Control of crystalline orientation of hot forged Nd-Fe-B magnet

Abstract

Nd-Fe-B powder obtained by melt spinning was compacted, and then forged to produce a magnet with even magnetic properties. There is a strong correlation between the strain introduced to the magnet while it is being forged and the obtained magnetic properties. In general, such strain is unevenly introduced to the magnet owing to the friction generated between the mold and magnet. Consequently, the obtained magnetic properties also become uneven. We obtained even magnetic properties by defining the optimum shape before forging with the use of finite element method (FEM), choosing the optimum mold material and lubricant, and introducing strain evenly. From the viewpoint of decreasing friction, we used a smooth-surface ceramic mold and a graphite-based lubricant. If a ceramic mold with a normal shape is used, its corners are easily broken during forging because stress is concentrated at these corners. Ceramic molds are also extremely expensive. In this study, we configured a mold composed of ceramic plates in a simple shape. This approach successfully prevented the mold from being broken and kept the mold price low.