Laser Manufacturing Research Articles

Development workflow based on in situ synchrotron investigations to optimize laser processing of copper pins

To design future laser manufacturing processes for welding of copper materials, more and more high-end analysis methods are required. A fundamental process understanding by analyzing cause-and-effect relations of process dynamics using inline in situ diagnostics allows for an improved description of laser material interaction. Strategies for a reliable and robust welding process are derived from the findings. In this study, a four-step advanced methodical approach is presented and discussed. In the first step, a fundamental process description of the geometry of the vapor capillary and the formation of weld defects is developed. Therefore, welds on electrolytic tough pitch copper (Cu-ETP) and CuSn6 are carried out to analyze the temporal and spatial vapor capillary dynamics depending on laser power, welding speed, and focal diameter. This fundamental process understanding is transferred to the welding of copper pins in the form of I-pins. For this purpose, impurities and imperfections were applied to the pin surface to investigate the effects on the process result. As a third step, strategies by means of laser intensity distributions were adapted to compensate for imperfections in the welding process. Finally, a sensor vision system is adapted for ideal welding results. Investigations are based on in situ synchrotron analysis at Petra III, DESY in Hamburg. For the experiments, a TRUMPF TruDisk laser (100/400 μm fiber diameter), a TRUMPF TruFiber 6000P (50/100 μm fiber diameter), and a single-mode fiber laser (14 μm fiber diameter) were used. The focal diameter was adjusted with the optical system depending on the investigation.

Thermal analysis of laser fabricated new composite brake drums in each orientation

In this study, a Fe-based alloy material was fabricated by laser on the inner shell of a brake drum. The thermal conductivity of the composite brake drum was analyzed and discussed by conducting experiments on the shell nodular cast iron substrate, laser manufacturing materials, and their composites, as well as different heat transfer directions of laser manufacturing materials. At 500 °C, the thermal conductivity of the matrix was 21.434 W/(m·K), the Fe-base alloy was 15.271 W/(m·K), and the composite sample was 17.442 W/(m·K), which was close to the average value of the two. The grain characteristics and microstructure of the alloy were different in different directions. The thermal conductivities of the samples in the x-, y-, and z-directions were 17.047 W/(m·K), 16.665 W/(m·K), and 15.271 W/(m·K), respectively; the diffusion was slower in the z direction and fastest in the x direction.

An in-situ hybrid laser-induced integrated sensor system with antioxidative copper

Integration of sensors with engineering thermoplastics allows to track their health and surrounding stimuli. As one of vital backbones to construct sensor systems, copper (Cu) is highly conductive and cost-effective, yet tends to easily oxidize during and after processing. Herein, an in-situ integrated sensor system on engineering thermoplastics via hybrid laser direct writing is proposed, which primarily consists of laser-passivated functional Cu interconnects and laser-induced carbon-based sensors. Through a one-step photothermal treatment, the resulting functional Cu interconnects after reductive sintering and passivation are capable of resisting long-term oxidation failure at high temperatures (up to 170 °C) without additional encapsulations. Interfacing with signal processing units, such an all-in-one system is applied for long-term and real-time temperature monitoring. This integrated sensor system with facile laser manufacturing strategies holds potentials for health monitoring and fault diagnosis of advanced equipment such as aircrafts, automobiles, high-speed trains, and medical devices.

Highly Efficient Laser Bidirectional Graphene Printing: Integration of Synthesis, Transfer and Patterning.

Graphene has tremendous potential in future electronics due to its superior force, electrical, and thermal properties. However, the development of graphene devices is limited by its complex, high-cost, and low-efficiency preparation process. This study proposes a novel laser bidirectional graphene printing (LBGP) process for the large-scale preparation of patterned graphene films. In LBGP, a sandwich sample composed of a thermoplastic elastomer (TPE) substrate, carbon precursor powder, and a glass cover is irradiated by a nanosecond pulsed laser. The laser photothermal effect converts the carbon precursor into graphene, with partial graphene sheets deposited directly on the TPE substrate and the remaining transferred to the glass cover via a laser-induced plasma plume. This method simultaneously prepares two face-to-face graphene films in a single laser irradiation, integrating synthesis, transfer, and patterning. The resulting graphene patterns demonstrate good performance in flexible pressure sensing and Joule heating, showcasing high sensitivity (7.7kPa-1), fast response (37ms), and good cycling stability (2000 cycles) for sensors, and high heating rate (1°Cs-1) and long-term stability (3000s) for heaters. It is believed that the simple, low-cost, and efficient LBGP process can promote the development of graphene electronics and laser manufacturing processes.

Portable Flexible Spherical Origami Joule‐Heaters with Aerogel

AbstractTrending portable smart devices are providing great convenience to the daily life. Thermal conductivity is efficient for contact heat transfer. Unfortunately, existing rigid surfaces can hardly heat objects in arbitrary shapes. Herein, a flexible origami‐structure heater fabricated by scalable laser manufacturing with temperature feedback control is proposed. The thin film origami heater is designed as a pair of semispherical origami patterns, which can conform to the curved surface of food samples more effectively. Therefore, the heat conducting area is increased to generate a fast and even heating profile to the surface of the food samples. The outer aerogel provides high thermal insulation to prevent heat dissipation in the environment. As proof of concept, the heating device can cook quail eggs within 3 minutes at a constant temperature of 100 °C. The power consumption of this heater is as low as 18 W, which standard portable chargers can power. This work significantly promotes the usability of portable heaters for cooking spherical objects, providing more conveniences during outdoor hiking and even in outer space where water‐boiling is impossible without atmosphere and gravity.

In-situ investigation of laser interaction with AlMg5 and Ti6Al4V alloys using spectroscopy and high-speed imaging for laser manufacturing

In-situ investigation of laser interaction with AlMg5 and Ti6Al4V alloys using spectroscopy and high-speed imaging for laser manufacturing

Implementation of energy interaction between laser beam and keyhole wall based on algebraically reconstructing free surface: An experimentally validated numerical framework

The interaction of the laser beam with the material is critical for determining laser processing quality, with ray tracing methods mostly used in energy transfer research. These techniques generally rely on only the volume of fluid (VOF) method or level set (LS) function to track the molten pool free surface, resulting in either accuracy loss or difficulty in ensuring mass conservation of the interface. The few coupled algorithms are built on geometric notions that are difficult to understand while being limited to structural grids. In this paper, we have proposed a revised ray tracing framework, so-called ARCLS, to derive the exact intersections of the rays with the keyhole wall which is represented by a continuous LS surface algebraically rebuilt on top of the VOF interface. It is easy to code and convenient for unstructured meshes. This framework is tested through a V-groove case and a set of Ti6Al4V titanium alloy laser welding examples. The findings reveal that the reconstructed LS surface perfectly matches the VOF interface, and the predicted molten pool profile agrees with the actual data well. The keyhole morphology and molten flow patterns are also consistent with the physical truths. Spattering, porosity, necking, and swelling are observed in the developing keyhole, which are the possible reasons for the potential welding defects. Further investigation suggested that the ARCLS-based algorithm collected more laser rays at the keyhole bottom compared to the standard technique, achieving a deeper keyhole profile and a reflection pattern that was more optically logical. The work presents a reliable approach for estimating laser energy distribution, which can be effectively applied to the heat-fluid coupling simulation for laser manufacturing processes in order to forecast the dynamic behaviors of keyhole and molten pool.

Janus Flexible Device with Microcone Channels for Sampling and Analysis of Biological Microfluidics.

Controlling the spontaneous directional transport of droplets plays an important role in the application of microchemical reactions and microdroplet detection. Although the relevant technologies have been widely studied, the existing spontaneous droplet transport strategies still face problems of complex structure, single function, and poor flexibility. Inspired by the spontaneous droplet transport strategy in nature, an asymmetric wettability surface with microcone channels (AWS-MC) is prepared on a flexible fabric by combining surface modification and femtosecond laser manufacturing technology. On this surface, the capillary force and Laplace pressure induced by the wettability gradient and the geometric structure gradient drive the droplet transport from the hydrophobic surface to the hydrophilic surface. Notably, droplets in adjacent hydrophilic regions do not exchange substances even if the gap in the hydrophilic region is only 1 mm, which provides an ideal platform for numerous detections by a single drop. The droplet transport strategy does not require external energy and can adapt to the manipulation of various droplet types. Application of this surface in the blood of organisms is demonstrated. This work provides an effective method for microdroplet-directed self-transport and microdroplet detection.

Multifunctional laser-induced graphene circuits and laser-printed nanomaterials toward non-invasive human kidney function monitoring

Faced with the increasing prevalence of chronic kidney disease (CKD), portable monitoring of CKD-related biomarkers such as potassium ion (K+), creatinine (Cre), and lactic acid (Lac) levels in sweat has shown tremendous potential for early diagnosis. However, a rapidly manufacturable portable device integrating multiple CKD-related biomarker sensors for ease of sweat testing use has yet to be reported. Here, a portable electrochemical sensor integrated with multifunctional laser-induced graphene (LIG) circuits and laser-printed nanomaterials based working electrodes fabricated by fully automatic laser manufacturing is proposed for non-invasive human kidney function monitoring. The sensor comprises a two-electrode LIG circuit for K+ sensing, a three-electrode LIG circuit with a Kelvin compensating connection for Cre and Lac sensing, and a printed circuit board based portable electrochemical workstation. The working electrodes containing Cu and Cu2O nanoparticles fabricated by two-step laser printing show good sensitivity and selectivity toward Cre and Lac sensing. The sensor circuits are fabricated by generating a hydrophilic-hydrophobic interface on a patterned LIG through laser. This sensor recruited rapid laser manufacturing and integrated with multifunctional LIG circuits and laser-printed nanomaterials based working electrodes, which is a potential kidney function monitoring solution for healthy people and kidney disease patients.

Beyond 99.5% Geometrical Fill Factor in Perovskite Solar Minimodules with Advanced Laser Structuring

AbstractPerovskite solar cells, known for high efficiency and compatibility with various photovoltaic (PV) applications, have garnered significant attention from academia and industry. Scaling up these cells conventionally involves fabricating modules with series‐connected cells using a monolithic interconnection based on the P1‐P2‐P3 scheme, a common approach for thin‐film PV modules. The Geometrical Fill Factor (GFF), representing the ratio between active area and aperture area, typically ranges from 90% to 95%. This study introduces an advanced laser manufacturing process to minimize interconnection area by reducing scribe width and minimizing distances between them, achieving an interconnection width of 45 µm with a GFF of 99.1%. Additionally, a discontinuous P2 design further reduces the dead area to an average of 19.5 µm, resulting in a record GFF of 99.6%. Using this interconnection in a highly efficient p‐i‐n stack, the study demonstrates the feasibility of the discontinuous P2 by fabricating 2.6 cm2 minimodules with an aperture area efficiency of 20.7%. The research highlights how proper design can minimize intrinsic losses during the scaling process from cell to module to a negligible level. Experimental studies, coupled with cell‐to‐module loss simulations and electroluminescence mapping for layer deposition uniformity, provide insights into the potential of the new P2 design.

Deep learning-based prediction of thermal residual stress and melt pool characteristics in laser-irradiated carbon steel

Residual stress is a crucial factor that must be managed in laser manufacturing processes. Neglecting it can result in product failure or unsuitability for the intended use. In this article, we present the first surrogate deep learning model based on generative adversarial network that predicts thermal residual stress and melt pool characteristics on the cross-section of laser-irradiated carbon steel. The model was trained using simulation data obtained from the unified momentum equation approach-based numerical model. Our model was designed to predict various aspects of the laser melting process only from three scalar inputs of laser power, beam diameter, and irradiation time at two different points in time (immediately after the laser heating is finished and when the steel is completely cooled down) and successfully predicted the distributions of 12 variables, including residual stress and temperature. Prediction results were not only qualitatively very similar to their ground truth, but also quantitatively accurate with the R2 values ranging from 0.975 to 0.999 and the mean absolute errors between 0.0015 and 0.0126. We demonstrated that complex experiments can be quickly performed using the surrogate model because a single deep learning prediction took only 0.13 s, compared to the 2.5–8 h numerical simulation times.

In situ preparation of nano cone-like structures on 3D printed titanium alloy implants via one-step femtosecond laser manufacturing for better osseointegration, anti-corrosion, and anti-fatigue

The poor surface conditions and osseointegration capacity of 3D printed Ti6Al4V implants (3DPT) significantly influence their performance as orthopedic and dental implants. In this work, we creatively introduce a one-step femtosecond laser treatment to improve the surface conditions and osteointegration. The surface characterization, mechanical properties, corrosion resistance, and biological responses were investigated. These results found that femtosecond laser eliminated defects like embedded powders and superficial cracks while forming the nano cones-like structures surface on 3DPT, leading to enhanced osseointegration, anti-corrosion, and anti-fatigue performance. Molecular dynamics simulations revealed the ablation removal mechanism and the formation of nano cone-like structures. These findings were further supported by the in vivo studies, showing that the FS-treated implants had superior bone-implant contact and osseointegration. Hence, the one-step femtosecond laser method is regarded as a promising surface modification method for improving the functional performance of Ti-based orthopedic implants.

Highly Efficient Cash Sterilization with Ultrafast and Flexible Joule‐Heating Strategy by Laser Patterning

AbstractSince ancient times, humans have learned to use fire and other heating methods to fight against dangerous pathogens, like cooking raw food, sterilizing surgical tools, and disinfecting other pathogen transmission media. However, it remains difficult for current heating methods to achieve extremely fast and highly efficient sterilization simultaneously. Herein, an ultrafast and uniform heating‐based strategy with outstanding bactericidal performance is proposed. Ultra‐precise laser manufacturing is used to fabricate the Joule heater which can be rapidly heated to 90 °C in 5 s with less than 1 °C fluctuation in a large area by real‐time temperature feedback control. An over 98% bactericidal efficiency on S. aureus for 30 s and on E. coli for merely 5 s is shown. The heating strategy shows a 360 times faster acceleration compared to the commonly used steam sterilization from the suggested guidelines by the Centers for Disease Control and Prevention (CDC), indicating that high temperatures with short duration can effectively disinfect microorganisms. As a proof of concept, this heating strategy can be widely applied to sterilizing cash and various objects to help protect the public from bacteria in daily life.

Roll-to-Roll Manufacturing of Breathable Superhydrophobic Membranes.

Self-cleaning and anti-biofouling are both advantages for lotus-leaf-like superhydrophobic surfaces. Methods for creating superhydrophobicity, including chemical bonding low surface energy molecular fragments and constructing surface morphology with protrusions, micropores, and trapped micro airbags by traditional physical strategies, unfortunately, have encountered challenges. They often involve complex synthesis processes, stubborn chemical accumulation, brutal degradation, or infeasible calculation and imprecise modulation in fabricating hierarchical surface roughness. Here, a scalable method to prepare high-quality, breathable superhydrophobic membranes is proposed by developing a successive roll-to-roll laser manufacturing technique, which offers advantages over conventional fabrication approaches in enabling automatically large-scale production and ensuring cost-effectiveness. Nanosecond laser writing and femtosecond laser drilling produce surface microstructures and micropore arrays, respectively, endowing the membrane with superior antiwater capability with hierarchical microstructures forming a barrier and blocking water infiltration. The membrane's breathability is carefully optimized by tailoring micropore arrays to allow for the adequate passage of water vapor while maintaining superhydrophobicity. These membranes combine the benefits of anti-aqueous corrosive liquid behaviors, photothermal effects, thermoplastic properties, and stretchable performances as promising comprehensive materials in diverse scenes.

Combined Use of Acoustic Measurement Techniques with X-ray Imaging for Real-Time Observation of Laser-Based Manufacturing

Ensuring high-quality control in laser additive manufacturing and laser welding relies on the implementation of reliable and cost-effective real-time observation techniques. Real-time monitoring techniques play an important role in understanding critical physical phenomena, namely, melt pool dynamics and defect formation, during the manufacturing of components. This review aims to explore the integration of acoustic measurement techniques with X-ray imaging for studying these physical phenomena in laser manufacturing. A key aspect emphasized in this work is the importance of time synchronization for real-time observation using multiple sensors. X-ray imaging has proven to be a powerful tool for observing the dynamics of the melt pools and the formation of defects in real time. However, X-ray imaging has limitations in terms of accessibility which can be overcome through combination with other more-accessible measurement methods, such as acoustic emission spectroscopy. Furthermore, this combination simplifies the interpretation of acoustic data, which can be complex in its own right. This combined approach, which has evolved in recent years, presents a promising strategy for understanding acoustic emission signals during laser processing. This work provides a comprehensive review of existing research efforts in this area.

Automatically Aligned and Environment-Friendly Twisted Stacking Terahertz Chiral Metasurface with Giant Circular Dichroism for Rapid Biosensing.

Chiral metasurfaces are capable of generating a huge superchiral field, which has great potential in optoelectronics and biosensing. However, the conventional fabrication process suffers greatly from time consumption, high cost, and difficult multilayer alignment, which hinder its commercial application. Herein, we propose a twisted stacking carbon-based terahertz (THz) chiral metasurface (TCM) based on laser-induced graphene (LIG) technology. By repeating a two-step process of sticking a polyimide film, followed by laser direct writing, the two layers of the TCM are aligned automatically in the fabrication. Laser manufacturing also brings such high processing speed that a TCM with a size of 15 × 15 mm can be prepared in 60 s. In addition, due to the greater dissipation of LIG than that of metals in the THz band, a giant circular dichroism (CD) of +99.5 to -99.6% is experimentally realized. The THz biosensing of bovine serum albumin enhanced by the proposed TCMs is then demonstrated. A wide sensing range (0.5-50 mg mL-1) and a good sensitivity [ΔCD: 2.09% (mg mL-1)-1, Δf: 0.0034 THz (mg mL-1)-1] are proved. This LIG-based TCM provides an environment-friendly platform for chiral research and has great application potential in rapid and low-cost commercial biosensing.

Digital precision in engineered ceramics: Tailoring toughness and flexibility through interlocking strategies

Precise material architectures and interfaces can render conventional ceramics tough, deformable and damage-resistant, offering a wide range of possibilities beyond those provided by conventional ones. This study explores the mechanical properties of topologically interlocked ceramic panels by systematically varying architectural parameters (i.e., interlocking angles and building block sizes) using a combination of experimental testing and finite element modeling based on COMSOL Multiphysics®. Three distinct designs were fabricated using digital laser manufacturing, categorized as designs with constant interlocking angles and tile sizes, constant interlocking angles and variable tile sizes, and variable interlocking angles and tile sizes and subjected them to out-of-plane quasi-static loads. The results show substantial enhancements in toughness (up to 110%) and strength (up to 120%) for ceramics with varying building block sizes, compared to those with constant block sizes. Additionally, these ceramics exhibit increased flexibility (up to 130%) compared to plain ceramics. Larger interlocking angles contribute to superior mechanical properties, fostering increased energy absorption and stability. The study also investigates post-failure behavior, revealing that increasing length ratios consistently augment the energy absorption. This research highlights the potential of these materials for flexible protection and the importance of controlling architectural parameters based on the interlocking angle and building block size to optimize performance while minimizing damage.

Analysis of self-supporting conformal cooling channels additively manufactured by hybrid directed energy deposition for IM tooling

Additive manufacturing (AM) of injection moulding (IM) tools has attracted significant interest in the polymer manufacturing industry for quite some time. However, hybrid manufacturing (HM) using directed energy deposition (DED), which involves concurrent additive and subtractive manufacture, has not been a commonly used process for IM tooling manufacture. This is apparent despite several advantages over the prevalent laser-powder bed fusion (L-PBF) alternative, including higher build rate, lower cost and integrated machining to directly achieve higher tolerances and surface finish. A key reason for this low utilisation is the limited ability of DED processes to produce circular channel profiles typically used in IM tooling, due to stricter constraints on the manufacturability of overhanging geometry. To address this, a range of self-supporting IM cooling channel profiles suited for hybrid laser and powder-based DED manufacture are proposed in this work. Numerical and experimental evaluations are conducted of the cooling performance of several non-circular conformal cooling channel (NCCC) profiles to identify a profile which achieves the maximum heat transfer for a constant cross-sectional area and coolant flow rate. Experimental studies included AM builds to evaluate the DED manufacturability of the selected NCCC profile on a conformally cooled HM benchmark model, followed by cooling performance characterisation, including a comparison against a reference L-PBF manufactured benchmark model. In conclusion, a shape correcting factor is obtained using response surfaces. This factor is used to convert thermal performance calculations for non-circular profiles to a conventional circular channel profile to simplify the DED manufacturing process for non-circular IM cooling channels.

Short review and prospective: chalcogenide glass mid-infrared fibre lasers

Rare-earth ion doped, silica glass, optical fibre amplifiers have transformed the world by enabling high speed communications and the Internet. Fibre lasers, based on rare-earth ion doped silica glass optical fibres, achieve high optical powers and are exploited in machining, sensing and medical surgery. However, the chemical structure of silica glass fibres limits the wavelength of laser operation to < 2.5 µm, which excludes the mid-infrared longer wavelength range of 3–50 µm. Rare-earth ion doping of fluoride glasses enables manufacture of fibre lasers up to a limiting 3.92 µm wavelength, but the fluoride glass chemical structure again prevents operation at longer wavelengths. Optical fibre lasers that are constructed from different rare-earth ion doped chalcogenide glass fibres will potentially operate across the 4–10 µm wavelength range, where suitable high-power lasers currently do not exist. We present a short review here of our recent work in achieving first time, continuous wave, mid-infrared fibre lasing beyond 5 μm wavelength in Ce3+-doped selenide chalcogenide fibre. We place this disruptive breakthrough into the wider fibre laser context, and also present the unprecedented advances in new cross-sector applications that will be enabled by mid-infrared fibre lasers in the 4–10 µm wavelength range. To surpass the few mW power output of the Ce3+-doped chalcogenide glass fibre lasing achieved to date, the glass quality of the doped chalcogenide fibres must now be improved, similar to the challenges originally facing the first glass fibre lasers based on silica.

Auto-focusing femtosecond laser manufacturing system via acoustic emission technology.

Auto-focusing technology in ultrafast laser processing, especially for non-planar structures, holds paramount importance. The existing methodologies predominantly rely on optical mechanisms, thereby being limited by the original system and material reflectivity. This work proposes an approach that utilizes laser-induced sound as a feedback signal for system control, thereby circumventing the need for optical system adjustments and facilitating almost real-time tracking. We established an ultrafast laser processing system augmented by acoustic emission technology, allowing for focus tracking on inclined planes. This system also exhibits the capability to generate diverse microscopic morphologies, including grooves and differently oriented laser-induced periodic surface structures (LIPSS), through the manipulation of the acoustic signal threshold. This method can be easily integrated into existing laser processing systems, offering new capabilities for curved surface processing, microstructure manufacturing, and transparent material processing.