Changes In Laser Power Research Articles

A Meshless Method of Radial Basis Function-Finite Difference Approach to 3-Dimensional Numerical Simulation on Selective Laser Melting Process

Selective laser melting (SLM) is a rapidly evolving technology that requires extensive knowledge and management for broader industrial adoption due to the complexity of phenomena involved. The selection of parameters and numerical analysis for the SLM process are both costly and time-consuming. In this paper, a three-dimensional radial basis function-finite difference (RBF-FD) meshless model is introduced to accurately and efficiently simulate the molten pool size and temperature distribution during the SLM process for austenitic stainless steel (AISI 316L). Two different volumetric moving heat source models were presented, namely the ray-tracing method heat source model and the double-ellipsoidal shape heat source model. The temperature-dependent material properties and phase change process were also considered, based on experiments and effective models. Results of the model for the molten pool size were validated with those of the literature. The proposed approach can be used to predict the effect of different laser power and scan speed on the molten pool size and temperature gradient along the depth direction. The result reveals that the depth of the molten pool is more sensitive to laser power than scan speed. Under the same scan speed, a 22% change in laser power (45 ± 10 W) affects the maximum temperature proportionally by about 9%. The developed algorithm is computationally efficient and suitable for industrial applications.

Operando visualization of porous metal additive manufacturing with foaming agents through high-speed x-ray imaging

Porous metals find extensive applications in soundproofing, filtration, catalysis, and energy-absorbing structures, thanks to their unique internal pore structure and high specific strength. In recent years, there has been an increasing interest in fabricating porous metals using additive manufacturing (AM), leveraging its unique advantages, including improved design freedom, spatial material control, and cost-effective small-batch production. In this study, we conducted pioneering operando visualization of AM porous metal using a laser powder bed fusion (L-PBF) setup combined with a high-speed synchrotron x-ray imaging system. Single track printing experiments using Ti6Al4V (Ti64) combined with titanium hydride (TiH2) and sodium carbonate (Na2CO3) as foaming agents, with varying mixing ratios were performed under different processing conditions. The results elucidate the dynamic development of porosity formation. The average pore size is significantly influenced by the particle size of foaming agents when pore coalescence is absent. For all foaming agent content tested in the current study, the number of pores is found to be more sensitive to changes in laser power than in laser scanning speed. Increasing linear energy density (increasing laser power or reducing laser scanning speed) promotes the foaming agent activation thereby porosity formation. However, high linear energy density skews pore distribution towards the surface despite forming deeper melt pools. In addition, the impact of additional factors including foaming agent’s laser absorptivity and decomposition kinetics with respect to AM time scales should be carefully considered to avoid ineffective activation of foaming agents during the AM of porous metals.

The effect of biomimetic laser surface treatment on the wear performance of high manganese steel

High manganese steel finds widespread applications in diverse friction and wear environments. The poor wear resistance of high manganese steel at low stress levels has prompted researchers globally to focus on studying its wear performance. Drawing inspiration from the protective features of pangolin scales, this study employed a pulsed radiation mode CO2 laser to conduct biomimetic laser surface treatment (BLST) on Mn13 high manganese steel. The BLST generated a biomimetic surface morphology consisting of tiny scales on the high manganese steel specimens. Subsequently, the biomimetic laser surface-treated (BLSTed) specimens underwent tests for surface morphology, microstructure, microhardness, and surface roughness. These tests employed metallographic microscopy, scanning electron microscopy, a microhardness tester, and a surface profilometer, respectively. A ring block friction and wear testing machine was utilized to evaluate the wear performance of the BLSTed specimens. Changes in laser power, laser frequency, and laser scanning velocity were found to alter the surface morphology of BLSTed specimens. The experimental results revealed that the microstructure of the BLSTed specimen surface comprised needle-like martensite. The increment in surface hardness and surface roughness of BLSTed specimens contributed to an elevation in their average friction coefficient. Furthermore, the surface hardness and wear performance of BLSTed specimens exhibited varying degrees of improvement with the increase in laser power, laser frequency, and laser scanning velocity. The tiny biomimetic scales, created through BLST, provided protection to high manganese steel akin to the protective scales on the body of pangolins. Finally, the study unveiled the wear resistance mechanism of BLSTed specimens.

Laser power changes observed ultrafast protein dynamics

Laser power changes observed ultrafast protein dynamics

Controlling nonlinear rogue-wave formation using the coherence length of phase noise

Weak phase noise present on an optical field can be amplified by a self-focusing nonlinearity (n2>0) and form intense “rogue-wave” features. Here, we study the effect of the coherence length (or grain size) of this phase noise on the likelihood of rogue-wave formation in the presence of a self-focusing nonlinearity. We show that while the likelihood of rogue-wave formation increases with laser power when the coherence length is only slightly smaller than the beam diameter, the likelihood is minimally affected by a change in laser power when the coherence length is significantly smaller than the beam diameter. Our study provides insight into the interaction of nonlinearity with phase instabilities on a field and could be useful in applications such as reducing the effect of turbulence-induced breakup of intense laser beams, and developing radiance limiters to reduce the focusable power in a beam. Published by the American Physical Society 2024

Influence of Laser Power on Achieving Ultra Low Stiffness in Resistive Strain Gauges Through on Laser Bonding Transfer‐Patterning of Multiwall Carbon Nanotubes (MWCNTs) onto Polydimethylsiloxane (PDMS) Film

AbstractThis study describes a novel stretchable and very sensitive strain gauge enabled by laser‐joining carbon nanotubes, resulting in unique architectures forming macroscopic web networks. The stiffness of the resistive strain sensor created by laser material patterning is reduced significantly, from 1.5824 to 0.142 kN m−1, corresponding to a change in laser power from 0 to 0.436 W. Many benefits of laser‐based bonding include precise and flexible local pattern production with minimal energy impact on the flexible substrate. Furthermore, the maximum Gauge factor of the sensor exhibits diverse trends with different strains, generating values of GF = 12.8 for strains less than 2.5% and GF = 165 for strains greater than 2.5% during extension‐retraction cycles. These disparities are the result of a dynamic fight between network degradation and regeneration.

Mesoscopic Simulation of Core-Shell Composite Powder Materials by Selective Laser Melting.

Mechanical ball milling is used to produce multi-materials for selective laser melting (SLM). However, since different powders have different particle size distributions and densities there is particle segregation in the powder bed, which affects the mechanical properties of the printed part. Core-shell composite powder materials are created and used in the SLM process to solve this issue. Core-shell composite powder materials selective laser melting (CS-SLM) has advanced recently, expanding the range of additive manufacturing applications. Heat storage effects and heat transfer hysteresis in the SLM process are made by the different thermophysical characteristics of the core and the shell material. Meanwhile, the presence of melt flow and migration of unmelted particles in the interaction between unmelted particles and melt complicates the CS-SLM molding process. It is still challenging to investigate the physical mechanisms of CS-SLM through direct experimental observation of the process. In this study, a mesoscopic melt-pool dynamics model for simulating the single-track CS-SLM process is developed. The melting characteristics of nickel-coated tungsten carbide composite powder (WC@Ni) were investigated. It is shown that the powder with a smaller particle size is more likely to form a melt pool, which increases the temperature in the area around it. The impact of process parameters on the size of the melt pool and the distribution of the reinforced particles in the melt pool was investigated. The size of the melt pool is significantly affected more by changes in laser power than by changes in scanning speed. The appropriate control of the laser power or scanning speed can prevent enhanced particle aggregation. This model is capable of simulating CS-SLM with any number of layers and enables a better understanding of the CS-SLM process.

Simulation Study on the Influence of a Laser Power Change on the Residual Stress of a Laser-Melting RuT300 Valve Seat

In order to effectively suppress the cracking induced by the excessive residual stress of a laser-melting RuT300 valve seat, the influence of a laser power change on the residual stress was studied by constructing a finite element simulation model of a new power valve seat. The absorption rate of the laser energy on the surface of the material and the change in thermophysical parameters with temperature were taken into account in the model. The results show that the melting and phase-change-hardening areas can be obtained by the laser-melting process. With the increase in laser power, the peak temperature of the molten pool increased almost linearly. The melting zone area and the phase-change-hardening zone depth increased. When the laser power was increased from 2000 to 2600 W, the peak temperature of the laser-melting RuT300 valve seat increased from 2005.09 to 2641.93 °C, the maximum depth of the melting area increased from 0.55 to 0.86 mm, the maximum width of the melting area increased from 3.42 to 4.21 mm, and the maximum depth of the phase-change-hardening area increased from 0.55 to 0.64 mm. The circumferential residual tensile stress in the melting area was much higher than in the radial and axial directions. Along the laser scanning direction, the residual stress in the melting area increased as a whole, and the residual stress in the laser-scanning finishing area greatly increased. With the increase in laser power, the circumferential residual stress at the previous scanning moment decreased, and at the closing moment of the scan, the circumferential residual stress increased with the increase in laser power.

Experimental study of heat affected zone for CO2 and fiber laser machining of SS 316L material

Stainless steel is a widely used engineering material. This material is difficult to machine by conventional methods because of its high melting point. The main aim of present experimental study is to investigate of the process parameters on HAZ (heat affected zone) for CO2 and fiber laser machining of SS 316L material. The cut qualities are analyzed by measuring the HAZ by altering the process variables like cutting speed, gas pressure and laser power. The experimentation is performed on Bystronic laser cutting machine. Design of experiment (DOE) technique using response surface methodology is used. Mathematical calculations are carried out using analysis of variance method. The main conclusion that is drawn from this study is change in laser power affects the HAZ. It is also observed that cutting speed is the most significant parameter as compared to gas pressure and laser power.

Multiresolution Quality Inspection of Layerwise Builds for Metal 3D Printer and Scanner

Abstract Automated optical inspection (AOI) is increasingly advocated for in situ quality monitoring of additive manufacturing (AM) processes. The availability of layerwise imaging data improves the information visibility during fabrication processes and is thus conducive to performing online certification. However, few, if any, have investigated the high-speed contact image sensors (CIS) (i.e., originally developed for document scanners and multifunction printers) for AM quality monitoring. In addition, layerwise images show complex patterns and often contain hidden information that cannot be revealed in a single scale. A new and alternative approach will be to analyze these intrinsic patterns with multiscale lenses. Therefore, the objective of this article is to design and develop an AOI system with contact image sensors for multiresolution quality inspection of layerwise builds in additive manufacturing. First, we retrofit the AOI system with contact image sensors in industrially relevant 95 mm/s scanning speed to a laser-powder-bed-fusion (LPBF) machines. Then, we design the experiments to fabricate nine parts under a variety of factor levels (e.g., gas flow blockage, re-coater damage, laser power changes). In each layer, the AOI system collects imaging data of both recoating powder beds before the laser fusion and surface finishes after the laser fusion. Second, layerwise images are pre-preprocessed for alignment, registration, and identification of regions of interests (ROIs) of these nine parts. Then, we leverage the wavelet transformation to analyze ROI images in multiple scales and further extract salient features that are sensitive to process variations, instead of extraneous noises. Third, we perform the paired comparison analysis to investigate how different levels of factors influence the distribution of wavelet features. Finally, these features are shown to be effective in predicting the extent of defects in the computed tomography (CT) data of layerwise AM builds. The proposed framework of multiresolution quality inspection is evaluated and validated using real-world AM imaging data. Experimental results demonstrated the effectiveness of the proposed AOI system with contact image sensors for online quality inspection of layerwise builds in AM processes.

Laser assisted method for synthesis Li4Ti5O12/polyether sulfone composite for lithium ion batteries anodic materials

Spinel Li4Ti5O12 (LTO) is a potential anode material for innovative high-power lithium-ion batteries (LIBs) because of its "zero strain" features during quick charging/discharging, extended cycle life, and elevated rate capability. However, LTO has limited application due to its poor ionic/electronic conductivity and slow ionic diffusion coefficient. In this work, LTO/polyether sulfone (PES) composite is synthesized via pulsed laser ablation in liquid media technique based on an infrared Nd:YAG nanosecond laser. The influences of laser ablation power were used to vary the particle sizes of the generated LTO nanoparticles on the formation of the LTO/PES structure, followed by the electrochemical performances of LTO. Various methods were used to investigate the composite's structural, optical, and morphological properties. The interactions between the polymer and nanoparticles, as well as the fine dispersion of NPs, were evident in the optical tests, which showed that the absorbance greatly improved and the energy band gap decreased. Also, the morphological images display the cubic shape of pure LTO NPs with varying particle sizes between 5 and 26 nm as the laser power changes. Furthermore, from XRD characterization, the intensity of this crystalline peak of PES decreases as a function of LTO wt. % increase without appearing of any other impurities. After that, the electrochemical performances were tested for all prepared samples, which showed that the as-prepared composite structure with a lower particle size exhibits excellent electrochemical performances. This result demonstrates that providing surface defects by forming Ti3+/Ti4+ pairs and oxygen vacancies in LTO is a successful method for increasing ion/electron mobility. This method can be applied to improve the battery efficiency of other substances with low ionic conductivities in the developed batteries.

Effect of additive and subtractive hybrid manufacturing process on the surface quality of 18Ni300 maraging steel

The effect of process parameters on the surface quality of 18Ni300 maraging steel formed by selective laser melting (SLM) was investigated. Surface modification of SLM specimens was performed using milling as a subtraction method to investigate the effect of milling process parameters on the surface quality of SLM specimens. Comparing and analyzing the surface quality after additive and subtractive processes, the results show that the increase of laser power during SLM can improve the surface morphology, but there is always a balling effect. The surface quality deteriorates when the scanning speed increases. When the laser power increases or the scanning speed decreases, the microhardness increases and the error decreases. The residual stress does not vary linearly with the change of laser power or scanning speed, and the scanning speed has a greater effect on the residual stress than the laser power. The best surface quality was achieved with a laser power of 180 W and a scanning speed of 300 mm s−1. The laser power and scanning speed did not significantly affect the microstructure of the SLM-formed specimens. In the milling process, an increase in the feed rate will make the surface quality worse, and an increase in the cutting speed will make the surface quality better. The best surface quality was obtained with a cutting speed of 10 m min−1 and a feed rate of 36 mm min−1. The grain refinement effect is weakened when the feed rate is increased, and the grain refinement effect is enhanced when the cutting speed is increased. The surface quality of SLM-formed maraging steel specimens improved somewhat after milling.

Numerical Simulation and Experimental Prediction of the Cladding Layer Based on the Response Surface Method

To study the surface morphology of laser cladding, Workbench simulated the influence of laser power and scanning speed on the width and height of the cladding layer numerically, as well as the temperature field change and residual stress distribution of the cladding layer. The simulation results reveal that the melting height and width of the cladding layer are inversely proportional to the scanning speed. When the scanning speed is from V = 3 mm/s to V = 5 mm/s, the Al cladding layer’s melting width and melting height are reduced by 15.59% and 20.8%, respectively. A positive correlation exists between the melting height and width of the cladding layer and the laser power. When the laser power changes from P = 23 w to P = 27 w, the welding width and height of the A1 cladding layer increase by 6.55% and 55.56%, respectively. The melting height and width of the second cladding layer are generally higher than those of the bottom cladding layer. The pre-experiment screening process parameters ranges are laser power P (23 w–27 w) and scanning speed (3 mm/s–8 mm/s). Based on the Minitab response surface central composite method, the most notable influence on the melting height and width is revealed to be the powder-feeding rate and laser power, respectively. The response surface analysis method establishes the regression prediction models of melting width and height. The predicted value of melting width was 95.68%, and the predicted value of melting height was 82.26%. The results show that the values of cladding width and height are within the 95% prediction interval, proving that the regression model is correct.

Influence of powder size on defect generation in laser powder bed fusion of AlSi10Mg alloy

The particle size distribution (PSD) often changes as powders are cycled for recycled and different powder batches are used, challenging a critical aspect of quality assurance in the Laser Powder Bed Fusion (LPBF) process. It is therefore important to understand how powder PSD affects the processability of powder in the context of LPBF. In this work, a batch of AlSi10Mg powder was sieved into four sets of powder with controlled PSD (D50 ranging from 16 μm to 76 μm). Single-track and cuboid samples were made from powders with variations in laser power whiling fixing other laser processing parameters constantly. It is shown that coarser powders are much more sensitive to changes in laser power in terms of melt pool characteristics, defect population and size, showing significant improvements in relative density upon increasing laser power. The simulations reveal with the combination of low laser power and coarse powders, pores mainly originate from insufficient melting of powders at the sides of melt pools due to insufficient and inhomogeneous absorption of laser energy. It is possible to achieve nearly fully-dense parts when processing coarse powders given that the incident laser beam energy is sufficient.

Laser Irradiation on Limestone and Cracking: An Experimental Approach

Using mechanical drilling to obtain energy resources stored in deep and hard rock layers is becoming increasingly challenging. Therefore, laser irradiation has emerged as a new and promising drilling method. In this study, the effects of immersion conditions on rock-breaking by laser irradiation on the temperature, hole size, rock-breaking efficiency, and macro-fracture after laser irradiation were investigated. Furthermore, the mineral changes and thermogravimetric analysis of rocks were studied. As indicated by the results, the temperature area over 100 °C increases with the increase of irradiation time, and the temperature range of between 2.27 cm2 and 13.20 cm2 varies with the change of laser power at between 90 W and 135 W. The hole-diameter value of the soaked sample was smaller than that of the dried sample. In addition, the hole depth of the soaked sample reduced by 15% at a power of 90 W and 45% at a power of 135 W, compared with that of the dried sample. The value of the modified specific energy of the soaked sample increased, which was particularly noticeable at low power. The soaked sample had a larger effect on the rate of perforation at high power and a smaller effect at low power. The cracks on the surface of the rock samples became larger after being placed for one month. Fracture length increased from 0.61 to 5.09 mm for dried samples and from 2.24 to 8.7 mm for soaked samples at a laser power of 90 W. Fracture length increased from 6.30 to 9.85 mm for dried samples and from 9.04 to 11.38 mm for soaked samples at a laser power of 135 W. The soaked sample began to show differences when heated at 100 °C, which was caused by the evaporation of some free water molecules in the rock. The main weight loss temperatures of the samples occurred in the range of 640 °C to 900 °C.

Tailoring phase transformation behavior, microstructure, and superelasticity of NiTi shape memory alloys by specific change of laser power in selective laser melting

In this study, NiTi shape memory alloys (SMAs) were fabricated by selective laser melting (SLM), and it is found that specific change of laser power (from 55 W to 70 W) was effective to tailor their phase transformation behavior, microstructure, and superelasticity. Results indicated that a minor increase of laser power made transformation temperatures increase significantly owing to the depletion of Ni and the formation of precipitates. The microstructure of SLM NiTi SMAs underwent the change from coarse grains to coarse together with ultrafine grains when laser power increased from 55 to 70 W. The superelastic responses demonstrated that SLM NiTi SMAs fabricated by specific laser power exhibited significantly different recovery strains. Specifically, SLM NiTi fabricated by 65 W showed stable phase transformation recovery strain, and obtained recovery strain of 3.91% at 1st cycle and only about 0.03% degeneration after 10 times cyclic compression. These outstanding stable recovery strains were ascribed to the coexistence of high-density dislocations formed in ultrafine grains and abundant nanoprecipitates interior of the grains, which impeded the formation of plastic deformation during loading effectively. These results make it possible to obtain the desired functional properties of SLM NiTi SMAs by specific change of laser power.

Iterative closest point-based data fusion of non-synchronized in-situ and ex-situ data in laser powder bed fusion

With the development of additive manufacturing (AM) processes, a variety of methods and technologies for process monitoring and post-process inspection have become available. These, together with modern computerized machines, generate large amounts of data about the process. Hence, efficient analysis methods for extracting useful information and knowledge from these datasets are needed. This paper presents a method for automated data fusion of machine input toolpath commands, on-axis intensity monitoring, and Computed Tomography (CT) scan measurement data in laser metal powder-bed fusion AM. The iterative closest point (ICP) point-clouds registration method is used for fine spatial alignments of (1) on-axis intensity measurements with machine input toolpath commands and (2) machine input toolpath and CT scan. The input-toolpath point cloud is selected as the reference point cloud. We further propose a post-processing method that can correct part of the wrong connections between measurements and toolpath points as results of ICP registration. The proposed method is suitable for merging data where there is no temporal synchronization between the machine commands and the monitoring system, and where the actual laser scan path may deviate from the machine input toolpath commands, e.g., due to dynamics constraints of scanning galvo mirror system. The method is designed to handle dynamic changes in input process parameters such as dynamic changes in laser power and scan speed, which lays a solid foundation for advanced AM process control, qualification and certification. A practical solution for organizing and storing the fused data, which allows for efficient analysis, is also presented. The results show that the method can spatially align all three different types of data and find the corresponding input toolpath command for each measurement point. The alignment of on-axis measurements and machine input toolpath commands has been improved by using a clustering algorithm. The main limitation is that, for estimating the improvement and error of spatial alignment, the average difference between the closest points of two point clouds is used, but this metric does not give an exact value of an actual registration error. The estimation of connectivity error is based on a visual comparison of registration results.

Integrated, reliable laser system for an 87Rb cold atom fountain clock

We designed, assembled, and tested a reliable laser system for 87Rb cold atom fountain clocks. The laser system is divided into four modules according to function, which are convenient for installing, adjusting, maintaining, and replacing of the modules. In each functional module, all optical components are fixed on a baseplate with glue and screws, ensuring the system’s structural stability. Mechanical stability was verified in a 6.11g RMS randomvibration test, where the change in output power before and after vibration was less than 5%. Thermal stability was realized by optimizing of the structure and appropriate selection of component materials of the modules through thermal simulation. In the laser splitting and output module, the change in laser power was less than 20% for each fiber in thermal cycles from 5 °C to 43 °C. Finally, the functionality of the laser system was verified for a rubidium fountain clock.

Design of a highly reliable and low-cost optical bench for laser cooling

High-reliability optical systems play an essential role in the wide application of precision cold atom quantum sensors such as cold atom clocks, cold atomic magnetometers and cold atom interferometers. Achieving thermal stability performance is especially critical because the long-term performance of a cold atom system is often ultimately limited by the thermal stability of the optical system. In this paper, we find that the material consistency of the parts on the optical bench is more important for the thermal stability of the optical system than reducing the expansion coefficient of the parts. On several optical benches with the same architecture but different fiber coupler material combinations, the minimum fiber coupling efficiency change reached approximately 3.5% in the variation range of ambient temperature from 8℃ to 43℃, and the coupling efficiency change was less than 0.3% before and after thermal cycling. In addition, a full-function optical bench for rubidium atom laser cooling was developed based on the assembly procedure of the test optical bench. In the multiple output fibers on the bench, the maximal coupling efficiency variation was less than 19% in the range of 8℃∼43℃, and the output laser power change was less than 2% in the bench before and after thermal cycling.

The Tribological Properties of Micro-textured AlCrN Coated Cemented Carbide

This paper presents the results of tests undertaken to examine the surface friction characteristics of cemented carbide when enhanced with a textured coating. A platform was built to analyze the sensitivity of different micro-texture and coating parameters on the friction and wear behavior of AlCrN coated cemented carbide, with the goal of revealing the friction and wear mechanisms associated with such surfaces. The results show that the selection of appropriate parameters can suppress vibration and reduce friction, with the time until failure of micro-textured AlCrN coated cemented carbide surfaces being 20–25 min. The main factors affecting the vibration and friction are the coating thickness, the interaction between various micro-texture preparation parameters, and the micro-pit diameter. When the coating is treated by a laser, the thinner the coating, the greater the surface hardness and the smaller the changes in the film/substrate bonding force. Changes in laser power, scanning speed and scanning times all affect the energy received per unit area of the material’s surface, affecting the target diameter and micro-texture quality. The kind of surface wear experienced by micro-textured AlCrN coated cemented carbide is mainly adhesive wear, accompanied by oxidative wear. Taking vibration, friction force and degree of wear degree as evaluation criteria, the optimal parameters are: a coating thickness of 1.2 μm; a laser power of 45W; a scanning speed of 1500–1700 mm s−1; 7–8 scans; a micro-pit diameter of 40–60 μm; and a distance of 150 μm between the micro-pits.