The present invention relates to the manufacture of an integrally bladed disk, especially for a turbomachine rotor. It relates more particularly to a process for manufacturing such a disk by friction welding. The manufacturing process comprises the following successive steps: arrangement of a plurality of blades ( 1 ) in the form of a ring in a mold ( 2 ) having symmetry of revolution; casting ofa degradable material ( 3 ), preheated to a temperature above its melting point, onto the ring of blades ( 1 ) in the mold ( 2 ); extraction of the molded ring ( 10 ) obtained after the degradable material ( 3 ) has solidified; welding of the molded ring ( 10 ) onto a disk ( 4 ); and elimination of the degradable material ( 3 ). According to the invention, the welding is carried out by friction welding.