Zhipeng Lai

Effects of Current Frequency on Electromagnetic Sheet Metal Forming Process

In the paper, the effects of current frequency on the electromagnetic sheet metal forming process are investigated using an efficient finite element model, which couples analysis of circuit, electromagnetic, and mechanical equations. Based on the initial electrical and structural parameters of the system, the model calculates the pulsed current flowing through the coil, the consequent magnetic force acting on the metal sheet, and finally the generated sheet deformation. The effects of current frequency on the maximum displacement in axial direction of the sheet are analyzed for two sheets by changing the capacitance of capacitor bank, while keeping the stored energy constant. The results show that there exist two optimum frequencies that produce relatively large sheet deformation and the optimum frequencies are related with the thickness of the sheet.

The Electromagnetic Flanging of a Large-Scale Sheet Workpiece

In this paper, an electromagnetic forming (EMF) system with an energy of 200 kJ (25 kV, 640 μF) was designed and fabricated to flange a large-scale aluminum alloy sheet with bore, whose outer diameter, bore diameter, and sheet thickness are 640 mm, 180 mm, and 5 mm, respectively. The stress distribution of the midplane of the coil was calculated to check the coil structural strength. And a multiphysics coupled finite element model, which involves the coupling of circuit, electromagnetic field, deformation field, and thermal field, was built to assess the forming capacity of the EMF system. Furthermore, the experimental results of electromagnetic flanging in the case of 155 kJ are presented and compared with the numerical results. Both the simulation forming depth 87 mm and experiment forming depth 90 mm show that the EMF system is effective to form the large-scale sheet workpiece.

Design, Implementation, and Testing of a Pulsed Electromagnetic Blank Holder System

In this paper, pulsed attractive electromagnetic force between two coils has been introduced for supplying blank holding force in sheet metal forming process. First, the requirements on the pulsed blank holding force and constraint conditions on the system were specified. Then, a design flow of the coil system fulfilling the requirements was presented. Based on the design, a prototype of a pulsed electromagnetic blank holder was fabricated. Numerical and experimental investigations were carried out to validate the feasibility of the designed system. Results show good agreement between the measured and simulated results of discharge currents and magnetic fields. The system generates a pulsed blank holding force with a magnitude of 930 kN and a rise time of 4.56 ms, which fulfills the specified requirements.

Axially Movable Electromagnetic Forming System for Large-Scale Metallic Sheet

How to generate strong enough electromagnetic forces in the electromagnetic forming process is an important issue for sheet forming. For this purpose, an axially movable electromagnetic forming system was designed, fabricated, and tested. To validate the effectiveness of the system, a series of experiments on the forming of AA1060 with a diameter of 440 mm and a thickness of 3 mm has been carried out. A pulsed magnet with an inner diameter of 100 mm and an outer diameter of 200 mm was used to drive the sheet. A capacitor bank power supply (200 kJ/25 kV/640 μF) has been used to energize the coil. The experimental results have shown that the maximum deformation depth of the workpiece is only about 90 mm when the forming coil was fixed after three discharges. This value can be greatly increased to 130 mm by the use of the proposed forming method in which the distance between the coil and the deformed workpiece was decreased in each discharge process. Meanwhile, the geometric accuracy between the final deformed workpiece and die is less than 3 mm according to the three-dimensional scanning analysis.

Design and Experimental Validation of a Pulsed Electromagnetic Sheet Shearing System

A pulsed electromagnetic shearing system consisting of a pulsed magnet driven by a capacitor bank and a conductive plate as a driver has been proposed, designed, and developed for thick plate cutting. The interaction of the pulsed magnetic field with the eddy current induced on the copper driver produces a huge Lorentz force that pushes a blade to cut off the steel sheet of heavy thickness. To validate the effectiveness of the system, magnetic force acting on the driver plate in the shearing process was analyzed and a series of experiments were carried out. Results show that the maximum of generated electromagnetic force reaches about 100 tons in the simulations and a steel plate with a thickness of 10 mm can be effectively cut without any burrs and slivers in the experiments.

Development of Space-Time-Controlled Multi-Stage Pulsed Magnetic Field Forming and Manufacturing Technology at the WHMFC*

In November 2011, the Project of Basic Research of Forming by Space-Time-Controlled Multi-Stage Pulsed Magnetic Field (Stic-Must-PMF) was supported by the National Basic Research Program of China (973 Project, 2011.11-2016.08). It is aimed at achieving breakthroughs in manufacturing technology to solve current problems in forming largescale and complex sheet and tube parts and components, imposed by the limitations of existing equipment and materials forming properties. The objective of our research group focuses on the design principles and structural layout optimization of Stic-Must-PMF facility. And this paper will report the development of Stic-Must-PMF forming and manufacturing technology at the Wuhan National High Magnetic Field Center (WHMFC) including numerical modeling, experimental setup and experimental studies.

Effect of Electromagnetic Ring Expansion on the Mechanical Property of A5083 Aluminum Alloy

Electromagnetic forming (EMF) is a promising metal-forming process for complex geometrical shape and light-weight construction. Ring expansion is one of the basic EMFs wherein the workpiece is under nearly uniform tensile stress. The final strains of the rings at different discharge voltages are measured. It is found that the strain increases with the voltage. The strain can exceed the maximum strain in the ASTM standard tension test when the voltage is higher than 8 kV, and it has the largest improvement of 53% at 9 kV. The Vickers hardness is also measured at each voltage. Also, a rising trend is observed as the voltage increases. The highest hardness is found at 9 kV with a value of 110.1. It has an increase of 46% compared to the ring without expansion. Finally, the microstructure of the expanded ring is observed with the electron backscatter diffraction technique.

Application of Triple-Coil System for Improving Deformation Depth of Tube in Electromagnetic Forming

To increase the deformation depth of a tube in an electromagnetic forming system, a triple-coil system was proposed and analyzed in this paper. The system consisted of three coils, in which one coil was placed in the middle plane, whereas the other two coils connected in series were placed at either end of the tube. The first type of coil was used for radial expansion, and the second type of coil was applied to introduce an additional axial electromagnetic force in the forming process. These two types of coils were energized by two independent pulsed capacitor banks for improving Lorentz force distribution of the tube. As a proof of concept, numerical simulations for investigating the Lorentz force distribution and deformation behavior of an aluminum tube (1060) were performed based on MATLAB 2015a and ANSYS 14.0. In addition, results show that the deformation depth can be improved by the use of the proposed system due to an obvious inhibition effect on wall thickness reduction.

Effect of Induced Current on the Flow Stress in the Electromagnetic Ring Expansion

The electromagnetic forming (EMF) is a promising metal-forming process for the complex geometric shape and lightweight construction. Material behavior in EMF is one of the important researches. Herein, an experiment system of the electromagnetic ring expansion is employed to study the flow stress in the EMF with the consideration of the induced current, high strain rate, and temperature rise. Compared with the simulation results, the experiment results are analyzed to investigate the effect of induced current on the flow stress of the aluminum alloy during the EMF.

Electromagnetically Driven Expanding Ring Test for the Strength Study of the Zylon/Epoxy Composite

An improved electromagnetically launched method for driving specimens of composite materials is developed. The electromagnetic expansion ring device consists of a solenoid and sample rings. The solenoid is made up of eight layers of copper wire reinforced with Zylon fiber, which can produce magnetic field up to 35 T. The sample ring is composed of a high-conductivity driver (6061-T6 aluminum ring) and a layer of Zylon/epoxy composite that is directly wound on the driver. The solenoid driven by a 100-kJ (25 kV, 320