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Electromagnetic impaction forming of 5052 aluminium alloy sheets using a V-shaped die and a conical die was performed. The conventional quasi-static forming limit curve (QS-FLC) is obtained according to the linear loading condition, which can only describe linear strain paths. However, it cannot accurately evaluate the formability of electromagnetic impaction forming, especially strain paths that have become highly non-linear. In this study, the formability of electromagnetic impaction forming, which considers a bilinear strain path and a continuous highly non-linear strain path, was investigated. The conventional QS-FLC is no longer suitable to evaluate the formability of electromagnetic impaction forming. Therefore, modified FLCs were established in strain space that follow bilinear strain paths and continuous non-linear strain paths. The actual formability improvement was compared with the modified FLC. The maximum safe strain of bilinear strain paths near the sidewall of V-shaped specimens increased in formability by approximately 30% at the discharge voltage of 20 kV compared with conventional QS forming. The maximum safe strains near the apex of the conical specimens increased in formability by approximately 100% at the same discharge energy. It should be noted that the increase in formability above the modified FLC is a conservative estimate, because the limit strains at the necking location were not known in the electromagnetic impaction forming. The influencing factors of the formability improvement of 5052 aluminium alloy sheet in electromagnetic impaction forming were also discussed. [ABSTRACT FROM AUTHOR]

A finite element model of electromagnetic blanking forming processes with field shape was established based on LS-DYNA R8.0 software for diaphragms used in carrier rocket n aerospace field, and the variation rules of current, magnetic field, and sheet stress states under the field shape case were revealed. Furthermore, the processing parameters of the discharge voltage and the billet diameter were optimized. The results show that the section quality is optimized and the shear deformation is intensified with using the field shape. The sheets present a tearing fracture mode under the forming processes. With the increase of the discharge voltages, the deformation degree of the sheets increases, the fillet area of the fracture decreases and the diameter of the blanking part decreases firstly increases. With the increase of the billet diameters, the deformation degree of the sheets increases firstly and then decreases, the fillet area of the fracture decreases firstly and then increases, and the diameter of the blanking part increases and then and then decreases. The optimum values of the discharges voltages and the billet diameters are as 12 kV and 130 mm respectively. [ABSTRACT FROM AUTHOR]

For the manufacturing of large-scale sheet parts, traditional stamping, spinning, and single-point incremental forming are limited by the rupture prone and severe springback of the formed parts and the requirement of large-scale forming equipment. In this paper, the method of electromagnetic incremental forming (EMIF) based on dual coil was creatively proposed to solve the manufacturing problem of large-scale parts of aluminum alloy. The forming results of EMIF based on single coil and EMIF based on dual coil are compared by finite element simulation. The effect of the two moving strategies on uniformity in EMIF based on dual coil was researched. In addition, the effect of the shaping voltage on uniformity in EMIF based on dual coil with the interval moving strategy was studied. It was observed that the forming quality of EMIF with dual coil was better than that of EMIF with single coil. For EMIF based on dual coil, the interval moving strategy is better than the sequential moving strategy in achieving better forming quality. For the first layer of EMIF based on dual coil with the interval moving strategy, the optimized forming voltage and shaping voltage were 12 kV and 18 kV, respectively. For the second layer of EMIF based on dual coil with interval moving strategy, the optimized forming voltage and shaping voltage were 18 kV and 27 kV, respectively. The shaping voltage was 1.5 times of forming voltage for both layers so that better forming uniformity was achieved. Then, the method of EMIF based on dual coil with interval moving strategy by multilayers is proposed to fabricate large-scale sheet parts. Finally, experiments were performed to confirm the feasibility of EMIF with dual coil, and the experiment results show good agreement with the simulation results. The findings of this work could provide guidance on deform large-scale parts of aluminum alloy by the EMIF method. [ABSTRACT FROM AUTHOR]

Electromagnetic flanging is a potential forming technology for aluminum alloy. However, due to the temporal and spacial varied magnetic force acting on the workpiece, the forming process is not easy to be studied by experimental method and the final shape of the workpiece is difficult to control. This paper aims to investigate the forming process by numerical simulation and to utilize an efficient method to control the formed shape. The result shows that the plastic strain before collision is determined by the geometry, but not dependent on the discharge energy. The collision between the workpiece and die is benefit to the forming. The strain to failure of the annealed 2219 aluminum alloy for electromagnetic forming is 77.8% higher than that for quasi-static. In addition, the final shape of the workpiece can be precisely controlled by designing an appropriate die compensation angle. [ABSTRACT FROM AUTHOR]

An increasing demand exists within the automotive industry to utilize aluminum alloy sheets because of their excellent strength-weight ratio and low emissions, which can improve fuel economy and reduce environmental pollution. High-speed automobile impactions are complicated and highly nonlinear deformation processes. Thus, in this paper, a Gurson-Tvergaard-Needleman (GTN) damage model is used to describe the damage behavior of high-speed electromagnetic impaction to predict the fracture behavior of 5052-O aluminum alloy under high-speed impaction. The parameters of the GTN damage model are obtained based on high-speed electromagnetic forming experiments via scanning electron microscopy. The high-speed electromagnetic impaction behavior process is analyzed according to the obtained GTN model parameters. The shape of the high-speed electromagnetic impaction in the numerical simulations agrees with the experimental results. The analysis of the plastic strain and void volume fraction distributions are analyzed during the process of high-speed impact, which indicates the validity of using the GTN damage model to describe or predict the fracture behavior of high-speed electromagnetic impaction. [ABSTRACT FROM AUTHOR]

The formability of aluminum alloy sheet in electromagnetic impaction deformation has attracted the attention of numerous researchers for the past decades. However, the influences of die geometry and high-speed impaction electromagnetic deformation on formability have not been well established, thereby resulting in the formability of the sheet not being developed fully. In this study, the influence of die geometry on the formability of 5052 aluminum alloy in electromagnetic deformation was investigated by comparing the formability of 5052 aluminum alloys formed using a hemispherical die and a cylindrical die. The intriguing finding is that the formability of the 5052 aluminum alloy formed using a cylindrical die is considerably higher than that formed using a hemispherical die. Therefore, die geometry significantly influences the formability of 5052 aluminum alloy. The influence of die geometry on the formability of 5052 aluminum alloy in high-speed impaction electromagnetic deformation was explained in terms of strain rate, pressure stress, and stress state. This investigation enhances insight into the interaction between sheets and dies, and provides a reference for the studying influence of dies on the forming limit of sheets in high-speed impaction deformation. [ABSTRACT FROM AUTHOR]

• An analytical model capturing mechanical performance of materials subjected to electromagnetic induced deformation is established based on the plastic dynamics. • A measuring analysis system with accurate acquisition of stress-strain-strain rate relationship is constructed utilizing electromagnetic ring expansion test. • The microsecond time-resolved imaging of high strain rate deformation, strain localization and fracture is realized. • The mechanical properties are contrastively analyzed with those under the split Hopkinson tension bar and quasi-static tests. • Improved ductility and formability of 5052 aluminum alloy is elucidated by SEM observation of fracture characteristics. The uniform one-dimensional tension can be easily realized by the electromagnetic ring expansion (EMRE) test at high strain rates of 103-104 s−1, which utilizes strong pulsed electromagnetic force to deform materials. However, the accurate and rapid acquisition of the time-dependent stress, strain and strain rate in EMRE test has been a bottleneck that hinders its wide application. Based on the electromagnetism and the principle of virtual velocity in plastic dynamics, a stress analytical model considering both the electromagnetic and inertial components is established. The whole EMRE process of deformation, strain localization and fracture for 5052 aluminium alloy (AA5052) which is widely used in the automotive and aerospace industries is collected by a measurement system with microsecond time-resolved imaging, and then the true stress-strain-strain rate relationship is calculated based on the above analytical model. In addition, the dynamic mechanical properties of AA5052 under EMRE test are contrastively analyzed with those under the split Hopkinson tension bar (SHTB) and quasi-static tests. The ductility and formability of AA5052 under EMRE are improved due to the inertial and eddy current effects which is demonstrated by fracture characteristics observed using Scanning Electron Microscopy (SEM). [Display omitted] [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Electromagnetic incremental forming (EMIF) is an effective manufacture method for large-size sheet parts of aluminium alloy due to the advantages of improving material formability and increasing the part dimensions. However, the dynamic deformation behaviour of sheets under local Lorentz force is so complex that it is difficult to achieve precise forming control of large-size sheet parts of aluminium alloy in the EMIF process. To address this challenge, a numerical simulation model was established and validated by experiments in this study. Then the forming height, plastic strain, and velocity propagation of a sheet were analysed. In addition, the Lorentz force action stage and inertia effect stage were distinguished quantitatively, and on this basis, the effects of Lorentz force and the inertia effect on deformation were analysed. Finally, the effects of discharge voltage and discharge position on the deformation were revealed. The results showed that there are differences between the distribution rules of forming height and plastic strain. The velocity peak first appears at the sheet area corresponding to the radius centre of coil, then the accelerating downward velocity peak propagates to the sheet centre, while the downward velocity spreads outside. The Lorentz force is the leading factor of the forming peak height, while the inertia effect is decisive on the forming area. The forming peak height and forming area, especially at the inertia effect stage, can be effectively controlled by changing the discharge voltage and the discharge position, thus guiding the adoption of the process parameters according to the requirement of the deformation. [ABSTRACT FROM AUTHOR]