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Electromagnetic blanking (EMB) based on force-free region deformation is proposed to meet the no burr forming requirement of diaphragm parts for carrier rockets in the aerospace field. Deformation behaviors of the part were revealed along with the effects of key process parameters on the forming quality investigated. During the EMB process, the electromagnetic force, effective stress, and plastic strain were distributed in a rather uniform annular region and peaked near the edge of the die. High-speed deformation coupled tension and bending were evidenced. With the increase in discharge voltage, the diameter of the part reduced slightly, and the filling degree of the trimmed edge section reduced remarkably, while the thickness uniformity was improved. It was found that the filling degree was dependent on the deformation degree and the interaction between two different regions. Similar effects of initial blank diameter and discharge voltage were observed. The interaction was notable at a larger initial blank diameter, causing the sharper drop in the filling degree. The forming quality could be improved by using a blank holder, but an undesirable extra deformation zone would appear. In a word, the proposed EMB process is capable of forming no burr diaphragm part with high quality. [ABSTRACT FROM AUTHOR]

Aiming to the precise control of forming quality in electromagnetic incremental forming (EMIF), deformation behaviors of a spherical crown-shaped thin-walled workpiece during a single layer forming of EMIF are analyzed by means of numerical simulation. The influences of the coil overlap ratio, coil moving strategy, and discharge voltage combination on the forming uniformity of the workpiece are revealed. The maximum electromagnetic force and forming depth represent a "dramatic decrease–long-term steady–moderate decrease" variation over the increase of discharge time for forming a single layer by sequential discharging. The difficult-to-deform region located outside the overlap region of coil positions deforms insufficiently, leading to poor overall uniformity. Better uniformity and higher forming efficiency are achieved by sequential discharging compared with interval discharging. With an increase in the coil overlap ratio, the circumferential uniformity of the workpiece is improved because the transition deformation region is reduced and the active deformation region subjected to electromagnetic force is increased. In addition, the forming uniformity of the workpiece can be improved significantly by an optimized discharge voltage combination with properly decreased first discharge voltage and increased last discharge voltage, respectively. A forming scheme for a spherical crown-shaped thin-walled workpiece is proposed based on the forming principles and a workpiece with high precision and good uniformity is obtained. Therefore, EMIF is demonstrated as capable to form high precision large-size thin-walled parts. [ABSTRACT FROM AUTHOR]

A new two-step electromagnetic forming (two-step EMF) which combines electromagnetic forming (EM forming) with electromagnetic calibration (EM calibration), is proposed for local features of large-size sheet metal parts, such as an oblique hole-flanging. During the process, the workpiece is firstly electromagnetic formed by a flat spiral coil and then electromagnetic calibrated by a helix coil with a similar shape to the final profile of the workpiece. To develop the process, an efficient geometric design method is established, the effects of key process parameters on forming quality are investigated, and the deformation behavior of the workpiece is revealed. The feasibility of two-step EMF is validated by the accurate oblique hole-flanging with a maximum die-fitting gap less than 0.2 mm. Moreover, experimental results show that there are critical discharge voltages for both EM forming and EM calibration which lead to the minimum die-fitting gap. Furthermore, EM calibration can reduce the die-fitting gap to 0.24~1 times of that for EM forming with more uniform distribution. In addition, simulation results show that during EM calibration, the stress distribution of the workpiece is improved, the bending moment is reduced which is responsible for the shape and size errors, then the rebound is restricted. Consequently, the fittability and forming accuracy are significantly enhanced. [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]

Abstract A new gradient electromagnetic forming (GEMF) approach that utilizes the gradient electromagnetic force generated by use of a sectional coil is proposed to meet force-field requirements concerning deformation of specially shaped variable-diameter tubes. To demonstrate the development of this approach, a variable-diameter tube made of copper-nickel alloy was formed via GEMF, as an example. An efficient geometric design for the sectional coil was established, and effects of the gradient electromagnetic force field on metal flow have been discussed along with investigation of the effects of key process parameters on tube forming. The deformation mechanism of GEMF has also been explained. Feasibility of the GEMF approach has been validated based on the accurate deformations of variable-diameter tubes made of copper-nickel alloy and characterized by a maximum die-fitting gap of less than 0.4 mm. Moreover, optimal combination of the coil proportion coefficient (85%) and discharge voltage (18 kV) have been obtained to ensure high forming accuracy. It was observed that the gradient electromagnetic force field prevented occurrence of stress concentrations by effectively improving stress distributions. Consequently, the forming accuracy and quality of variable-diameter tubes was significantly improved using the GEMF approach. Graphical abstract Image 1 Highlights • GEMF utilizing gradient electromagnetic force field produced by sectional coils is proposed. • Effects of key process parameters on the variable-diameter tube deformation by GEMF is analyzed and discussed. • GEMF improves forming accuracy and quality by releasing uneven stress distributions. [ABSTRACT FROM AUTHOR]