Advances in Manufacturing最新文献

Deformation allocation is an important factor that affects 720° curling forming from copper-coated steel strips to double-walled brazed tubes (DWBTs). In this study, four schemes of deformation allocation, considering different weights of the total feed distance, are proposed, and a 3D finite element (FE) model of the multi-pass roll forming process for DWBT is developed and verified to investigate the cross-sectional evolution and deformation features. The results show the following. (i) In the 720° curling forming process from the steel strip into double-walled tubes, the curvature of the formed circular arc initially increases and then remains stable with roll forming, and the inner and outer tubes of the DWBT are formed in the third and fifth forming passes. Size forming can eliminate the gap between the double walls and improve the overall roundness. (ii) For different deformation allocations, the cross-sectional profiles of the roll-formed parts exhibit a discrepancy, and the deformation amount varies with the roll-forming process. The deformation amount in Scheme three is the maximum, and the cross-sectional profile deviates significantly from the ideal shape and fails to form a DWBT, which indicates that the deformation allocation is unsuitable. (iii) The roundness of the outer tube is better than that of the inner tube. Therefore, the roundness of the inner tube is the key to restricting the forming accuracy of the DWBT. Compared with Schemes one and two, Scheme four with a linear allocation of the total feed distance exhibits the best roundness, and the deformation allocation is reasonable; i.e., when the contact points between the rollers and steel strip are in a straight line, the roundness of the DWBT is in good agreement with the ideal condition.

Distortion during the forging or machining processes of a blade causes problems in subsequent manufacturing. This paper proposes an alternative multipoint correction method integrated with blade measurement, determination of correcting parameters, and adjustment of the correcting die. An iterative algorithm for determining the correcting parameters is proposed. Measuring equipment combining a laser displacement sensor with multipoint flexible support is manufactured to measure the blade shape. Multipoint correcting equipment with an adaptive lower die and rapid adjustment is manufactured, and software is developed for data analysis and equipment control. The correction experiment for a rough-machined steam-turbine blade indicates that the correcting parameters can be determined after one modification based on numerical simulation, and that a rough blade that meets the allowance for finish machining can be obtained using the determined correction parameters.

Abrasive waterjet (AWJ) is widely applied in 2D machining as it offers high machining efficiency and low machining cost. However, machining a 3D surface, especially for a small curvature radius freeform surface (SCRFS), results in over-erosion of the corner, and has been one of the greatest issues of AWJ. To solve this problem, a local smoothing algorithm for SCRFS is developed by the junction of two linear segments at the corner by inserting cubic second-order B-spline to smooth the nozzle path and posture under the setting tolerance error, which is aimed to avoid over-erosion due to the change in dwell time. Analytical solutions of the smooth corner position and orientation of the nozzle path are obtained by evaluating a synchronization algorithm. According to the set tolerance error of the nozzle position and orientation, the interpolation of the smooth path of the corner meets the constraint conditions of the linear feed drive. Path simulation and experimental results show that the proposed method is validated by the experimental results and has been applied to the integral blisk machining of an aero-engine.

The second-generation high-temperature superconductor tape (2G-HTS, also known as a coated conductor) based on REBaCuO (REBa₂Cu₃O_7–δ) exhibits high current density and potential cost-effective price/performance, compared with conventional superconducting materials. Using commercial 2G-HTS tapes, more than a dozen cable vendors had been manufacturing REBCO cables, such as the latest kilometer-class REBCO cable, which was incorporated into a civil grid on December 2021, as part of the record-breaking 35-kV-voltage superconductor cable demonstration project in downtown Shanghai. This paper describes the development of HTS-coated conductors, then outlines the various technological routes for their preparation, reviews the artificial flux pinning of coated conductors, and finally summarizes the technological breakthroughs, the latest research advances, and provides an outlook on their application prospects.

The heat generated and accumulated on the machined surface of an Inconel 718 workpiece causes thermal damage during the cutting process. Surface-active media with high thermal conductivity coated on the workpiece to be machined may have the potential to reduce the generation of cutting heat. In this study, a theoretical model for predicting the instantaneous machined surface temperature field is proposed for surface-active thermal conductive medium (SACM)-assisted cutting based on the finite element and Fourier heat transfer theories. Orthogonal cutting experiments were performed to verify the results predicted using the proposed surface-temperature field model. Three SACMs with various thermal conductivities were used to coat Inconel 718 surface to be machined. Thermocouples embedded into the workpiece were used to measure the cutting temperature at different points on the machined workpiece surface during the cutting process. The experimental results were in agreement with the predicted temperatures, and the maximum error between the experimental results and predicted temperatures was approximately 9.5%. The cutting temperature on the machined surface decreased with an increase in the thermal conductivity of the SACM. The graphene SACM with high thermal conductivity can effectively reduce the temperature from 542 °C to 402 °C, which corresponds to a reduction of approximately 26%. The temperature reduction due to SACM decreases with an increase in the distance between the temperature prediction point and machined workpiece surface. In conclusion, the cutting temperatures on the machined workpiece surface can be reduced by coating with SACM.

Understanding the fracture behavior of fused silica in contact sliding is important to the fabrication of damage-free optics. This study develops an analytical method to characterize the stress field in fused silica under contact sliding by extending the embedded center of dilation (ECD) model and considering the depth of yield region. The effects of densification on the stress fields were considered by scratch volume analysis and finite element analysis. Key mechanisms, such as crack initiation and morphology evolution were comprehensively investigated by analyzing the predicted stress fields and principal stress trajectories. The predictions were validated by Berkovich scratching experiment. It was found that partial conical, median and lateral cracks could emerge in the loading stage of the contact sliding, but radial and lateral cracks could be initiated during unloading. It was also found that the partial conical crack had the lowest initiation load. The intersection of long lateral cracks makes the material removal greater.

Robotic autonomous operating systems in global n40avigation satellite system (GNSS)-denied agricultural environments (green houses, feeding farms, and under canopy) have recently become a research hotspot. 3D light detection and ranging (LiDAR) locates the robot depending on environment and has become a popular perception sensor to navigate agricultural robots. A rapid development methodology of a 3D LiDAR-based navigation system for agricultural robots is proposed in this study, which includes: (i) individual plant clustering and its location estimation method (improved Euclidean clustering algorithm); (ii) robot path planning and tracking control method (Lyapunov direct method); (iii) construction of a robot-LiDAR-plant unified virtual simulation environment (combination use of Gazebo and SolidWorks); and (vi) evaluating the accuracy of the navigation system (triple evaluation: virtual simulation test, physical simulation test, and field test). Applying the proposed methodology, a navigation system for a grape field operation robot has been developed. The virtual simulation test, physical simulation test with GNSS as ground truth, and field test with path tracer showed that the robot could travel along the planned path quickly and smoothly. The maximum and mean absolute errors of path tracking are 2.72 cm, 1.02 cm; 3.12 cm, 1.31 cm, respectively, which meet the accuracy requirements of field operations, establishing the effectiveness of the proposed methodology. The proposed methodology has good scalability and can be implemented in a wide variety of field robot, which is promising to shorten the development cycle of agricultural robot navigation system working in GNSS-denied environment.

Wire electrochemical machining (WECM) is a potential method for manufacturing macrostructures from difficult-to-cut materials, such as turbine slots, with good surface integrity and low costs. In this study, a novel tube electrode with array holes in the front and insulation in the back was applied using WECM to improve the machining precision and efficiency. Additionally, assisted by an immersion electrolyte and axial flushing, the electrolyte-deficient gap was supplemented to achieve the cutting of a very thick workpiece. The simulation results indicated that this method could effectively reduce the machining gap and improve the uniformity of the electric- and flow-field distributions. Experiments verified that when the uninsulated range (machining angle) was reduced from 360° to 90°, the side machining gap was reduced from 462.5 µm to 175 µm. Finally, using optimized machining parameters, array slits with gaps as small as (175±10) μm were machined on a powder superalloy René 88DT sample with a thickness of 10 mm at a feed rate of 16 µm/s. The feasibility of fabricating complex profiles using this method was verified using a self-designed servo device.

Vertical centrifugal casting can significantly enhance the filling capability of molten metals, enabling the production of complex thin-walled castings at near-rapid cooling rates. In this study, the melt flow, solidification structures, and defects in 316 L steel cast strips with a geometry of 80 mm × 60 mm × 2.5 mm produced by vertical centrifugal casting were numerically and experimentally analyzed under different rotation speeds. With gradually increasing the rotation speed from 150 r/min to 900 r/min, the simulated results showed the shortest filling time and minimum porosity volume in the cast strip at a rotation speed of 600 r/min. Since a strong turbulent flow was generated by the rotation of the mold cavity during the filling process, experimental results showed that a “non-dendritic” structure was obtained in 316 L cast strip when centrifugal force was involved, whereas the typical dendritic structure was observed in the reference sample without rotation. Most areas of the cast strip exhibited one-dimensional cooling, but three-sided cooling appeared near the side of the cast strip. Moreover, the pores and cracks in the 316 L strips were detected by computed tomography scanning and analyzed with the corresponding numerical simulations. Results indicated the existence of an optimal rotational speed for producing cast strips with minimal casting defects. This study provides a better understanding of the filling and solidification processes of strips produced by vertical centrifugal casting.

Atomic and close-to-atomic scale manufacturing (ACSM) is the core competence of Manufacturing III. Unlike other conceptions or terminologies that only focus on the atomic level precision, ACSM defines a new realm of manufacturing where quantum mechanics plays the dominant role in the atom/molecule addition, migration and removal, considering the uncertainty principle and the discrete nature of particles. As ACSM is still in its infant stage, only little has been systematically elaborated at the core proposition of ACSM by now, hence there is a need to understand its concept and vision. This article elucidates the development of ACSM and clarifies its proposition, which aims to achieve a clearer understanding on ACSM and direct more effective efforts toward this promising area.