Scan Spacing Research Articles

Development and application of a simplified thermo-evaporative multi-track laser powder bed fusion model for Ti6Al4V

Often the parametric analyses of the laser powder bed fusion (LPBF) process are concerned with laser power or scan speed, and other parameters such as scan spacing are paid lesser attention, particularly due to the huge computational power required for their investigation. Hence, in this study a simple and efficient thermo-evaporative model is developed for multi-track LPBF that excluded the solution of melt pool flow dynamics and thus enabled faster and economic simulation of the problem. Material evaporation was added to control the temperature rise up to reasonable levels, which acted only as a heat loss flux on the top boundary. The model has been first validated against the single track results and then applied to multi-track modeling for several different values of scan spacing while other parameters are kept constant. The study showed the potential of the developed thermo-evaporative model in simulating the multi-track problem and conducting a parametric analysis concerning the variation of scan spacing. The results were verified against the experimental results at a higher scan spacing where the computed and experimental porosities were compared qualitatively, and it was observed that the proposed model predicted the lack of melting porosity very well. The temperature field and other thermal characteristics such as thermal gradients and heating/cooling rates were calculated and discussed as well.

Effects of the Laser Micromelting Process Parameters on the Preparation of Micron-Sized FeCrAl Coatings on Zr Alloy Surfaces

Laser micromelting (LMM) technology allows for the remelting of pre-positioned coatings on the surface of a specimen to form a metallurgical bond with the substrate material, significantly improving the coating’s film–base bond. However, the high energy input from the laser modification process can cause severe element diffusion, rendering the coating susceptible to deformation and cracking. This can be mitigated by controlling the laser power, scanning speed, and offset of the LMM process. The temperature and stress fields of the samples in the LMM process were analyzed via finite element simulation. The effects of the LMM process parameters on the coating morphology were analyzed in conjunction with experiments. The results indicated that the laser power significantly affected the morphology of the coating after remelting, and a higher scanning speed was more likely to cause the coating to accumulate stress. Additionally, a smaller offset inhibited crack generation. At a laser power of 30 W, a scanning speed of 1200 mm/min, and a scanning spacing of 0.035 mm, the surface of the coating had no obvious defects and was relatively flat, and the adhesion and corrosion resistance were significantly improved. This study provides valuable guidance for improving the preparation of micron-sized protective coatings on Zr alloy surfaces.

Laser-induced localized and maskless electrodeposition of micro-copper structure on silicon surface: Simulation and experimental study

The simulation and experimental study of laser-induced localized and maskless electrodeposition of micro-copper (Cu) structures on p-type silicon (Si) surface is investigated. Firstly, calculations of the internal temperature field and free electron density distribution within Si under nanosecond laser irradiation were carried out, to demonstrate the selective enhancing effect of laser irradiation on electrical conductivity via the thermal and photoconductive manner. Secondly, experimental tests of the laser-induced electrodeposition of micro-wires, regional coatings and complicated patterns on Si surface without mask were performed successively, to illustrate the effectiveness of the proposed method. The experimental results indicate that laser pulse width and scanning space significantly affect the quality of the deposited layer. Specifically, dense and flat micro wires can be achieved when the laser pulse width is 100 ns, which is associated with a width of about 71.7 μm and thickness of around 10.9 μm. In addition, the laser scanning space should be well optimized to balance the uniformity of the regional coating and the stray deposition near the edge. Finally, the reduction of Cu2+ and deposition of Cu atom at Si surface were discussed, as well as the development of transitional layer, to supply an in-depth analysis of the electrodeposition mechanism.

Vat‐photopolymerization‐based complex ceramic: Optimization of slurry, printing process, and postprocessing parameters

AbstractVat photopolymerization is an effective and economical method for preparing ceramic specimens with complex structures. However, the improper selection of process parameters during the preparation process limits the scope of its application. In this study, the most suitable shear rate was determined based on the solid content and rheological properties of the ceramic slurry. In addition, the specific printing‐process parameters were objectively selected, and the gray correlation method was used to determine the improved weight resolution coefficient through orthogonal experiments combined with the entropy weight method to select the most suitable printing parameters. Finally, the main debinding and sintering parameters that affect the heat treatment performance were considered, and multiple characterization methods were used to detect the specimens and study the impact of parameter changes on specimen performance. The experimental results show that when the laser power is 210 mW, the slice layer thickness is .04 mm, the scanning spacing is .05 mm, and the filling mode is XY, the green bodies have the best forming quality. When the sintering temperature is 1600°C, and the holding time is 4 h, the specimens have the best mechanical properties (the flexural strength reaches 114 MPa).

Effect of processing parameters on the quality of overhanging round hole structure in AlSi10Mg selective laser melting

To improve the forming quality of overhanging round hole parts without support, the effects of different processing parameters on the forming quality of the structure were investigated by numerical simulation and experiment. The response surface method was used to analyze the collapse of the overhanging surface. A quadratic response model was established, which can be used to predict the optimization of processing parameters. Finally, three groups of parts under different processing parameters were fabricated by SLM, and the forming quality of the parts was analyzed from the macroscopic and microcosmic perspectives. The results showed that the roundness, the collapse of the overhanging surface and the surface roughness increased with the increase of laser power. The result of increasing scanning speed was opposite. With the increase of scanning spacing, the surface roughness decreased continuously, and the roundness and collapse of the overhanging surface increased first and then decreased. When the scanning spacing was 0.15 mm, the roundness and collapse of the overhanging surface reached the minimum. With the increase of the three, the density and hardness increased first and then decreased. The results of response surface analysis were in good agreement with the experimental results.

Optimization of Laser Powder Bed Fusion Process for Forming Porous Ta Scaffold

To improve the performance of porous tantalum (Ta) manufactured by laser powder bed fusion (L-PBF) and meet its application requirements in medicine, the authors of this paper studied the influence of L-PBF process parameters on the strut surface morphology and mechanical performance. It was found that the powder layer thickness had a significant influence on the microstructure and mechanical properties based on statistical analysis. We proposed optimal process parameters of laser power of 150 W, scanning speed of 270 mm/s, thickness of 0.05 mm, and scanning spacing of 0.07 mm. After parameter optimization, we successfully obtained Ta samples with an elastic modulus of 1.352 ± 0.007 GPa and yield strength of 53.217 ± 0.114 MPa. The results show that the elastic modulus and yield strength of porous Ta samples with a porosity of 80% under the optimal process parameters are significantly superior to previous studies. The porous Ta scaffolds with higher mechanical properties fabricated with the optimized process parameters of L-PBF have significant value for applications in medicine.

Detection of lung cancer using novel attention gate residual U-Net model and KNN classifier from computer tomography images

Computed tomography (CT) scan pictures are routinely employed in the automatic identification and classification of lung cancer. The texture distribution of lung nodules can vary widely over the CT scan space and requires accurate detection. The evaluation of discriminative information in this volume can tremendously aid the classification process. A convolutional neural network, the Attention Gate Residual U-Net model, and KNN classifiers are utilized to detect lung cancer. The dataset of 1097 computed tomography (CT) images utilized in this study was obtained from the Iraq-Oncology Teaching Hospital/National Centre for Cancer Diseases (IQ-OTH/NCCD) to segment and classify lung tumors from CT images using the novel Attention Gate Residual U-Net model, i.e., AGResU-Net and CNN architecture. The initial step is applying CNN to detect normal, benign, and malignant patients in CT images. Second, use AGResU-Net to partition lung tumour areas. In the third section of the project, a KNN classifier is used to determine if an instance is malignant or benign. In the initial phase, CNN was proposed to classify three distinct regions. Three optimization strategies are used in this work: Adam, RMSP, and SGDM. The classifier’s accuracy is 97%, 85%, and 82%, respectively. When compared to the RMSP optimizer, the Adams optimizer predicts probability rates more accurately. In the second phase, AGResU-Net is used for schematic segmentation of the tumor region. In the third phase, a KNN classifier is used to classify benign and malignant tumor from the segmented tumor regions. A new segmentation of the lung tumor model is proposed. In this developed algorithm, the labelled classified data set and the segmented tumor output result provide the same accuracy. The study results demonstrate high tumour classification accuracy and high probability of detection in benign and malignant cases.

Surface microtexturing design, laser-etching and adhesive failure of aluminum alloy single-lap-joint: Experiment and simulation

This study investigates the design and laser etching of surface microtextures on Al substrate to significantly improve the adhesive performance. Microstructures with different patterns were designed and fabricated. Also laser etching parameters such as etching power, line space and number of scans were thoroughly studied. The obtained microstructures exhibit excellent hydrophilicity, which is beneficial for the permeation of adhesives and formation of micromechanical interlocking. When testing the shear strength of the Al single-lap-joint, the results show great improvement compared with unetched specimens. In terms of the significance of laser parameters and textures on shear strength, power is the most significant, followed by number of scans, and finally line space and textures. The specimen designed with X-texture and etched by 20 W with scan space of 0.2 mm and number of 2 scans achieves the highest shear strength of 24 MPa and presents an improvement of 1225% in shear strength. In addition, multi-scale simulations were conducted to effectively demonstrate the interfacial bonding behavior and damage process of Al single-lap-joint. The proposed method shows great potential in improvement of bonding performance.

Rolling preparation process and interface toughening mechanism of Al/CFRTP/Al composite laminates

AbstractIn this study, a highly efficient method for preparing Al/CFRTP/Al composite laminates by roller preparation was proposed. Three different surface treatments, namely, anodic oxidation, laser texture and surface modification, were used to improve the strength of the metal‐fiber interface. Results show that composite laminates can be prepared efficiently by using reasonable roll pressing technology. The composite laminates with a thickness of 3 mm has good shear strength when the reduction amount is 0.02 mm. Laser texturing increases the contact area at the laminate interface. The surface roughness of Al alloy sheet is improved after laser texture. Moreover, the matrix in the fiber layer of the laminate can be embedded in the gullies formed by the laser texture to form a mechanical interlocking structure. The shear strength of the laminates was further increased when the laser scanning spacing was 2 mm. The highest shear strength of the laminate is 52.4 MPa after using a coupling agent to modify the surface of the Al alloy sheet. X‐ray photoelectron spectroscopy analysis showed that a new chemical bond was generated at the interface between CFRTP and the Al alloy sheet modified with silane coupling agent, thereby forming a molecular bridge among different materials. Mechanical interlocking structure and the generation of new chemical bonds cause the interface to need to absorb more energy during the failure process, which is conducive to the improvement of the interface strength.Highlights Propose roller pressing to prepare Al/CFRTP/Al composite laminates. Effect of laser texture of the laminates interface is clarified. Mechanism of coupling agents at the interface has been elucidated. Efficient preparation of thermoplastic fiber metal laminates has been achieved.

Microwave dielectric properties and frequency-controlled beam scanning application of Nb5+-substituted calcium-magnesium vanadate low-temperature sintered ceramics

Beam scanning devices in the X-band allow spatial reorientation of the beam, but this poses challenges for material and device design. To meet such challenges, the development of microwave dielectric materials and the design of special structures are crucial. Here, the microwave dielectric properties of Ca5Mn4V6-xNbxO24 (x = 0.00–0.08) ceramics are systematically investigated by using first-principles calculations and microstructural analysis. The ceramic has the best microwave dielectric properties (εr = 10.92 ± 0.14, Q × f = 50032 ± 1795 GHz (@10.52 GHz), τf = −59.58 ± 3.81 ppm/°C) when x = 0.04 and T = 875 °C. As a concept demonstration for device applications, a frequency-controlled beam scanning device in the X-band is designed by using this ceramic and copper electrode. This device has a beam scanning space of 3.248° (from 27.143° to 32.371°) in the frequency range of 10–11 GHz while maintaining high reflectivity (≥0.6). This function is verified by simulation results for far-field amplitude and far-field phase. This work contributes to the application of microwave dielectric ceramics.

Integrated factor of efficiency of antenna system using in the radar

Integrated efficiency factors are used not only at the design stage, but also in the case of choosing a ready-made system. In this case, the purpose of the research is to get an answer to the question of the expediency of its purchase (deployment), or monitoring the effectiveness of the system during its operation and developing proposals for optimizing the ways of its use and modernization. Since any system has limited resources when solving assignment tasks, it is necessary to develop a generalized efficiency factor from the standpoint of analyzing the effective allocation of radar resources when using antenna systems of various types in its composition. The aim of the article is to increase the efficiency of the use of radar resources in the antenna system. Achieving this goal includes solving the following tasks: substantiation of an integrated efficiency factor of the use of the antenna system in the radar, the use of an integrated efficiency factor to compare different types of antenna systems in the radar. А comparison of the efficiency of using a digital antenna array (DAA) with two-dimensional electronic scanning of the radiation pattern and parallel space surveillance, a reflector antenna, a passive phased antenna array with one-dimensional scanning, as well as an active phased antenna array with one-dimensional scanning and parallel space surveillance has been performed. It has been shown that the efficiency of using a DAR with two-dimensional electronic scanning is 2.3...15.6 times higher than the efficiency of other types of antenna systems. The proposed efficiency factor makes it possible to compare the efficiency of the use of radar resources when using different types of antenna systems, taking into account the features of their construction and the requirements for the purpose of the radar.

Effect of scanning spacing on the efficiency of CFRP hole-cutting with multi-pass scanning strategy by nanosecond laser

Short-pulse laser processing of CFRP can reduce heat damage, but the efficiency is limited. In this paper, the efficiency of CFRP hole-cutting with multi-pass scanning strategy by nanosecond laser was investigated. The differences in material removal mechanisms at different scanning spacing and the effect of different scanning spacing on processing efficiency were investigated. The results show that the material is removed by the combined effect of laser ablation and mechanical erosion effect with different scanning spacing, and the appropriate scanning spacing and number of passes can effectively utilize the effect of mechanical erosion to improve processing efficiency. With a repetition frequency of 80 kHz (pulse energy is 141.25 μJ), the shortest cutting time is 73.3 s, and the optimal scanning spacing is 0.06 mm (focused spot diameter is 22 μm), which is 26.8 % more efficient compared to the scanning spacing of 0.08 mm and number of passes with 3; As laser repetition frequency increases, the optimal scanning spacing for processing efficiency increases and the optimal number of passes decreases.

Metallic ferrimagnetism and magnetic domain structure in (001) NiCo2O4 films grown at various temperatures

Epitaxial 31-nm-thick (001) NiCo2O4 films exhibiting metallic and ferrimagnetic properties at room temperature were grown on (001) MgAl2O4 substrates at various deposition temperatures. θ/2θ scan and reciprocal space mapping X-ray diffraction measurements indicated that tetragonal lattice distortion in the (001) NiCo2O4 films increased with the deposition temperature. Metallic ferrimagnetism and perpendicular magnetic anisotropy (PMA) were observed for (001) NiCo2O4 films grown at deposition temperatures below 350 °C. Remarkably, the ferrimagnetic transition temperature continuously decreased with increasing deposition temperature up to 350 °C, whereas images of the magnetic domains indicated that the density of the nucleated small domains during the early stage of magnetic reversal increased with the deposition temperature. Consequently, the PMA of the (001) NiCo2O4 films at room temperature was optimized using a deposition temperature of approximately 320 °C. The results of this study indicate that the deposition temperature is a useful parameter for adjusting the PMA and magnetic domain structure of NiCo2O4 films by inducing variations in structural distortion and metallic ferrimagnetism.

Study on anisotropic heat transfer and thermal damage in nanosecond pulsed laser processing of CFRP

AbstractNanosecond pulsed laser processing is an efficient method of processing carbon fiber reinforced plastic(CFRP), which is widely used in the manufacturing field of aviation, medical, and auto industries. The anisotropic heat transfer of carbon fiber is a key factor degrading the surface integrity of laser processing CFRP. So it is urgent to explore the significant mechanism of anisotropic heat transfer of laser interacting with CFRP. A novel numerical model considering anisotropic heat transfer was established to analyze heat transfer and thermal damage of CFRP laser machining. By comparison of simulation and experiments, the average error of ablation depth and width ranges from 4.71% to 15.09%, so the model could precisely simulate the CFRP laser machining. It demonstrates that the heat conductivity along the axial carbon fiber is higher than that along the radial, resulting in an elliptical ablation morphology. And when the laser scanning direction is parallel to the direction of the carbon fiber, deeper and narrower microgrooves can be obtained. In addition, laser processing at the edge of the CFRP plate causes serious heat accumulation, leading to severe thermal damage. The simulation and experiments were conducted to explore the effect of parameters including laser energy, scanning speed, and scanning space on the depth and width of laser ablation. A deeper micro‐channel with a smooth machined surface and small thermal damage was obtained when laser energy E = 0.275 mJ, scanning speed v = 630 mm/s, and scanning space h = 21 μm.

Research on selective laser sintering process of ternary composite materials (PP/MCMB/CNT)

The composite material composed of polypropylene and conductive filler has good corrosion resistance, light weight and good conductivity, and is one of the preferred materials for fuel cell bipolar plates. The formation of ternary composite materials composed of polypropylene, mesocarbon microbeads and carbon nanotubes is realized by selective laser sintering. The influences of laser power, scanning speed, scanning spacing and defocus amount on forming quality are studied. The formability of mixed powders with different composition proportions as well as the conductivity, bending strength and hydrophobicity of the formed samples are investigated. The results show that when the input energy density is insufficient, it is easy to form defects such as spheroidized particles and worm-like structures. The parameters with good forming quality are in the following range: defocus amount is + 3 mm; line energy density is 2.94–3.85 J/mm2; peak power density is 1.13 × 104-1.48 × 104 W/mm2 and scanning spacing is 0.1–0.14 mm. The conductive filler in composite material is beneficial to improving the conductivity, but it will reduce the formability of the mixed powders and reduce the bending strength and hydrophobicity of the sample. The effect of mesocarbon microbeads on improving conductivity or on reducing hydrophobicity is smaller than that of carbon nanotubes.

Parameters Optimization of Laser-Grinding Chain for Processing Groove of 2.5-Dimensional C/SiC Composites.

Aiming at problems such as poor precision of laser processing C/SiC composites, low efficiency of grinding C/SiC composites, and serious wear of grinding wheel, a method of laser-grinding chain processing C/SiC composite groove was proposed in this paper. The method combined the high efficiency characteristic of laser ablating and the high precision characteristic of grinding. The relationship between laser processing parameters and the characteristics of ablative grooves was investigated, and the appropriate laser processing parameters were optimized, and then, to further improve the processing quality of the grooves, the grinding parameters optimization experiments of the grooves of C/SiC composites were carried out. The results showed that the C/SiC composites could be quickly removed by laser processing, and the grooves with relatively good size and shape accuracy could be obtained by laser parameters optimization experiments, but the side wall of the groove still had a certain inclination and the surface quality of the groove was yet poor; meanwhile, the size accuracy, shape accuracy, and surface quality of the grooves were greatly improved by further grinding. In addition, then, through the laser and grinding optimization experiments, the optimized parameters were obtained, where the laser power was 80 W, the scanning speed was 300 mm/s, the scanning frequency was 50 kHz, the scanning spacing was 25 μm, the depth of cut was 30 μm, the liner speed of wheel was 62.832 m/min, and the feed speed was 10 mm/min. With these parameters, the time used to process the groove with the laser-grinding chain was about 23/40 of the grinding process, and the quality of grooves could be guaranteed. Therefore, combined with the optimized process parameters, the laser-grinding chain processing scheme could be used to achieve high efficiency and precision grinding of C/SiC composite grooves.

Preparation of high-performance ZrO2 bio-ceramics by stereolithography for dental restorations

Stereolithography (SLA) 3D printing technology is an advanced technology with great advantages and prospects in the field of dental repair that needs personalization and high precision. In this work, we tried to optimize the printing parameters, including laser power, scanning space, and layer thickness, from the dimension accuracy, warpage, and surface quality of the prepared samples and focus on the research and optimization of the debinding process in the heat treatment process. Starting from dimensional accuracy, warpage and surface quality, the optimal combination of printing parameters was 160 mW laser power, 0.07 mm scanning spacing and the ratio of layer thickness (Lt) to cured depth (Cd) was 1/3. In addition, it was found that the debinding atmosphere had a significant impact on the debinding effect of zirconia green body. The process of debinding in the nitrogen atmosphere and decarbonizing in the air atmosphere was finally adopted, which reduced the pyrolysis rate of organic matter, avoided the defects such as cracking of green body and bulging of sintered body, and improved the performance of ceramic samples. It was worth emphasizing that Vickers hardness, flexural strength and fracture toughness of the ZrO2 dental ceramics were 13.67 ± 0.72 GPa, 820 ± 59 MPa and 5.89 ± 0.63 MPa m1/2, respectively, and had good biocompatibility. The research results could provide some useful guidance for the selection of SLA printing parameters and the optimization of the heat treatment process.

Study on Laser Selective Curing Additive Manufacturing of Foamed Structural Ceramics

An additive manufacturing method for ceramic materials with internally formed foaming structure was proposed in this paper with the adoption of ceramic powder and sodium silicate binder to prepare sizing agent. The forming process on each layer consists of three basic processes, including spreading, freezing and laser scanning. Foaming structure arises due to the foaming effect of the frozen sodium silicate caused by laser gasification. After 3D printing, the support material in frozen state will be removed when it has been melt in water. Then finally the green ceramic parts internally filled with foaming structures will come into being. Experimental results show that the laser parameters, the content of ceramic, the scanning spacing and other factors affect the interior appearance of the green part. At the scanning speed of 100 mm·s-1, laser power of 20 W, and 0.3 mm scanning spacing, the ceramic parts are processed with a slurry with 50% solid content. The support materials in the deep fine structure can be quickly removed without mechanical damage or swelling in the water. This new process can be used to process thermal insulation ceramic parts.

4D printing of polyamide 1212 based shape memory thermoplastic polyamide elastomers by selective laser sintering

4D printing technology, also known as additive manufacturing technology for smart devices, offers a wide range of promising applications in aerospace, automobile, biomedical and soft robotics. However, there are only a limited number of commercialized elastomer materials for 3D printing which needs further development, especially smart elastomers. In this work, polyamide 1212 (PA1212) based thermoplastic polyamide elastomer (TPAE) was synthesized by one-pot melt polycondensation of 1,12-dodecanedioic acid (DA), 1,12-dodecanedioic amine (DN) and polyetheramine in a stainless steel reactor and then the TPAE powder for selective laser sintering (SLS) was obtained after freeze-crushing and sieving. Subsequently, the effects of sintering temperature, laser power, layer thickness, and scan spacing during SLS processing on the properties of the sintered parts were fully investigated. The tensile strength, elastic modulus and elongation at break of the sintered parts could reach 13.7 MPa, 124 MPa and 200 %, respectively, when the sintering temperature, laser power, layer thickness and scan spacing were set as 156 °C, 21 W, 0.10 mm and 0.10 mm, respectively. Moreover, PA1212-based TPAEs fabricated by SLS showed excellent and stable shape memory behavior. This work not only provides a designing strategy of 4D printable materials and referential SLS-processing parameters, but also broadens the application of polyamide-based elastomer materials into 4D printing fields.

Laser sintering of polyether sulfone/carbon black composite powders using near-infrared laser

Low-cost miniaturized laser sintering equipment remains lacking at present; therefore, the development of laser sintering technology and its widespread applications are significantly hindered. Traditional laser sintering equipment is composed of a carbon dioxide laser, water cooling system, powder-box-heating device, and thermal insulation device. Such requirements are the main factors limiting the miniaturization and economic efficiency of laser sintering equipment. Herein, a laser-sintered material was fabricated by sintering using a near-infrared laser light source with a wavelength of 1064 nm without heating, and its microstructure and properties were systematically studied. Polyether sulfone (PES) and carbon black (CB) powders were selected as the raw materials for preparing PES/CB composites by mechanical mixing. For synthesizing the PES/CB composite powders, the CB powder content was varied within the range of 0.25%–1.5%. The PES/CB powders with different component ratios were subjected to laser sintering treatment, and the corresponding microstructural evolutions of the sintered parts were analyzed. The effects of different component ratios on the mechanical properties and dimensional accuracy of the sintered part were investigated, and the optimal content of CB powders of the PES/CB composite material was determined. Additionally, the effects of laser power (10–18 W), scanning speed (1200–1600 mm/s), and scanning spacing (0.04–0.08 mm) on the forming quality of the sintered parts of the PES/CB composite powders were evaluated. The processing parameters of the laser sintering of PES/CB composite powders were explored using orthogonal experimental tests and optimized using the comprehensive weighted method.