines the influence of fluence, average power, pulse duration and number of passes on the material removal rate and surface quality. The surface integrity after machining is ascertained using a surface profilometer, optical microscopy and Raman spectroscopy. The results have shown that a high material removal rate of 33 mm3/min (0.11 mm3/min W) at a surface roughness of 2.3 μm is achievable using a fluence of 0.9 J/cm2 at 41.3 MHz and 300 W average power. Raman’s analysis of the machined sample suggests a laser-induced graphitisation which is prevalent at high pulse overlap, peak power, and the number of passes. Overall, the study strengthens the idea that with optimised process parameters, a balance is established between productivity and high surface integrity.

Investigation on the Coaxial-Annulus-Argon-Assisted Water-Jet-Guided Laser Machining of Hard-to-Process Materials.

In this study, the novel coaxial-annulus-argon-assisted (CAAA) atmosphere is proposed to enhance the machining capacity of the water-jet-guided laser (WJGL) when dealing with hard-to-process materials, including ceramic matrix composites (CMCs) and chemical-vapor-deposition (CVD) diamond. A theoretical model was developed to describe the two-phase flow of argon and the water jet. Simulations and experiments were conducted to analyze the influence of argon pressure on the working length of the WJGL beam, drainage circle size, and extreme scribing depth on ceramic matrix composite (CMC) substrates. A comparative experiment involving coaxial annulus and helical atmospheres revealed that the coaxial annulus atmosphere disrupts the water jet proactively, while effectively maintaining the core velocity within the confined working length and enhancing the processing capability of the WJGL beam. Single-point percussion drilling experiments were performed on a CMC substrate to evaluate the impact of machining parameters on hole morphology. The maximum depth-to-width ratio of the groove and depth-to-diameter ratio of the hole reached up to 41.2 and 40.7, respectively. The thorough holes produced by the CAAAWJGL demonstrate superior roundness and minimal thermal damage, such as fiber drawing and delamination. The average tensile strength and fatigue life of the CMCs specimens obtained through CAAAWJGL machining reached 212.6 MPa and 89,463.8 s, exhibiting higher machining efficiency and better mechanical properties compared to femtosecond (194.2 MPa; 72,680.2 s) and picosecond laser (198.6 MPa; 80,451.4 s) machining. Moreover, groove arrays with a depth-to-width ratio of 11.5, good perpendicularity, and minimal defects on a CVD diamond were fabricated to highlight the feasibility of the proposed machining technology.

Investigations on 355 nm picosecond laser machining of carbon fiber reinforced polymer composites

Carbon fiber reinforced polymer (CFRP) composites have emerged as excellent performance structural materials with a wide range of applications in the aerospace industry. Ultrafast laser is a promising and versatile tool for manufacturing these composites due to its advantages of high peak intensity and ultrashort pulse duration. Herein, a theoretical model based on the Fokker–Planck law and the two-temperature equation, i.e. the ultrafast responses of a two-dimensional heterogeneous material assembly of resin matrix padded with carbon fiber reinforced phase irradiation by 355 nm picosecond laser is established. The evolution of laser-excited free electron density is analyzed, and the relationship between the optical properties of substrate and electron density is revealed. The spatial and temporal distribution of electron and lattice temperatures are thus characterized. The ablation thresholds of resin and carbon fiber are determined, the accuracy of which are verified by experiments. On this basis, orthogonal experiments are conducted to analyze the influence law of process parameters on the ablation depth and heat affected zone (HAZ) width. Optimized parameter groups are discovered to realize the high-quality machining of CFRP composite with considerable depth-to-width ratio and limited HAZ width. This work offers new insight into the fundamental regimes and high-quality machining for picosecond laser manufacturing of CFRP composites.

Machine learning-driven process of alumina ceramics laser machining

Laser machining is a highly flexible non-contact manufacturing technique that has been employed widely across academia and industry. Due to nonlinear interactions between light and matter, simulation methods are extremely crucial, as they help enhance the machining quality by offering comprehension of the inter-relationships between the laser processing parameters. On the other hand, experimental processing parameter optimization recommends a systematic, and consequently time-consuming, investigation of the available processing parameter space. An intelligent strategy is to employ machine learning (ML) techniques to capture the relationship between picosecond laser machining parameters for finding proper parameter combinations to create the desired cuts on industrial-grade alumina ceramic with deep, smooth and defect-free patterns. Laser parameters such as beam amplitude and frequency, scanner passing speed and the number of passes over the surface, as well as the vertical distance of the scanner from the sample surface, are used for predicting the depth, top width, and bottom width of the engraved channels using ML models. Owing to the complex correlation between laser parameters, it is shown that Neural Networks (NN) are the most efficient in predicting the outputs. Equipped with an ML model that captures the interconnection between laser parameters and the engraved channel dimensions, one can predict the required input parameters to achieve a target channel geometry. This strategy significantly reduces the cost and effort of experimental laser machining during the development phase without compromising accuracy or performance. The developed techniques can be applied to a wide range of ceramic laser machining processes.

Picosecond pulsed laser machining of hardened martensitic stainless steel drive shaft

A fundamental method for estimating the laser parameters and for predicting the achievable ablation rate is demonstrated for hardened martensitic stainless steel X46Cr13. The laser ablation rate is evaluated for a range of pulse energies. The effective threshold fluence for ablation and the effective penetration depth are determined for a low and a high energy regime applying the Neuenschwander model. These parameters are used for numerical prediction of the ablated geometry. A very time efficient processing strategy and parameter set is selected and applied for laser machining of micro channels into a high precision drive shaft to increase friction for torque transmission leading to a processing time of 30 s per part, which corresponds to a structuring rate of 0.88 mms-1 . The deviation between the simulation and the ablated depth in the experiment are measured to be below 7 % at a total ablation depth of 25 µm. This demonstrates that the Neuenschwander model is suitable to determine the parameters needed for the prediction of the geometry resulting from an ablation process on martensitic stainless steel.

Picosecond laser machining of ceramic matrix composite

In recent years, there has been increased interest in using silicon carbide (SiC) based ceramic matrix composites (CMC) materials for aero-engine applications; however, both conventional and non-conventional machining of SiC CMC is challenging. Ultrashort pulse laser machining is evolving as an attractive option for materials like SiC CMC; however, the current understanding is based only on low-power lasers, whose removal rate is not in-line with the industrial requirements. This paper presents the results of 300 W picosecond laser machining of SiC CMC. The laser machining characteristics of SiC CMC were investigated at high average power and discussed in detail. A 300 W picosecond laser can be used to achieve a material removal rate of ∼230 mm3/min (0.76 mm3/minW) for a machining depth of 2 mm in SiC CMC, however, irrespective of the laser parameters a wall taper of ∼7° was observed over the sides of the slots that need to be addressed.

High-Throughput Picosecond Laser Machining of Aerospace Nickel Superalloy

This manuscript discusses the experimental results on 300 W picosecond laser machining of aerospace-grade nickel superalloy. The effect of the laser’s energetic and beam scanning parameters on the machining performance has been studied in detail. The machining performance has been investigated in terms of surface roughness, sub-surface thermal damage, and material removal rate. At optimal process conditions, a picosecond laser with an average power output of 300 W can be used to achieve a material removal rate (MRR) of ∼140 mm3/min, with thermal damage less than 20 µm. Shorter laser pulse widths increase the material removal rate and reduce the resultant surface roughness. High scanning speeds improve the picosecond laser machining performance. Edge wall taper of ∼10° was observed over all the picosecond laser machined slots. The investigation demonstrates that high-power picosecond lasers can be used for the macro-machining of industrial components at an acceptable speed and quality.

Two-step laser based surface treatments of laser metal deposition manufactured Ti6Al4V components

Surface treatment is required in additive manufacturing (AM) to improve the surface quality. However, laser polishing (LP) with a small molten zone cannot directly remove the surface waviness generated by laser metal deposition (LMD). In this study, a two-step surface treatment involving picosecond laser machining (PLM) and LP is presented to improve the surface quality of Ti6Al4V components fabricated by LMD. The effectiveness of PLM on the surface waviness removal is investigated by evaluating 3D surface topography and 2D surface profile under different processing parameters. The surface roughness improvement is mainly contributed by LP as compared to PLM. The surface quality can be greatly improved by the present two-step laser based treatment. The microstructure evolution in the present treatment is also investigated through experimental observation and thermal analysis based on finite element method.

Glass surface micromachining with simultaneous nanomaterial deposition by picosecond laser for wettability control

Glass surface micromachining with simultaneous redeposition of nanomaterials in the vicinity of machined microscale trenches is achieved using a picosecond laser of visible wavelength in ambient air. After investigating the spatial distribution of redeposited nanomaterials by a unit discrete laser micromachining line, multi-line patterns machined with variable interline separations are characterized using optical and scanning electron microscopes. For large interline separations, laser machined debris was redeposited in the form of web-like nanofibrous aggregates with significant spatial variation in density. Reduced separations improved spatial uniformity but the increased material density induced noticeable conversion from web-like nanofibrous to fractal-like nano-cauliflower structures. In this way, picosecond laser machining processes enabled a single-step fabrication of multi-hierarchical micro/nanostructures on arbitrary glass surface areas with tunable nanomaterial structures. Based on the wetting behavior on patterned surfaces in ambient air by using the patterned surfaces as Wilhelmy plates in force-displacement measurements and in-situ optical microscope inspection, we find that contact angle hysteresis is suppressed for surfaces patterned with sufficiently small line separations due to the water infusion in the deposited nanomaterials. The studied laser processing method can be potentially employed for fast and effective fabrication of liquid infused surfaces with complex microscale patterns combined with controllable nanofeatures.

Surface modeling and component analysis of picosecond laser ablation of CVD diamond

Chemical vapor deposition diamond (CVDD) has several advantages as micro mill material. Picosecond laser machining technology is promising method to machine CVDD, but there are multiple uncertainties. This study aims to optimize the irradiation of CVDD surface via controllable prediction of CVDD surface after picosecond laser irradiation. Based on theories of Gaussian pulse beam and picosecond laser ablation material, machined surface morphology model was developed to predict surface roughness Sa and removal depth of CVDD. Then, the effects of picosecond laser parameters on the morphology, roughness Sa, removal depth, and components of CVDD surface were analyzed. Results showed that the trend of changes in roughness and removal depth based on theoretical model was approximately the same as that in experimental machined surface, with average relative errors of roughness and removal depth of 9.6% and 16.6%, respectively. In addition, removal depth of CVDD surface decreased with the increase in scanning speed and filling pitch, and increased with the increase in average laser power. The variation in surface roughness Sa was the same as that of removal depth in terms of average laser power and scanning speed, while had a concave point at a filling pitch of 7.5 μm. A decrease in overlapping area of pulse spot can reduce the aggravation of sp2 hybrid amorphous carbon defects.

Investigation to Improve the Pool Boiling Heat Transfer Characteristics Using Laser-Textured Copper-Grooved Surfaces

Improving the performance of pool boiling with critical heat flux of pool boiling and enhancing the coefficient of heat transfer through surface modification technique have gained a lot of attention. These surface modifications can be done at different scales using various techniques. However, along with the performance improvement, the durability and stability of the surface modification are very crucial. Laser machining is an attractive option in this aspect and is gaining a lot of attention. In the present experimentation research work, pool boiling attributed performance of copper-grooved surfaces obtained through picosecond laser machining method is investigated. The performance of the modified surfaces was compared with the plain surface serving as reference. In this, three square grooved patterns with the same pitch (100 μm) and width (100 μm) but different depths (30, 70, and 100 μm) were investigated. Different depths were obtained by varying the scanning speed of the laser machine. In addition to the microchannel effect, the grain structuring during the laser machining process creates additional nucleation sites which has proven its effectiveness in improving the pool boiling performance. In all aspects, the pool boiling performance of the grooved laser-textured surface has showed increased surface characterisation as compared with the surface of copper.

Wettability Control of Copper Surface Using Picosecond Laser for Enhancing Condensation Heat Transfer

One of the most important and widely visualized process taking place in nature is condensation. Superhydrophobic surfaces, which facilitates dropwise condensation has been the principal area of research in the last decade or so. Fabrication of superhydrophobic surface can be achieved by either surface modification using mechanical process, surface treatment like coating or by the combination of both. But, the major drawback of coating is its durability and vulnerability. So, in this work we have fabricated a robust surface by means of picosecond laser machining. Apart from being a simple process, this method has an advantage of cutting down the surface fabrication time by several hours as compared to other methods like one-step immersion, electro-deposition, top-down fabrication method, etc. In our work three different work specimens irradiated with different laser power were studied for its surface morphologies by scanning electron microscope (SEM) images and its wettability was measured using contact angle meter. It is found that the wettability of surface changes with different laser power and hence it is possible to control the wettability by adjusting the laser parameters. Condensation experiment was carried out on these different surfaces and its performance was compared with plain surface.

Plasma Printing of an AISI316 Micro-Meshing Punch Array for Micro-Embossing onto Copper Plates

Packaging using thermoplastic molding for hollowed GaN chips were requested for a leak-proof micro-joining between plastic molds and copper-based substrates. The design and engineering of micro-textures is a key technology for putting leak-proof packaging into practice. In the present paper, a micro-meshing punch array was prepared using plasma-nitriding-assisted printing. Two-dimensional original patterns were screen-printed onto an AISI316 die substrate and plasma nitrided at 673 K for 14.4 ks (or 4 h). The unprinted surfaces were selectively nitrogen super-saturated to have more nitrogen content than 5 mass% and a higher hardness than 1200 HV. The printed surfaces were selectively sand blasted to fabricate the micro-meshing punch array for micro-embossing. A computer numerically controlled stamping system was utilized to describe the micro-embossing behavior onto copper substrates and to investigate how the micro-textures on the array was transcribed onto the copper. Reduction of takt time as well as flexibility in the micro-grooving were discussed with reference to the picosecond laser machining and mechanical milling processes.

Quantifying the uncertainty of picosecond pulsed laser ablation in sapphire

One of the most prevalent materials used in sensor technologies is silicon which suffers degradation in operating regimes that exceed 1000 °C unless the sensor is actively cooled. Substitution of silicon with sapphire in pressure sensors offers unique capabilities due to its high melting point and chemical inertness; however, these same properties present manufacturing challenges for micromachining sensor components. To overcome the manufacturing challenges, research has focused on picosecond laser machining. A series of picosecond pulsed laser experiments have been conducted and compared to both one-dimensional and three-dimensional modeling of the ablation process. Bayesian uncertainty analysis is used to quantify the parametric uncertainty and error propagation from continuum scale constitutive approximations that can be directly compared with laser ablation experiments. The one dimensional model calibration is found to provide accurate estimations of picosecond laser ablation of sapphire and it enables extrapolation to predict three dimensional ablation.

Fabricating ceramics with embedded microchannels using an integrated additive manufacturing and laser machining method

AbstractIn this paper, we demonstrate the feasibility of an innovative method to fabricate flexibly embedded microchannels in bulk ceramics of complex geometries. This innovative method is an integration of extrusion freeforming (EFF) and picosecond (PS) laser machining. The bulk ceramic green body of complex geometries was fabricated using the extrusion method. After one green layer was extruded, in‐plane microchannels with variable cross‐section sizes and aspect ratios were fabricated using a picosecond laser. After the microchannels were fabricated, a cover layer was extruded. The green state processed structures ceramics were pressurelessly sintered to a bulk density of ~94%. In this paper, sinuous channels, channel networks, and patterns have been demonstrated. Vertical channels can also be drilled using the picosecond laser layer‐by‐layer with uniform diameters. The wall between the neighboring channels can be as thin as ~60 μm without any observable defects after firing. With the correct paste rheology, the cover layer did not sag into the microchannels and the bonding between layers was excellent. We did not observe any debonding between layers. During extrusion, the gaps between the adjacent filaments can be eliminated by controlling the filament spacing and the distance between needle tip and substrate. After firing, microchannels did not distort or collapse. The laser can cut through multiple layers without damage to the bonding between layers. Due to the uniform shrinkage during pressureless sintering, the green shapes of the microchannels were well preserved.

Engineering of microstructures of protonic ceramics by a novel rapid laser reactive sintering for ceramic energy conversion devices

The solid state reactive sintering (SSRS) characteristic with the assistance of sintering aids (e.g., NiO) has been proven to be an effective method for achieving high-quality proton conducting oxide electrolytes at relatively low sintering temperatures (e.g., <1400 °C). In this work, instead of performing a long-term (e.g., >10 h) SSRS in a conventional high-temperature furnace, a novel rapid laser heating process was used to perform SSRS, which was named as rapid laser reactive sintering (RLRS). This RLRS method was confirmed to be able to sinter protonic ceramics with well-engineered microstructures within a short time (e.g., <10 s). Using the proton conducting oxides of BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb) and BaZr0.8Y0.2O3-δ (BZY20) as case study, the crack-free protonic ceramic parts of straight strips (~10 mm in length, ~1 mm in width, and 30–200 μm in thickness), spiral strips (~200 mm in length, ~1 mm in width, and 30–200 μm in thickness), and squared films (~4.5 mm in both length and width and 30–200 μm in thickness) were successfully fabricated by RLRS method. The sintered parts usually showed fully dense large-grained and highly porous regions, which can potentially serve as electrolytes and electrode scaffolds for single cells or half-cells. The X-ray diffraction results indicated that the pure perovskite structures were obtained for both BCZYYb and BZY20 by RLRS from inexpensive carbonates and single metal oxides. The preliminary electrochemical impedance measurement for the dense strips after removal of porous regions by picosecond laser machining showed a reasonable in-plane protonic conductivities. This new RLRS method demonstrated the feasibility and promise of the rapid additive manufacturing of hierarchical ceramic energy conversion devices.

Efficient and damage-free ultrashort pulsed laser cutting of polymer intraocular lens implants

Ophthalmic intraocular lenses are conventionally machined by diamond tools. A promising alternative approach is contour cutting by ultrashort pulsed laser micromachining. To improve process knowledge, a parametric study of picosecond and femtosecond laser machining of medical grade hydrophilic copolymers and PMMA is carried out. Material removal rates and machining quality with respect to main process parameters are determined. Reasons for chipping and formation of heat affected zones are identified and an optimized process strategy is derived. By choosing a defined pulse overlap, heat accumulation is kept minimal while increasing absorptivity through incubation avoids chipping.

Characterization and Modeling of K-Band Coplanar Waveguides Digitally Manufactured Using Pulsed Picosecond Laser Machining of Thick-Film Conductive Paste

Microdispensing of thick-film conductive paste has been demonstrated as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper frequency range of these lines is limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around $100~\mu \text{m}$ . In this paper, a picosecond Nd:YAG laser is used to machine slots in a 20–25- $\mu \text{m}$ -thick layer of silver paste (Dupont CB028) that is microdispensed on a Rogers RT5870 substrate, producing coplanar waveguide (CPW) transmission lines with 16– $20~\mu \text{m}$ -wide slots. It is shown that the laser solidifies an about 2- $\mu \text{m}$ -wide region of the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 to 30 MS/m, which represents a $100\times $ improvement when compared to the values obtained with the exclusive use of microdispensing. This paper demonstrates that a hybrid approach of additive manufacturing and laser machining enables the fabrication of higher frequency circuits (up to at least 40 GHz) with improved performance.

Character and mechanism of surface micromachining for C/SiC composites by ultrashort plus laser

ABSTRACTA new surface micromachining way of ultrashort plus laser for C/SiC composites with high quality and efficiency was demonstrated, including picosecond and femtosecond laser. Surface morphologies, element content and bonding states of C/SiC composites were analysed in detail after machined by picosecond and femtosecond laser power respectively. For femtosecond laser machining, the amount of nanoparticles increased with increasing laser power. At 20 and 50 mW, Si–C, C–C and Si–O bonds existed in nanoparticles, while Si–C bonds disappeared at 70 mW. For picosecond laser machining, cauliflower-like particles and periodic ripple with certain depth were formed distinctly. Furthermore, thermal ablation phenomenon occurred, and only Si–O bonds existed in particles due to the oxidation of the carbon fibres and SiC matrix. The results showed that femtosecond laser with low power was more suitable to the surface machining due to better machining quality and less machining damage compared with high power picosecond laser.