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A novel blank holder technique based on electropermanent magnet (EPM) technology is proposed, in which independent loading of blank holding force (BHF) can be realized in sheet metal forming process. The magnetic force and the resulting BHF are applied by permanent magnets rather than electromagnets, and the current is only required at the moment of loading or unloading the BHF. The BHF is convenient in control, low in energy consumption, and without overheating problem using this technique. In this paper, an experimental setup consisting of magnetic cushion, die, punch, and other components is designed based on the characteristics of EPM and requirements of deep drawing process. The magnetic cushion including blank holder and magnetic pole units is used to generate magnetic force and realize loading and unloading of BHF. Then, magnetic field analyses of a pair of magnetic pole units and the designed cushion are carried out by FEM. Also, the coupling problem involving magnetic field and stress field is further analyzed and solved by means of theoretical method and FEM, and the BHF and the blank holding pressure on the sheet using the new technique can be obtained. The deformation of the designed setup is small, and the stiffness can satisfy the requirements. The deep drawing processes of cylindrical cup of 08Al sheet with 0.98 mm thickness are simulated by using conventional blank holder and the new technique, respectively, and there are small differences of the strain distributions of the drawn parts with the two techniques. The experiments of cylindrical cup deep drawing applied four different BHFs, respectively, are carried out using EPM bank holder technique. The results indicate that the BHF applied by the designed cushion is large enough for the deep drawing process of the selected sheet. [ABSTRACT FROM AUTHOR]

The ANSYS software was used to establish an electromagnetic-structural coupling model and simulate the electromagnetic tube bulging process. Compared to the experimental results, the maximum simulation error was approximately 4 % at the longitudinal center of the tube. Then, the simulation method was used to analyze the effects of multidirectional magnetic force on the tube bulging process. The results indicate that an axial magnetic force can be generated at the tube end by setting the coil at the end of the tube. The values of material flow, stress, plastic strain, and thickness in different forming processes were compared. Compared to traditional forming processes, electromagnetic tube bulging with multidirectional magnetic pressure can significantly increase the axial feeding, decrease the tensile stress, and reduce the thickness at the easily broken position. Therefore, a higher bulging height can be obtained by the new method. [ABSTRACT FROM AUTHOR]

The ANSYS software is used to establish the electromagnetic-structural coupling model and predict the electromagnetic sheet forming process. In comparison with experimental result, the maximum simulation error, about 4.5 %, occurs at the sheet center. Then, the simulation method is used to analyze the effect of discharge voltage on thickness distribution. The results indicated that the location of the maximum thickness reduction transfers from sheet center to the region near the sheet center (A region) and then to the region corresponding to the die corner (B region) with the voltage increases, which also cause the first principle strain changed. In addition, lager magnetic force and the material at sheet flange restrained to flow are the two reasons for the thickness reduction at B region. While the direction of material flows changed by inertial effect is the reason for thickness reduction at A region. [ABSTRACT FROM AUTHOR]

In the past, many simulation methods for electromagnetic forming (EMF) just consider the effect of the first half current pulse on electromagnetic forming process. And it is deemed that the sequence coupling method has a higher accuracy than loose coupling method because the effect of workpiece deformation on magnetic analysis is considered. In this work, the loose coupling method and sequence coupling method are both used to investigate how the second half current wave affects the simulation result. If the first current pulse is only considered in the simulation process, higher accuracy can be obtained by loose coupling method at 4,366 Hz of discharge current or sequence coupling method at 2,183 Hz of discharge current. If the second current pulse is also considered, the sequential coupling method can obtain more precise results than loose coupling method in the two different current frequencies. With the increase of displacement, the loose coupling method could cause a bigger overestimation than sequential coupling method. Then, the total resistance in EMF system is adjusted to obtain different damping exponent. It is found that the effect of the second current pulse on sheet deformation increases with the increasing of the discharge frequency. [ABSTRACT FROM AUTHOR]

The deposition of metal droplets has been attracted wide interests for potential applying in microstructures fabrication. A uniform droplet generator with image acquiring system and droplet temperature measuring system was established. A coupling analysis method on combination of droplets dynamic and thermal models was proposed. Effect of experimental parameters on deflected trajectory and the temperature history of the uniform droplets was investigated. The measured trajectory and temperature history agreed well with the predicted results, indicating the validity of the proposed analysis method. The predicted results with different experimental parameters showed that the deflected trajectories and thermal histories of the droplets with diameters close to 100 μm or less were strongly dependent on their sizes. Small droplets had a narrow deposition length for obtaining parts with good metallurgical bonding. The predicted results also showed that it was effective in controlling the deflected trajectories and thermal histories of droplets by adjusting the pressure when it was low. At last, micro alloy tubes with good metallurgical bonding were obtained using 50 μm diameter nozzle when the experimental parameters were chosen according to theoretical models. The deposited results show that proper parameters for microstructures deposition can be obtained according to the proposed analysis method. [ABSTRACT FROM AUTHOR]