Analyses of thermal field and coupled magnetic-mechanical field in electro-permanent magnet blank holder technique

In this study, problems involving thermal field and coupled magnetic-mechanical fields of electro-permanent magnet (EPM) blank holder used in deep drawing are analyzed. Since a short current is applied to coils at the beginning of the loading or unloading of blank holding force (BHF) using this technique, the heat transfer problem in the designed magnetic cushion (EPM blank holder) is investigated. The thermal fields of double magnetic pole units (DMPUs) and magnetic cushion with 46 magnetic pole units were analyzed, respectively, by FEM, and the coil temperatures in DMPUs were measured. The results show that under normal conditions, the maximum temperature of DMPUs does not exceed 340 K after 3 h. After increasing the convective heat transfer boundary conditions, the maximum temperature can be significantly reduced. The simulated maximum temperature of the cushion increases to about 327 K after 3 h, which does not affect normal use. A coupled thermal-mechanical field of the EPM cushion was analyzed by FEM, and the results show that thermal deformation has little effect on the calculated magnetic force. Then, a coupled magnetic-mechanical field of the cushion and related components was simulated, and the distribution of blank holding pressure on the sheet was obtained. The deep drawing processes of the cylindrical cup were simulated and experimentally tested based on coupled magnetic-mechanical field analysis. The results show that the determination of air gap and magnetic level based on the analysis of coupled magnetic-mechanical field is simplified and reliable. At last, the energy consumption using the EPM blank holder technique is predicted, and it can save more than 60% energy compared with conventional blank holders.