A process for manufacturing an integrally bladed disk for a turbomachine rotor by friction welding is disclosed. The manufacturing process includes arranging a plurality of blades in the form of a ring in a mold having symmetry of revolution; casting a degradable material, preheated to a temperature above its melting point, onto the ring of blades in the mold; extracting the molded ring which is obtained after the degradable material has solidified; welding the molded ring onto a disk; and eliminating the degradable material.