Plastic deformation modeling of die-upset process for magnequench NdFeB magnets

Abstract

The die upset of hot pressed NdFeB magnets modifies the equiaxed grains to platelets, develops the c-axis texture parallel to press direction, and improves magnetic properties. The mechanism of c-axis alignment has been suggested to be a combination of grain-boundary sliding and anisotropic grain growth in a direction normal to the applied stress. To clearly understand the role of deformation process in grain-boundary sliding or anisotropic grain growth simulations of the die-upset process were performed using ANATARES, a three-dimensional finite element method based deformation modeling software. The stresses and strains in the different regions of a cylindrical Nd–Fe–B magnet at different stages of the die-upset process were determined. The average value of the maximum principal stress (parallel to the upset direction) and total effective strain increased as the upset increased from 50% to 70%. The maximum principal stress and total effective strain show a maximum at the center and decrease in both the thickness and the radial direction due to friction at the die-wall/magnet interface. The stress and effective strain uniformity improves with increase in upset. The data agree well with the variations of texture in the magnet observed using pole figure measurements in this study and texture studies using a synchrotron source.