Scanning Strategy Research Articles

Crack inhibition and mechanical property enhancement of a CM247LC alloy fabricated by laser powder bed fusion through remelting strategy

High cracking susceptibility arising from the high thermal gradients is a critical issue of high γ'-fraction Ni-base superalloys fabricated by laser powder bed fusion (LPBF). Here in, laser remelting was used to inhibit cracking and enhance the strength-ductility synergy of additively manufactured CM247LC alloy by LPBF. The effects of laser remelting with different energy densities and scan strategies on microstructure, cracking behavior and mechanical properties of LPBF-processed CM247LC superalloy were systematically investigated. The crack inhibition mechanisms of laser remelting during the LPBF process were revealed. Low energy density of remelting and scan strategy with a rotation of 90° between remelting and prior melting were promising for decreasing the crack density. The crack inhibition caused by laser remelting could be attributed to the partial elimination of defects (e.g., lack-of-fusion pores), the mitigation of the segregation of elements, the backfilling of the grain boundaries and liquid film, and the reduction of the residual stress and the high-angle grain boundaries (HAGBs). Enhanced mechanical strength and ductility (ultimate tensile strength of 1280 MPa, yield strength of 885 MPa, and elongation of 11.9%) of LPBF-processed CM247LC samples were obtained by optimized-remelting parameters. This work demonstrated the potential of laser remelting in improving the printability of high γ'-fraction Ni-base superalloys fabricated by LPBF.

CRASH2p: Closed-loop Two Photon Imaging in Freely Moving Animals.

Direct measurement of neural activity in freely moving animals is essential for understanding how the brain controls and represents behaviors. Genetically encoded calcium indicators report neural activity as changes in fluorescence intensity, but brain motion confounds quantitative measurement of fluorescence. Translation, rotation, and deformation of the brain and the movements of intervening scattering or auto-fluorescent tissue all alter the amount of fluorescent light captured by a microscope. Compared to single-photon approaches, two photon microscopy is less sensitive to scattering and off-target fluorescence, but more sensitive to motion, and two photon imaging has always required anchoring the microscope to the brain. We developed a closed-loop resonant axial-scanning high-speed two photon (CRASH2p) microscope for real-time 3D motion correction in unrestrained animals, without implantation of reference markers. We complemented CRASH2p with a novel scanning strategy and a multi-stage registration pipeline. We performed volumetric ratiometrically corrected functional imaging in the CNS of freely moving Drosophila larvae and discovered previously unknown neural correlates of behavior.

THE INFLUENCES OF SCANNING STRATEGY AND READING INTEREST TOWARDS THE EIGHTH GRADE STUDENTS’ READING COMPREHENSION ON LABEL TEXTS OF PGRI JUNIOR HIGH SCHOOL 1 OF PALEMBANG

The writer used a strategy calls scanning strategy to solve students’ problems in reading comprehension. Scanning Strategy and reading interest give a significant influence on the students’ reading comprehension achievement especially for students who havea low reading interest. The teacher of English should be more creative to choose the technique for students.The main problem of this study was formulated as follows: ‘Was there any significant difference in reading comprehension achievement between the eighth grade students who had high reading interest taught by using scanning strategy and those who were taught by using conventional technique at Junior High School PGRI 1 of Palembang, was there any significant difference in reading comprehension achievement between the eighth grade students who had low reading interest taught by using scanning strategy and those who were taught by using conventional technique at Junior High School PGRI 1 of Palembang, was there any significant difference in reading comprehension achievement between the eighth grade students taught by using scanning strategy who had high and low reading interest at Junior High School PGRI 1 of Palembang, was there any significant difference in reading comprehension achievement between the eight grade students taught by using conventional technique who had high and low reading interest at Junior High School PGRI 1 of Palembang and were there any interaction effects of scanning strategy and students’ reading interest towards the eighth grade students’ reading comprehension achievement at Junior High School PGRI 1 of Palembang. This study used experimental research. method. The subjects of this study were eighth grade students of PGRI Junior High School 1 of Palembang. While the object of this research is the used 2 x 2 (two by two) factorial designs because there were two factors (Scanning Strategy and reading Interest) and two levels (low and High Reading Interest).

Mechanical Properties and Interfacial Characterization of Additive-Manufactured CuZrCr/CoCrMo Multi-Metals Fabricated by Powder Bed Fusion Using Pulsed Wave Laser.

In this study, CoCrMo cuboid samples were deposited on a CuZrCr substrate using laser powder bed fusion (L-PBF) technology to investigate the influence of process parameters and laser remelting strategies on the mechanical properties and interface characteristics of multi-metals. This study found that process parameters and laser scanning strategies had a significant influence on the mechanical properties and interface characteristics. Samples fabricated with an EV ≤ 20 J/mm3 showed little tensile ductility. As the volumetric energy density (EV) increased to a range between 40 J/mm3 and 100 J/mm3, the samples achieved the desired mechanical properties, with a strong interface combining the alloys. However, an excessive energy density could result in cracks due to thermal stress. Laser remelting significantly improved the interface properties, especially when the EV was below 40 J/mm3. Variances in the EV showed little influence on the hardness at the CuZrCr end, while the hardness at the interface and the CoCrMo end showed an increasing and decreasing trend with an increase in the EV, respectively. Interface characterization showed that when the EV was greater than 43 J/mm3, the main defects in the L-PBF CoCrMo samples were thermal cracks, which gradually changed to pores with a lack of fusion when the EV decreased. This study provides theoretical and technical support for the manufacturing of multi-metal parts using L-PBF technology.

3D printing slicing algorithm and partition scanning strategy for big data

3D printing technology is a popular new technology that combines information technology with mechanical engineering and material science, and is being widely used in various fields. From the computer point of view, the basic technology of 3D printing is to slice and scan each part of the 3D model. The slicing algorithm used directly affects the speed of slicing and the effect of post-printing, and the result of slicing needs to be optimized. This paper analyzes the slicing algorithm and partition scanning strategy related technologies of 3D printing models and solves the practical problems of models in the 3D printing process. This paper first studies the slicing algorithm in the 3D printing process, then obtains and intercepts the cross-sectional contour, and finally performs mosaic and partition scanning on the sliced polygon, and uses experiments to verify the effectiveness of the research. The experimental results show that compared with other 3D printing methods, the printing method in this paper reduces the slicing time by 23.61%, and the fitting error range and the fluctuation range of the residual height of the fusion volume are smaller.

Scanning strategies for the 316L part with lattice structures fabricated by selective laser melting

Scanning strategies for the 316L part with lattice structures fabricated by selective laser melting

Renal toxicity of Aconitum plants? A study based on a new mass spectrometry scanning strategy and computer virtual screening.

Radix Aconiti Lateralis (Fuzi), a mono-herbal preparation of Aconitum herbs in the genus Aconitum, is commonly used in traditional Chinese medicine (TCM) to treat critical illnesses. The curative effect of Fuzi is remarkable. However, the toxic effects of Fuzi are still a key clinical focus, and the substances inducing nephrotoxicity are still unclear. Therefore, this study proposes a research model combining "in vitro and in vivo component mining-virtual multi-target screening-active component prediction-literature verification" to screen potential nephrotoxic substances rapidly. The UHPLC-Q-Exactive-Orbitrap MS analysis method was used for the correlation analysis of Fuzi's in vitro-in vivo chemical substance groups. On this basis, the key targets of nephrotoxicity were screened by combining online disease databases and a protein-protein interaction (PPI) network. The computer screening technique was used to verify the binding mode and affinity of Fuzi's components with nephrotoxic targets. Finally, the potential material basis of Fuzi-induced nephrotoxicity was screened. Eighty-one Fuzi components were identified. Among them, 35 components were absorbed into the blood. Based on the network biology method, 21 important chemical components and three potential key targets were screened. Computer virtual screening revealed that mesaconine, benzoylaconine, aconitine, deoxyaconitine, hypaconitine, benzoylhypaconine, benzoylmesaconine, and hypaconitine may be potential nephrotoxic substances of Fuzi. Fuzi may interact with multiple components and targets in the process of inducing nephrotoxicity. In the future, experiments can be designed to explore further. This study provides a reference for screening Fuzi nephrotoxic components and has certain significance for the safe use of Fuzi.

Investigation of scanning strategies on performance of nanosecond and picosecond laser volume ablation of bronze

Understanding of laser volume ablation performance in different scanning strategies is indispensable for practical applications. This study investigates the influence of different laser scanning parameters on the performance of volume ablation of bronze material. The results reveal significant differences between the selected pulse durations of 16 ns (ns) and 12 picoseconds (ps), despite both using an identical maximum average power of 40 W. In both cases, increasing the scanning area resulted in a proportional increase in ablation depth. Compared to the ns-laser, the ps-laser exhibited significantly lower ablation depths, approximately 35 % to 40 % less, with consistent performance across different scanning directions. Surface topography analysis showed that scanning direction played a crucial role in determining the final surface quality, with a nearly 50 % improvement observed with the mixed scanning strategy. With the ps-laser, expanding the scanning area led to reduced surface roughness, primarily due to pure ablation and minimal surface re-melting. Further strategies, such as interlace and halftone were also explored. Adjusting the line delay time was also considered, with longer delays potentially resulting in deeper ablation and slightly improved surface roughness. The study also investigated the pitting phenomenon, which was found to be intensified around contour edges. Notably, pitting was more pronounced in ns ablation during the initial scanning layers, while in ps ablation, pitting distribution intensified with an increase in scanning layers and ablation depth.

Permeability and strength of gradient printed permeable steel manufactured by selective laser melting

Based on the forming principle of laser rapid melting and layered manufacturing, the selective laser melting (SLM) process is suitable for the preparation of permeable metal materials with a certain porosity. One of the important applications of this special structure is the development of permeable steel. In this study, the permeable steel with micron-sized controllable pores was prepared by gradient printing using SLM process. The formation and connectivity mechanism of pore structure were analyzed by adjusting the interlayer arrangement of scanning melt channels, and the influence of process parameters on the pore characteristics, permeability and mechanical properties was systematically investigated. The results revealed that the porosity and pore size of permeable steel were effectively improved by controlling the hatch distance and scanning strategy, with the results ranging from 7.81 % to 17.32 % and 57 μm to 121 μm, respectively. Based on the gas permeation test, it was verified that the permeability of permeable steel showed a clear upward trend with increasing porosity, and the results ranged from 2.17 × 10−12 m2 to 4.26 × 10−12 m2, indicating that the pore structure provides a strong basis for gas flow. Moreover, the mechanical properties of permeable steel decreased significantly with the increase of porosity and pore size, and the compressive strength and tensile strength ranged from 1061 MPa to 528 MPa and 1018 MPa to 609 MPa, respectively. The mechanical behavior and deformation mechanism were closely related to the gradient evolution of the pore structure. Overall, the gradient printed permeable steel using SLM process has good permeability and mechanical properties.

Numerical investigation of laser powder bed fusion of glass

Additive manufacturing of glass using laser powder bed fusion has been recently developed, demonstrating its potential to be applied in small scale applications such as flow reactors for the chemical engineering and pharmaceutical manufacturing industries. While previous research demonstrated that complex 3-dimensional shapes can be manufactured, built parts are often brittle, exhibit high porosity and lack transparency. This study employs a transient, heat transfer finite element analysis to shed light on the thermal response of laser—glass powder bed interaction and the impact of processing parameters. Through this understanding, the research seeks to identify practical strategies that can be employed to improve the quality and properties of the built parts. Bulk solid and powder soda lime silica glass properties are used as input in the model, while the laser heat flux and scan strategy, conversion of powder feedstock to bulk solid glass and heat losses from convection and radiation effects are introduced in the model through Fortran coding. The study showed that effective powder consolidation, resulting in well-defined geometrical features, is achieved for temperatures near the glass melting point. Additionally, uniform consolidation depths and widths can be achieved by increasing laser power, elevating substrate temperature and reducing scan speed within certain limits, whilst ensuring hatch spacing is below the corresponding single scan track width for unidirectional adjacent laser trajectories.

Scan Time Reduction by Fewer Projections - an Approach for Circular and Spherical Trajectories

For most computed tomography scans a circular or helical trajectory is used to acquire the necessary radiographic projections. However, these standard trajectories are not necessarily the best choice since the shape of the inspected object is not considered which leads to a suboptimal sampling of the part. In contrast, workpiece-specific and more efficient scan strategies hold the potential for time and cost savings. Such adaptions might be of particular interest for future robotic CT systems that allow greater flexibility in the positioning of X-ray tube, object, and detector than conventional setups or multi-source applications with predefined positions by the setup. We propose a scan planning algorithm to adapt the acquisition trajectory considering the shape of the investigated part. For this task, we present an algorithm that is able to identify the projections from a set of projections that contribute most to the reconstruction of the object. As input information, only the localization of the area of interest and projections from the feasible range of motion are necessary. Also, a reasonable amount of projections to pick from needs to be provided, which can originate from an earlier scan or computer simulations that consider the range of motion of the available CT setup. The optimization method has been implemented for circular and spherical trajectories and can be extended towards arbitrary acquisition paths. Since for modern CT systems the duration for the scan itself takes significantly longer than the reconstruction, this approach appears to be well-suited to significantly reduce the throughput time if several identical parts need to be inspected. Additionally, new applications such as inline CT are conceivable and certain artifacts can be suppressed if spherical trajectories are used instead of circular ones. For the subsequent reconstruction itself no previous knowledge of the object is included, i.e. the reconstruction workflow does not need to be modified. We demonstrate the capabilities of the optimization method for two industrial relevant examples and show that a scan time reduction of more than 50 % is feasible for some cases by reducing the number of acquired projections. Furthermore, for all investigated projection numbers and parts the optimized trajectory yields an identical to clearly improved image quality in the reconstructed volume than the reference trajectories.

Multiple interaction electron beam powder bed fusion for controlling melt pool dynamics and improving surface quality

Low surface quality of fabricated parts and long processing times are two commonly stated reasons against a more wide-spread adoption of electron beam powder bed fusion (PBF-EB) as a commercially viable manufacturing technique. Aside from the large particle size distribution (45–150 µm) of processed powders, the surface roughness, limited structural resolution and process instabilities are attributed to unwanted dynamics of the melt pool, like spattering, balling, evaporation and melt pool displacement. As a result, a contouring step using slow but stable melting parameters is usually added to the process to improve surface quality, leading to increased processing times.In this study, we demonstrate how the surface quality can be improved by supplying the energy for melt pool formation over multiple, timely separated interactions. To investigate the effect of this multiple interaction processing (MIP), series of single line melt structures with increasing number of interactions were fabricated, characterized and corresponding thermal diffusion simulations performed. The experimental results show how MIP allows to lower surface roughness of melted structures through a reduction of spattering, balling and melt pool displacement during processing, while our simulation model identifies these benefits to be caused by a significant reduction in surface temperature and thus evaporation, with increasing number of interactions for melt pool formation. Our model further demonstrates, how a relatively simple, computationally inexpensive and thus scalable thermal diffusion model is capable of providing valuable information about thermal conditions during melt pool formation. Lastly, we introduce a few simple equations to calculate appropriate MIP parameters for any kind of scan strategy.

Weakening the mechanical property anisotropy of additively manufactured medium entropy alloy by controlling the cellular structure

Cellular structure is a unique microstructure characteristic of the additively manufactured face-centered cubic phase metallic materials. It typically grows preferentially along the temperature gradient, leading to anisotropy in mechanical properties and restricting the practical application. Herein, we adopted a discontinuous laser scanning strategy for fabricating the face-centered cubic FeCrNi alloy. The scanning layer is divided into nine discontinuous equal-width regions along which the laser beam prints discontinuously. This strategy can increase the temperature gradient in the melt pool by weakening the thermal influence between the adjacent scanning regions, which helps to suppress cellular structure growth along the temperature gradient. Compared with the sample prepared by the conventional continuous laser scanning strategy, the sample printed using the discontinuous laser scanning strategy exhibits finer cellular structures with a significantly shorter length along the growth direction, and the anisotropy of mechanical properties is weakened. The in-plane anisotropy of ultimate tensile strength decreases from 21.6 to 6.4. This study presents a novel approach to optimize the mechanical properties of additively manufactured face-centered cubic phase metallic materials.

Dislocation Distribution, Crystallographic Texture Evolution, and Plastic Inhomogeneity of Inconel 718 Fabricated by Laser Powder Bed Fusion

Plastic inhomogeneity, particularly localized strain, is one of the main mechanisms responsible for failures in engineering alloys. This work studies the spatial arrangement and distribution of microstructure (including dislocations and grains) and their influence in the plastic inhomogeneity of Inconel 718 fabricated by additive manufacturing (AM). The bidirectional scanning strategy with no interlayer rotation results in highly ordered alternating arrangements of coarse Goss‐like {110}<001> textured grains separated by fine Cube‐like {100}<001> textured grains. The bidirectional strategy also results in an overall high density of geometrically necessary dislocations (GNDs) that are particularly dense in the fine grains. Although the Cube‐like texture desirable for isotropy is dominant, it gradually weakens during plastic deformation and the undesirable Goss‐like component (second most dominant in the as‐built microstructure) increases. The highly clustered and bimodal distribution of fine and coarse grains, textures, and GND densities causes fast localized roughening during deformation, particularly along the line row of fine Cube‐like grains. However, the chessboard strategy results in a lower GND density and a comparatively more random distribution of crystallographic texture and GNDs, with a dominant Cube‐like component (and much lower Goss‐like texture) that remains stable throughout plastic deformation. This results in more uniform deformation, reducing plastic inhomogeneity.

Stress localization investigation of additively manufactured GRCop-42 thin-wall structure

A full-field crystal plasticity (CP) framework is presented for the GRCop-42 alloy to study microscopic mechanical behavior and local stress heterogeneities. The microstructures of additively manufactured (AM) materials are often unique relative to conventionally processed materials, and the local thermal histories drive these differences during the build process. These thermal histories depend on the process parameters (laser power, scan speed, and scan strategy) and the part geometry. Prior research has shown that the mechanical properties of thin-walled structures can vary significantly with wall thickness due to changes in the thermal boundary conditions during manufacturing. It is, therefore, desirable to perform CP simulations based on the phenomenological constitutive model to predict the local mechanical responses induced by microstructural heterogeneities. This work generates representative microstructures based on experimentally collected grain information (i.e., texture) for grain scale stress analysis, and the material constitutive parameters are calibrated using the experimental mechanical testing data. We specifically investigated the effect of crystallographic texture and grain morphologies on the size-dependent mechanical properties of AM GRCop-42. The selection of appropriate material properties for implementing an effective free surface boundary condition and the influence of adjacent buffer layers are also discussed. Analysis of local field results reveals a strong correlation between stress localization and the initial grain orientation. However, no significant relationship between the misorientation of the individual adjacent grains and the average misorientation is observed.

Scan strategy optimization and repeatability testing during laser powder bed fusion additive manufacturing of AlSi10Mg

Scan strategy optimization and repeatability testing during laser powder bed fusion additive manufacturing of AlSi10Mg

Experimental Study on Parameters Optimization of Selective Laser Melting 316L Stainless Steel Based on the Response Surface Methodology

Abstract The use of 3D printing technology can prepare flexible and varied special-shaped complex structures while realizing resource-saving and cost reduction. For this purpose, a 316L stainless steel sample was formed by selective laser melting technology, and the quality of samples was optimized by the Box–Behnken surface response method. Taking the surface roughness Sa as the response value, a regression analysis of four parameters of selective laser melting (laser power, scanning speed, scanning spacing, and scanning strategy) was designed using design expert software. The results showed that the scanning spacing and scanning speed have the greatest influence on the surface roughness, while the laser power and scanning strategy have no significant influence on the surface roughness. Meanwhile, the established surface roughness response surface model is effective and can be used for quality optimization of 316L structural trim. When the laser power was 185 W, the scanning speed was 615 mm/s, the scanning spacing was 110 μm and concentric scanning strategy was adopted, the surface adhesion powder was less, and the minimum surface roughness Sa was 9.001 μm.

Effects of Laser Scanning Strategy on Bending Behavior and Microstructure of DP980 Steel

Laser bending is a kind of cumulative forming technology and bending efficiency is one of its most important indexes. This study investigates the bending behavior and the microstructure of DP980 steel plates under different laser scanning strategies, using an IPG laser system. Two sets of experiments varied the accumulated line energy density (AED) by altering the laser scanning velocity and number of scans. The results show that, for the single laser scanning process, the bending angle of the plate increases with AED, due to a larger temperature gradient through the thickness direction; however, this relationship is nonlinear. A higher AED led to a sharper initial increase in bending angle, which then plateaued. Under the same AED conditions, the bending angle of the plate undergoing multiple laser scans increases by at least 26% compared to the single one, due to the microstructure changes. It is revealed that the bending efficiency is affected by both the AED and the resultant microstructure evolution in the DP980 steel. Higher AED values and appropriate peak temperatures facilitate better bending behavior due to the formation of uniform martensite and grain refinement. Conversely, excessive peak temperatures can hinder bending due to grain growth.

Low-temperature creep performance of additive manufactured Ti–6Al–4V

Abstract Additive manufacturing enables the fabrication of versatile and cost-effective metallic-alloy components from a digital data model. This study explores the prospects of selective laser melting (SLM), an additive manufacturing technique, for fabricating Ti6Al4V alloy components from Ti6Al4V alloy powders. Selective laser melting parameters, such as laser power, scanning speed, powder thickness, hatching space, and scanning strategy, are carefully selected through a series of experiments. The metallurgical characteristics (microstructure, grain orientation, and phase composition), microhardness, and creep performance of the as-fabricated specimens are tested and analyzed. The kinetics of phase transformation and rupture mechanism are determined using advanced instrumental characterization tools, such as field emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and transmission electron microscope.

Microstructure-Based Modeling of Deformation and Damage Behavior of Extruded and Additively Manufactured 316L Stainless Steels.

In this study, we investigated the micromechanical deformation and damage behavior of commercially extruded and additively manufactured 316L stainless steels (AMed SS316L) by combining experimental examinations and crystal plasticity modeling. The AMed alloy was fabricated using the laser powder bed fusion (LPBF) technique with an orthogonal scanning strategy to control the directionality of the as-fabricated material. Optical microscopy and electron backscatter diffraction measurements revealed distinct grain morphologies and crystallographic textures in the two alloys. Uniaxial tensile test results suggested that the LPBFed alloy exhibited an increased yield strength, reduced elongation, and comparable ultimate tensile strength in comparison to those of the extruded alloy. A microstructure-based crystal plasticity model was developed to simulate the micromechanical deformation behavior of the alloys using representative volume elements based on realistic microstructures. A ductile fracture criterion based on the microscopically dissipated plastic energy on a slip system was adopted to predict the microscopic damage accumulation of the alloys during plastic deformation. The developed model could accurately predict the stress-strain behavior and evolution of the crystallographic textures in both the alloys. We reveal that the increased yield strength in the LPBFed alloy, compared to that in the extruded alloy, is attributed to the higher as-manufactured dislocation density and the cellular subgrain structure, resulting in a reduced elongation. The presence of annealing twins and favorable texture in the extruded alloy contributed to its excellent elongation, along with a higher hardening rate owing to twin-dislocation interactions during plastic deformation. Moreover, the grain morphology and defect state (e.g., dislocations and twins) in the initial state can significantly affect strain localization and damage accumulation in alloys.