An infrared camera after calibration test was used to capture the surface temperature of the deposited thin-wall parts for investigating the thermal behavior of gas metal arc welding (GMAW) based ...additive manufacturing (AM). The temperature field cloud pictures indicated that as the deposition height increased, the heat accumulation of the deposited parts became serious. Through extending the inter-layer cooling time, the high temperature area and the mean temperature of the thin-wall part decreased while the temperature gradient and cooling rate of the deposited part increased. But excessive inter-layer cooling time cannot reduce heat accumulation of the deposited parts effectively and will make the deposition process time-consuming. The comparison of the final parts in forming appearance with different inter-layer cooling time indicated that the moderate prolongation of inter-layer cooling time contributed to improvement of the surface quality and reduction of the total height difference. Using the alternate inter-layer cooling time can improve the forming quality of the thin-wall part distinctly with a little increase of the deposition time in GMAW based AM.
A passive vision sensor system has been developed to monitor the nozzle to the top surface distance (NTSD) in layer additive manufacturing (LAM) using gas metal arc welding (GMAW). The deviations in ...the NTSD are compensated by the movement of the working flat, and the adjustment of the deposition rate on next deposition layer. After simplification of the controlled process into a linear system, an adaptive control system has been designed to keep the NTSD constant. The effectiveness of the controller is evaluated through deposition of single-bead multi-layer walls, and the experimental results confirm that the process stability can be improved when applying the developed controller.
The detection and identification of impact craters on a planetary surface are crucially important for planetary studies and autonomous navigation. Crater detection refers to finding craters in a ...given image, whereas identification means to actually mapping them to particular reference craters. However, no method is available for simultaneously detecting and identifying craters with sufficient accuracy and robustness. Thus, this study proposes a novel end-to-end fully convolutional neural network (CNN), namely, CraterIDNet, which takes remotely sensed planetary images of any size as input and outputs detected crater positions, apparent diameters, and identification results. CraterIDNet comprises two pipelines, namely, crater detection pipeline (CDP) and crater identification pipeline (CIP). First, we propose a pre-trained model with high generalization performance for transfer learning. Then, anchor scale optimization and anchor density adjustment are proposed for CDP. In addition, multi-scale impact craters are detected simultaneously by using different feature maps with multi-scale receptive fields. These strategies considerably improve the detection performance of small craters. Furthermore, a grid pattern layer is proposed to generate grid patterns with rotation and scale invariance for CIP. The grid pattern integrates the distribution and scale information of nearby craters, which will remarkably improve identification robustness when combined with the CNN framework. We comprehensively evaluate CraterIDNet and present state-of-the-art crater detection and identification performance with a small network architecture (4 MB).
A novel additive manufacturing (AM) system using double electrode gas metal arc welding (DE-GMAW) was developed to fabricate metallic products. The width of the deposited multi-layer parts decreased ...with the increasing of the bypass current and the deposited height increased in proportion to the bypass current under the same deposition rate. The height difference between arc striking point and arc extinguishing point in the deposited parts was reduced by the bypass arc. The coefficient of materials utilization increased more than 10% using DE-GMAW for depositing thin-wall parts within a certain range of bypass current. The DE-GMAW based AM shows promise to fabricate narrower thin-wall components with high deposition rate and has higher deposition efficiency, compared with the normal GMAW based AM.
The recent progress of wide bandgap (WBG) donor polymers for non-fullerene polymer solar cells (NF-PSCs) were reviewed in detail, which was classified by D-type and DA type molecular backbones to ...discuss the related structure-property correlations and put forward an outlook for future innovations.
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This review summarized the recent progress of highly efficient wide bandgap (WBG) donor polymers and their applications in non-fullerene polymer solar cells (NF-PSCs). A brief introduction of the background of WBG donor polymer developments was given. Then the research progress of the reported WBG donor polymers by classification of D-type and DA type molecular backbones was reviewed. The resulting structure-property correlations of the WBG donor polymers were also discussed to highlight the importance of chemical modifications, which have promoted the great progress of NF-PSC field. Finally, an outlook for future innovations of WBG donor polymers and their NF-PSCs was provided.
Two novel wide bandgap copolymers based on quinoxalino6,5‐fquinoxaline (NQx) acceptor block, PBDT–NQx and PBDTS–NQx, are successfully synthesized for efficient nonfullerene polymer solar cells ...(PSCs). The attached conjugated side chains on both benzodithiophene (BDT) and NQx endow the resulting copolymers with low‐lying highest occupied molecular orbital (HOMO) levels. The sulfur atom insertion further reduces the HOMO level of PBDTS–NQx to −5.31 eV, contributing to a high open‐circuit voltage, Voc, of 0.91 V. Conjugated n‐octylthienyl side chains attached on the NQx skeletons also significantly improve the π–π* transitions and optical absorptions of the copolymers in the region of short wavelengths, which induce a good complementary absorption when blending with the low bandgap small molecular acceptor of 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno2,3‐d:2′,3′‐d′‐s‐indaceno1,2‐b:5,6‐b′dithiophene. The wide absorption range makes the active blends absorb more photons, giving rise to a high short‐circuit current density, Jsc, value of 15.62 mA cm−2. The sulfur atom insertion also enhances the crystallinity of PBDTS–NQx and presents its blend film with a favorable nanophase separation, resulting in improved Jsc and fill factor (FF) values with a high power conversion efficiency of 11.47%. This work not only provides a new fused ring acceptor block (NQx) for constructing high‐performance wide bandgap copolymers but also provides the NQx‐based copolymers for achieving highly efficient nonfullerene PSCs.
Two novel wide bandgap copolymers based on quinoxalino6,5‐fquinoxaline (NQx) acceptor block, PBDT–NQx and PBDTS–NQx, are successfully synthesized for efficient nonfullerene polymer solar cells. These new polymers exhibit high absorption at short wavelength, matching well with low bandgap acceptors, and have deep highest occupied molecular orbital (HOMO) levels, allowing their use in highly efficient nonfullerene solar cells with up to 11.47% power conversion efficiency.
A wide bandgap small molecular acceptor, SFBRCN, containing a 3D spirobifluorene core flaked with a 2,1,3‐benzothiadiazole (BT) and end‐capped with highly electron‐deficient ...(3‐ethylhexyl‐4‐oxothiazolidine‐2‐yl)dimalononitrile (RCN) units, has been successfully synthesized as a small molecular acceptor (SMA) for nonfullerene polymer solar cells (PSCs). This SMA exhibits a relatively wide optical bandgap of 2.03 eV, which provides a complementary absorption to commonly used low bandgap donor polymers, such as PTB7‐Th. The strong electron‐deficient BT and RCN units afford SFBRCN with a low‐lying LUMO (lowest unoccupied molecular orbital) level, while the 3D structured spirobifluorene core can effectively suppress the self‐aggregation tendency of the SMA, thus yielding a polymer:SMA blend with reasonably small domain size. As the results of such molecular design, SFBRCN enables nonfullerene PSCs with a high efficiency of 10.26%, which is the highest performance reported to date for a large bandgap nonfullerene SMA.
A wide bandgap small molecular acceptor, SFBRCN, containing a 3D spirobifluorene core flanked with two 2,1,3‐benzothiadiazole groups and end‐capped with two highly electron‐deficient (3‐ethylhexyl‐4‐oxothiazolidine‐2‐yl)dimalononitrile units, has been successfully synthesized as a small molecular acceptor for nonfullerene polymer solar cells with a high efficiency of 10.26%.
Rapid manufacturing technologies have made it possible to reduce material wastes and to remanufacture valuable dies and tools. This paper focuses on reasonable utilization of materials and energies ...in gas metal arc welding (GMAW) for rapid manufacturing. During the weld-based additive manufacturing process, geometries of the deposited weld beads should be monitored and controlled. Using a composite filtering technique, a computer vision-sensing system was designed. Features of the weld bead image were analyzed. A corresponding image processing technology was used to extract parameters of the deposited weld beads. An on-line control of the deposited beads was realized based on a segmented neuron self-learning controller. The results show that the proposed control system is capable of keeping the deposited bead width of a thin-walled part consistent, making an efficient use of materials and energies possible.
► A vision sensing system was designed for bead width detection. ► An improved proportional summational differential controller was developed. ► Keeping bead width consistent was realized based on closed-loop control. ► Material and energy saving were realized in weld-based rapid manufacturing.
Weld-based rapid prototyping enables the capacity of forming 3D complex parts. In rapid prototyping there exists the particular thermal cycling, being repeatedly heated at the same place, which is ...the basic cause of complex thermal stress. In this paper experiments are carried out to investigate the thermal characters of single-pass ten-layer deposition. Meanwhile a 3D transient heat transfer numerical simulation with temperature-dependent material properties is conducted to investigate temperature field evolution, thermal cycling character, temperature gradient and the effects of depositing directions on the thermal process of single-pass ten-layer rapid prototyping. The calculated results match the experimental measurements well. The research results show that the heat diffusion condition of molten pool becomes worse as the depositing height increases. With other parameters being constant, the heat diffusion condition can be significantly improved by optimizing the depositing directions. The heat diffusion condition of component with the same depositing directions is better than reverse directions.
In this paper, the magnetic immunity model of STT-MRAM is established. The influence of the external magnetic field on the effective energy barrier of STT-MRAM is investigated, which is the crucial ...issue to influence the reliability of STT-MRAM cells in the standby, active read and active write modes. The influence factors on the magnetic immunity of STT-MRAM array are also discussed in the paper, such as the electrode, package material, insert layer and array spacing, etc. Moreover, the magnetic shield models in the BGA and QFP packages are designed and analyzed for the enhancement of the magnetic immunity of STT-MRAM, whose shielding efficiency is up to 98.2%.
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