US Patent 8413318 Method for manufacturing armature core

A method for manufacturing an armature core is provided, in which a plurality of split cores, which are formed by laminating core pieces produced through punching by punching dies, are coupled together to form an annular shape as a whole, so as to manufacture one armature core. The method includes: preparing a plurality of sets of the split cores, each set having three split cores, so as to form one armature core; and arranging the three split cores in each set at intervals of 120° in the circumferential direction. The three split cores in each set are formed by core pieces that have been punched by the same part of the same punching die.