Method for preparing rare earth sintered magnet

摘要

A rare earth sintered magnet is prepared from a corresponding alloy powder (11), using a mold comprising a die (21), an upper punch (22), and a lower punch (23) which is divided into a plurality of punch segments (23a-c) which are independently movable within the die (21). The method comprises the steps of filling the mold cavity with the alloy powder (11) when one or more selected punch segments (23a+b) are moved to a higher position than the remaining punch segments (23c); moving the selected punch segments (23a+b) down to the position where the selected (23a+b) and remaining punch segments (23c) assume the normal shape of the lower punch (23) during the compression step; compressing the alloy powder (11) between the upper and lower punches (22+23) under a magnetic field while the normal shape of the lower punch (23) is maintained, for thereby molding a compact; and heat treating the compact.