Improving the fatigue life of hole components is very important since cracks are often initiated from the hole wall due to stress concentration. In this study, the non-contacting electromagnetic cold ...expansion process (EMCE) was employed to improve the fatigue life of the AZ31 sheet with fastening hole. Simulation was done to investigate the distribution of residual stress and strain around the hole during the EMCE process. The effect of EMCE process on the surface integrity of the hole specimen was investigated via 3D super depth digital microscope. EBSD was utilized to observe the deformation and grain size distribution near the hole edge. Fatigue test was done to verify the feasibility of EMCE process on improving the fatigue life of thin AZ31 sheet specimen, and the fatigue fracture was observed by SEM. Results showed that the EMCE process can improve the fatigue life and fatigue limit of the AZ31 specimen. The specimen treated by EMCE process showed well surface integrity, and grain refinement was observed near the hole edge.
Accurate calculation of electromagnetic parameters in electromagnetic forming (EMF) process is crucial for predicting the deformation behavior of metallic workpieces. Previous theoretical and ...numerical studies for EMF process with a die have assumed that the die near the workpiece is non-conductive. However, the simplified treatment could be invalid for the cases with a conductive die since an eddy current would also be induced in the die under transient magnetic fields, thus resulting in the change of electromagnetic force acting on the workpiece. In this work, a coupled finite element method and circuit simulation approach with an improved circuit model for analyzing the workpiece deformation is presented, in which the mechanical analysis of the workpiece is done using ANSYS, while the circuit analysis is performed using an improved current filament model. Numerical simulations have been carried out for two types of EMF process, revealing the potential effects of an electrically conductive die on the electromagnetic force distribution and workpeice deformation. The coupled modeling method and simulation results could be useful for better understanding EMF process and designing EMF systems.
The size of the plastic deformation zone caused by fastener hole strengthening is a critical indicator of the strengthening performance. In this study, 2A12-T4 aluminum alloy specimens with a hole ...diameter of 6 mm and thickness of 1.5 mm were strengthened by Lorentz force through the electromagnetic strengthening method. The numerical results show that the Lorentz force can introduce tensile stress in both hoop and radial directions in the specimen during the strengthening process and produce a high compressive hoop residual stress around holes without serious axial deformation compared with the conventional cold hole expansion process. The simulation results are experimentally validated by the grid method in verifying the residual strain, and the fatigue life can be improved by several times after strengthening. Furthermore, under the same discharge energy, there is an optimal capacitance of around 40 μF in this work to achieve the maximum size of the plastic deformation zone. In addition, a larger crowbar resistance can cause a stronger radial inward Lorentz force during the unloading process and result in lower residual stress; therefore, the crowbar resistance should be as small as possible.
How to reduce the temperature rise of coil winding is an important issue for improving the production and lifetime performance of the tool coil in electromagnetic forming system. To address the ...problem, this paper proposes a new discharge circuit configuration with a crowbar circuit to control the discharge current flowing in the tool coil and then to reduce the Joule heating generated without affecting the forming efficiency. A detailed numerical analysis of the mechanism of the temperature rise reduction was first carried out, and then numerical simulation and experimental investigation of the effects of the crowbar circuit on the coil current and surface temperature rise were investigated. The simulation results show that the Joule heating in the coil winding can be reduced from 4.62kJ to 2.07kJ when a crowbar circuit with a resistor of 0.3Ω was applied, and the corresponding temperature rise in the coil can also be effectively reduced. Meanwhile, the experimental results show good agreements with the simulation results, further verifying the effectiveness of the proposed method.
This paper reported an analytical formulation for the optimum geometry of a uniform pressure coil used in electromagnetic forming and welding. To characterize the energy efficiency of the coil, we ...defined the objective function as the ratio between the produced magnetic pressure and the required magnetic energy. We then deduced an analytical formulation of the objective function in terms of the geometry and electromagnetic parameters. Based on the analytical formulation, we finally deduced the optimum configuration of the coil geometry in analytical form. To validate the proposed analytical formulation, we analytically and numerically analyzed a uniform pressure coil fabricated in our laboratory, showing that the proposed analytical formulation can well reproduce the numerical results over a broad range of geometric parameters. In addition, it was found that the uniform pressure coil exhibits an optimum channel height, which can be analytically expressed in terms of the coil geometry. In summary, the present study provides an efficient method for designing a uniform pressure coil.
The Lorentz force distribution on a tube is the dominant factor that determines the tube deformation behavior in the electromagnetic forming process. However, the existing forming technologies in ...this field are mainly based on a single-coil system, which results in a relatively fixed Lorentz force distribution and makes it difficult to control the forming process or the final tube shape. To solve this problem, a three-coil forming system composed of three sub-coils and two pulsed power supplies is developed for tube forming in this work. Both numerical simulation and experimental results show that the three-coil system can be easily applied to alter the Lorentz force distribution through adjusting the discharge voltage of sub-coils, providing an effective way to improve the deformation uniformity and control the deformation shape. It is found that an AA6061-O aluminum alloy tube with an inner diameter of 76 mm and a thickness of 2 mm can be deformed with a homogeneous deformation range of about 23.56 mm via the three-coil system in the experiments, while the range is only about 11.48 mm under the same conditions when using the conventional single-coil system. Meanwhile, it is demonstrated that the three-coil system can achieve a variety of tube shapes including concave and convex profiles with different uniformity. The developed method and obtained results are of good value for expanding the application of electromagnetic tube forming.
The Lorentz-force-driven stamping process is a newly developed forming process, which combines the advantages of the quasi-static stamping and electromagnetic forming to a certain extent. It involves ...complex physical problems such as strong electro-magneto-mechanical interactions and considerable deformation. Therefore, it is still a challenge to accurately predict the electromagnetic parameters (coil current and Lorentz force, etc.) and workpiece deformation (forming height and material flow) during the stamping process for different forming conditions. To solve this problem, taking the cylindrical cup forming of 5052-O aluminum alloy sheet metal as an example, a numerical method based on the iterative calculation of a circuit-electromagnetic model and an electromagnetic-mechanical model is developed and systematically validated. Numerical tests show that, compared with the non-iterative model, the proposed iterative mode can significantly improve the simulation accuracy for different forming conditions (such as varied discharge voltages and initial gaps between the coil and the punch). It has been confirmed that the iterative procedure can well consider the effect of the increased distance between the coil and the punch on the calculations of electromagnetic and mechanical parameters. Furthermore, numerical and experimental investigations for a Lorentz-force-driven stamping system using a discharge circuit with an additional crowbar branch are carried out, showing the simulation data of discharge current and workpiece deformation agree well with that of experiment measurement. This confirms the applicability of the proposed method to different discharge circuits.
In order to overcome the limitations of the existing electromagnetic forming systems for deep drawing, a dual-coil system has been developed for deep drawing of sheet metal with large drawing ratio. ...In addition to the conventional driving coil that generates the axial Lorentz force on the workpiece, a radial inward force in the flange region is generated by a second coil that is energized by an individual power supply. The axial force pushes the sheet into the die in axial direction, while the radial Lorentz force enhances the material flow of the flange. The effectiveness of the novel system is validated by a series of experiments for deep drawing a cup of AA1060-H24 with drawing ratio of 3.25. It is demonstrated that with the dual-coil system the material flow of the flange can be significantly enhanced, and the maximum forming depth without failure is greatly increased from 8.44mm to 20.28mm. The new electromagnetic forming method is expected to break through the bottleneck of deep drawing and enable major advances in forming metallic parts and components that are difficult to form, by developing driving coils with advanced design.
Untethered capsules hold clinical potential for the diagnosis and treatment of gastrointestinal diseases. Although considerable progress has been achieved recently in this field, the constraints ...imposed by the narrow spatial structure of the capsule and complex gastrointestinal tract environment cause many open-ended problems, such as poor active motion and limited medical functions. In this work, we describe the development of small-scale magnetically driven capsules with a distinct magnetic soft valve made of dual-layer ferromagnetic soft composite films. A core technological advancement achieved is the flexible opening and closing of the magnetic soft valve by using the competitive interactions between magnetic gradient force and magnetic torque, laying the foundation for the functional integration of both drug release and sampling. Meanwhile, we propose a magnetic actuation strategy based on multi-frequency response control and demonstrate that it can achieve effective decoupled regulation of the capsule's global motion and local responses. Finally, through a comprehensive approach encompassing ideal models, animal ex vivo models, and in vivo assessment, we demonstrate the versatility of the developed magnetic capsules and their multiple potential applications in the biomedical field, such as targeted drug delivery and sampling, selective dual-drug release, and light/thermal-assisted therapy.
Deep magnetic capture and clinical application are the current trends for magnetic targeted drug delivery system. More promising and possible strategies are needed to overcome the current limitations ...and further improve the magnetic targeting technique. Recent advances in the development of targeting magnet system show promise in progressing this technology from the laboratory to the clinic. Starting from well-known basic concepts, current limitations of magnetic targeted drug delivery system are analyzed. Meanwhile, the design concepts and evaluations of some effective improvements in magnet system are discussed and reviewed with reference to (i) reasonable design of magnet system; (ii) control modes of magnet system used to generate dynamical magnetic fields; and (iii) magnetic field driving types.
► The current limitations of MTDDS for deep capture and clinical application are analyzed. ► The development of magnet system shows promise in progressing MTDDS to clinical application. ► The design concepts and evaluations of improvements in magnet system are reviewed and discussed. ► The key to improve magnet system lies in controllable magnets and different excitations.
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