Laser Manufacturing Processes Research Articles

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.

Enhanced heat source modeling in particle-based laser manufacturing simulations with ray tracing

Particle-based spatial discretization methods such as smoothed particle hydrodynamics (SPH) possess suitability for the high-fidelity simulation of laser manufacturing processes due to their capability in treating complex free-surface and multiphase problems. In such simulations, laser heat source modeling remains a central concern as the mechanisms governing the material deformations and phase changes strongly depend on the input laser energy and its distribution details. Ray tracing (RT) is a realistic and accurate approach for high-fidelity heat source modeling that can capture surface heterogeneity and multiple reflections. However, RT heat source modeling for particle-based numerical methods faces additional challenges rooted in the lack of explicit surface representation, intensive computational efforts, and implementation complexities. This work addresses these issues by proposing an enhanced and efficient RT heat source model for particle-based laser manufacturing simulations with negligible computational overhead and without requiring background nodes or surface mesh reconstruction. After validating the RT heat source model versus analytical and experimental results, we assess its computational performance through two test cases, showing that the computing workload imposed by our RT model is between 0.1% and 25% of the total runtime in different SPH-based laser manufacturing simulations. With the achieved efficiency and robustness, it becomes convenient yet advantageous to simulate processes like laser drilling and laser powder bed fusion with precision far beyond the conventional approaches using volumetric heat sources.

Ultra-Fast Heating Process of Cu-Pd Bimetallic Nanoparticles Unraveled by Molecular Dynamics Simulation

This paper investigates the ultra-fast heating process of Cu-Pd bimetallic nanoparticles from an atomic-scale perspective, which is essential for laser manufacturing processes, such as laser cladding and selective laser melting. The behavior of high surface ratio nanoparticles during these processes is strongly influenced by their properties and the heating process, which is governed by atomic dynamics. Previous studies have mainly focused on the combination process in pure metallic nanoparticles under slow or isothermal heating, but this work demonstrates that the ultra-fast atomic dynamic process between bimetallic nanoparticles differs significantly. Specifically, in Cu-Pd nanoparticles, the combination process is primarily dependent on the surface atomic motion of the lower melting point particles rather than plastic deformation in the grain boundary between particles. Moreover, the ultra-fast heating process is size-dependent. For small nanoparticles, the atomic kinetics exhibit two different mechanisms depending on temperature: Low-temperature jointing is controlled by localized atomic rearrangement, while high-temperature coalition is governed by the atomic flow of surface atomic melting in the low-temperature melting particle. The combination mechanism is the same for large particles as it is for small particles at high temperatures. The findings of this study provide important insights into the behavior of bimetallic nanoparticles during ultra-fast heating and can inform the development of coat and lubricant.

Orthogonal dual-channel single-camera spectral imaging for online measurement of three-dimensional space–time evolution of temperature field in laser melt pool

Current temperature measurement technology in laser manufacturing cannot obtain the internal three-dimensional (3D) temperature distribution of the melt pool. Necessary information for laser-manufacturing process optimization is lacking, including the melt pool depth and depth-to-width ratio. We propose a method for 3D temperature measurement based on orthogonal dual-channel single-camera spectral imaging. The 3D temperature field distribution of the melt pool can be obtained by collecting projected radiation data from two perpendicular angles. Use of a single monochrome camera for spectral imaging at three wavelengths ensures excellent spatial and temporal consistency during measurements. To verify the feasibility of the method, we measured the 3D temperature field in a melt pool of 304 stainless steel irradiated by a Gaussian laser beam (continuous laser, 500 W) with different irradiation times. The results indicate that the temperature field exhibits an approximately axisymmetric distribution on each cross-section at different depths. The temperature is highest in the center and gradually decreases around it. As the depth increases, the high-temperature area (>1730 K) gradually becomes smaller, and the temperature of each cross-section decreases. The maximum temperature, depth, width, and depth-to-width ratio of the melt pool at different times were obtained from the measured 3D temperature distributions. With an irradiation time of 0–80 s, the maximum temperature of the melt pool exhibited three stages: rapid increase (20–2230 K), slow increase (2230–2280 K), and stabilization. The growth of the width and depth of the melt pool indicated a similar process, increasing rapidly at first and gradually slowing. The depth-to-width ratio decreased rapidly at first and gradually stabilized. The proposed method for 3D temperature measurement has potential use in laser manufacturing for process control and quality improvement.

Laser‐Based Micro/Nano‐Processing Techniques for Microscale LEDs and Full‐Color Displays

AbstractMicro light‐emitting diode (Micro‐LED) display is an emerging display technology thanks to its high brightness, fast switching speed, and low power consumption. The commercialization of this technique is being explored by developing advanced processing techniques on an industrial scale. Recent ground‐breaking advances in the manufacture of Micro‐LEDs are mainly based on powerful laser micro/nano‐processing techniques with the unique ability to fabricate materials, structures and devices with the advantages of non‐contacting processing, high efficiency, adjustable coverage from micro‐ to macroscale and the compatibility with organic and inorganic materials. This paper categorizes, reviews and analyzes the main challenges and technical solutions in the Micro‐LED displays by various laser manufacturing processes, covering chip dicing, geometry shaping, laser annealing, laser lift‐off (LLO), laser‐based Micro‐LED transfer, laser‐assist bonding (LAB) and laser repair. The fundamental principles of these techniques are discussed along with their basic mechanisms, followed by an exploration of the latest progress in the field. Finally, a detailed analysis of the advantages and disadvantages of these techniques is given, and the future research directions of laser techniques in Micro‐LED display are discussed.

Spatially modulated femtosecond laser direct ablation-based preparation of ultra-flexible multifunctional copper mesh electrodes and its application.

Multifunctional electrodes possess superior properties such as high photoelectric properties and high stability. Laser manufacturing process is one of the widely used method for electrode fabrication. However, the current multifunctional electrode laser manufacturing process suffers from low fabrication speed. Here, we report a high-efficiency laser digital patterning process to fabricate copper-based flexible transparent conducting electrodes. By using a spatially modulated, one single laser spot is modulated into an array of spots with equal intensity, and the fabrication speed can be improved by more than 20 times over the traditional single pulse processing. In addition, copper mesh electrodes with a high photoelectric property have been fabricated. A transparent touch screen panel and multifunctional windows are fabricated with transparent electrodes to demonstrate their use in vehicle defogging, portable heating, and wearable devices.

Keyhole-induced Porosity in Laser Manufacturing Processes: Formation Mechanism and Dependence on Scan Speed

Laser welding and laser-based powder-bed fusion additive manufacturing in the deep penetration (keyhole) mode are promising technologies for the synthesis of metal components. The significant potential of these technologies remains latent because of structural defects (porosity), which significantly degrade the structural integrity and performance of the end products. Practical strategies for reducing those defects are addressed through fundamental understanding of their formation. In this study, pore formation of hydrodynamic origin is investigated, including the dynamics and mechanisms of the formation based on the above mentioned technologies. The pore volume and frequency of pore appearance, depending on the amplitude and frequency of capillary vibrations, are considered. Physical analysis is performed to obtain the scanning velocity values for the maximum and zero amplitudes and the frequency of capillary waves. A comparison between calculated curves and experimental data confirms both the capillary origin of the pores and the estimated scanning speeds at which the parameters of the pores exhibit their maximum values or vanish. The results obtained may facilitate in the selection of the optimal scanning speed when designing a pore-free technology.

Laser Welding Multimodel Quality Forecast Method Based on Dynamic Geometric Features of the Molten Pool.

Laser welding quality forecast is highly significant during the laser manufacturing process. However, extracting the dynamic characteristics of the molten pool in the short laser welding process makes predicting of the welding quality in real time difficult. Accordingly, this study proposes a multimodel quality forecast (MMQF) method based on dynamic geometric features of molten pool to forecast the welding quality in real time. For extraction of geometric features of molten pool, an improved fully convolutional neural network is proposed to segment the collected dynamic molten pool images during the entire welding process. In addition, several dynamic geometric features of the molten pool are extracted by using the minimum enclosed rectangle algorithm with an evaluation of the performance by several statistical indexes. With regard to forecasting the welding quality, a nonlinear quadratic kernel logistic regression model is proposed by mapping the linear inseparable features to the high dimensional space. Experimental results show that the MMQF method can make an effective and stable forecast of welding quality. It performs well under small data and can satisfy the requirement of real-time forecast.

Crosstalk-Free, High-Resolution Pressure Sensor Arrays Enabled by High-Throughput Laser Manufacturing.

Simultaneously achieving high spatial resolution and low crosstalk interference has been a fundamental challenge for flexible pressure sensor arrays. Here the authors present a high-resolution flexible pressure sensor array fabricated through a two-step laser manufacturing process, where individual sensing pixels and their interconnects are sequentially defined by laser-induced graphenization and ablation to minimize crosstalk interferences. The geometry of the interconnects is optimized through theoretical modeling and experimental validation. Characterization results show that the new device design induces a remarkable reduction of the crosstalk coefficient, from -8.21 to -43.63 dB, of the 0.7 mm-resolution sensor arrays, and the crosstalk suppression is particularly beneficial for application scenarios involving pressure sensing on soft surfaces (e.g., human skin and organs). Applications of the sensor array in tactile pattern recognition and minimally-invasive cancer surgery are demonstrated.

An Effective Strengthening Strategy of Nano Carbide Precipitation and Cellular Microstructure Refinement in a Superalloy Fabricated by Selective Laser Melting Process

An effective strategy to strengthen a superalloy processed by selective laser melting (SLM) is proposed. The aim is to increase the yield strength of Inconel 718 fabricated by SLM to beyond 1400 MPa, which has never been achieved before. In this study, various NbC additions (0.0%, 0.5%, 1.0%, and 5.0% by weight) were added in the powder bed of Inconel 718, and two types of post-SLM heat treatments were investigated, i.e., solution heat treated plus aging (STA) and direct aging (DA). With NbC addition, smaller depth of melt pool and finer dendritic cells were obtained. Both STA and DA promoted the precipitations of γ′ and γ″. STA eliminated the cellular dendrites and induced grain growth while DA retained the as-built cellular dendrites, grain size, and nano-carbide from NbC addition, rendering a significant 326.2 MPa increase in yield strength. In this work, 0.5% NbC addition exhibited a record-high yield strength of 1461 MPa and ultimate tensile strength of 1575 MPa for Inconel 718 processed by laser manufacturing process according to literature data to-date.

Soft matter laser micro-texturing for friction reduction: An experimental investigation

Abstract In this paper, a femtosecond laser manufacturing process is effectively employed to produce a pattern of micro dimples on a fluoroelastomer. To quantify the microtexture tribological performance, two configurations are implemented: non-conformal and conformal contacts are tested on a pin-on-disk tribometer. Due to the reduced number of dimples engaged in the contact region, no significant friction enhancement is obtained in the non-conformal configuration. On the contrary, in the case of conformal contacts, outstanding outcomes in terms of friction reduction - up to 60% - can be achieved by a properly designed micro-texture. Such a result is obtained by improving the wear debris entrapment and the cavitation respectively at low and high speed, without increasing significantly the occurrence of flow eddies.

Minimum Quantity Lubrication in Fibre Laser Processing For Permanent Stents Manufacturing

Despite Bioresorbable Stents (BRS) are the main research line nowadays, permanent stent, both Bare Metal Stents (BMS) as Drug Eluting Stents (DES) will always be useful in some patient-specific cases. To produce permanent stents the current industrial technique is the Laser Micro Cutting. However, this technology produces some thermal damages which raise the manufacture cost. Most of the works done in the last decades have tried to reduce this damages adding traditional cooling techniques. This work aims to study the fibre laser micro cutting process of SS316 tubes assisted by Minimum Quantity Lubrication (MQL). The influence of pulse power, cutting speed, and quantity of coolant upon cutting quality was studied. Cut samples were analyzed by Optical Microscopy with Nikon SMZ – 745T attached to digital camera CT3 ProgRes and a Scanning Electron Microscopy Quanta 3D FEG. MQL has demonstrated an average reduction of the dross deposition area (43.3 %), recast layer (37.8 %), kerf width (7.1 %) and heat affected zone (7.46 %) becoming in an effective, economic, and ecologic technique to reduce the thermal damages in laser manufacturing process.

Tomographic Characterization of a Multifunctional Composite High-Impedance Surface

The performance of a multifunctional composite high-impedance surface (HIS) has been evaluated using the coherent Doppler tomography (CDT) and finite-impulse response (FIR) filtering techniques. A combination of embroidery and advanced laser manufacturing processes were used to fabricate the conformable multifunctional glass fiber reenforced polymer HIS. The CDT method was utilized because it enabled the generation of a high-resolution tomographic map of the HIS reflectivity. Tomograms generated at high incidence angles (>80° from normal) were used to localize and FIR filter unwanted scattering associated with the ground plane edges and HIS transition regions. The resulting scattered fields from a defect (metallic block positioned in the center of the tomogram) were then used to gain a significantly distinctive insight into the HIS scattering properties. Furthermore, unlike traditional methods for characterizing HISs, the CDT and FIR methods presented herein are applicable to electrically large and conformal HISs.

A New Era Has Started

Laser Technik JournalVolume 15, Issue 3 p. 21-23 Technology ReportFree Access A New Era Has Started Additive laser manufacturing processes on the road to success First published: 24 May 2018 https://doi.org/10.1002/latj.201870306AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume15, Issue3June 2018Pages 21-23 RelatedInformation

Galvanic exchange platinization reveals laser-inscribed pattern in 3D-LAM-printed steel

Galvanic exchange involving dissolution of iron and the simultaneous growth of platinum onto 316 L stainless steel was investigated for specimens manufactured by 3D-printing, and the behavior was compared to conventional stainless steel. Novel phenomena associated with the 3D-printed steel, but not conventional steel, reacting in three distinct phases were observed: first, with low platinum loading, a bright etching pattern linked to the laser-manufacturing process is revealed at the steel surface; second, a nanostructured pore pattern with platinum nano-deposits forms; and third, a darker platinum film coating of typically 500-nm thickness forms and then peels off the steel surface with further platinum growth underneath. Unlike the conventional steel (and mainly due to residual porosity), 3D-printed steel supports well-adhered platinum films for potential application in electrocatalysis, as demonstrated for alkaline methanol oxidation.Graphical abstractᅟ

Assembly processes comparison for a miniaturized laser used for the Exomars European Space Agency mission

A miniaturized diode-pumped solid-state laser (DPSSL) designed as part of the Raman laser spectrometer (RLS) instrument for the European Space Agency (ESA) Exomars mission 2020 is assembled and tested for the mission purpose and requirements. Two different processes were tried for the laser assembling: one based on adhesives, following traditional laser manufacturing processes; another based on a low-stress and organic-free soldering technique called solderjet bumping technology. The manufactured devices were tested for the processes validation by passing mechanical, thermal cycles, radiation, and optical functional tests. The comparison analysis showed a device improvement in terms of reliability of the optical performances from the soldered to the assembled by adhesive-based means.

Laser and arc manufacturing processes: A review

Manufacturing can be defined as the transformation of raw materials into desired products by various processes, such as machining, welding and coating. Today, laser and arc heat sources are largely used as the means for processing raw materials. The laser is one of the most widely used non-contact thermal energy sources in various processes, and the development of laser processes and devices for effective manufacturing is still ongoing. Arc heat sources are widely used in welding and coating processes. In particular, the types of welding processes using arc heat sources are very different depending on the materials used and the purpose of welding. In this paper, individual processes using laser and arc heat that have been reported over the past five years are reviewed, including machining, welding, sintering and coating. Then, hybrid processes that use laser and arc heat sources together are also reviewed. The final part of this review provides a summary and discusses future trends for individual and hybrid processes using laser and arc heat sources.

Application of Riblets on Turbine Blade Endwall Secondary Flow Control

Within the past 10 years, significant improvements have been achieved in the laser manufacturing process. It is feasible now to design various small-scale surface features (such as dimples, riblets, grooves, etc.) in gas turbine applications with the current manufacturing readiness level of laser surface texturing techniques. In this paper, the potential of adding riblets on a turbine endwall has been investigated through combined computational fluid dynamics and experimental studies in a low-speed linear cascade environment. Detailed comparisons of the flow structures have been made for cases with and without riblets on the endwall. The numerical results show that endwall riblets can effectively reduce the strength of the pressure side leg of the horseshoe vortex, lower the cross-passage pressure gradient, and alleviate the lift up of the passage vortex. Oil film flow visualization and exit aerodynamic loss survey in experiments support the computational fluid dynamics observations: The passage vortex loss core moves closer to the endwall with the addition of riblets. The present study consistently demonstrates that the addition of riblets can be an effective approach to reduce the endwall secondary flow. Further research questions are raised for the applicability of the riblets concept in actual engine conditions and options for design optimization.

Laser polishing of additive laser manufacturing surfaces

The additive laser manufacturing (ALM) technique is an additive manufacturing process which enables the rapid manufacturing of complex metallic parts and the creation of thin parts so as, for example, to decrease parts weight for biomechanical or aeronautic applications. Furthermore, compared with selective laser sintering technology, the ALM process allows creating more huge parts and material gradient. However, for aesthetic or tribological functions, the ALM surfaces need an additional finishing operation, such as the polishing operation. Polishing processes are usually based on abrasive or chemical techniques. These conventional processes are composed by many drawbacks such as accessibility of complex shape, environmental impact, high time consumption and cost, and health risks for operators. In order to solve these problems and to improve surface quality, the laser polishing (LP) process is investigated. Based on melting material by laser, laser polishing process enables the smoothing of initial topography. However, the ALM process and the laser polishing processes are based on laser technology. In this context, the laser ALM process is used directly on the same machine for the polishing operation. Moreover, an alternation between both processes can be established during the manufacturing operation in order to treat nonaccessible surfaces. Currently, few studies focus on laser polishing of additive laser manufacturing surfaces, and it tends to limit the industrial use of additive manufacturing technology. The proposed study describes an experimental investigation of laser polishing surfaces obtained by additive laser manufacturing process. The investigation results in the improvement of complete final surface quality, according to laser polishing parameters. This experimental study introduces the laser polishing of thin section parts, in order to develop laser polishing applications. According to a manufacturing chain context, the final objective is to create a multiprocess mastery in order to optimize the final topography and productivity time.